reproductive and teratologic effects of low-frequency electromagnetic fields: a review of in vivo...

Reproductive and Teratologic Effectsof Low-Frequency Electromagnetic Fields:A Review of In Vivo and In Vitro StudiesUsing Animal ModelsROBERT L. BRENT*Thomas Jefferson University, Philadelphia, Pennsylvania 19107; duPont Hospital for Children,Wilmington, Delaware 19899

ABSTRACT In order to evaluate the reproduc-tive risks of low-frequency electromagnetic fields (EMF),it is important to include epidemiological and animalstudies in the evaluation, as well as the appropriatebasic science information in developmental biology andteratology. This review presents a critical review of invivo animal studies and in vitro tests, as well as thebiological plausibility of the allegations of reproductiverisks. In vitro or in vivo studies in nonhuman species canbe used to study mechanisms and the effects that havebeen suggested by human investigations. Only welldesigned whole-animal teratology studies are appropri-ate when the epidemiologists and clinical teratologistsare uncertain about the environmental risks. Even theinference of teratogenesis cannot be drawn from cul-ture experiments, because the investigator is not in aposition to know whether any of his observations will bemanifested in living organisms at term. Other aspectsof reproductive failure such as abortion, infertility,stillbirth, and prematurity, cannot be addressed by invitro or culture experiments. In fact, they are verydifficult to design and interpret in nonprimate in vivomodels. The biological plausibility some of the basicmechanisms involved in reproductive pathology wereevaluated, concentrating primarily on the mechanismsinvolved in the production of birth defects. The studiesdealing with mutagenesis, cell death and cell prolifera-tion using in vitro systems do not indicate that EMFshave the potential for deleteriously affecting proliferat-ing and differentiating embryonic cells at the exposuresto which populations are usually exposed. Of course,there is no environmental agent that has no effect,deleterious or not, at very high exposures. The animaland in vitro studies dealing with the reproductive effectsof EMF exposure are extensive. There are .70 EMFresearch projects that deal with some aspect of repro-duction and growth. Unfortunately, a large proportion ofthe embryology studies used the chick embryo andevaluated the presence or absence of teratogenesisafter 48–52 h of development. This is not a stage ofdevelopment at which an investigator could determinewhether teratogenesis occurred. The presence of clini-cally relevant teratogenesis can only be determined at

the end of the gestational period. The chick embryostudies are also of little assistance to the epidemiolo-gist or clinician in determining whether EMF representsa hazard to the human embryo, and the results are, inany event, inconsistent. On the other hand, the studiesinvolving nonhuman mammalian organisms dealing withfetal growth, congenital malformations, embryonic loss,and neurobehavioral development were predominantlynegative and are therefore not supportive of the hypoth-esis that low-frequency EMF exposures result in repro-ductive toxicity. Teratology 59:261–286, 1999.r 1999 Wiley-Liss, Inc.

Several considerations are helpful in establishingthat an environmental exposure causes maldevelop-ment in the human: (1) human epidemiologic studiesshould consistently report the association of an environ-mental agent with an increased incidence of reproduc-tive effects and congenital malformations; (2) for com-mon exposures, secular trend data should support theallegation; (3) there exists an animal model that mimicsthe reproductive effort suspected in humans at expo-sures experienced by pregnant woman; (4) the terato-genic effect or reproductive effect should increase withdose; and (5) the suggested reproductive effect shouldbe biologically plausible and not contradict establishedscientific principles, although there may be, and in-deed, there have been exceptions to this rule (Brent,’78, ’83, ’86; Shepard, ’86) (Table 1). This approach is ofgreatest value when utilized for the evaluation ofenvironmental agents that have been in use for sometime or for evaluating new agents that have a similarmechanism of action, function, chemical structure,pharmacology, or physical effect of other agents thathave been extensively studied.

How do investigators interested in determiningwhether a particular environmental agent such aselectromagnetic fields (EMF) represents significant re-

*Correspondence to: Dr. Robert L. Brent, Room 308 R/A, Division ofDevelopmental Biology, duPont Hospital for Children, P.O. Box 269,Wilmington, DE 19899.

TERATOLOGY 59:261–286 (1999)

r 1999 WILEY-LISS, INC.

productive risks to human populations? We examine allscientific studies that deal with the question whichincludes epidemiological studies, in vivo and in vitroanimal studies and by applying the principles of biologi-cal plausibility (Table 1). Competently performed epide-miological studies usually provide the most reliablerisk estimates, since the study of human of populations,rather than animal models, eliminates the problem ofspecies differences. Epidemiological studies of EMF areplagued with difficulties that make the planning andcompletion of epidemiological studies very difficult: (1)no populations are unexposed to some frequency andexposure of EMF, (2) small populations may vary intheir reproductive performance and incidence of congeni-tal malformations, and (3) exposure levels frequentlyhave to be estimated by indirect means. Fortunately,these problems are eliminated in competently plannedand performed animal studies. Furthermore, studieswith ionizing radiation indicate that the reproductiveeffects are primarily the direct effect of exposing theembryo, indicating that low exposures of maternalionizing radiation contribute minimally to reproductiveand teratogenic effects (Brent, ’60, ’69; Brent andMcLaughlin, ’60, Brent and Bolden, ’67a,b, ’68). Thismakes biological sense, since the reaction of individualmammalian cells does not vary among species. Becauseultrasound, EMF, and microwaves are all physicalforms of ‘‘radiation,’’ it makes biological sense to con-clude that if biological effects occur, they are attribut-able to the direct exposure of the embryo and not toindirect maternal effects. Of course, microwaves andultrasound exposures have the potential for resultingin whole organism and embryonic hyperthermia, whichcould potentially result in an indirect maternal effect.

But low-frequency EMF exposures from 60-Hz powersources or video display terminals (VDTs) do not havethe ability to produce significant hyperthermia.

While a number of epidemiological studies are re-ported in the scientific literature, and most of thesestudies have not concluded that low-frequency EMFrepresents a significant reproductive hazard, somefederal agencies and a few scientists still express someconcern. The human epidemiological studies are dis-cussed in detail in another paper in this symposium(Robert, ’99) and in prior publications from the OakRidge Associated Universities Panel for the Committeeon Interagency Radiation Research and Policy Coordi-nation (Davis et al., ’92; Brent, ’92; Brent et al., ’93) andthe National Academy of Sciences (’96). Because of theability to control the magnitude of the exposure and thestage of exposure; and to obtain unexposed pregnantanimals for controls, a large number of animal studieshave been performed and published. It is these studiesthat will be discussed in detail (Table 2).

REPRODUCTIVE EFFECTSOF EMF IN ANIMALS

Coupling of ambient EMFsin mammalian organisms

Electric field. While the ambient electric field, un-perturbed by the human body, can be measured and/orcalculated with some precision, the electric field insidethe body is a difficult to measure or calculate. The bodyis a conductor, and the problem is complicated by thefact that different tissues have different conductivities.In general, a conducting medium perturbs the field,therefore, theoreticians look for models of the body, andexperimentalists look for measuring devices. The resultis that only estimates of the internal fields are avail-able. The estimates at sites in the electrolytes withinthe human body range from 1025 to 1028 of the externalfield. A range of three orders of magnitude in theestimated electric field at a sites within the bodyrelative to the field outside the body confounds efforts todefine effects and dose-response relationships.

Magnetic field. In contrast to the electric field, themagnetic field is essentially unperturbed by the humanbody; it penetrates the body, with little recognition thatthe body is present. This occurs because the body hasalmost no magnetic materials that will interact withthe field. It will be helpful to consider two different60-Hz magnetic field levels:

First, a field of B 5 650 G acting over the largestdiameter (e.g., 40-cm) loop of tissue in the body willinduce current densities (<1 A/m2) large enough tostimulate cells. Such field levels are usually found onlyin industrial or laboratory situations.

Second, a field of B 5 6.5 G acting over the same areawill induce current densities (<0.01 A/m2) comparableto those produced by natural and unavoidable thermalelectric fields at the cell level. This field is at least 10times higher than the largest magnetic fields foundunder common urban distribution lines and is compa-

TABLE 1. Proof of teratogenesis in the human*

1) Controlled epidemiologic studies consistantly demon-strate an increased incidence of a confined group of con-genital malformation in exposed human population.

2) Secular trends demonstrate a relationship between theincidence of particular malformations and a reduction orincrease in exposure to an environmental agent in humanpopulations. This analysis can only be performed when ahigh proportion of the population has been exposed andthere has been a marked change in exposure.

3) An animal model mimics the human malformations atclinically comparable exposures:a) without evidence of maternal toxicity.b) without reduction in food and water ingestion.c) with careful interpretation of malformations that occur

in isolation, such as anophthalmia in the rat, cleftplalate in the mouse, vertebral, limb and rib malforma-tions in the rabbit, and omphalocele in the ferret.These malformations are epigenetic malformationsthat can be altered nonspecifically by environmentalstresses.

4) The teratogenic effects increase with dose within theusual range of human exposures.

5) The mechanisms of teratogenesis are understood and/orthe results are biologically plausible based on the prin-ciples of developmental biology and teratology.

*Modified from Brent (’85b) and Brent et al. (’92).

262 R.L. BRENT

TABLE 2. Reproductive risks of EMF in animals and in vitro systems

Author Year Species and stageEx-

posedCon-trols Exposure Effects evaluated Reprod effects Remarks

1 Algers andHultgren

1987 Cows exposed to hightension lines duringthe breeding seasonfrom June to Octoberfor a period of 120days; Swedish whiteand red breed heifers;equal number of con-trols maintained

58 58 B & E:Exposed in proximity to

400 kV, 50-Hz high-voltage transmissionlines. Exposure:E 5 4k V/m, B 5 20mG

FertilityEstrous cycle normalcyProgesteron levelsIntensity of estrousViability of fetuses

None of the reproduc-tive parametersstudied differed fromthe unexposed group

Although the incidenceof malformations wasnot increased, alarger group of ani-mals would be neces-sary to identify asmall increase; pro-portion of live fetuses13% greater in theexposed group

2 Bardasanoet al.

1986 Chick embryos exposedto magnetic field forthe first 6 days ofdevelopment

24 24 B 5 800 mG, 60 Hz Birth defectsPineal gland of chick

embryos was evalu-ated after 6 days of Bexposure; embryosevaluated at stage 28

Birth defects: gross ana-tomic examination ofthe embryos did notreveal any changes;examination of thepineal gland revealedanomalous Feulgen 1cells with multipolarspindles

Authors suggest thatmagnetic fields mayalign microtubules. Itwas of interest thatwhile other investiga-tors reported malfor-mations when theembryos are exam-ined at 48 h; in thisexperiment, theywere normal at 6 days

3 Bermanet al.

1990 Chick embryos exposedfor the first 48 h andimmediately evalu-ated for malforma-tions; experimentsperformed in 6 labo-ratories around theworld, using identicalequipment and 100controls and exposedin each laboratory

600 600 B: Unipolar pulsed mag-netic field of 500 µspulses with a 2 µs riseand fall time; B 5 10mG

Viability (%)Somite (number)Stage% normalTotalLive

C .955; E .951C 18.3; E 18.2C 12.9; E 12.8C .705; E .698C .85; E .79

While all laboratoriesagreed on viability,stage and somitedevelopment, therewas disagreement onmalformations; fourof the laboratorieshad no increase inmalformations, onehad a fourfoldincrease and one atwofold increase

4 Cameronet al.

1985a,b Medaka fish eggs. Fer-tilized eggs (2 and 4cell embryos) wereexposed to E, B, or Eand B for 48 h;number of control andexposed eggs not pro-vided

B 5 1 G, rms, 60 Hz;E 5 300 mA/m2, 60Hz; combined B and Eexposure as well

Birth defectsDevelopmental delay

Birth defects: noincrease in birthdefects in theembryos exposed tothe E, B or combinedE 1 B fields; develop-mental delayobserved with the Band B 1 E fields, butnot with the E field

Authors believe B fieldsof this intensity canretard growth in thevertebrate embryo; inthe mammalianembryo, this earlystage is resistant toboth the malformingand growth retardingeffects of embryotoxicagents

5 Delgadoet al.

1982 Chick embryos exposedduring 49 h postcon-ception

43 26 B: Unipolar pulsed Bfields of 500 µs; 6exposure groups forthe 43 embryos, 10,100, and 1,000 Hzand 1.2, 12, and 120mG

Abnormalities studiedgrossly and by histo-logical section

Controls: 16% defectiveExposed: 78.5% defec-

tive

Very few embryos werein each group butinvestigator con-cluded that 100 Hz,12 mG had a ‘‘power-ful’’ effect on inducingabnormalities; nogroup of embryoswere allowed to hatch

TABLE 2 continues on next page

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TABLE 2. Reproductive risks of EMF in animals and in vitro systems (continued)



6 Durfee et al. 1975 Chick embryos exposedfor the duration ofembryogenesis

B: Exposed developingembryos to 1, 5, 8, 30,45, 60, 75 Hz

Hatchability There was no differencebetween hatchabilitybetween control andexposed embryos

If ‘‘malformations’’observed by otherinvestigators per-sisted, they shouldhave contributed toan increase in mor-tality, which did notoccur

7 Hanson 1981 Rabbits exposed fromconception to 7.5weeks postdelivery inan outdoor situationin approximation toan electrical substa-tion; control rabbitsreared in outdoorsituation, but in elec-trically protectedcages

E 5 14 kV/m, 50 Hz Histopathology of thedeveloping brain

Formation of abnormalcytoplasmic struc-tures in the Purkinjenerve cells of the cer-ebellum

8 Hanson 1987 Rabbits, rats, and miceexposed to an electricfield similar to thatreported by Hanson[1981], but in a labo-ratory setting

E 5 14 kV/m, 50 Hz Histopathology of thedeveloping brain

Changes in glial andPurkinje cells werefound in exposed ani-mals, although theappearance ofabnormal cytoplasmicstructures (lamellarbodies) was infre-quent

No weight differencesbetween exposed andcontrols.

9 Heinrichset al.

1988 Mice, Balb/c wereexposed to MB fieldsproduced by magneticresonance imagingequipment; exposureoccurred on day 8.75for 16 h

231 194 B 5 3,500 G, static elec-tric field; the RFexposure was 15.05MHz with a peakpower of 1 W andyielding 2.89mW/cm2; the peak RFmagnetic field in thecoil was 73.8 mG

Birth defects, still-births, birth weight,fetal length at term

There was no alterationin the frequency ofbirth defects,homeotic skeletalshifts, or stillbirths inthe exposed embryos;there was a statisticaldifference (reduction)in fetal length at term

The fetal length reduc-tion is of interestbecause weight isusually a more sensi-tive barometer offetal effects and therewas no difference inweight between theexposed and controlterm fetuses

10 Joshi et al. 1978 Chick embryo exposedto magnetic fieldsfrom fertilization tothe primitive streakstage; the embryoswere cultured invitro, using New’stechnique; theembryos wereexposed to B for 1 h

25 25 B 5 5,000 Oe Birth defectsSomite development

Birth defects: All 25exposed embryosexhibited some typeof brain abnormality,open neural tube,microcephaly, or both;there were also heartabnormalitiesreported and dimin-ished somite develop-ment

Authors attributed‘‘malformations’’ inthe neural tube aredue to the B fieldeffect ‘‘on the interki-netic nuclear migra-tion and mitotic activ-ity’’ (there was nodata that indicatedthese effects werepresent at hatching)


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11 Juutilainen 1986 Chick embryos (Makela16) exposed duringfirst 48 h of develop-ment; each experi-ment had 10 controlsand 10 exposed eggs

230 224 B: Sinusoidal 100 Hzmagnetic fields.B 5 12.5 mG; groupswere divided intoexposed and controls,as well as twomethods of handlingand four differenttemperatures (36.3–38.5°C)

Malformation incidencedetermined at 2 daysfrom fertilization; noeggs were allowed tohatch

Control: 8% at 36.3°C &5% at 37°C.

Exposed: 23% at 36.3°C& 25% at 37°C.Higher temperaturesand storage of eggsfor three to four daysincreased the per-centage of abnormalembryos

‘‘The results demon-strate the importanceof the handling of theeggs in this kind ofexperiment’’

12 Juutilainenand Saall

1986 Chick embryos (Makela16) were exposedfrom conception to 52h (about 48 h develop-ment time); therewere 20 eggs in eachcontrol and exposedgroup

640 160 B: Sinusoidal oscillatingmagnetic field of 1,10, 16.7, 30, 50, 1K,10K, and 100K Hzand at field strengths(B) 5 1.25, 12.5, 125,and 1250 mG

Malformation incidencedetermined at 2 daysfrom fertilization; noeggs were allowed tohatch

Of the 32 exposedgroups 15 had a sta-tistically increasedincidence of abnormalembryos; authors con-cluded a thresholdbelow 16.7 Hz and12.5 mG and that bio-logical effect is resultof B field and not theE field

Authors review datathat supports the‘‘existence of intensitywindows’’—their datasuggest 1 and 10 Hzmay be less effective.Although there doesnot appear to be adose response curvefor B there are too fewembryos in eachgroup

13 Juutilainenet al.

1987 Chick embryos (Makela16) were exposedfrom conception to 54h (about 50 h of devel-opment time)

347 77 B: Field strength of geo-magnetic field in labwas 440–550 mG at70°; embryos exposedto 50 Hz sinusoidalmagnetic fields of1.25, 3.75, 12.5, and125 mG; in a 2ndexpt, embryosexposed to 5, 7.5,10.75, and 16.9 mG

Malformation incidencewas determined whenthe exposure stopped,approximately 2 daysafter fertilization; noeggs were allowed tohatch

Control abnormalities,16% & 17% in the twoexperiments. %abnormalities inexposed: 1.25mG—16%; 3.75mG—14%; 12.5mG—29%; 125mG—32%

50-Hz magnetic fieldscauses abnormalitiesin embryos but noneare induced below11.25–12.5 mG

14 Juutilainenet al.

1986 Chick embryos (Makela16) were exposedfrom conception to 52h (about 48 h of devel-opment time)

B: Sinusoidal, square,and pulsed wave-forms were used withB fields of 1.25–100mG at 100 Hz

Malformations presentat the end of the cul-ture period

Unipolar square wavesdid not increase thepercentage ofabnormal embryos atany exposure; bipolaroscillations increasedthe rate of malforma-tions above 12.5 mG

15 Konemannand Monig

1986 Mice; pregnant albinomice were exposed tomagnetic fields ondays 7, 10, or 13 post-conception

1,363 319 B 5 10,000 G, 0 Hz Birth defects (external),skeletal malforma-tions, embryolethality, birthweight; postnatalevaluations of weight,brain weight, diam-eter of the neocortexand alignment of theneural cortex

No developmentaleffects were observed


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16 Koundakjianet al.

1996 Drosophila melano-gaster cells exposedfor 16 h

B: 60-Hz magnetic fieldat 10 µT or 100 µT(100 or 1,000 mG)

Expression of heatshock protein (hsp) 23or 70

EMF exposure did notalter expression ofhsp 23 or 70 from thatobserve in unexposedcultures and did notalter expression ofhsp when cells werecultured with threeteratogens (Cd, reti-noic acid, andhydroxyuria)

‘‘These data do not sup-port the thesis thatEMF exposure servesas a biologicalstressor’’

17 Kowalczukand Sun-ders

1990 Mice: male C3H miceexposed for two weeksand then mated totwo females eachweek for a period of 8weeks

20 40 E 5 20 kV/m, 50 Hz;current densities inthe mouse testes wereestimated to be 100µA/m2

Dominant lethal effectin offspring of femalemice mated to malmic receiving E expo-sure prior to fertiliza-tion

There was no effect onthe offspring derivedfrom matings ofexposed male mice;the pregnancy rateand survival of theoffspring was thesame in the controland exposed groups

18 Kowalczuket al.

1994 CD 1 mice, 90 pregnantmice exposed and 86were sham irradiated.Fetuses examined onthe 17th day

1,132 1,035 B: 50-Hz sinusoidalmagnetic field at 20µT; 250 fetuses wereselected for examina-tion for internal mal-formations andanother 250 wereselected for skeletalevaluation in thesham and exposedgroups

Preimplantation andpostimplantation sur-vival, sex ratio,internal and externalmalformations

There was no statisti-cally field-dependenteffects on preimplan-tation and postim-plantation survival,sex ratio, or internaland external malfor-mations

‘‘The results lend nosupport to sugges-tions of increasedrates of spontaneousabortions or con-genital malforma-tions following pre-natal exposure topower frequency mag-netic fields’’

19 Kruegeret al.

1975 Chickens: adult layinghens and cocksexposed to variousforms of EMF; expo-sures were for 3 con-secutive 4-weekperiods. E: 53 chick-ens; B: 50 chickens

103 50 B & E:E 5 1600 V/m (60 Hz)53 chickens;B 5 1.4 G (1.0–2.0) (60

Hz)50 chickens

Egg productionFertilityEgg hatchabilitySex ratioAbnormalities in

hatched chicks ordead embryos

Birds in E field loweredproduction butregained it by 11weeks, while B fieldbirds dropped to 31%and did not regain itby 12th week; neitherB or E affected fer-tility; sex ratio low-ered in B field (32.3%males)

In none of the fivegroups (B, E, 260MHz, 915 MHz, or2,435 MHz was therean increase in malfor-mations in either thehatched or deadembryos

20 Kubiak andTarkowski

1985 Mice: electrofusion of2-cell cleaving mouseembryo

562 0 E:Direct current electric

pulses applied toembryo. Fieldstrength 5 100 kV/m.Two pulses wereadministered rangingfrom 20 µS to 1 mS

Following fusion theembryos were exam-ined for normal devel-opment.

Electrofusion results infused embryos thatare viable and resultin normal offspring;this is a very largeexposure of a singlepulse during aninsensitive stage toteratogenesis


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21 Levengood 1969 Ambystoma maculatumand Rana sylvata(165 controls and 320exposed)

128 94 B 5 6,300 G or 17,700G, approximate dccurrent 12 mA; thiswas a static field

Birth defects in ambys-toma and frogembryos

Although there were legdeformities in thecontrols, the inci-dence was increasedin the exposedembryos at the tad-pole stage: the inci-dence of malforma-tions in ambystomawas slightly increasedin the exposed

22 Maffeo et al. 1984 Chick embryo (whiteleghorn) fertilizedeggs were incubatedfor 48 h; there weretwo control groupsand one 48-h con-tinuous irradiatedgroup; one of the con-trol groups was shamirradiated

75 150 B: Pulsed square wavesof 500 µsec durationand at frequencies of100 and 1,000 Hz;B 5 12 and 120 mG.

After exposure, theembryos were scoredfor the developmentof eight structuralfeatures: primaryvesicles, anterior neu-ropore, optic vesicles,auditory pits, truncalnervous system,somites, and bloodvessels

There was no differencein the development ofthese structuresbetween exposed,sham-exposed, andcontrol eggs withregard to the develop-ment of these struc-tures

While the exposureswere similar to thosereported by Delgado,the results contra-dicted Delgado’sresults; the embryoswere examined veryearly in development

23 Maffeo et al. 1988 Chick embryo (whiteleghorn) fertilizedeggs were incubatedfor 48 h while exposedto a magnetic field;there were 10 sepa-rate experimentswith 24 eggs in each,6 exposed, 6 controls,6 sham exposed & 6x-irradiated

60 180 B: Pulsed waves of500-µS duration andat frequencies of 100Hz; exposures of 12and 129 mG wereused; there was a42-µs-risetime;B 5 10 mG; the posi-tive control wasgroups of embryosreceiving 15.52 Gy(1,552 rad)

After exposure, theembryos were scoredfor the developmentof eight structuralfeatures: primaryvesicles, anterior neu-ropore, optic vesicles,auditory pits, truncalnervous system,somites, and bloodvessels

There was no differencein the development ofthese structuresbetween exposed andcontrol eggs withregard to the develop-ment of these struc-tures; 100% of theirradiated embryoswere abnormal

Because of discrepancyin the chick embryoexperiments amongvarious laboratorieswith regard to malfor-mation production,the authors ‘‘suggestthat factors otherthan field impositionmay be operating inthese experiments

24 Marino et al. 1976 Mice: three successivegenerations of micewere raised in a low-strength 60-Hz electicfield

331 233 E:Vertical field, E 5 130

V/cm, 60 HzHorizontal field,

E 5 100 V/cm, 60 Hz

Mortality during firstweek postpartum;mortality 8–35 dayspostpartum; theseparameters wereevaluated for animalsexposed to verticaland horizontal fields

Mice exposed to verticalelectric fields exhib-ited decreased bodyweight at 35 dayspostpartum andincreased mortalityrates for three succes-sive generations

The number of experi-mental animals areapproximated; theresults may be due togrounding microcur-rents the animalsexperienced whilefeeding; these cur-rents were larger inthe vertical field

25 Marino et al. 1980 Mice: three successivegenerations of micewere raised in a lowstrength 60-Hz electicfield; there were 19–24litters each genera-tion that were dividedinto the 2 exposedand 2 control groups

497 519 E 5 3.5 kV/m, 60 Hz;there were fourexperimental groups

Horizontal-exposedHorizontal-controlVertical-exposedVertical-control

Mortality and weight ofanimals over threegenerations; therewas no examinationof fetuses for birth-weight or malforma-tion frequency

The electric field wasassociated with anincreased mortality ineach generation andan increase in bodyweight in only thethird generation

Sufficient dataregarding mortalitywere not provided inthe paper for inde-pendent review andanalysis; the numberof experimental ani-mals are approxi-mated


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26 Martin 1988 Chick embryos: exposedembryos during thefirst 48 h of develop-ment in order todetermine which timeperiod was more sen-sitive—the first orsecond 24 h of devel-opment

1,200 300 B 5 10 mG, 100 Hz with2-µs rise and falltimes, 500-µS dura-tion

Abnormal developmentfollowing exposureduring only the first24 h of development;the second group ofexperiments examinethe frequency of mal-formations for expo-sures during thesecond 24 h of devel-opment

A significant decrease inthe poportion ofnormal embryos onlyoccured in the chickembryos exposedduring the first 24 hof development; con-trols had 93% normaland the exposed had76% normals

27 Martucciet al.

1984 Chick embryos exposedto magnetic fields for48 h after fertilization

B: 500-µs pulsed mag-netic field of 12 mGand 100 Hz; the pulsewidth was 0.5 mswith a 1.5-µs risetime

Malformations No difference in the fre-quency of malforma-tions in the exposedand controlo groups

28 Nahas et al. 1975 Rats: continuous expo-sure for 28–32 days tomagnetic fields

15 6 B: Three exposuregroups of pubescentrats were exposed tovery high flux mag-netic fields of 200,400, and 1,200 G

Mortality, growth, andmicroscopic pathologywere evaluated

These large magneticfields produced nomortality or histo-logical effects, but theexposed groups had adramatic increase inweight when com-pared to the controls

In spite of the verysmall number of ani-mals in the controland experimentalgroups the resultswere of interest;authors state that ‘‘noundesirable effects’’were seen

29 Osbakkenet al.

1986 Mice (156 mice, total);the mice were raisedfrom 1 to 3 months ina magnetic field;there were 6 experi-mental groups, eachwith a control,exposed and sham-exposed; three groupswere adults & threegroups were offspring

50 100 B 5 18,900 G (staticfield, 0 Hz) adultgroups 1 and 2exposed for 6.4hrs/day for 75 days;adult group 3 exposedfor 12 hrs/day for 30days; three groups ofoffspring wereexposed for 12 h/dayand 360, 432, and 624total hours

Mortality, growth,microscopic pathologyand blood chemistrieswere evaluated inexposed adults andoffspring. There wasno difference in any ofthe groups withregard to pathology,hematological find-ings and blood chem-istry (CBC, hct)

None of the adultsexposed to this verylarge magnetic fielddied or became ill;while body weightswere lower in exposedgroup when comparedto controls, they werenot any different thansham exposed group

The authors concludedthat this large mag-netic field had aminimal effect; theyattributed their posi-tive findings to theenvironment createdby the method ofexposure, rather thanthe magnetic field

30 Ossenkoff 1972 Rats B 5 Postnatal activityobserved postpartum

Reduced activity levelsin both males andfemales exposed inutero, with the malesmore affected

Replicated Persinger(1969) study, but theactivity differenceswere less markedthan in the Persingerstudy (only a trend)

31 Ozil andModlinski

1986 Rabbit: 2-cell blasto-meres fused by elec-trofusion, utilizingfive exposures of 1,1.5, 2.0, 2.5, or 3.0kV/cm; while manyembryos were fusedfollowing the applica-tion of E field, somewere exposed and didnot fuse

38 0 E 5 100–300 kV/m;pulse duration from35–1,000 µs;maximum toleranceof the plasma mem-brane of a 2 cellembryo is 300 kV/mfor 1,000 µs

Development of non-fused blastomeresexposed to E fieldsand allowed todevelop

The results suggest thatthe electric field canbe applied success-fully in a relativelywide range of magni-tude and durationwithout causing anyvisible teratogeniceffect on the treatedembryos


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32 Persinger 1969 Rats exposed duringpregnancy to mag-netic fields

B 5 3–30 G, 0.5 Hz Postnatal activityobserved 27 dayspostpartum

Reduced activity levelsin both males andfemales exposed inutero, with the malesbeing more affected

33 Persingerand Foster(Persingerand Pear1972)

1970 Rats exposed prenatally B 5 0.5 to 30 G, 0.5 Hz Behavioral effectsevaluated in post-natal animals; controland exposed animalstrained on an oper-ant-avoidance taskthat required the ratto learn a leverpressing response toavoid a time sched-uled shock to the feet

Evaluation of rats at 80days of age; ratsexposed prenatallyperformed the task ata slower rate, butwere able to avoid theshock to the sameextent as the controls

In the 1974 study theprocedure was modi-fied by using a foodreward and an audi-tory stimulus pairedwith the foot shock;there was no signifi-cant difference in therate of lever pressing,although exposed ani-mals displayed lessactivity

34 Prasad et al. 1990 Frog (leopard, Ranapipiens); fertilizedeggs were exposed toeither the low or highmagnetic field for 1 h.Stage: undergoing2nd meiotic division;a suspension ofnormal spermatazoawas also exposed for1 h

842 822 B 5 1,500 and 45,000 G,0 Hz for the mainfield (magnetic reso-nance imaging); char-acteristics of the fieldwere equivalent tothe MRI exposureconditions that areemployed clinicallyfor the 1,500-Gimager

Percentage of exposedand control eggscleaving or devel-oping normal tailbuds after 1,500 and45,000 G

Percentage of embryosfertilized by exposedor normal spermcleaving or devel-oping normal tailbuds

There was no effect onthe development ofthe embryos whetherthe fertilized eggs orthe sperm wereexposed to 1,500 or45,000 G

The experiments ben-efited from largenumbers of exposedand control embryos.No evidence of trip-loidy was observed;characteristics of themagnetic field weremore complicatedthan a simple staticfield

35 Rommereimet al.

1987 Rat: At 3 months of age,female rats and theirsubsequent offspringwere exposed to Efields for 19 h/day forthe duration of theexperiment; after 4weeks of exposure,the females weremated to unexposedmales

1,831 1,780 E 5 60 Hz, vertical, 100kV/m field; the expo-sure system did notproduce detectablelevels of corona,audible noise, orozone and vibration ofthe cages was lessthan 1.4 µm (60 Hz,peak to peak)

Copulatory behaviorIntrauterine mortality

No indication of alteredmating behavior;effect on fertility wasnot consistant, beingpresent in one groupof exposed and absentin another; fetaldeath was lower inone exposed groupthan it was in thecontrols

This very large studydid find some positivefindings, but theywere not repeated inidentical duplicateexperiments; theseinconsistent resultscould be due torandom variation orbecause the dose theyutilized was just atthe threshold dose

36 Rommereimet al.

1987 Rat: At 3 months of age,female rats and theirsubsequent offspringwere exposed to Efields for 19 h/day forthe duration of theexperiment; after 4weeks of exposure,the females weremated to unexposedmales

1,831 1,780 E 5 60 Hz, vertical, 100kV/m field; the expo-sure system did notproduce detectablelevels of corona,audible noise, orozone and vibration ofthe cages was lessthan 1.4 µm (60 Hz,peak to peak)

Birth defects This very large studyhad three studiesthat did not agree; inthe one, there was aincrease in malforma-tions in the exposedgroup, although notsignificantly differentfrom the controls

The types of malforma-tions were therandom pattern ofmalformations onewould see in any con-trol group, and therewas no recognizedpattern associatedwith E exposure


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37 Rommereimet al.

1989 Rat: One month expo-sure of females to Efields before mating;exposure for 19 h/daywas continuedthrough mating, preg-nancy, parturition,and rearing theyoung

450 223 E 5 60 Hz, 112 and 150kV/m

Litter size, sex ratio,mortality, maternaland fetal weight gainand growth

None of the reproduc-tive parametersevaluated differedbetween the exposedand control litters

This experiment wasinitiated to answerone question raised intheir 1987 publica-tion; one explanationfor the inconsistentresults was that theirdose was at thethreshold dose; thisproved not to be cor-rect

38 Rommereimet al.

1990 Rat: Exposure to Efields for 19 h/daywas continuedthrough pregnancy,parturition, andrearing the young fortwo generations;there were 3 exposuregroups and one con-trol group; the litterwas the experimentalunit

204 68 E 5 0, 10, 65, and 130kV/m and 60 Hz;there were threeexposed groups andone control

Percent pregnantGestational weight gainOffspring per litterNeonatal mortalityJuvenile mortalitySex ratioPostnatal weight gain

Overall, no evidence ofdetrimental effects onsurvival or growth ofthe offspring wasobserved in animalsexposed to electricfields. Reduced bodyweight in maternalF-0 130kV group, wasnot significant

This very large studywas a follow-up ofprevious research bythese investigators.Even the body weightreduction can beexplained by thereduced corporalutea, and number ofimplantations in the130-kV/m group atthe experiment’s start

39 Rommereimet al.

1990 Rats in the F-1 genera-tion in the previousexperiment weremated continued to beexposed continuouslyfor 19 h/day and theiroffspring were evalu-ated for birth defects;the embryo was theexperimental unit inthis study

3,714 1,362 E 5 0, 10, 65, and 130kV/m and 60 Hz;there were threeexposed groups andone control

Placental weightNumber of corpora luteaNumber of implanta-

tionsNumber of resorptionsFrequency of congenital

malformations

In the F-1 generationfemales were unaf-fected by exposure.The lack of malforma-tion differencesbetween groups, withthe litter as the basisfor comparison, indi-cates that E exposurewas not teratogenic

These studies furthersubstantiated theauthors’ findings thattheir originalequivocal findingswere not due to thefact that the exposurethey used was just atthe threshold for pro-ducing an effect

40 Ryan et al. 1996 Rats (Sprague-Dawley),approximately 55 lit-ters per group; expo-sure from 6 to 19 daysof pregnancy

2,219 623 B: 60 Hz MF, 0, 0.02, 2,10, G, intermittent (1on and 1 h off ); expo-sure or sham expo-sure for 18.5 h/day

Maternal toxicity andweight gain; fetalviability and weightgain; incidence offetal malformations

No observable maternalor fetal effects; therewas no increase in theincidence of con-genital malforma-tions

These results do notsupport the hypoth-esis that exposure topure, linearly polar-ized 60-Hz NF is asignificant risk factorfor the developingfetus

41 Salzingeret al.

1990 Rats were exposed for20 h/day to a 60 Hzelectromagnetic fieldfor 22 days in uteroand the first 8 dayspostpartum

21 20 E: Electromagneticfield: 60 Hz; the elec-tric field componentwas; 30 kV/m rms.B 5 1 G

Animals exposedinutero were trainedto emit an operantresponse when rein-forced with food

The exposed rats gradu-ally responsed atlower rates than didsham-exposed con-trols; exposed rats didnot differ from con-trols in body mass,appearance, grosslyobserved activitylevel or incidence ofdisease

Although our resultswith electromagneticfields do not neces-sarily signify delete-rious effect, theirrobustness over timeand changing condi-tions indicates thatthey leave a lastingimprint and thereforecannot be ignored


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42 Sandstromet al.

1987 Chick embryo exposedto B for first 48 h ofembryonic develop-ment

136 149 B: Asymmetrical saw-tooth waveform mag-netic field. Threeexposures of 1, 15,and 160 mG; timederivatives of 300,3,000, and 33,000 G/s

The control (C) andexposed (E) chickembryos were scoredafter 48 h for embry-onic staging, for non-fertilization and forfrequency of abnor-malities

Defects 1 no develop-ment—1 mG, 15 mG,160 mG

E 12.9%, 4.9%, 17.9%C 12.9%, 11.9%, 13.5%The mean stage in the

160 mG group was10.3 in the controland 10.8 in theexposed

There were 27–46embryos in each ofthe six experimentaland control groupsand 2–6 abnormalembryos in thesegroups; while therewas no statisticalincrease in abnor-malities, the groupswere small

43 Seto et al. 1984 Rats chronicallyexposed 60 Hz electric(E) field in which theywere conceived, born,and raised for 4 gen-erations, beingexposed 21 h/day

1,346 1,337 E 5 80 kV/m, 60 Hz;ambient E and Bfields were 0.1 V/mand 0.1 mG, respec-tively; there was acapacity to exposelarge numbers of ani-mals continuouslyand the cages weredesigned to eliminatethe potential forshock in the exposedgroup

Fertility, litter size atbirth, litter size atweaning, sex ratio,weight of males andfemales at weaning,and the frequency ofmalformations in thecontrol and exposedgroups; this studyhad very large groupsof animals when com-pared to other studies

There were no signifi-cant differencesbetween the controlsand exposed for anyof the parametersthat were studied;there was not evenminimal differences.These results may bedue to the magnitudeof the study

While most of the end-points were carefullystudied, they did notobtain weights of thenewborns, nor didthey examine thoseexposed in utero formalformations in acareful manner; theauthors discussed thepower of their study

44 Sienkiewiczet al.

1994 CD 1 mice, 23 pregnantmice exposed and 21sham irradiated

184 168 B: 50-Hz sinusoidalmagnetic field at 20µT throughout preg-nancy

Standard develop-mental indicesincluded (eyeopening, pinnadetachment, haircoat, tooth eruption,sexual maturity, andgrowth) and reflexbehaviors (airrighting, surfacerighting, forepawgrasp, cliff avoidanceand negative geo-taxis)

The results suggest thatprenatal exposure to50-Hz magnetic fielddoes not engenderany gross impair-ments in the post-natal development orbehavior of mice

Well-planned andexecuted study; theinvestigations noted afew differences insome of the param-eters, but the fewpositive or negativeresults were not con-sistently associatedwith the exposed orsham group

45 Sikov et al. 1984 Rat: (1) females exposedto (E) 6 days beforemating until term; (2)females exposed fromconception, and litterand mother exposedfor another 8 days: (3)same as 2, exceptexposure began 17thday and ended 25days postpartum

337 128 E: 60 Hz; E 5 100 kV/m;exposure for 20 h/day

Fertility, resorptions,viability, sex ratio,birth weight, post-partum growth, mal-formations

Postnatal behavioraltests such as move-ment, grooming,standing and rightingreflex and geotropism

E did not affect any ofthese reproductiveparameters

Transient behavioralchanges wererecorded in the neo-natal period, but werenot found when theanimals were tested21 days postpartum

Finding occasional sig-nificant differencescannot be dismissed,but if enough com-parisons are madesome will be positivejust by chance. Ratscan perceive andrespond to 60-Hz fieldstrengths below thoseused in these studies


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46 Sikov et al. 1987 Hanford miniatureswine: F-0 group wasexposed for 4 mobefore breeding andfor the first 100 dayspostpartum for tera-tology study; this isnot a species forwhich there areextensive birth defectdata

261 114 E 5 30 kV/m; uniform,vertical 60-Hz field;exposure for 60 h/day,7 days/week

F-0 and F-1 study werea birth defect studies;birth weight andlitter size demon-strated primarilynegative findings;rates of malforma-tions seemed veryhigh in this study,including the controls

F-0 exposed group hadslight increase inmalformations butthe difference was notsignificant; the F-1groups did have a sta-tistically significantincrease in malforma-tions in the exposedgroup

The increase in malfor-mations was in themusculoskeletal anddigit category; thesewere not described.There were no CNS orcardiovasculardefects described;increase in malforma-tions not consistantfinding in theseexperiments

47 Sisken et al. 1986 Chick embryo (whiteLeghorn) fertilizedeggs were exposedcontinuously to amagnetic field for 7days or for 24 h; theembryos were fixedafter 7 days of devel-opment and blindlyevaluated for malfor-mations

454 344 B. Two complicatedpulses were used; onesignal was similar tothe pulse used in thebone healing studies;the B fields of the twopulses were: B 5 2.5G peak, 0.1 G aver-age; the second pulsewas B 5 16 G peak,0.5 G average

Birth defects No increase incidence ofmalformations in theembryos exposed for 7days or 24 h, whencompared with thecontrols. Study wasable to discern a 30%increase in malforma-tions with a 99%probability

There was a significantdifference in the inci-dence of malforma-tions in the controlsin this experimentand the controlsreported by Ubedaand Delgado, but theexposures and experi-mental design werenot identical

48 Soeradi andTadjudin

1986 Rat: 90 male rats weredivided into 10groups and placed inan electrostatic field;each group consistedof 7 exposed and 2controls; there were 6exposure groups; theywere observed 3, 30,60, and 90 days afterexposure for fertility

152 51 E 5 1, 2, 3, 4, 5, 6, and 7kV; the 7 experi-mental groups wereexposed to increasingincrements of E; ani-mals were exposed for1 mo; only malesexposed

Fertility, litter size, andbirth defect incidence

All male animals in allexposure groupsremained fertile; thelitter size wasreduced 30% in theexposed; all exposuregroups were equallyreduced and thereduction was present3, 30, 60, and 90 dayspostexposure

While litter size wasreduced in all dosegroups, malforma-tions only appearedin the groups receiv-ing 6 and 7 kV; themalformations wereinadequately de-scribed, and the littersize data were notbiologically plausible

49 Steen andOftedal

1967 Drosophila egg hatch-ing; eggs exposed tostatic magnetic fieldfor 20 h and the per-centage hatching wasdetermined

400 400 B 5 1,600 G to 500 G ina static magnetic field

Egg hatching abilitywas determined inexposed and controleggs; the endpointwas the time requiredto go from 20% to 80%of the eggs havingcompleted hatching

There was no differencein the hatching timebetween the eggs inthe magnetic fieldand the unexposedeggs

50 Stern andLaties

1985 Rats: adult female rats,120 days old, weretrained to press alever if they perceivedan electric field

5 0 E fields used in thestudy varied at 1–30kV/m; vertical 60-Hzelectric field; femalerats were trained topress a lever in thepresence of a 55-kV/mRMS electric field

Recognition of an elec-tric field in adultfemale rats

Female rats coulddetect a vertical elec-tric field; thethreshold of detectionranged between 3 and10 kV/m; theseresults were indis-tiguishable from thestudies with malerats

The fact that femalerats can perceive Efields adds anotherdimension to the com-plexity of evaluatingthe effects of E fieldson reproduction, sincechanges in behaviorcould indirectly influ-ence reproductiveperformance


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51 Stuchlyet al.

1988 Rat: female rats wereexposed 2 weeksbefore conception andthroughout preg-nancy

987 340 B alternating field.Sawtooth waveform(18,000 Hz) similar toa VDT, but at a muchhigher exposure;exposure was at 0, 57,230, and 660 mG for7 h/day

Maternal weight gainFetal and placental

weightLitter sizeLive fetuses and resorp-

tionsMajor and minor mal-

formations

All reproductive param-eters were indistigu-ishable from controlresults; there werefewer skeletal vari-ants in higher expo-sure groups & anincrease in minorskeletal anomales byfetal but not litteranalysis

This well designedstudy utilized appro-priately large controland exposed groups;while there were noreproductive effects,there was a reductionof the maternal lym-phocyte count,although it was stillwithin the normalrange

52 Tribukaitet al.

1986 Mice: Pregnant micewere exposed to apulsed magnetic fieldfrom conception tothe 14th day of preg-nancy; at 18th day ofpregnancy the fetuseswere examined; therewere 4 experimentalgroups with 2 wave-forms and 2 doses

1,065 517 B: Sawtooth (ST) andrectangular (R) wave-forms were used; 10-and 150-mG expo-sures were used witheach waveform;fetuses were notequally distributedamong 4 exposedgroups (ST 10 and150 mG, R 10 and 150mG

Total implantationsLiving and dead fetusesFetal weight (after fixa-

tion)MalformationsSkeletal malformations

(ribs & vertebrae)

There were no positiveresults from R pulseexposure; the STpulse group wasequally negative butthere were 5umbilical hernias inthe 150-mG group,but malformationswere not statisticallyincreased

The authors concludedthat ST pulses mighthave a teratogeniceffect, yet the dataindicated that theexposure did notaffect growth, mor-tality or litter size,and the malformationdata was not signifi-cantly different fromthe controls

53 Tyndall 1993 C57BL/61 mouse, 15dams in the controland exposed groups;exposure on the 7thpostconception day;three dams dis notbecome pregnant

102 102 MRI: pregnant animalsplaced in isocenter ofthe magnet or at themagnet lumen; 1.5Telsa magnet with aT2-weighted spinecho technique of 36minute duration witha TR and TE of 2100and 50 ms, respec-tively

Cranialfacial perimeterand crown rumplength

Decrease in crown rumplength and craniofa-cial perimeter whenmeasured on the 14thpostconception day

No actual measure-ments are provided;teratogenicity cannotbe acribed to a growthparameter if you donot allow the animalsto reach term; it ispossible that thesefindings are not per-manent

54 Tyndall 1990 Mice: C57BL/6J micewere chosen becauseof their genetic pre-disposition to eyemalformations; preg-nant mice wereexposed to both X-rayand a magnetic fieldon day 7 of pregnancy

443 116 B 5 15,000 G; the mag-netic field was gener-ated by a GyroscanMRI T 2 spin-echotechnique; TE 50 ms,TR 2,100 ms; Expo-sure was on day 7, 30min after 0.3-Gy X-ir-radiation

The investigator wasexamining whetherthere was an additiveor synergistic terato-genic effect of B whencombined with X-ray;teratogenesis of theeye was the specificendpoint evaluated,although data onlitter size wereobtained

This very large MRIfield did not enhanceX-ray teratogenicityof the eye; moreimportant was thefact that, at 15,000 G,the exposure did notaffect litter size or theincidence of resorp-tions

The author concludedthat the MRI expo-sure did not con-tribute to the inci-dence of eyemalformations, butthen he questions ofwhether MRI canlower the thresholdfor X-ray teratogen-esis; his data indicatethat this is unlikely


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55 Ubeda et al. 1983 Chick embryo: Exposedto B during the first48 h of development;fixed in Carnoy’s andexamined under abinocular microscope;at 48 h percentageabnormals was deter-mined, although noembryos wereobserved at term

259 364 B exposures were all100 Hz and had apulse of 500 µs; thepulse had 4 differentshapes due to rise-times of 100 µs (A); 2µs (B); 42 µs (C) and42 µs with ripples (D).There were 5 expo-sures in each groupranging from 4 mG to1,040 mG

Malformations thatwere evaluatedincluded

cephalic nervous systemtruncal nervous systemheart; extraembryonic

vascularization;Somites. (authorsstate earth’s B field is75 times .4 mG)

Teratogenesis wasobserved with the100-µs pulse (Apulse), but with anexposure window of10–139 mG; not aboveor below; when 4 and10 mG were deliveredwith 2 and 42-µspulses teratogeneseinvolved all systems

Authors confirm sensi-tivity of chick to EMFat extremely low fre-quencies and inten-sity. The pulse shapemay be a decisivefactor in determininga ‘‘no’’ or ‘‘severe’’effect; there were4-fold shifts in theincidence of malfor-mations in controls

56 Wiley et al. 1992 Mice: CD 1 mice wereexposed to a 20-kHzsawtoothed magneticfield, similar to thoseassociated with aVDT, from day 1 today 18 of pregnancy;there were at least140 pregnant dams ineach of 4 exposuregroups

5,296 1,782 B 5 0, 40, 170, and 2000mG at 20 kHz; therewere 3 exposuregroups and a controlgroup

0 G 40 mG% preg-nant 76.2% 81.2%

# im-plants 11.2 11.8

% deadfeti 7.1% 5.3%

Ext. mal-form. 6.4% 113.%

Visc mal-form. 13.6% 14.7%

170 mG 2 G

87.6% 77.4%

11.5 11.4

8.0% 6.3%

6.8% 4.2%

13.6% 19.4%

This study reflects theimpact of largesample sizes on sta-tistical tests; varia-tions in smallsamples may be mis-interpreted to havebiological meaning;these and all otherreproductive param-eters studied werenegative

57 Zervins 1973 Chick embryo: exposedto 160 G B field forfirst 19 days ofembryonic develop-ment and were theobserved for hatch-ability and the pres-ence of CNS malfor-mations

62 70 B 5 160 G, peak topeak, 26 kHz;embryos wereexposed to this fieldfor the first 19 days ofdevelopment

HatchabilityMalformations in

hatched eggs

The hypothesis thatEMF exposurereduces hatchabilitywas rejected; no grossCNS malformationswere observed in anyof the hatchedembryos

64.5% of the exposedembryos hatched, butonly 48.5% of the con-trols; it would havebeen helpful to knowthe status of theembryos at 48 h ofdevelopment, just asin the 48-h studies, itwould have beenimportant to havehatch data

58 Zusmanet al.

1990 Mice: blastocyst devel-opment

Rats: embryotoxicity in10.5 day cultured ratembryos

In vivo rat tratologystudy. (animal num-bers apply to thisstudy)

301 86 E: Mouse blastocyststudy: EMF pulse of1, 20, 50, 70, and 100Hz. E 5 0.6 V/m,pulse cycle 5 0.1 sec,the pulse pause willvary with the fre-quency, rat embryoculture and in vivorat teratology studieshad continuous expo-sure at 20, 50, and 70Hz

Mouse blastocyst devel-opment

Rat embryo cultureIn vivo rat teratology

study with 20, 50 and100 Hz examinedlitter size, fetalgrowth, birth defects,and postnatal devel-opment

20 and 50 Hz wereembryotoxic, inhib-iting blastocyst devel-opment. 50% did nothatch; 50 (22%) & 70(30%) Hz affected thedevelopment of fore-brain, optic and oticvesicles, limb bud,and neural tube clo-sure

In the in vivo teratologystudy, there was apossibility that thebirth weight wasincreased and littersize decreased in theexposed; there was noincrease in malforma-tions due to EMF;authors ask about thenature of thematernal protectiveeffect

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rable to the largest fields encountered in very closeproximity (,10 cm) to household appliances such asspiral wound electric hot plates.

The current density induced in the body is propor-tional to the diameter of the body (or the body compo-nent), the frequency of the field (for the frequenciesbeing considered), and the conductivity of the tissue.Unlike the coupling of electric fields into the bodywhere the field inside is orders of magnitude below thefield outside the body, magnetic fields readily enter thebody; therefore, the magnetic fields inside and outsideare virtually of the same strength. However, the in-duced currents in the body are difficult to determinebecause of the inhomogeneity of the body, as reflected inthe conductivities of the various tissues. When themagnetic field is pulsed, there is a spectrum of frequen-cies in the output that includes the fundamental pulserepetition frequency and many of its harmonics. Oftenthe spectral information is missing or incomplete in thereports of experiments making the results impossible,or at least very difficult to interpret.

The ability to interpret all these studies properly willdepend on some understanding of how organisms andcells interact with electric and magnetic fields. It isimportant to recognize the vast range in exposuresexperienced by the population when evaluating theepidemiological studies, the secular trend data, theanimal experiments and the biological plausibility of someof the results that have been reported. The followingdiscussion will address the nature of these interactions.

Environmental risk parameters or modifiers

If attention is directed toward environmental influ-ences or agents that interfere with embryonic develop-ment, there are several scientific or embryologic prin-ciples that have an important impact on assessing theeffect of various environmental agents on the develop-ing embryo. These include the impact of: (1) embryonicstage, (2) dose or magnitude of the exposure, (3) thresh-old concept (Table 3), and (4) species differences. Theimportance of the embryonic stage and magnitude ofthe exposure is quite obvious. But the threshold concept

is particularly important and is frequently ignoredwhen attempting to determine reproductive risks. Tera-togenic effects are deterministic or threshold effects(Table 3). This means that if reproductive effects can becaused at high EMF exposures, there will still be ano-effect dose. Other factors such as pharmacokineticsand metabolism and placental transport are of noimportance when evaluating the reproductive risks ofan external physical agent such as EMF. Whether thereis a variation in species susceptibility to EMF is amatter for conjecture, but it is evident that the actualexposure to EMF will vary with the size of the organismbeing exposed within the same EMF.

Mechanisms of teratogenesis

Based on his review of the literature, Wilson (’73)provided a format of theoretical teratogenic mecha-nisms: mutation; chromosomal aberrations; mitotic in-terference; altered nucleic acid synthesis and function;lack of precursors, substrates, or coenzymes for biosyn-thesis; altered energy sources; enzyme inhibition; osmo-lar imbalance, alterations in fluid pressures, viscosi-ties, and osmotic pressures; and altered membranecharacteristics. Even though an agent can produce oneor more of these pathologic processes, exposure to suchan agent does not guarantee that maldevelopment willoccur. Furthermore, it is possible that a drug, chemical,or physical agent can have more than one effect on thepregnant women and the developing conceptus, andtherefore the nature of the agent or its biochemical orphysiological effects will not in themselves predict theexistence or the magnitude of the human reproductiveeffect. The discovery of human teratogens has comeprimarily from the evaluation of human exposures.Animal studies and in vitro studies can be very helpfulin determining the mechanism of teratogenesis (Brent,’81, ’88). The mechanisms of teratogenic agents arelisted in Table 4 (Beckman and Brent, ’86). A review ofthe mechanisms of teratogenesis listed in Table 4 showsthat most of the mechanisms associated with terato-genic agents do not apply to the effects of EMF. Cytotox-icity, receptor-mediated effects, metabolic inhibition,

TABLE 3. Comparison of stochastic phenomena and threshold phenomena in the etiology of diseases producedby environmental agents and the risk of occurrence*

Relationship Pathology Site Diseases Risk Definition

Stochastic phe-nomena

Damage to a singlecell may result indisease

DNA Cancer, mutation Exists at all expo-sures, althoughat low exposure,the risk is belowthe spontaneousrisk

The incidence ofdisease increaseswith exposurebut the severityand the nature ofthe disease in thepatient remainthe same

Threshold phe-nomena

Multicellular injury Great variation inetiology affectingmany cell andorgan processes

Malformation,death, growthretardation,chemical toxicity,etc.

Completely disap-pears below acertain thresholddose

Both the severityand incidence ofdisease increasewith higher expo-sures

*Modified from Brent (’86b).

REPRODUCTIVE/TERATOLOGIC EFFECTS OF LOW-FREQUENCY EMF 275

mechanical problems of constraint, and vascular disrup-tion are not effects that are likely to occur followinglow-frequency EMF exposure.

However, even if one understands the pathologiceffects of an agent, one cannot predict the teratogenicrisk of an exposure without taking into considerationthe developmental stage and the magnitude of theexposure and reparability of the embryo. This would beespecially true for physical agents such as EMF.

In vivo animal studies and in vitro tests

Background information. The study of reproduc-tive effects in animals has involved the use of the in vivoanimal testing with the chick embryo, chickens, cows,mice, rats, and Hanford miniature swine, and the use ofin vitro studies.

The purpose of in vitro tests and in vivo animaltesting is to determine whether exposure to a newenvironmental agent represents a human reproductiverisk. The difficulty with the present in vitro testingsystems is that these systems have not been reliablepredictors of human teratogenicity for drugs and chemi-cals (Brent, ’64, ’72, ’81, ’86a,b, ’88; Schardein, ’88).While every drug that has been used for cancer chemo-therapy in humans has been teratogenic in animalmodels, only a small fraction have resulted in humanteratogenesis. Many drugs and chemicals can producemalformations, embryonic death, or growth retardationat doses far above the usual human exposure. Theseagents are therefore teratogens, but they are not neces-sarily responsible for human teratogenesis. Similarly,there may be animal experiments that demonstratesome reproductive effect with EMF at frequencies andintensities that are very unlikely to occur in humanpopulations; therefore, such an exposure would notrepresent a realistic reproductive risk.

In reality, the largest group of drugs and environmen-tal agents are the potential human teratogens becausethey include all drugs, chemicals, and physical agentsthat can produce embryotoxic and fetotoxic effects atsome exposure. Because these exposures are not used

or attained in the human, they represent no, or mini-mal, risk to the human embryo.

The greatest problem facing the regulatory agenciesand the teratologist is how to determine the margin ofsafety that should be required for exposures to poten-tial reproductive toxicants. This can be accomplished ifwe recognize that the threshold concept of teratogen-esis pertains and that even when drugs, chemicals, andenvironmental agents have toxic effects, there are alsosafe exposures for these agents. In most instances, expo-sures of one to two orders of magnitude below the no-effectdose represent safe exposures to the embryo (Table 3).

Furthermore, we could better interpret the animaldata if we included in our evaluation the ratio of theno-effect dose to the usual human dose. If the moremodern reproductive testing protocols for reproductivetesting are used, safe levels of exposure can be approxi-mated with greater accuracy (Brent, ’64, ’88; Slikker, ’87).

Despite extensive efforts to improve in vivo animaltesting (Warkany et al., ’63; Brent, ’64, ’88; Wilson, ’65;Chernoff and Kavlock, ’82; Vorhees, ’83; Kimmel et al.,’85, ’86) and to design in vitro test systems (Brent, ’88;Schardein, ’93), there are still important limitations ofour ability to apply these in vitro and in vivo testingmodels directly to human risk assessment (Brent, ’64,’72, ’88; Fraser, ’77; Schardein, ’93). In spite of theextensive use of animal testing and in vitro tests, theyhave been minimally involved in identifying humanteratogens since the thalidomide tragedy. Most of thehuman teratogens have been identified since 1960 bymeans of human epidemiological studies, i.e., alertphysicians reporting of clusters, case control studies, orbirth registries (Brent, ’85a,b, ’88; Brent et al., ’86;Brent and Holmes, ’88). In a few instances, animalstudies have predicted human teratogenicity and/orsupported the suspicion of teratogenicity in the human(valproic acid, retinoids).

In an excellent recent review of the subject of testingfor reproductive effects, Schardein (’93) pointed outthat whole-animal testing has not been modified orimproved dramatically from the original two-litter andthree-litter tests. He said: ‘‘the segment II phase of the1966 Food and Drug Administration (FDA) Guidelinesfor Reproduction Studies . . . remains after two decadesof use, a valid testing procedure for identifying thepotential for teratogenic induction and other develop-mental toxicity in laboratory animals. Its chief limita-tion resides in the extent to which such testing proce-dures are predictive of toxicity in the pregnant human,not in any inherent inadequacy of the testing proce-dure.’’ In 1964, it was suggested that every whole-animal mammalian testing protocol used for predictingteratogenicity in humans should have certain essentialfeatures (Brent, ’64) beyond those already suggested in1963 by an international committee. Reproductive tox-icity testing should include (1) the determination of theratio of the maternal LD50 to the fetal LD50; (2) theevaluation of embryonic death and growth retardation,as well as teratogenicity; and (3) exposures during fetal

TABLE 4. Mechanisms of actionof environmental teratogens*

1. Cell death, delayed differentiation, mitotic delay beyondthe recuperative capacity of the embryo or fetus (ionizingradiation, chemotherapeutic agents, alcohol)

2. Biologic and pharmacologic receptor-mediated develop-mental effects (i.e., etretinate, isotretinoin, retinol, sexsteroids, streptomycin, thalidomide)

3. Metabolic inhibition (i.e., warfarin, anticonvulsants,nutritional deficiencies)

4. Inhibition of cell migration, differentiation and cell com-munication.

5. Physical constraint, vascular disruption or insufficiency,inflammatory lesions, amniotic band syndrome.

6. Interference with histogenesis by processes such as celldepletion, necrosis, calcification or scarring.

*Modified from Beckman and Brent (’86).

276 R.L. BRENT

stages because of the importance of critical cell loss ofimportant organs (brain, gonads) during mid- and lategestation.

These suggestions have been only partially includedin routine whole-animal testing procedures for reproduc-tive toxicity some 30 years after the original suggestion(Brent, ’64). Because of advances in science in generaland teratology specifically, teratology and reproductivetoxicity testing that is more meaningful and morepredictive of human effects can and will be designed.

While the cost of such an evaluation would be greaterthan for the 1966 FDA segment II reproductive studies,the ability to predict human reproductive risks andeven more important, human reproductive safety, wouldbe improved. A ratio between the no-effect level and thehuman therapeutic dose that is considered safe shouldbe established. If this concept is not emphasized, thereproductive toxicologists will have no incentive todetermine the no-effect level, and they will not generatedata that will support the value of the ratio of theno-effect level to the therapeutic dose in establishingsafe levels of usage or maximum permissible exposures.

In vitro tests. Each test system has some uniquefeatures that have been attractive to some investiga-tors. With the proliferation of these systems, it isobvious that the cost of performing a combination ofthese techniques could be more than a whole-animalreproductive study.

More important than these unique features or pos-sible reduced cost is an important principle, ‘‘the natureof these tests indicate that they can NEVER be morepredictive of teratogenicity or embryotoxicity than invivo systems’’ (Schardein, ’93). Schardein (’88) stated itquite eloquently ‘‘the real dilemma in their use iseliminating procedures in animals and at the sametime making tests more predictive; an incongruity tosay the least.’’

In vitro tests offer the experimental embryologists anopportunity to study various facets of their field. Theycan be used (1) to study normal embryonic developmentand differentiation, (2) to study some mechanisms ofteratogenesis and embryotoxicity, (3) to study pharma-cokinetics and the effect of isolated or combined meta-bolic products, and (4) to screen for cytotoxicity andinterference with differentiation.

It is also obvious that in vitro testing, using a singlesystem, is going to fail to delineate important reproduc-tive toxicity effects, including: (1) late central nervoussystem effects (brain histogenesis, behavior); (2) uniqueunpredictable embryotoxic specificity (aspermatogen-esis, cardiovascular hemodynamic changes, vasculardisruption, yolk sac, or chorioplacental effects; (3) differ-entiating between recuperable versus nonrecuperablegrowth retardation; (4) transplacental carcinogenesis;(5) lethal effects in the preimplantation period; and (6)effects not previously reported.

Chick embryo. One of the most frequently usedanimal models to study EMF effects has been the chickembryo. There have been approximately 20 studies of

chick embryos exposed to EMF, which have not yieldedconsistent results. In fact, the results were in suchdisagreement that an international study was designedin an effort to resolve the discrepancies (Berman, ’90).Six laboratories located in Europe and the UnitedStates used the same method of exposing chick embryosjust after fertilization (unipolar pulsed magnetic field of500 ms with a 2-ms rise and fall time and a magneticfield, B 5 10 mG, 48-h exposure). The six laboratoriesagreed that the EMF had no effect on viability, stage ofdevelopment, and somite development. They disagreedon the ability of a 10-mG magnetic field to producemalformations. Two of the laboratories reported anincrease in malformations in the exposed embryos,while the other four laboratories did not.

The chick embryo has not been an acceptable modelfor studying the potential for teratogenic effects ofdrugs and chemical in humans. It is an excellent modelfor studying normal and abnormal development andthe mechanisms involved in abnormal development.The proponents of the chick embryo model have rea-soned that EMF research should be an exception to therule since EMF characteristics are very much likeionizing radiation, having a direct effect on the embryo(Brent, ’60; Brent and McLaughlin, ’60; Brent et al., ’86;Brent and Bolden, ’68). Since metabolic differences andplacental transport differences among species are notlikely to affect the results of EMF exposure, the investi-gators have justified the studies in the chick embryo tobe appropriate for determining potential human risks.

The controversy over the results in the chick embryoexperiments involves two areas: (1) does EMF exposureincrease the incidence of congenital malformations?,and (2) is there a window of susceptibility that involvesboth frequency (Hz) and exposure (G) as suggested byUbeda et al. (’83)?

The large number of experiments do not answer thequestion of teratogenic potential because of their de-sign. The initial experiments examined fertilized em-bryos after approximately 48 h of exposure. All theother experiments essentially copied this design (Table2). The embryos were either examined carefully under adissecting microscope or were prepared for histologicalexamination. The presence of abnormalities was judgedby the individual investigators. There are two seriousdifficulties with this model. By examining the embryosat such an early stage, there is no way to be certain thatthe variations that were observed are malformations. Ifthey are malformations, would the embryos survive?The first step in any series of experiments is to deter-mine the potential for teratogenicity by examining theoffspring at the end of gestation or incubation. This tellsthe investigator whether there is an increase in mal-formed survivors and/or embryonic death (resorptionsin a rodent model). None of the chick embryo investiga-tions addresses this problem and therefore their re-sults, by themselves are difficult to interpret. On theother hand, Krueger et al. (’75) exposed chickens tolarge EMF fields throughout pregnancy (E 5 1,600


V/m, 60 Hz, and B 5 1.4 G, 60 Hz). The results did notdemonstrate an increase in malformed chicks at thetime of hatching. The exposures were high, and thisrelates to the next controversy.

Ubeda et al. (’83) used the chick embryo model, whichinvolved a 48-h exposure after obtaining the fertilizedegg. The exposure consisted of a 100-Hz magnetic fieldwith pulses of 500 ms and four differently shapedpulses. The exposure levels ranged from 4 to 1,040 mG.The investigators concluded that malformations of manyorgan systems were produced and that there was awindow of sensitivity for producing teratogenesis of10–139 mG. The serious difficulty with this experimentand many of the others is the small number of chickembryos in each group. Furthermore, fourfold differ-ences in the incidence of malformations were found inthe control groups. Using the same data, Ubeda andcolleagues concluded that the shape of the pulse wouldalso dramatically change the teratogenic effect at 10–139 mG.

The chick embryo data available for analysis are notuseful for predicting reproductive effects in humans, orfor raising concerns about reproductive problems inhumans. If the results in the chick embryo were subse-quently duplicated in appropriate animal models, thedata derived from the chick embryo experiments mightbe interpretable.

Three recent papers using the avian embryo havereported conflicting results. Pafkova et al. (’96) exposedchick and rat embryos to 50 Hz at 6 microtesla (µT) or10 µT. No significant alterations of the chick or ratembryogenesis were found after repeated exposures.They reported that EMF exposure decreased the terato-genicity of X-irradiation. But the authors provide noexplanation for this finding. Terol and Panchon (’95)exposed quail embryos to 50-Hz and 100-Hz EMF atexposures of 0.2–3.2 µT. Although they reported somepositive findings, they examined the embryos very earlyin development, a serious error of previous investiga-tors using avian embryos. Yip et al. (’94) exposed chickembryos to 1.5 T from a magnetic resonance imaging(MRI) facility, but these investigators also examinedthe embryos very early in development. It is importantto have some embryos complete their incubation sowhatever effects are observed early in development canbe evaluated at hatching. That is the only way you candetermine whether you have an irreversible develop-mental effect. We will next examine some of the mamma-lian data involving EMF exposures.

Cows. Algers and Hultgren (’87) measured six repro-ductive parameters in pregnant cows. The cows wereexposed for a 4-month period beginning in June. Therewere 58 cows in the exposed and control group. Theexperimental group was exposed to 50-Hz, 400-kVhigh-power lines. The continuous exposure to the cowswas; E 5 4 kV/m and B 5 20 mG. There were nochanges in any of the reproductive parameters thatwere studied—fertility, estrous cycle, progesterone lev-els, intensity of estrous, and viability of the offspring.

There was no increase in the incidence of malforma-tions. This study contained too few animals to deter-mine, for example, a twofold increase in malformations.It is of interest that the B exposure was in the middle ofthe range that was supposed to be most teratogenic inthe chick.

Mouse. The experiments with pregnant mice weremost interesting. Table 2 summarizes 10 studies, aswell as others that have been briefly reported (Bellossi,’91; Frolen and Svedenstal, ’89). The experiments var-ied in size, goals, and quality. For example, the study byWiley et al. (’92) was designed to examine the risk ofVDTs, indicated by the frequency of the magnetic fieldthey selected. The mice were exposed to 0, 40, 170, and2,000 mG. The study contained more mice than all theother reports combined: 5,296 exposed and 1,782 con-trols. The reproductive parameters that were studiedincluded the percentage of inseminated females thatbecame pregnant, the number of implantations, thepercentage of dead embryos, and the percentage ofexternal and visceral malformations. The results, sum-marized in Table 2, indicate that there were no reproduc-tive effects in the exposed mice, even with a very highmagnetic field exposure.

In another large study of pregnant mice, Tribukait etal. (’86) examined the effects of a wide spectrum ofelectromagnetic waves on pregnant mice. Two of theseexposures included pulsed 100-Hz magnetic fields,where B 5 10 and 150 mG. These exposures were at thelevel and frequency reported to produce malformationsin the chick embryo. The mice were exposed fromconception until the 14th day of development. Thefollowing reproductive endpoints were evaluated: totalimplantations, number of living and dead fetuses, fetalweight (after fixation), and percentage malformationsat term. Most of these parameters were not signifi-cantly different from those of the controls.

There may be some benefit in comparing the chickembryo data with those reported by Zusman et al. (’90)using embryo cultures exposed to electrical fields. Theyexposed preimplantation mouse embryos and moni-tored their development until the blastocyst stage.These investigators also observed the effect of a 0.6-V/melectric field on 10.5-day cultured rat embryos. Both thecultured mouse and rat embryos were affected by theexposure. The mouse zygotes were retarded, and the ratembryos exhibited abnormal limb development. Butwhen rats were exposed throughout pregnancy to thesesame fields at 20, 50, or 70 Hz, and the offspring wereexamined at term, there was no increase in congenitalmalformations. This is an excellent example of thedifficulty of interpreting the significance of embryoculture experiments, if the evaluation is performedearly in development, and the investigator has noknowledge of the status of the fetuses at the end ofpregnancy (mammals) or incubation (chick).

Tyndall (’90) exposed pregnant mice to magneticfields comparable to magnetic resonance imaging expo-sures (15,000 G, 0 Hz). Unfortunately, these exposures

278 R.L. BRENT

were in combination with a teratogenic dose of X-ray.Tyndall concluded that the B exposure did not add tothe teratogenic effect of X-irradiation. In a subsequentpaper, Tyndall (’93) reported that MRI exposure (Table2) on the 7th postconception day in the C57BL/61mouse resulted in a significant decrease in crown-rumplength and craniofacial perimeter when measured onthe 14th postconception day. No actual measurementsare provided. It is important to note that teratogenicitycannot be ascribed to a growth parameter if you do notallow the animals to reach term. It is possible thatthese findings are not permanent and therefore cannotbe labeled as a teratogenic result. Other serious prob-lems with this study were that insufficient data wereprovided to evaluate the results reported.

Kowalczuk et al. (’94) and Sienkiewicz et al. (’94),from the laboratory of the Radiation Protection Boardin the United Kingdom, used CD 1 mice exposed to a50-Hz sinusoidal magnetic field at 20 µT. The evaluated(Table 2) developmental indices which include thepreimplantation and postimplantation survival, sexratio, internal and external malformations, standarddevelopmental indices included (eye opening, pinnadetachment, hair coat, tooth eruption, sexual maturity,and growth) and reflex behaviors (air righting, surfacerighting, forepaw grasp, cliff avoidance and negativegeotaxis). They reported that there were no statisticallysignificant field-dependent effects on preimplantationand postimplantation survival, sex ratio, or internaland external malformations. They also reported: ‘‘Theresults suggest that prenatal exposure to 50 Hz mag-netic field does not engender any gross impairments inthe postnatal development or behavior of mice.’’

Rat. There are 12 rat studies summarized in Table2, in which pregnant or nonpregnant rats were exposedto electric or magnetic fields, as well as a brief report(Butenkotter et al., ’89). Investigators have demon-strated that rats and other species can recognize andcan be conditioned to an EMF (Cabanes and Gary, ’81;Stern, ’83; Stern and Laties, ’85). Male and female ratswere able to detect 50–60 Hz electric fields with athreshold range from 2 kV/m to 10 kV/m. Sagan et al.(’85, ’87) demonstrated a threshold for electric fieldsranging from 7.9 to 13.3 kV/m. Cooper et al. (’81)reported detection thresholds of 21 kV/m and 50 Hz forpigeons; Rogers (’89) reported a detection threshold of12 kV/m for baboons. The fact that female rats canperceive E fields adds another dimension to the complex-ity of evaluating the effects of E fields on reproduction,because changes in behavior could indirectly influencereproductive performance and postnatal rearing prac-tices in animals.

The research group at the Battelle Northwest Labora-tories that is interested in reproductive toxicants haspublished a number of investigations using rats ex-posed to electrical fields (Rommereim et al., ’87, ’89, ’90;Sikov et al., ’84, ’87). These five studies were notduplicate experiments; rather, they represent pursuitsof unanswered questions raised in their previous stud-

ies. They evaluated a battery of reproductive outcomesfollowing the exposure of pregnant animals to electricfields (E). Most of their findings were negative, but theyindicated in their report that if a battery of tests wereperformed, it would not be unexpected to have a smallpercentage of positive results. In a 1987 study, theyreported that exposure to an electric field (E 5 100kV/m, 60 Hz) altered mating behavior and fertility, butthe results were inconsistent. One of their conclusionswas that the 100-kV/m exposure may have been justabove the threshold dose. They exposed the next groupsto 112 and 150 kV/m and found that none of thereproductive parameters was altered in this experi-ment, thus refuting their hypothesis. These investiga-tors used a total of 4,653 exposed and 3,979 controlanimals in their studies. Their conclusion was thatthere were some effects that were observed, but theywere transient, not repeatable or were normal varia-tions of biological behavior. Behavioral effects observedpostnatally were transient; the other reproductive ef-fects could not be reproduced consistently. They werenot convinced that the electric fields they studied had ateratogenic effect.

Stuchly et al. (’88) exposed 987 fetuses to magneticfields ranging from 57 to 660 mG at 18,000 Hz. Theseinvestigators evaluated the following reproductive out-comes: maternal weight gain, fetal and placental weight,litter size, fetal resorptions, and malformations. Allreproductive parameters were indistinguishable fromthe control embryos.

Nahas et al. (’75) exposed pubescent rats to continu-ous magnetic fields (B 5 200, 400, and 1,200 G). Therewas no increase in mortality at these large exposures,although the exposures were very large and of longduration. The remaining studies were with electricfields and concluded that reproductive effects wereminimal or non existent (Table 2). One study thatrelates to conflicting observations which were reportedin humans deals with the effect of an electric field onpreconception male rat fertility. Soeradi and Tadjudin(’86) exposed male rats for 1 month to electric fields of1–7 kV. There were seven exposure groups. This wasnot a pregnancy study, but rather the equivalent of adominant lethal study or a genetic study. None of themales became infertile, but the investigators did reporta decrease in litter size that was not dose related andthe occurrence of congenital malformations in the off-spring of the two groups with the highest exposure.Neither result is plausible.

A very large and competently performed study waspublished by Ryan et al. (’96). Four exposure groups ofSprague-Dawley rats, totaling 2,219 exposed embryosand 623 sham-irradiated controls, were exposed fromthe 6th to 19th day of pregnancy. The exposures were 60Hz, 0, 0.02, 2, and 10 G, administered intermittently;1 h on, and 1 h off for 18.5 h each day of exposure. Thepregnant rats were monitored for maternal toxicity andweight gain, and the fetuses were evaluated for viabil-ity, growth, and the incidence of congenital malforma-


tions. In spite of the relatively high exposures, therewere no maternal effects, and all the fetal parametersthat were evaluated in the exposed fetuses were thesame as the controls.

Exposure of preimplantation embryos. Onegroup of observations that has been brought to theattention of investigators interested in the effects ofEMF on the embryo is the ability to use electric pulsesto fuse embryonic cells. This procedure has been success-ful in both rat, rabbit, and sea urchin embryos (Kubiakand Tarkowski, ’85; Ozil and Modlinski, ’86; Richter etal., ’81). While these investigators report that survivingtransplanted embryos did not exhibit an increase inmalformations, it should be pointed out that at thisearly stage of development, mammalian embryos arenot susceptible to teratogenic milieu.

Biological plausibility. Because reproductive pa-thology encompasses so many disparate problems, theconcept of biological plausibility must include the con-sideration of many basic science areas. This is due tothe fact that the etiology and mechanisms involved invarious reproductive failures will vary with the repro-ductive problem being considered. For example, endo-crine abnormalities (Free et al., ’81) may be an impor-tant contributor to prematurity, infertility, and abortionbut may be minimally involved in the production ofcongenital malformations and stillbirth.

Let us examine the biological plausibility that EMFhas a teratogenic effect. Teratogens produce congenitalmalformations by interfering with developmental eventsthat are quite identifiable. One of the truisms interatology is that mutagenic agents frequently haveteratogenic potential. This is certainly true for ionizingradiation and cancer chemotherapeutic agents. Whatscientific data pertain to the mutagenic potential ofEMF?

Because mutagenic agents can affect mitosis, DNAsynthesis, DNA structure at the molecular level and thechromosomes at the morphological and submicroscopiclevel, these agents can affect embryonic and fetaldevelopment. It is unlikely that teratogenesis is theresult of induced mutations in surviving embryoniccells that have an impact on development. The terato-genic effect of mutagens resides more in their capacityto kill cells at high doses and affect other vital develop-mental processes. Although many mutagens can bedemonstrated to produce mutations in vitro or in wholeanimal models, they may not be teratogenic unless thedose is raised substantially.

The mutagenic and DNA-altering potential of EMFhas been examined by a number of investigators (Hisen-kemp et al., ’78; Steen and Ofted, ’67; Skipper andSchabel, ’73). Juutilainen and Limatainen (’86) usedthe Ames test to determine whether external magneticfields had any mutagenic potential. The investigatorsused field strengths and frequencies that reportedlyproduced malformations in chick embryos (0.1, 1, 10,and 100 A/m at 100 Hz). Besides the usual controls, theinvestigators used a sodium azide-positive control. The

Ames test was negative for the control groups and forall the exposures to magnetic fields. The sodium azide-exposed group exhibited a predictable mutagenic effect.Liboff et al. (’84) reported that magnetic fields (15–4kHz, 230 mG to 5.6 G) enhanced DNA synthesis inhuman fibroblasts grown in culture. The authors reporta threshold for this effect and further suggest ‘‘thepossibility of mutagenic interactions directly arisingfrom short-term changes in the earth’s field.’’ This is asurprising conclusion, since their experiments did notdemonstrate a mutagenic effect. Goodman et al. (’76,’83, ’86, ’88) exposed dipteran salivary gland cells topulsed electromagnetic fields and noted that differenttype pulses had different effects. Both pulses resultedin an increased specific activity of messenger RNA, butthe time necessary for the effect varied with the pulse.The increase in RNA transcription occurred in most ofthe bands and interbands of the chromosomes.

The dominant lethal assay has been used to studyone aspect of mutagenesis (Kowalczuk and Saunders,’90), and the investigators were unable to demonstrateany reproductive effect after exposing male mice toelectric fields (50 Hz, 20 kV/m rms) before fertilization.Cohen et al. (’86) studied the effect of a 60-Hz EMF withan electric field of 3,000 mA/m and a magnetic field of1–2 G. They used human lymphocytes from 5 men and 5women. The lymphocytes were exposed for 69 h in vitro.The cytological endpoints that were measured weremitotic rate and chromosome breakage. There were nodifferences in these parameters between the controland exposed lymphocytes.Another laboratory has exam-ined the effect of EMF on the repair of induced single-stranded breaks (Reese et al., ’88; Frazier et al., ’90).The experiments reported by this laboratory involvedtwo separate in vitro systems. DNA damage was in-duced in isolated human lymphocytes with 5-Gy ioniz-ing radiation and then exposed to 60 Hz (E 5 1.0 or 20V/m or B 5 10 mG). None of the exposures interferedwith the repair of DNA or the repair of single-strandedchromosome breaks. These investigators used Chinesehamster ovary (CHO) cells in culture and exposed themfor one hour to 60-Hz magnetic (1 or 20 G) and electricfields (1 or 38 V/m), as well as combined electric andmagnetic fields. After the exposures, the cells werelysed and examined for single-stranded breaks. Therewas no evidence of an increase in single-strandedbreaks in the exposed cells. Rosenthal and Oboe (’89)studied the effect of 50-Hz EMF (1–75 G) on culturedhuman lymphocytes and noted that the exposure didnot alter the frequency of sister chromatid exchanges(SCE) or chromosomal aberrations (CA). They alsonoted that combining EMF with chemical cytotoxicagents increased the frequency of SCE and CA to a levelthat was greater than the frequency produced by thecytotoxic agents alone. The authors explained that thisphenomenon was not due to a mutagenic effect of theEMF, but to alterations of the culture technique.

Whitson et al. (’86) studied the effect of extremelylow-frequency electric fields (60 Hz, 10 kV/m) on cell

280 R.L. BRENT

growth and DNA repair in human skin fibroblastsgrown in vitro. The exposure to this field was found notto alter cell growth or survival or to alter the capacityfor DNA excision and repair, as compared with theunexposed control cultures. Kronenberg and Tenforde(’79) studied the effect of low-intensity magnetic fields(60 Hz, 23.3 mG) on the growth of EMT6 cells grown invitro. The cultured cells were exposed for #6 days butwere examined daily by sampling the flasks. The re-sults ‘‘clearly demonstrate the absence of a magneticfield effect on EMT6 cell growth characteristics.’’ Aar-holt et al. (’81) studied the effect of low-frequencymagnetic fields (50 and 16.66 Hz, 2–220 mG) on cul-tures of Escherichia coli and obtained the followingresults. Aarholt and colleagues observed that the meangeneration time for cultures subjected to alternatingmagnetic fields is significantly reduced. They observeda threshold dose, below which no effect on generationtime was observed. In discussing their results, theyattempted to resolve the conflicting results in theliterature and they concluded that technical errors andexperimental variations may be responsible for some ofthe differences. For example, a slight change in tempera-ture can change the generation time of a cell culture.They also suggested that their results may not beappropriately applied to multicellular organisms.Ramon et al. (’81) also used E. coli as their testorganism. They exposed E. coli to 60- to 600-Hz mag-netic fields with a field strength of 220 G and reported a40% reduction in bacterial count due to lysis of theorganisms. Iwasaki et al. (’78) studied the effect ofmagnetic fields (5,000 G) on three systems: CHO cellsin culture (cellular growth and multiplicity), culturedslime mold (presence of mitotic delay), and fertilizedfrog eggs (hatchability and the presence of delay indevelopment). The endpoints for each system variedbut none of these systems deviated from the controls.Chandra and Stefani (’79) studied the effect of constantand alternating (60-Hz) magnetic fields (1,000–10,000G) on tumor cell growth in vitro and in vivo. There wasno regression or retardation in tumor growth whenexposed to either constant or alternating magneticfields.

Portnov et al. (’75) studied the mutagenic effect of astatic electric field on Drosophila females. They re-ported that fields of 15 kV/m and 33 kV/m inducednondisjunction and sex-linked recessive lethal muta-tions. There was no dose response relationship betweenthe magnitude of the effect and the magnitude of thestatic electric field. Diebolt (’78) exposed Drosophilamales to electrostatic (3 kV/m) and magnetic fields(10,000 G) for 24 h in order to determine the influence oflow-energy fields on the production of sex-linked reces-sive mutations in immature motile sperm. The fre-quency of lethals was identical in the exposed andcontrol groups.

Tabrah et al. (’78) studied the effect of alternating(60-Hz) magnetic fields (60–100 G) on Tetrahymenapyriformis and neuroblastoma cells. The authors found

alternating fields more effective than the permanentmagnet in altering growth. The authors observed re-duced cell division in Tetrahymena, no effect on thegrowth of neuroblastoma in culture, but an effect onneuroblastoma cells in vivo. Goodman et al. (’76),Greenbaum et al. (’82), and Marron et al. (’75) investi-gated the effect of low-frequency EMFs (45, 60, and 75Hz, 2 G, 0.7 V/m) on the slime mold. The exposurelasted .700 days. Exposure resulted in mitotic delaybut, when the culture was removed from the electricfield, the mitotic delay disappeared in approximately 40days.

The predominance of reports indicate that EMFs arenot mutagenic agents. The literature indicates that afew, but not most, biological systems can be perturbedby EMF fields if the exposure is sufficiently high. Itcannot be determined whether these effects are in anyway deleterious and whether they will occur in vivo orhave any effect on the whole organism. In many in-stances, the investigators are concerned that the artifi-cial nature of the culture system has contributed to theresults. One has to remember that all environmentalagents will have an effect if the exposure is highenough. There is no agent that will not have some effecton living organisms as the exposure increases.

The next concept that has to be dealt with is theinference that many of the negative studies are due tothe fact that not only is there a threshold for some ofthese effects but a ceiling, as well. Thus, the concept hasbeen introduced that EMF effects may have a narrowwindow of opportunity in which to produce deleteriousbiologic effects. This explanation is used to explain whyso many studies, both in vivo and in vitro are negative.The window effect reported by Ubeda (’83) using chickembryos has not been confirmed by investigators usingthe chick embryo as well as other species. But thishypothesis is one of the driving forces behind continuedresearch in this field.

A key feature of reproductive toxicity that is missingin the EMF literature is the production of cell death.Cell killing is an important component of many terato-genic agents (Table 4). Yet even very high exposures failto result in cell death in rapidly proliferating tissues,thus indicating the relative noncytotoxicity of EMF. Infact, if one examines the six mechanisms of teratogen-esis listed in Table 4, it is apparent that EMF does nothave the potential to invoke any of these mechanismsexcept for interference with cell migration, differentia-tion or the rate of mitosis. Obviously, there is nopotential for receptor-mediated teratogenicity, cell deple-tion due to cytotoxicity, or contribution to the produc-tion of mechanical effects (Table 4).

One other aspect of teratogenesis that must beaddressed is the fact that all established teratogenshave a constellation of effects that enable the teratolo-gist to identify the teratogenic agent with the syn-drome. With the extensive studies and the relativelylarge proportion of the population that is exposed, thereis not even the beginning of a conceptualization of the


malformations that are part of the EMF syndrome.When one cannot even suggest the components of thesyndrome after all these human and animal investiga-tions, it is most likely because a syndrome does notexist.

It is possible that the diverse and inconsistent find-ings that have been reported in the animal studies maybe due to differences in experimental design and equip-ment. As an example, few of the investigators measuredthe food and water intake of the control and exposedanimals. Small animals and humans (Smith, ’47a,b;Stein et al., ’75; Warkany, ’45; Saitoh and Takahashi,’73) have been reported to have an increase in thefrequency of birth defects if there is a substantialreduction in food or water intake or the animals aresubjected to stress (Runner and Miller, ’56; Rosenzweigand Blaustein, ’70; Szabo and Brent, ’74, ’75; Meyere etal., ’89; Berg, ’65).

The suggested reproductive risks of EMFs are notsupported by most of the clinical, animal, and basicscience studies that pertain to reproduction and terato-genesis. By contrast, the suggestion that human repro-ductive risks may have EMF frequencies and exposurecombinations that are deleterious can never be ad-equately investigated. It appears that reproductiveproblems are not a major consequence of EMF exposureand, although the data do not suggest a risk, a reproduc-tive risk from EMF exposure is possible but unlikely.Because of the allegation that there may be particularwindows of frequency, wave shape, and intensity thatmay be deleterious, it is impossible to disregard low-frequency EMF exposures as having no deleteriousreproductive effects. Yet the epidemiological and ani-mal data that are available would point in that direc-tion.

CONCLUSIONS AND RECOMMENDATIONSCONCERNING IN VIVO ANIMAL STUDIES

AND IN VITRO TESTS: RECOMMENDATIONS

1. In vivo experiments using the chick embryo, cellculture, or mammalian embryo culture will addlittle to our understanding of EMF reproductiveeffects. These techniques should be utilized to studymechanisms of effects that have been demonstratedin humans or animal models. Before these tools areinvoked to study the effects of EMF, well-designedwhole-animal studies must be completed. Thesewhole-animal experiments should be similar in de-sign to the one reported by Wiley et al. (’92) butshould focus on specific reproductive problems. Mostof the early in vivo experiments exposed the animalsthroughout gestation. This is appropriate for prelimi-nary investigations in order to generate hypotheses.In retrospect, many of the experiments which ex-posed the animals throughout pregnancy, createdmore problems then they solved. If one is interestedin major organ teratogenesis, then pregnant ratsshould be exposed from the 9th to the 12th day of

development. If one is interested in neurobehavioraleffects or central nervous system effects in the rat,the EMF exposure should be performed during brainhistodifferentiation, which begins on the 13th dayand continues past term. Because the mother canperceive EMF, it is essential that she not be continu-ously exposed to EMF if it is not essential to theexperiment, because an alteration in postpartumcare may be the dominant contributor to postpartumneurobehavioral effects. It is also essential to use awide range of exposures and frequencies (over threeorders of magnitude) in order to address the elusive‘‘window effect.’’

2. Some of the animal experiments with EMF wereundermined by the presence of electric currentsinduced in the cage’s food and watering system. Itmay be useful to establish guidelines for the designof EMF exposure facilities in order to eliminate thepossibility that extraneous induced currents couldinfluence the experimental results.

CONCLUSIONS

In order to evaluate the reproductive risks of lowfrequency EMF it is important to include epidemiologi-cal and animal studies in the evaluation as well as theappropriate basic science information in developmentalbiology and teratology. This review presents a criticalreview of in vivo animal studies and in vitro tests, aswell as the biological plausibility of the allegations ofreproductive risks.

In vitro or in vivo studies in nonhuman species can beused to study mechanisms and the effects that havebeen suggested by human investigations. Only well-designed whole-animal teratology studies are appropri-ate when the epidemiologists and clinical teratologistsare uncertain about the environmental risks. Withoutdata from epidemiology or animal studies indicatingthe possibility of a teratogenic effect, one cannot con-clude a teratogenic effect from culture experiments,because the investigator is not in a position to knowwhether any of his pathologic observations will bemanifested in living organisms at term. Other aspectsof reproductive failure such as abortion, infertility,stillbirth, and prematurity cannot be addressed by invitro or culture experiments. In fact, they are verydifficult to design and interpret in nonprimate in vivomodels.

The biological plausibility of some of the basic mecha-nisms involved in reproductive pathology were evalu-ated, concentrating primarily on the mechanisms in-volved in the production of birth defects. The studiesdealing with mutagenesis, cell death, and cell prolifera-tion using in vitro systems do not indicate that EMFshave the potential for deleteriously affecting proliferat-ing and differentiating embryonic cells at the exposuresto which populations are usually exposed. Of course,there is no environmental agent that has no effect,deleterious or not, at very high exposures.

282 R.L. BRENT

The animal and in vitro studies dealing with thereproductive effects of EMF exposure are extensive.There are over 70 EMF research projects that deal withsome aspect of reproduction and growth. Unfortu-nately, a large proportion of the embryology studiesused the chick embryo and evaluated the presence orabsence of teratogenesis after 48–52 h of development.This is not a stage of development at which an investi-gator could determine whether teratogenesis occurred.The presence of clinically relevant teratogenesis canonly be determined at the end of the gestational period.The chick embryo studies are also of little assistance tothe epidemiologist or clinician in determining whetherEMF represents a hazard to the human embryo, andthe results are, in any event, inconsistent. On the otherhand, the studies involving nonhuman mammalianorganisms dealing with fetal growth, congenital malfor-mations, embryonic loss and neurobehavioral develop-ment were predominantly negative and therefore arenot supportive of the hypothesis that low-frequencyEMF exposures lead to reproductive toxicity.

LITERATURE CITEDAaholt E, Flinn EA, Smith CW. 1981. Effects of low frequency

magnetic fields on bacterial growth rate. Phys Med Biol 26:613–621.Algers B, Hultgren J. 1987. Effects of long-term exposure to a 400-kV,

50-Hz transmission line on estrous and fertility in cows. Prev VetMed 5:21–36.

Bardasano JL, Meyer AJ, Picazo L. 1986. Pineal cells with multipolarspindles in chicken embryos exposed to magnetic fields—first trials.Z Mikrosk Anat Forsch Lpz 100:85–92.

Beckman DA, Brent RL. 1986. Mechanism of known environmentalteratogens: Drugs and chemicals. In: Brent RL, Beckman DA,editors. Clinics in perinatology. Vol 13. Philadelphia: WB Saunders.p 649–687.

Bellossi A. 1991. Effect of pulsed magnetic fields on leukemia-proneAKR mice. No effect on mortality through five generations. Leuk Res15:899–902.

Berg BN. 1965. Dietary restriction and reproduction in the rat. J Nutr87:344–348.

Berman E, Chacon L, House D, Koch BA, Koch WE, Leal J, Lovtrup S,Mantiply E, Martin AH, Martucci GI, Mild KH, Monahan JC,Sandstrom M, Shamsaifar K, Tell R, Trillo MA, Ubeda A, Wagner P.1990. Development of chicken embryos in a pulsed magnetic field.Bioelectromagnetics 11:169–187.

Berman E. 1990. The developmental effects of pulsed magnetic fieldson animal embryos. Reprod Toxicol 4:45–49.

Brent RL. 1960. The indirect effect of irradiation on embryonicdevelopment. II. Irradiation of the placenta. Am J Dis Child100:103–108.

Brent RL. 1964. Drug testing in animals for teratogenic effects:Thalidomide in the pregnant rat. J Pediatr 64:762–770.

Brent RL. 1969. The direct and indirect effects of irradiation upon themammalian zygote, embryo and fetus. In: Nishimura H, Miller JR,editors. Methods for teratological studies in experimental animalsand man. Proceedings of the second international workshop interatology, Kyoto, Japan, 1968. Tokyo: Igaku Shoin. p 63–75.

Brent RL. 1972. Drug testing for teratogenicity: Its implication,limitations and application to man. Adv Exp Med Biol 27:31–43.

Brent RL. 1978. Editorial: Method of evaluating alleged humanteratogens. Teratology 17:183.

Brent RL. 1981. The prediction of human diseases from laboratory andanimal tests for teratogenicity, carcinogenicity and mutagenicity. In:Lasagna L, editor. Controversies in therapeutics. Philadelphia: WBSaunders. p 134–150.

Brent RL. 1985a. The magnitude of the problem of congenital malfor-mations. In: Marois M, editor. Prevention of physical and mental

congenital defects. Part A. The scope of the problem. New York: AlanR Liss. p 55–68.

Brent RL. 1985b. Methods for evaluating the alleged teratogenicity ofenvironmental agents. In: Marois M, editor. Prevention of physicaland mental congenital defects. Part C. Basic and medical science,education, and future strategies. New York: Alan R Liss. p 191–195.

Brent RL. 1986a. Evaluating the alleged teratogenicity of environmen-tal agents. Clin Perinatol 13:609–613.

Brent RL. 1986b. The complexities of solving the problem of humanmalformations. In: Brent RL, Beckman DA, editors. Clinics inperinatology. Vol 13. Philadelphia: WB Saunders. p 491–503.

Brent RL. 1988. Predicting teratogenic and reproductive risks inhumans from exposure to various environmental agents using invitro techniques and in vivo animal studies. Cong Anom 28 (suppl1):S41–S55.

Brent RL. 1992. Reproductive effects. In: Davis JG, Bennett WR,Brady JV, Brent RL, Gordis L, Gordon WE, Greenhouse SW, ReiterRJ, Stein GS, Susskind C, Trichopoulos D, editors. Health effects oflow-frequency electric and magnetic fields, executive summary.Washington, DC: Oak Ridge Associated Universities Panel for theCommittee on Interagency Radiation Research and Policy Coordina-tion. p 10–13.

Brent RL, Beckman DA, Jensh RP. 1986. The relationship of animalexperiments in predicting the effects of intrauterine effects in thehuman. In: Kriegel H, Schmahl W, Gerber GB, Stieve FE, editors.Radiation risks to the developing nervous system. New York: GustavFisher. p 367–397.

Brent RL, Bolden BT. 1967a. The indirect effect of irradiation onembryonic development. III. The contribution of ovarian irradiation,uterine irradiation, oviduct irradiation and zygote irradiation tofetal mortality and growth retardation in the rat. Radiat Res30:759–773.

Brent RL, Bolden BT. 1967b. The indirect effect of irradiation onembryonic development. IV. The lethal effects of maternal irradia-tion on the first day of gestation in the rat. Proc Soc Exp Biol Med125:709–712.

Brent RL, Bolden BT. 1968. Indirect effect of x-irradiation on embry-onic development. V. Utilization of high doses of maternal irradia-tion on the first day of gestation. Radiat Res 36:563–570.

Brent RL, Holmes LB. 1988. Clinical and basic science lessons fromthe thalidomide tragedy: What have we learned about the causes oflimb defects? Teratology 38:241–251.

Brent RL, McLaughlin MM. 1960. The indirect effect of irradiation onembryonic development. I. Irradiation of the mother while shieldingthe embryonic site. Am J Dis Child 100:94–102.

Brent RL, Gordon WE, Bennett WR, Beckman DA. 1993. Reproductiveand teratologic effects of electromagnetic fields. Reprod Toxicol7:535–580.

Buntenkotter S, Brinkman K, Zittlau E, Zwingleberg R. 1989. Resultsof teratological investigations on rats after exposure to magneticfields (50 Hz). Int Symp High Volt Eng 6:1–4.

Cabanes J, Gary C. 1981. Direct perception of electric field. ConferenceInternationale des Grands Reseaux Electriques a Haute TensionRep. 233–08.

Cameron IL, Hunter KE, Winters WD. 1985a. Retardation of embryo-genesis by extremely low-frequency 60-Hz electromagnetic fields.Physiological chemistry and physics and medical. NMR 17:135–138.

Cameron IL, Lawrence WC, Lum JB. 1985b. Medaka eggs as a modelsystem for screening potential teratogens. Prog Clin Biol Res163C1:239–240.

Chandra S, Stefani S. 1979. Effect of constant and alternatingmagnetic fields on tumor cells in vitro and in vivo. In: Proceedings ofthe 18th annual Hanford life sciences symposium, Richland, Wash-ington.

Chernoff N, Kavlock RJ. 1982. An in vivo teratology screen utilizingpregnant mice. J Toxicol Environ Health 10:541–550.

Cohen MM, Kunska A, Astemborski JA, McCulloch D, Paskewitz DA.1986. Effects of low-level, 60-Hz electromagnetic fields on humanlymphoid cells. I. Mitotic rate and chromosome breakage in humanperipheral lymphocytes. Bioelectromagnetics 7:415–423.


Cooper LJ, Graves HB, Smith DT, Poznaniak DT, Majid H. 1981.Behavioral responses of pigeons to high-intensity 60-Hz electricfields. Behav Neural Biol 32:214–228.

Davis JG, Bennett WR, Brady JV, Brent RL, Gordis L, Gordon WE,Greenhouse SW, Reiter RJ, Stein GS, Susskind C, Trichopoulos D,editors. 1992. Health effects of low-frequency electric and magneticfields. Washington, DC: Oak Ridge Associated Universities Panel forthe Committee on Interagency Radiation Research and PolicyCoordination.

Delgado J, Leal J, Monteagudo J, Gracia M. 1982. Embryologicalchanges induced by weak, extremely low frequency electromagneticfields. J Anat 134:533–551.

Diebolt JR. 1978. The influence of electrostatic and magnetic fields onmutation in Drosophila melanogaster spermatozoa. Mutat Res57:169–174.

Durfee WK, Glante PR, Muthukrishnan S. 1975. Extremely low-frequency electric and magnetic fields in domestic birds. Part I. Theinfluence of ELF, magnetic and electric fields upon hatchability andearly development of chicks. NMRDC report, compilation of Navy-sponsored ELF biomedical and ecological research reports.

Fraser FC. 1977. Relationship of animal studies to man. In: Wilson JG,Fraser FC, editors. Handbook of teratology. New York: PlenumPress. p 75–76.

Frazier ME, Reese JA, Morris JE, Jostes RF, Miller DL. 1990.Exposure of mammalian cells to 60-Hz magnetic or electric fields:Analysis of DNA repair of induced, single-strand breaks. Bioelectro-magnetics 11:229–234.

Free MJ, Kaune WT, Phillips RD, Cheng HC. 1981. Endocrinologicaleffects of strong 60 Hz electric fields on rats. Bioelectromagnetics2:105–121.

Frolen H, Svedenstal BM. 1989. The effect of a pulsed magnetic fieldon fetal development in the mouse: Complementing and expandingon a previously reported investigation. Swedish National Instituteof Radiation Protection. SSI Report 493.88.

Goodman EM, Greenebaum B, Marron MT. 1976. Effects of extremelylow frequency electromagenetic fields on Physarum polycephalum.Radiat Res 66:531–540.

Goodman R, Basset CAL, Henderson AS. 1983. Pulsing electromag-netic fields induce cellular transcription. Science 220:1283–1285.

Goodman EM, Sharpe PT, Greenebaum B, Marron MT. 1986. Pulsedmagnetic fields alter the cell surface. FEBS Lett 199:275–278.

Goodman R, Henderson AS. 1988. Exposure of salivary gland cells tolow frequency electromagnetic fields alters polypeptide synthesis.Proc Natl Acad Sci USA 85:3928–3932.

Greenebaum B, Goodman EM, Marron MT. 1982. Magnetic fieldeffects on mitotic cycle length in Physarum. Eur J Cell Biol27:156–160.

Hansson HA. 1981. Lamellar bodies in Purkinje nerve cells experimen-tally induced by electric fields. Brain Res 216:187.

Hansson HA, Rozell B, Stemme S. 1987. Effects of experimentalexposure to power-frequency electromagnetic fields on the nervoussystem. In: Anderson LE, Kelman BJ, Weigel RJ, editors. Interac-tion of biological systems with static and ELF electric and magneticfields. Twenty-third Hanford Life Sciences Symposium, October.1984. Richland, WA: Pacific Northwest Laboratory. p 297.

Heinricks WL, Fong P, Flannery M, Heinrichs SC, Crooks LE, SpindleA, Pedersen RA. 1988. Midgestational exposure of pregnant BALB/cmice to magnetic resonance imaging conditions. Magnet ResonImaging 6:305–314.

Hinsenkamp MA, Chiabrera A, Pilla AA, Bassett CAL. 1978. Cellbehavior and DNA modification in pulsing electromagnetic fields.Acta Orthopaed Belg 44:636–650.

Iwasaki T, Ohara H, Matsumoto S, Matsudaira H. 1978. Test ofmagnetic sensitivity in three different biological systems. J RadiatRes 19:287–294.

Joshi MV, Khan MZ, Damle PS. 1978. Effect of magnetic field on chickmorphogenesis. Differentiation 10:39–43.

Juutilainen J. 1986. Effects of low frequency magnetic fields on chickembryos. Dependence on incubation temperature and storage of theeggs. ELF magnetic fields, chick embryo, teratology, temperature. ZNaturforsch 41c: 111–115.

Juutilainen J, Liimatainen A. 1986. Mutation frequency in Salmo-nella exposed to weak 100-Hz magnetic fields. Hereditas 104:145–147.

Juutilainen J, Saali K. 1986. Development of chick embryos in 1-Hz to100-kHz magnetic fields. Radiat Environ Biophys 25:135–140.

Juutilainen J, Harri M, Saali K, Lahtinen T. 1986. Effects of 100-Hzmagnetic fields with various waveforms on the development of chickembryos. Radiat Environ Biophys 25:65–74.

Juutilainen J, Laara E, Saali K. 1987. Relationship between fieldstrength and abnormal development in chick embryos exposed to50-Hz magnetic fields. Int J Radiat Biol 5:787–793.

Kimmel CA, Buelke-Sam J, Adams J. 1985. Collaborative behavioralteratology study: Implications, current applications and futuredirections. Neurobehav Toxicol Teratol 7:699–673.

Kimmel GL, Kimmel CA, Francis EZ. 1986. Evaluation of maternaland developmental toxicity. Consensus Workshop on the evaluationof maternal and developmental toxicity. Teratogen Carcinog Muta-gen 7:201–338.

Konermann G, Monig H. 1986. Studies on the influence of staticmagnetic fields on prenatal developmental of mice. Radiology 26:490–497.

Koundakjian EJ, Bournias-Vardiabasis N, Haggren W, Adey WR,Phillips JL. 1996. Exposure of Drosophila melanogaster embryoniccell cultures to 60-Hz sinusoidal magnetic fields: Expression of heatshock proteins 23 and 70. In Vitro Toxicol 9:281–290.

Kowalczuk CI, Saunders RD. 1990. Dominant lethal studies in malemice after exposure to a 50-Hz electric field. Bioelectromagnetics11:129–137.

Kowalczuk CI, Robbins L, Thomas JM, Butland BK, Saunders RD.1994. Effects of prenatal exposure to 50 Hz magnetic fields ondevelopment in mice. I. Implantation rate and fetal development.Bioelectromagnetics 15:349–361.

Kronenberg SS, Tenforde TS. 1979. Cell growth in a low-intensity, 60Hz magnetic field. Prepared by the Office of Environment for theU.S. Department of Energy under Contract W1-7405-ENG-48.

Krueger WF, Giarola AJ, Bradley JW, Shrekenhamer A. 1975. Effectsof electromagnetic fields on fecundity in the chicken. Ann NY AcadSci 247:391–400.

Kubiak JZ, Tarkowski AK. 1985. Electrofusion of mouse blastomeres.Exp Cell Res 157:561–566.

Levengood WC. 1969. A new teratogenic agent applied to amphibianembryos. J Embryol Exp Morphol 21:23–31.

Liboff AR, William T Jr, Strong DM, Wistar R Jr. 1984. Time-varyingmagnetic fields: Effect on DNA synthesis. Science 223:818–820.

Maffeo S, Miller MW, Carstensen EL. 1984. Lack of effect of weak lowfrequency electromagnetic fields on chick embryogenesis. J Anat4:613–618.

Maffeo S, Brayman AA, Miller MW, Carstensen EL, Ciaravino V, CoxC. 1988. Weak low frequency electromagnetic fields and chickembryogenesis: Failure to reproduce positive findings. J Anat157:101–104.

Marino AA, Becker RO, Ullrich B. 1976. The effect of continuousexposure to low frequency electric fields on three generations ofmice: A pilot study. Experientia 32:565–566.

Marino AA, Reichmanis M, Becker RO, Ullrich B, Cullen JM. 1980.Power frequency electric field induces biological changes in succes-sive generations of mice. Experientia 36:309–311.

Marron MT, Goodman EM, Greenebaum B. 1975. Mitotic delay in theslime mould Physarum polycephalum induced by low intensity 60and 75 Hz electromagnetic fields. Nature 254:66.

Martin AH. 1988. Magnetic fields and time dependent effects ondevelopment. Bioelectromagnetics 9:393–396.

Martin AH, Moses GC. 1995. Effectiveness of noise in blockingelectromagnetic effects on enzyme activity in the chick embryo.Biochem Mol Biol Int 36:87–94.

Martucci GI, Gailey PC, Tell RA. 1984. Investigations of possibleeffects of weak, pulsed magnetic fields on the chick embryo. InAbstracts of the sixth annual meeting of the BioelectromagneticsSociety, July, Atlanta, GA.

284 R.L. BRENT

Meyere RE, Aldrich TE, Easterly CE. 1989. Effects of noise andelectromagnetic fields on reproductive outcomes. Environ HealthPerspect 81:193–200.

Nahas GG, Boccalon H, Berryer P, Wagner B. 1975. Effects in rodentsof a 1-month exposure to magnetic fields (200–1200 Gauss). AviatSpace Environ Med 46:1161.

National Academy of Sciences. 1996. Possible health effects of expo-sure to residential electric and magnetic fields. Washington, DC:National Academy Press. p 314.

Osbakken M, Griffith J, Taczanowsky P. 1986. A gross morphologic,histologic, hematologic and blood chemistry study of adult andneonatal mice chronically exposed to high magnetic fields. MagnReson Med 3:502–517.

Ossenkopp KP. 1972. Maturation and open-field behavior in ratsexposed prenatally to an ELF low-intensity rotating magnetic field.Psychol Rep 30:371–374.

Ozil JP, Modlinski JA. 1986. Effects of electric field on fusion rate andsurvival of 2-cell rabbit embryos. J Embryol Exp Morphol 96:221–228.

Pafkova’ H, Jera’bek J, Tejnorov’a I, Bedna’r V. 1996. Developmentaleffects of magnetic field (50 Hz) in combination with ionizingradiation and chemical teratogens. Toxicol Lett 88:313–316.

Persinger MA. 1969. Open-field behavior in rats exposed prenatally toa low intensity-low frequency, rotating magnetic fields. Dev Psycho-biol 2:168–171.

Persinger MA, Foster WS. 1971. A prenatal exposure to an ELFrotating magnetic field, ambulatory behavior and lunar distance atbirth: A correlation. Psychol Rep 28:435–438.

Persinger MA, Foster WS. 1972. A prenatal exposure to an ELFrotating magnetic field and subsequent increase in conditionedsuppression. Dev Psychobiol 5:269–274.

Portnov FG, Shakarins VF, Maiore DJ. 1975. Study of mutagenic effectof static electric fields in Drosophila melanogaster females. Gene-tika 11:177.

Prasad N, Wright DA, Ford JJ, Thornby JI. 1990. Safety of 4-T MRimaging study of effects on developing frog embryos. Radiology174:251–253.

Ramon C, Ayaz M, Streeter DD Jr. 1981. Inhibition of growth rate ofEscherichia coli induced by extremely low-frequency weak magneticfields. Bioelectromagnetics 2:285–289.

Reese JA, Jostes RF, Frazier ME. 1988. Exposure of mammalian cellsto 60-Hz magnetic or electric fields: Analysis for DNA single-strandbreaks. Bioelectromagnetics 9:237–249.

Richter HP, Scheurich P, Zimmerman U. 1981. Electric field-inducedfusion of sea urchin eggs. Dev Growth Diff 23:479–486.

Robert E. 1997. Effects of EMF and RF on human reproduction.Review of epidemiologic studies. Presented at the Thirty-thirdAnnual Meeting of the National Council on Radiation Protectionand Measurements. The Effects of Pre- and Postconception Expo-sure to Radiation, April 2–3, 1997, Arlington, VA.

Rogers WR. 1989. Studies on the effects of 60-Hz electric and magneticfields on neuroendocrine circadian rhythmicity in nonhuman pri-mates. In: Conference on electromagnetic fields and circadianrhythmicity, Boston, MA.

Rommereim DN, Kaune WT, Buschbom RL, Phillips RD, Sikov MR.1987. Reproduction and development in rats chronologically ex-posed to 60-Hz electric fields. Bioelectromagnetics 8:243–258.

Rommereim DN, Kaune WT, Anderson LE, Sikov MR. 1989. Ratsreproduce and rear litters during chronic exposure to 150-kV/m,60-Hz electric fields. Bioelectromagnetics 10:385–389.

Rommereim DN, Rommereim RL, Sikov MR, Buschbom RL, AndersonLE. 1990. Reproduction, growth, and development of rats duringchronic exposure to multiple field strengths of 60-Hz electric fields.Fundam Appl Toxicol 14:608–621.

Rosenthal M, Obe G. 1989. Effects of 50-Hertz electromagnetic fieldson proliferation and on chromosomal alterations in human periph-eral lymphocytes untreated or pretreated with chemical mutagens.Mutat Res 210:329–335.

Rosenzweig S, Blaustein FM. 1970. Cleft palate in A/J mice resultingfrom restraint and deprivation of food and water. Teratology 3:47–52.

Runner MN, Miller JR. 1956. Congenital deformity in the mouse as aconsequence of fasting. Anat Rec 124:437–438.

Ryan BM, Mallett E Jr, Johnson TR, Gauger JR, McCormick DL. 1996.Developmental toxicity study of 60 Hz (power frequency) magneticfields in rats. Teratology 54:73–83.

Sagan PM, Stell ME. 1985. How rats detect 60-Hz electric fields. In:Abstracts of the seventh annual meeting of the BioeectromagneticsSociety, San Francisco, CA.

Sagan PM, Stell ME, Bryan GK, Adely WR. 1987. Detection of verticalelectric fields by rats. Bioelectromagnetics 8:303.

Saitoh M, Takahashi S. 1973. Changes of embryonic wastage duringpregnancy in rats fed low and high energy diets. J Nutr 103:1652–1657.

Salzinger K, Freimark S, McCullough M, Phillips D, Birenbaum L.1990. Altered operant behavior of adult rats after perinatal expo-sure to a 60-Hz electromagnetic field. Bioelectromagnetics 11:105–116.

Sandstrom M, Mild KH, Lovtrup S. 1987. Effects of weak pulsedmagnetic fields on chick embryogenesis. In: Nave B, Wideback PG,editors. Work with display units. B.V. North Holland: ElsevierScientific Publishers. p 135–140.

Schardein JL. 1985. Chemically induced birth defects. New York:Marcel Dekker.

Schardein JL. 1988. Teratologic testing: States and issues after twodecades of evolution. Rev Environ Contam Toxicol 102:1–78.

Schardein JL. 1993. Chemically induced birth Defects. New York:Marcel Dekker.

Seto YJ, Majeau-Chargois D, Lymangrover JR, Dunlap WP, WalkerCF, Hsieh ST. 1984. Investigation of fertility and in utero effects inrats chronically exposed to a high-intensity 60-Hz electric field.IEEE Trans Biomed Eng 11:693–702.

Shepard TH. 1973. A catalog of teratogenic agents. Vol XV. 1st ed.Baltimore, MD: Johns Hopkins University Press.

Sienkiewicz ZJ, Robbins L, Haylock RGE, Saunders RD. 1994. Effectsof prenatal exposure to 50 Hz magnetic fields on development inmice. II. Postnatal development and behavior. Bioelectromagnetics15:363–375.

Sikov MR, Montgomery LD, Smith LG, Phillips RD. 1984. Studies onprenatal and postnatal development in rats exposed to 60-Hzelectric fields. Bioelectromagnetics 5:101–112.

Sikov MR, Rommereim DN, Beamer JL, Buschbom RL, Kaune WT,Phillips RD. 1987. Developmental studies of Hanford miniatureswine exposed to 60-Hz electric fields. Bioelectromagnetics 8:229–242.

Sisken BF, Fowler I, Mayaud C, Ryaby JP, Ryaby J, Pilla AA. 1986.Pulsed electromagnetic fields and normal chick development. JBioelect 5:25–34.

Skipper HT, Schabel FM Jr. 1973. Quantitative and cytokineticstudies in experimental tumor models. In: Holland JF, Frei E III,editors. Cancer medicine. Philadelphia: Lea & Febiger. p 629–650.

Slikker W Jr. 1987. The role of metaboism in the testing of developmen-tal toxicants. Regul Toxicol Pharmacol 7:390–413.

Smith C. 1947a. Effects of maternal undernutrition upon the newborninfant in Holland (1944–1945). J Pediatr 30:229–243.

Smith C. 1947b. The effect of wartime starvation in Holland uponpregnancy and its product. Am J Obstet Gynecol 53:599–606.

Soeradi O, Tadjudin MK. 1986. Congenital anomalies in the offspringof rats after exposure of the testis to an electrostatic field. Int JAndrol 9:152–160.

Steen HB, Ofted P. 1967. Lack of effect of constant magnetic fields onDrosophila egg hatching time. Experientia 23:814.

Stein Z, Susser M, Saenger G, Marolla F. 1975. Famine and humandevelopment. The Dutch hunger winter of 1944/45. New York:Oxford University.

Stern S, Laties VG, Stancampiano CV, Cox C, deLorge JO. 1983.Behavioral detection of 60 Hz electric fields by rats. Bioelectromag-netics 4:215.

Stern S, Laties VG. 1985. 60-Hz electric fields: Detection by femalerats. Bioelectromagnetics 6:99–103.


Stuchly MA, Ruddick J, Villeneuve D, Robinson K, Reed B, LecuyerDW, Tan K, Wong J. 1988. Teratological assessment of exposure totime-varying magnetic field. Teratology 38:461–466.

Szabo KT, Brent RL. 1974. Species differences in experimental terato-genesis by tranquilizing agents. Lancet 1:565.

Szabo KT, Brent RL. 1975. Reduction of drug-induced cleft palate inmice. Lancet 1:1296–1297.

Tabrah FL, Guernsey DL, Chou S-C, Batkin S. 1978. Effect ofalternating magnetic fields (60–100 gauss, 60 Hz) on Tetrahymenapyriformis. TITJ Life Sci 8:73–77.

Terol FF, Panchon A. 1995. Exposure of domestic quail embryos toextremely low frequency magnetic fields. Int J Radiat Biol 68:321–330.

Tribukait B, Cekan E, Paulsson LE. 1986. Effects of pulsed magneticfields on embryonic development in mice. In: Proceedings of theinternational scientific conference: Work with display units. Stockholm:Swedish National Board of Occupational Safety. p 68–70.

Tyndall DA. 1990. MRI effects on the teratogenicity of x-irradiation inthe C57BL/6J mouse. Magn Reson Imag 8:423–433.

Tyndall DA. 1993. MRI effects on craniofacial size and crown-rumplength in C57BL/6J mice in 1.5T fields. Oral Surg Oral Med OralPathol 76:655–660.

Ubeda A, Leal J, Trillo MA, Jimenez MA, Delgado JMR. 1983. Pulseshape of magnetic fields influences chick embryogenesis. J Anat137:513–536.

Vorhees CV. 1983. Behavioral teratogenicity testing as a method forscreening for hazards to human health: A methodological approach.Neurobehav Toxicol Teratol 5:469–474.

Warkany J. 1945. Manifestations of prenatal nutritional deficiency.Vitam Horm 3:73–103.

Warkany J. et al. 1963. Conference on prenatal effects of drugs.Commission on Drug Safety Bull. p 1–3.

Whitson GL, Carrier WL, Francis AA, Shih CC, Georghiou S, ReganJD. 1986. Effects of extremely low frequency (ELF) electric fields oncell growth and DNA repair in human skin fibroblasts. Cell TissueKinet 19:39–47.

Wiley MJ, Corey P, Kavet R, Charry J, Agnew D, Harvey S, Walsh M.1992. The effects of continuous exposure to pulsed 20 KHZ saw-toothed magnetic fields on the litters of CD 1 mice. Teratology46:391–398.

Wilson JG. 1965. Methods for administering agents and detectingmalformations in experimental animals. In: Wilson JG, Warkany J,editors. Teratology. Principles and techniques. Chicago: Universityof Chicago Press. p 263–277.

Wilson JG. 1973. Environment and birth defects. New York: AcademicPress.

Yip YP, Capriotti C, Talagala SL, Yip JW. 1994. Effects of MR exposureat 1.5T on early embryonic development of the chick. J Magn ResImag 4:742–748.

Zervins A. 1973. Chick embryo development in a 26-kHz electromag-netic field. Am Ind Hyg Assoc J 34:120–127.

Zusman IP, Yaffe HP, Ornoy A. 1990. Effects of pulsing electromagneticfields on the prenatal and postnatal development in mice and rats:in vivo and in vitro studies. Teratology 42:157–170.

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