40165977

SUPERFUND RECORDS NO I' The

_ , v . . i f e VSoil Is an Important Pathwayof Human Lead ExposureHoward W Mielke1 and Patrick L Reagan2

Institute for Bioenvironmental Toxicology Xavier University ofLouisiana New Orleans Louisana 2Midwest EnvironmentalEducation and Research Association St Paul Minnesota

This review shows the equal or greater importance of leaded gasoline contaminated dustcompared to lead based paint to the child lead problem and that soil lead resulting from leadedgasoline and pulverized lead based paint is at least or more important than lead based paint (intactand not pulven/ed) as a pathway of human lead exposure Because lead based paint is a high-dosesource the biologically relevant_dosage is similar to lead in soil^Both jpad based paint and soil leadare associated with severe lead poisoning}Leaded gasoline and lead in food but not lead basedpaint are strongly associated with population blood lead levels in both young children and adultsSoil lead and house dust but not lead based paint are associated with copulation blood l< ad levelsin children Most soil lead and house dust are associated with leaded gasoline Lead based paintdust is associated with cases of renovation of either exterior or interior environments in which thepaint was pulverized (Based upon the limited data to date abatement of soil lead is more ef ectivethan abatement of lead based paint in reducing blood lead levels of young children/About equalnumbers of children under 7 years of age are exposed to soil lead and lead based paintSeasonably studies point to soil lead as the main source of population blood lead levels Soil lead isa greater risk rtctor than lead based paint to children engaged in hand o mouth and pica behaviorIn summary boil lead is important for addressing the population of children at nst of leadpoisoning When soil lead is acknowleoged by regulators and the public health community as an

ipor*ant pa hway of human lead exposure then more effe tive opportunities for irrprovmg•imafy lead prevention can become a reality — Environ Health Perspect 106(Suppl 1} 217-229'998) http/'ehpnetl mehs nih gov/docs/1998/Suppl 1/217 229mielke/dbstract html

Key words lead soil gasoline paint causality urban blood ecological abatement sourcespathway's

IntroductionDespite an impressive research effort overthe last three decades recognition that leadin soil is an important pathway of humanlead exposuie remains controversial Someargue that lead based p a i n t is the mostimportant source of lead exposure Othersargue that the evidence is insufficient totreat soil and paint as equally importantpathways of human exposure Hundreds ofstudies have investigated the sources of lead

exposure ( p r i n c i p a l l y leaded gi ohneindus t r i a l point sources and lead basedp-iint) the movement of lead in the envil o n m e n t ( f rom nr to soil to d u s t to achild s hand to a child s mouth) and theeffects of lead on human health Clearlythere are many factors that influence theintensit) of exposure experienced by anindividual including age sex season handto mouth behavior (pica) occupation race

Manuscript receved at EHP3 June 1997 accepted 14 October 1997This review has resulted from discussions with many people We especially thank S N Rountree for her edi

tonal assistance with this review The urban research in New Orleans discussed in th s review is supported bythe Agency for TOXIC Substances and Disease Reg stry cooperative agreement U50/ATU398948 to XavierUniversity and the support of the Midwest Environmental Education and Research Associaton and Robert FNelson is greatly appreciated

Address correspondence to Dr H Mielke Institute for Bioenvironmental Toxicology College of PharmacyXavier University of Louisiana 7325 Palmetto St New Orleans LA 70125 Telephone (504)4837424 Fax(504)488-3108 Email hmielkeOxulaedu

Abbreviations used ADVT average daily vehicle traffic ATSDR Agency for Toxic Substances and Diseaselegistry CDC Centers for Disease Control and Prevention dl deciliter HUD Department of Housing and

Fjroan Development NHANES National Health and Nutrition Examination Survey Pb lead PbB blood leadpm paits per million =ug/g ug micrograms pg/dl microgtams per deciliter of whole blood pgPb/dl

microgram of lead per deciliter of whole blood ug/ft2 microgram per square foot pg/g microgram per grampm micrometer

socioeconomic status diet and culturalpractices Some of these factors will beweighed but only as the) relate to the roleof lead in soil as a contributor to the childlead problem This review shows the greiterimportance of leaded gasoline compared tolead based paint as a source of exposureand that soil lead result ing from leadedgasoline pulverized lead based paint andother sources is equally or more importantthan lead based paint (intact or not pulverized) as a pathway of human lead exposiueWhen the role of leaded gasoline and Icidcontaminated soil and dust are acknowledged as an important pathway of humanlead exposure more effective opportunitiesfor impro\ing primary lead prevention cmbecome a reality

Human beings no longer live in a naturilsetting All around us are the artifacts ofhuman existence Our built environmentp a r t i c u l a r l y the design of the modernindustr ial city is a prime example of thesynthetic character of our emironment Tounderstand the flow of energy and matuials w i t h i n the bui l t en \ i ronmen t and itsconsequences for h u m a n existence n isnecessary to understand the geochemistryand the toxicit) of trace metals in the environment at both a planetary and regionalperspective (/) Nnagu and Pacyna (2)have argued that from a global perspec i\ethe toxicity of trace metals released into thee n v i r o n m e n t exceeds tha t of all otherradioact ive and organic pollutants combmcd I ead is a trace metal that has beenassociited with human civilization sincethe eailiest practice of metallurgy In diecourse of min ing and concentrat ing theore smelting the ore to purify the metaland manufacturing useful products fromlead there has been a geochemical transferof lead from the mine to human habitats

Two produc t s have added massivequantities of lead to the built environmentin modern t imes These are lead basedpaint and lead additives to gasoline Froma gross tonnage perspective in the UnitedStates about equal amounts of lead wereused in white lead paint pigment between1884 and 1989 as in leaded gasol inebetween 1929 and 1989 (34) (Figure 1)The peak use of lead based paint occurredin the 1920s when the U S economy wasagrarian rural and relied mainly on railtransportation for moving goods and providing services The lead based paints wereused as a protective coating on buildingsand structures in both large and small

Environmental Health Perspectives Vol 106 Supplement I February 1998 2 J 7

MIELKE AND REAGAN

8

Years 1884-1989

Figure 1 Lead used in gasoline and white lead paintpigments (3 4}

communities throughout the country Mostlead based paint still exists as a thin mass onwalls and structures In contrast the peakuse of leaded gasoline occurred in the earl)1970s at a t ime when the U S economjVMS industrial urban and relied on automobiles for transportation About 75% ofthe gasoline lead was emitted from -uiromobile exhaust pipes in the form of a fine leaddust (the remaining 25% of the lead endedup in the oil or was trapped on internal surfaces of the engine and exhaust svstem) (5)It is estimated that the use of leaded gasoline left a residue of 4 to 5 million metrictons in the environment (67)

The global distribution of lead used inj^isoline was not even Over 10 million metuc tons of lead wjs transferred to die globalenvironment via the motor vehicle fleetibout 5 9 million metric tons were dispersedinto the United States alone (8) On a localscale the flow of leid additives in gisohneinto the built environment has also resultedin an uneven dispersal of lead The modernindus t r i a l city has two features that conr r ibute to the urban pattern of lead Firstihe modern city contains a central businessdistrict which is the daytime address for akrge number of workers who commute ona daily basis from outl}ing areas Secondthe modern city has a ground transportanon system dominated by privately ownedlutomobiles and a highway network thatconcentrates traffic flows within the centralbusiness district Add leaded gasoline tothis picture and the result is a system forthe inadvertent delivery and accumulationof lead in the densely populated areassurrounding the city center (7)

Soil studies conducted in MarylandMinnesota Louisiana and elsewhere show aconsistent pattern of lead geochemistry inurban environments based upon city size andcommunity location (9-14) Specificallylarge cities have median lead concentrations

1 or 2 orders of magnitude higher than thoseof small cities The distance-soil concentracion function from cit) center to suburbs/rural areas is curvilinear For examplein Baltimore Mainland (9) the highest garden soil contamination was so tightly clustered toward the city center t ha t theprobability that the concentration could bedue to chance was 1 in 1023 Median soillead concentrat ions in the Twin Cities(Minneapolis and St Paul Minnesota) (11)were 10 times higher than those in adjacentsuburbs with older housing where leadbased paint concentrations were higherSimilar lesults were found when comparingNew Orleans Louisiana vvidi smaller towns(13) Mieike et al (15) calculated estimatesbased on average d a i l y vehicle t ra f f ic(ADVT) wi th in 1 mi le d iamete r areaswithin city cores When the annual metrictons of lead emitted by New Orleans traffic(ADVT = 95 000) was compared to that forThibodaux Louisiani (ADVT- 10 000)New Orleans was found to be more than10 times higher (5 15 metric tons) thanThibodaux (0 4} metric tons) Median soillead concentrations wuc 300 to 1200 ug/gin the high traffic arc is of New Orleansversus 60 ug/gTn the high traffic areas ofThibodaux In summiry the cultural useof metals has changed the pattern of plinetary geochemistry and the main locationsof accumulation are in ihe built environm e n t There now c \ i s t u r b a n me ta lislands analogous to uiban heat islandsmeteoiologists use to describe the modernindusinal city (14) The geochemica! reali ty of the urban e n v i i o n m e n t results inenormous health and policy implicationsfor society

Within the U S bu i l t environment over12 million children are exposed to the riskof adverse health effects from 10 mil l ionmetric tons (1019 ug) of lead residues resulting from gasoline and punt use (616) Thetotal tolerable daily int ike of lead for children is about 6 ug lead per day We measurelead in micrograms of lead per deciliter ofwhole blood (ug/dl) The mass of lead inour built environment potentially availablefor exposure to children is about 19 ordersof magnitude greater than the quantity oflead relevant to a child Clearly there is analmost inconceivable amount of lead potentially available to children The critical concern then is the amount of lead actuallyavailable to the child

For most urban areas the child leadproblem is a function of previous paint andgasoline use and their accumulation intothe soil pathway of exposure (17) The

immediate societal issue is prevention ofexposure to those ~who ire being excessively overexposed and main ta in ing thehealth status of those who are not It isimportant for those who have power andinfluence over implementing lead prevention activities to understand the enormityof the soil lead contr ibut ion to the childlead problem Many have claimed that leadin soil is nothing like the contribution oflead f rom pa in The D e p a r t m e n t ofHousing and Urban Development (HUD)for example minimizes the regulatoryrequirements for lead in soil compared tolead in paint in their rules recentl) proposed in the federal register (18) This isoccurring despite the fact that HUD andother federal agencies (16 19-21) haveconcluded that lead in soil is an importantsource of lead The Agency for ToxicSubstances and Disease Registry (ATSDR)(7.9) specific-all) stated thit lead in pa in tand dust /soi l lead were the two majorsources of lead The Centers for DiseaseControl and Prevention (CDC) (20) statesthat lead based paint and lead contaminated dusts and soil remain the primarysources HUD (21) st-ues t"hat forinfants and young children surface dustand soil are important pathways TheU S Envi ronmenta l Protect ion Agency(US EPA) (16) states t h a t the threemajor sources of elevated blood lead arelead based paint urban .soil and dustand lead in drinking water In addition tothese statements bv government agenciesthere are more than 20 other governmentreports tha t recognise soil/dust lead as amajor contributor to lead in children (22)

An understanding of the relative risk oflead sources is importanr because Title X(the Residential Lead Based Paint HazardReduction Act of 1992) focuses on leadhazards not on the mere presence of leadbased pa in t and hazard is def ined toinclude lead in soil Community and sitespecific responses to environmental leadmust consider soil and dust to address theproblem effectively (23) It is clear that soilis not being considered an equal threat tochildren For example only 9 of the 26member countries of the Organization forEconomic Cooperation and Developmentregulate lead in soil in contrast to 17 forlead in paint (24) Hence to effectivelyintegrate soil lead exposures in activities toreduce lead risk it is necessar) to contrastand compare lead in soil with the sourcecommonly believed perhaps mistakenly tobe the most important contributor to thechild lead problem i e lead based paint

218 Environmental Health Perspectives Vol 106 Supplement I February 1998

SOIL AN IMPORTANT PATHWAY Of HUMAN LEAD EXPOSURE

LiThe Relative Risks of LeadBased Paint and Leadin Soil and DustWhene\er one addresses the issue of lead insoil the first statement one hears is thatlead based paint is the number one problem and an\ or all other lead sources mustbe a distant second The implication is thatlead in gasohn or its pathways of soil andhouse dust are t r ivial in comparison todirect exposure to lead based paint itselfWhen reviewing the eudence na t iona lstudies usually frame the argument as follows Lead based pain t is the most concentrated source of lead to children andh i s t o r i c a l l y is the source most closelylinked to lead poisoning in children (25)

Lead based paint is the largest source ofhigh dose lead exposure for children (6)And lead based paint is widely regarded asthe source of the most imensi%e and damaging exposures to lead and the preeminentcause of childhood lead poisoning in theUnited States (26) The contention thatlead based paint is the number one problem uses the fo l lowing reasoning it is ahigh dose source it is closely linked to leadpoisoning and the principle source of leadn house dust and soil is lead paint Let usximine these reasons as well as the

^ddicional risk assessment factors for leadin paint

Does a High Dose Source MeanGi eater Risk?Many argue that lead based paint is then u m b e r one source of lead in ch i ldrenbceiuse it is a high dose source If a measui ible amount of lead is a criterion usedto rl termine delivered dose then lead acidbat ter ies should be a larger hazard thanlead based pa in t Is measurable lead theonly factor considered when determiningthe level of risk of a hazardous matcnal-'Obviously the issue is not just measurablelead but the accessibility and bioavailability of the lead For example lead acid battenes are encapsulated and generally out ofharm s way for children Lead based paintpresents another type of problem Imaginethis scenario a 2 year old child eats a 1 gpaint chip containing 2% or 20 000 ug oflead The blood volume of that child is100 dl At 50% absorp t ion the chi ldwould have a blood lead (PbB) level of100 ug/dl Lead can kill at PbB levels of100 ug Pb/dl or less Why then are notyoung children dying in large numbers'

he answer has to do with the bioavailabil i ty of lead i e the likelihood of thechild ingesting a sufficient dose of lead

and the i b i l i t y of the in te s t ina l t ract toabsorb and retain lead

Several key factors aie it issue besjdesthe total lead a\ailable from the source Itis k n o w n chat about 50% of ingesteddietary lead is absorbed by chi ldren lessthan 5 years of age (27) Experiments onlead in soi l and p a i n t show tha t 2 to 6t imes as much lead can be bio logica l lyextracted from soil than from paint (28)Most studies use 30% i c 3 times morelead is bioavailable from lead in soil thanin p a i n t (2930) Moreover h u m a nabsorption and retention of lead is a function of both particle sue and chemicalspecies (31) The smallei the particle themore easily it is absorbed by the digestiveS)Stem Nearly half the exhaust emit tedfrom gasol ine was less thin 0 25 um insize with most of the remaining emissionsb tween 10 and 20 um (5) In contrastthe particle size of lead in paint dust/chipsranges from 200 to 300 um to the visiblerange Hence large pait icles containinglead such as pamr chips ire less easi lyabsorbed and therefore I ss bioavailableI t is wel l known t h a t p imt chips passthrough the digestive sjstcm intact Thishelps explain wh\ a single lead paint chipdoes not kill a child

Albo b i o a s a i l a b i l i t ) is not s impjy afunction of particle size Research has shownthat mueh lead is reabsoibcd by food orother substances already in the digestive sysrem t h c i e b y l imi t ing the ava i lab i l i ty oflead to membrane absorpu<_n sites A childabsorbs less lead just aftu firing than duri n g t h e pe r iod be tween meals ( 3 1 )Fur the r the capabi l i ty of the digesmesystem to absorb lead ib l imited Consequent!) although the f i r s t increment oflead is absoibed subsequent increments areless likely to be absorbed unt i l some pointwhen the receptor s i tes a re s a t u r a t e dResearch shows that after a dose exceeds500 ug (even of small pn tides) there is adramatic flattening of the absorption capabi l i ty of lead in food soil dust drinkingwater and paint (1732 33) As the doseincreases beyond 500 ug the incrementaleffect of more lead decreases un t i l it haszero effect upon absorption Hence it isthe f i r s t i nc remen ta l a m o u n t of lead(100-500 ug) not the total lead ingestedthat poses the largest risk of lead absorptionto young children

For the above reasons extremely highconcentrations of lead in a paint chip donot translate into a linear increase in PbBlevels The fact that the amount of lead ina p a i n t chip measures higher than the

amount of lead in soil is biologically irrelevan t Measurable lead does not equatewith either the effects e dose or the hazardthat lead imposes Potential dose does notequal hazard

Is Lead Based Paint die Primary Causeof Lead Poisoning*Central to die argument that paint is thenumber one lead source is thit lead basedpain t is closely linked with lead poisoning Here again this ev idence must becritically evaluated

Nature & Extent Report to CongressIn response ro the 1986 Superfund reauthonzation legislation the ATSDR examinedarea stratified lead exposure among U Spreschool children (19) This examinationconsisted of both e n u m e r a t i o n andestimation merhodologies to yield prevalences of preselected blood lead criterion levels and those children whose environmentalsetting would be expected to provide a significantly ele\ated risk of systemic exposuredespite the absence of specific blood leadpre\alence data The report estimated thenumber of black and whi te chi ldren withPbB levels above selecred criterion \aluesactual counts of children identified throughU S screening programs for 19S4 and then u m b e r of ch i l d r en in 318 SMSAs(Standard Metropolitan Stat is t ical Areas)who have the highest potential exposure tolead paint (3-4)

The premise of the ATSDR report wasthat since the age of housing indicatesthe degree of exposure to lead in paint andplumbing we analyzed the distnbunon ofchi ldren l i v i n g in SMSAs by the age oftheir housing u n i t s (3-4) The reportconcluded that

the counts in terms of housing aDeand family income p oduced tl e unexpeered finding that more childrc i in olderhousing (high lead paint and plumbinglead levels) were also in nonceiurjl citynonpoverty families than were childrenassociated in t>pica! risk groups Thisobservation is consistent with the stratified distributions of the report i projectednumbers of the nat ion s children withelevated PbB levels (34)

The report goes on to conclude that

estimates of exposure and toxicity basedon data gathered in isolated points oft ime such as the estimates and enumerat ions given in the report to Congress greatly understate the cumulativerisk for a population that is posed by au n i q u e l y p e r s i s t e n t and u b i q u i t o u s

Environment?! Health Perspectives Vol 106 Supplement I February 1998 219

MIELKE AND REAGAN

pol lu tan t such as lead This cumulativet o l l ove r extended t i m e is of m u c hgreater magni tude than the pre\elanceor tonl exposure esnmar s for a givenyear (34)

The effccc of these conclusions dominatedthe creation of the 1992 Lead Based PajruHazard Reduct ion Act w i t h all i ts subsequent mandates and problems

Are the methodologies and conclusionsof the AFSDR report valid t e is age ofhousing a \alid surrogate variable for leadexposure' ATSDRs own data particularlyin conjunction wi th National Health andNutrition Examination Survey (NHANES)II and NHANES III data can answer thisquestion T ables 1 and 2 summarize theextent of the problem as ATSDR found itO\er half the housing in the U S containslead based paint based on age of housingFurther 87% of children under 7 vears ofage live in housing with lead based paintIn add i t ion 7 7% of U S lead pa in tedhousing is in unsound or deteriorated condition Further 12 8% of US children livein unsound lead painted housing If onecontrasts these figures with the NHANESII dataset (Table 3) one sees a close correspondence between the number of children

less than 6 >e i r s of age w i rh PbB le \ e l sgreater t han 10 ug/dl (87 8%) and thenumber of children in lead painted housing (87%) Fur ther the number of ch i ldren wi th PbB le\els greater than 25 ug/dl(14 3%) close!) matches the n u m b e r ofchildren in unsound lead painted houses(12 8%) who p r e s u m a b l y w o u l d ha \ egreater exposures to lead Consequent!) atfirst ghnce the presence and deteriorationof lead based p a i n t appears to e x p l a i npopulation PbB levels in >oung children

ATSDR did not of course base theirconclusions on the NHANES II datasetRather they selected 1984 lead screeningdata adjusted for NHANES II results withcensus data for 318 SMS^s to determineprevelance rates for children in lead paintedhouses Their analysis revealed that 46% ofchildren undei 7 >ears of age had PbB levelsgreater than 10 ug/dl and only 1 5% hadPbB le\els greater than 25 ug/dl (Table 3)From these data they then calculated anes t ima te of the p e r c e n t of c h i l d r e n inu n s o u n d lead pa in ted houses aboveselected PbB lc\els (Table 2) 1 hey calculated that about half (50 5%) the childrenwith PbB levels greater than 15 pg/dl livedin unsound leid painted houses md that

Table 1 A1SDR best estimate of pre 1980 lead painted houses and thifuJinber of children under 1 years of aaeby deterioration criteria in the United States

Category

Total United SlatesLead paintedUnsound lead painted

TotalPeeling paintBroken plasterHolds) in w II

Houses no1000

8039041964

51991°7215942602

Houses

1000522

7 7

Base population 6

10001384012043

1 772567458747

Population

1000870

128

Lead paint levels greater than 0 7 mgPb/cm2 'U S white and black populations only Data from ATSOR TablesVI 3 anrj VI 4 (19)

Table 2 ATSDil best estimate ol the percent of children under 7 yeais of age abo\e selected blood lead levels inunsound leid painted housing

Category

ATSDR base populationChildren in unsound lead painted housingChildren4 in unsound lead paintedhousing selected PbB levels

> 15 ug/dl> 20 ug/dl> 25 ug/dl

Children6 in unsound lead painted housingcompared to total base population

Total children1000

138401772

2380671552007

13840

Percentage of children withPbB levels (urj/dl| greater than15 20 25

172678

505

87

5 2308

762

4 0

15106

93714

Percentage ofU S children

1000128

1725215

1000

*U S white and black population only 'Translated from actual numbers into percents Data from ATSDR Tablesl-3andVI-6(79)

93 7% of the c h i l d r e n w i t h PbB leve lsgreiter than 25 ug/dl did so Based on thesedata they reached ihe conclusions notedabove i e that their estimates underesnmated the risk of lead exposure in )oungch i ld ren Nothing in cheir analysis challenged their premise t h a t l i v i n g in leadpainted houses was ihe dominant risk factorfor )oung children

There are a number of indicators thatthe ATSDR conclusions requite a cirefulreview in light of NHANES III (35-37)First even if we assume that all childrenwith PbB levels greater than 10 ug/dl livedin lead painted houses over 47% of thechildren living in leaded painted houses hadPbB levels below 10 ug/dl (46% > 10Hg/dlx 100 - 87% living in lead paintedhouses 529% 100-529 = 471%) Thisis very close to chance and does not indicatethat intact lead based paint correlates withpopulation PbB levels Second e\en if weassume that all chi ldren with PbB le\elsgreater than 25 pg/dl lived in unsoundlead painted houses 88% of the childrenliving in such houses had PbB levels below25 ug/dl (1 5 % > 2 5 ug/dl x 100-12 8%l i v ing in unsound lead painted houses= 117% 100-117=883%) TheATSDRdata indicate that l iving in unsound leadpainted houses is a riecessarv condition tohaving PbB levels greater than 25 pjd\But with over 88% of children less than 7years of age l i v i n g in u n s o u n d leadpainted houses with PbB levels less than25 (Jg/dl and nearly half with PbB levelsless than 10 pg/dl it is not a suff ic ientcondition Third the ATSDR analysis prediets that the highest PbB levels will occurin noncentral ciry areas among the highestincome groups I t was c lear in theNHANES II dataset that the opposite wastrue the highest prevalences were m centtal city areas among the poor This mdicates that perhaps the anal) sis is skewedand their premise fault) i e that age ofhousing is a good predictor of PbB levels inthe U S population Fourth contrary tothe ATSDR conclusion that they may haveunderestimated the risk to the U S population the NHANFS III data clearly showa massive decrease in PbB levels within theU S population (Table 3) The NHANESIII dataset continues to show the highestPbB levels in larger cities among people ofcolor and the poor F u r t h e r the steepdecline in PbB levels took place in theabsence of any significant effort to abateu n s o u n d lead pa in ted houses (35)Consequently the primary source of information used by Congress to derive lead

220 Environmental Health Perspectives Vol 106 Supplement I February 1998

SOIL AN IMPORTANT PATHWAY OF HUMAN LEAD EXPOSURE

Table 3 Distribution of blood lead levels above selected values for children 6 months to 6 years of agp in theUnited Slates

Survey3

NHANES IIATSDRNHANES III

Phase 1Phase 2

Reference

l/fi)I '9)

I3fi){37}

Mid year

19781984

19901993

Mean PbB levelsugrti1567 9

362 7

Percentage of children uilhPbB levels (ug/dll greater than

10 ID 25

87846 0*

894 4

562172

271 3

14315

05< 0 4

Differenc s between values in text and tables reflect different numbers used by different sources 'Data fromCrocetii et al (34} PbB > 25 ug/dl not provided DbB > 20 ug/dl- 0 4 /

abatement policy had overstated conclusions and was based on a faulty premisethat the presence of lead paint or its detenoration as measured b> age of housing isthe best predictor of population PbB levels

The Presence of Lead Paint inPoisoning Cases In data published or madei\aihble by the CDC a U S EPA analysisfound in 3 fiscal years between 1974 and1981 that out of 125 060 children withblood lead levels of 30 or 40 ug/dl in 40 50percent of confirmed cases of elevated bloodlead levels a possible source of lead painthazard was not located (5) Further justbecause a lead p a i n t source was locatedabout half the ume does not mean ipsofacto, that lead based paint was the source

/of the child s lead In cases of elevated PbBlevels the relative, contribution from varioussources cannot be determined with certa inty—whether it be lead pa in t leadedgasoline indust r ia l emissions or diet—\vithout conduct ing isotopic analyses andeven this approich has limited unlit) (39)If lead based paint were present only abouthalf the time m the U S EPA analysis of125 060 cases then lead based paint is thenumber one potentially contributing sourceto elevated PbB levels by a relatively slimmargin There is no question however thatwhen paint is pulverized into a lead dustduring renovation or inadequately abatedor a child has pica for paint chips severelead poisoning in young children is boundto result

Lead Poisoning from SmelterEmissions It is important to recognizethat lead in dust and soil can cause highPbB levels in the complete absence of leadbased paint (Studies of smelter communities have revealed that soil ind dust alonecan cause epidemics of lead poisoning) Forexample Yankel et al (40) found that99% of children 1 to 9 years of age whowere I n m g less than 1 mi l e from thesmelter had PbB levels greater than 40ug/dl Mean soil lead concentrations were7500 ug/g At 2 5 miles from the smelter

mean soil lead concentrations had declinedto 1400 ug/g—an amount comparable toinner cit) areas in the U S (13) At thisdistance 28% of the children had PbB levels greater than 40 ug/dl Similarl) studiesin neighborhoods near the El Paso Texassmelter found 53% of the children l ivingclosest to the smelter Ind PbB levels grc iterthan 40 ug/dl where mean soil lead levelswere about 1800 ug/g (41) It is importantto note tha t the r o u t e of exposure insmelter studies is believed to be h indto m o u t h ac t iv i ty (Studies m O m a h aNebraska (32) and in Be lg ium (42)showed that after air lead emissions weresubstant ia l ly reduced children I n i n g insoil-dust areas connming high leid andwho v,ere closest to the lead mdu&inesexperienced little if in) decline in memPbB leveU )This indicates that the overwhelming PbB contnbution was from leaddust via hand to mouth activity demonstrating that soil and house dust can causeepidemics of lead poisoning In contrast tothese lead industry studies showing 50 tomore than 90% of young children withPbB levels g rea t e r than 40 ug/dl theChicago Lead C l i n i c in i ts wors t year(1969) found that only 8% of children hadPbB levels greater than 50 pg/dl (with anaverage of 3 2% having levels greater ihan50 pg/dl out of hundreds of thousands ofchildren screened for the years 1967-1971)(43) These studies suggest that lead dustcan be a major source of the lead contnbutmg to population PbB levels in inner citiesand are similar to those in smelter commumties albeit from a different sourceThe data also imply indirectly that the linkbetween lead paint and popula t ion PbBlevels is not absolute

Population PbB Levels Decrease withGasoline Lead Reduction Another line ofevidence that raises questions about thehypothesized link between paint and population PbB levels is the change in the distribution of population PbB levels as the leadcontent of gasoline was reduced Data from

the N H A N E S II (5 1944-46) andNHANES III (3637) scudies show a significant reduction in mean population PbBlevels for verv voung children (1-3 years ofage) from 15 8 ug/dl in 1976 to 7 9 ug/dlin 1984 to 4 4 ug/dl in 1994 Data fromthe NHANES III Phase One stud) shov, am a j o r and o v e r w h e l m ! ng r educ t ion inmean population PbB levels in young chitdren 77% for white childien and 72% forblack children compared to the NHANESII Study (36) These studies indicated thatthe change in mean PbB was due to thedecl ine m the lead con ten t of gasol ine(53645 46) and a decreise in the lead content of foodstuffs and lead, solder in cannedfood (47) The overwhelming source clearlywas leaded gasoline (5 36 45) Fur therana lyses have been c o n d u c t e d of thechanges in air lead concentrations dur ingthis time frame (5) and the dose-responserelationship between air lead concentrationsand PbB le\els as a function of both directinha la t ion and indirect ingestion of leaddust (19) A review of this evidencestrongly supports the conclusion that ir wasthe decline in the a \a i labi l i ty of fresh leaddust via ingestion of lead contaminatedsoil and house dust that resulted in thesteep decline in population PbB levels inyoung children during this period (48)

During the NHANES II and III timef rames (1976-1984 and 1988-1994)there was also a significant decline in theextreme upper range of the d is t r ibut ionThe distribution of PbB levels in the U Spopulation of children less than 6 years ofage was r o u g h l ) a long the l i n e s of aGaussian d i s t r ibu t ion It is an i n t r i n s i cproperty of Gaussian d is t r ibut ions t h a tsmall changes in the mean imply majorchanges in the extremes i e the tails of thedistribution Indeed a comparison can bemade between mean population PbB levelsfor the mid year of the NHANES II study(15 6 ug/dl in 1978) and the ATSDRstudy (7 9 ug/dl in 1984) based on screenmg data m 1984 and adjus ted for theNHANES II model This shift of 7 7 ug/dlin mean population PbB levels shifted thedistr ibut ion of population PbB levels asshown in Table 3 In addition a companson pf NHANES II with NHANES IIIshows a s imilar decrease of 12 9 ug/dl inmean PbB levels of children 1 to 5 )ears ofage wi th a decrease from 14 3% to lessthan 0 4% in PbB levels greater than 25pg/dl (3637) A shift in the populationmean of 7 7 ug/dl from 1978 to 1984resulted in a decline of nearly half the caseswith PbB levels greater than 10 ug/dl and a

Environmental Health Perspectives Vol 106 Supplement I February 1998 221

MIELKE AND RCAGAN

uduct ion b) more than 10 t imes in thenumber of cases greater than 25 ug/dlSimilar ly a mean shift of 12 9 ug/dl from19/8 to 1993 resulted in a decline of )5%of die PbB levels greater than 10 ug'dl andi decline of 97 2% of rhe PbB cases LI catert h in 25 pg/dl These data suggest that therehtionship is \er) strong between leadedgaso l i ne and popula t ion PbB levelsD u r i n g t he > e a r s when lead was b e i n gremoved from gasol ine there was l i t t l eaction to remove leid based pa in t fiombuildings (38 49)

Soil and Dust Lead Dominate thePathway Multimedia studies suggest thatlead based paint is not closely linked withpopula t ion PbB l e v e l s M a n > anecdotalcases of lead poisoning have been attributedto lead based pain: Although the numberof individual cases i l a t i ve to the population at risk has ne\er been very high maminvestigators simpl) assumed that all leadpo i son ings and a l l exposures could beattributed to lead based paint Multimedialead studies help to tease out the relationship between various exposures and sourcesto PbB levels For example Menton et al(50) found that detailed structural equationmodels in a longitudinal study in Bostonwere consistent in showing diat blood leadlevels are siDmficantly related to dust leadand soil lead and the incidence of refinishing act iv i t ies Buigoon et al (51) in are\ icw of 11 studies found that theseresults reaffirm the soil to dust to bloodpathvva) said to represent the d o m i n a n tmechanism of childhood lead exposuie1 here are of cour e conditions that allowpaint to overwhelm soil as a pathwa) i ewhenever housing is icnovated with unsafewoik practices that pulverize paint into adust when subsequent cleaning is not conducted or is inadequate for the situation orwheie lead contaminated soil conceturations are low (52) Yet it must be notedthat lead contamimted hire soil can poisonchi ldren when ingested via geophagia orhand to mouth activity

Inner city Children Show UniformlyHighej PbB Levels Several studies explainpopulation based PbB levels Sayre et al(53) who conducted pioneering work onthe role of lead dust in the exposure ofchildren to lead questioned the hypothesisof paint chip pica for all lead exposuresthat prevailed wi thin the medical communi ty The cr i t ic ism of Sayre et al wasbased on observations of uniform elevationof lead exposure by inner city childrenThey noted that exposures to lead dust\\ere the same regard-less of the condition

of lead p a i n t and reasoned that if p a i n tchips were the major souice of lead exposure they should see huh PbB levels in afew chi ldren and low levels in those noti n g e s t i n g p a i n t c h i p s I n s t e a d theyobserved that elevated 1 bB leve ls tendedto persist to 5 years of ij-.e which is difficult to account for because pica behaviorrarel) persists bejond ige 3 It is important to distinguish between pica and handto mouth behaviors Pica behavior is thrd e l i b e i a t e i nges t ion of nonfood i temsincluding soil (geophagu) Children w i t hsoil pica routinely ingest 5 g of soil per dayw i t h 20 g not uncommon In contrasthand to mouth behavior is the inadvertentingestion of lead dust (particle size OO um)adhering to fingers hands or objects Thehand to mouth behavior pathway of exposure results in the ingestion of quantities ofdust that rarel) exceed 0 20 g per da) Theubiquitous occurrence of the behavior combined with the ph)sical-chemical cha racter isncs of smal l dus t par t ic les makehand to mouth behavior a potent pathwayof lead exposure After comparing innercity and suburban children hand-dust leadl e v e l s and the env i ronmen t and no t inglarge differences based on community locanon relative to cit) core they proposedlead dust as a major lead source in children They did not propose leaded gasolineas an a l t e r n a t i v e but it should be notedtha t lead a d d i t i v e s in gasoline peakedbetween 1970 and 1972 when Sayre et alwere conducting their field lesearch

Charney et al (54) compared twogroups of high risk inner city black children group I had PbB levels greater than40 ug/dl group II had PbB levels less than30 ug/d l They found tha t four factorse x p l a i n e d 40 to 91% of the v a r i a n c ebetween these two groups They assertedthat hand lead level house dust lead levellead in outside soil and a histor) of pica allappear to be mult ipl icat ive factors contnbutmg independent!) to the very highpropor t ion of total var iance explained[p va lues <0 005 0 0 0 5 004 0 0 0 1respective!)] I n t e r i o r p a i n t was not istrong independent factor in this study

The Sichs (43) study and other similarstudies seem to imply that children withPbB levels greater than 40 ug/dl and wholive in deteriorating housing obtain theirlead only through paint chip pica In aneffor t to see if this was always t rueHammond et al (55) examined youngchildren with PbB levels in the 40 to 70ug/dl range and who lived in houses with alead paint hazard He expected to find paint

chips in c h i l d r e n s stools and fecal leadspikes indieatmg in termit tent hiph sourcedoses Inste d he found relative!) high cont i n u o u s exposure to lead e\en!y mixedthroughout the stool wich no p mt chips orhigh lead fecal spikes He concluded thatthe lead exposure was due to ingestion oflead dus t v i a hand to m o u t h a c t i v i t jFurther it could not be estibhshed thatlead paint was the source of the dust (56)Children moved to low lead dust housingexperienced an immedia te drop in fecallead concentrations

Note that like Sayre et aJ (53) someliterature refutes the idea that deterioratinglead paint is correlated with population PbBlevels Angle et al (57) examined the aistribution of PbB levels based on the locationof d i l ap ida ted hous ing \Mth lead pa in thigh traffic roads and indus t r i a l pointsources in Omaha The distribution of PbBlevels matched the locations of point sourcesand traffic but not dilapidated housing Thiswould appear to indicate that the presenceof flaking peeling paint is insufficient bvitself to significantly raise PbB levels in aneighborhood relative to the contribution ofother sources such as leaded gasoMne ori n d u s t r i a l / c o m m e r c i a l p o i n t sourcesAngle s stud) suggests that a l though thepresence of deteriorated lead paint may beevidence of a hazard it does not necessarilyexplain population PbB levels

Mielke et al (12) f ound tha t theconcentrat ion of Pb in chi ldren s bloodvaried in the sime direction as the concentration of lead in soil but not wi th the ageof housing (Table 4) A small older communiry with low traffic flows (RochesterMinnesota) and an older inner citv comm u n i t y w i t h low t raff ic flows ( N o r t hMinneapolis Minnesota) had statisticallysignificant lower concentrations of lead inblood and soil compared to those in a relativel) younger inner city community w i t hhigh traffic flows (South Minneapolis)The d i f f e rence in PbB l eve l s can beexplained by soil lead concen t ra t ionswhich reflected the historic pattern of traffie density and ultimatel) the lead usedin gasoline These results are consistentwith the NHANES II and III studies andthe published literature

It is important to note that research ongeographic areas larger than a single residence has demonstrated a consistent centraltendenc) of soil lead resu l t s in givenneighborhoods or communities indicatesthe reliabili ty of soil sampling for purposes of c o m p a r i n g D eograph ic areaslarger than a single residence Median soil

222 Environmental Health Perspectives Vol 106 Supplement I February 1998

SOIL AN IMPORTANT PATHWAY OF HUMAN LEAD tXPOSURE

Table 4 Comparison of select d variables between Rochester Minnesota and inner city South andMinneapolis

Variable

PbS levels ^>10pg/dl>15pg/dl>25pg/dl

Housing built before 19bO %Soil lead > 1 50 ug/g /

Foundation samplesStreetside samplesYard samples

Rochester

000 000

7 4 2

38911 100

Inner cityNorth Minneapolis

2647 61 4

671

676533623

Inner city-Soutn Minneapolis

46729364

588

9397 8 2819

Mielke et a! 172)

lead concentrations reflecting a neighborhood zone commumt) location or city sizecan be readily compared (58) For exampleteams collecting in the same neighborhoodsby two d i f f e r e n t research groups inMinneapolis and St Paul showed strongcorrelations of 0 66 for houseside samples (pvalue = 0 001) and 0 60 for Streetside sampies (/> value = 001) (59) One neighborhood in Minneapolis was sampled by fivedifferent teams independent of each otheryet the distributions and measures of centraltendency between groups were similar

These studies ind more like them indicate->thac PbB levels in the general populacion are closel) linked to lead in soil andhouse dust and that only some unknownfraction is direct!) linked to lead basedpunt Both the U S EPA and the RoyalSociety of Canada have concluded that at aminimum 30 to 40% of children s elevatedPbB levels is atnibutable to lead from gasoline (1660} A comparison of the decline inchildren s PbB levels from NHANES II andNHANES III suggests thac 75 to 9?% ofcases of children with PbB le\els above 9pg/dl assumed to be attributable to leadpaint were in fact from leaded gasoline

Is Lead Based Paint die PrincipleSource of Lead in Sodand House Dust?Some researchers have argued (26} thatlead based paint contributes lead to bothinterior house dust and exterior dust andsoil but tha t gasoline cont r ibu tes leadonly to exterior soil and dust In otherwords paint is said to be the sole sourceof interior house dust lead

The primary argument in favor of theidea that lead based paint is responsible forincreased PbB levels is that very high PbBlevels are often found in children living inolder housing Most of the lead based paintused in the U S (92%) was manufacturedprior to 1950 (Figure 1) Therefore it is

concluded that the lead paint in the olderhousing caused the lead poisoning Anotherway to view older housing is as lead trapsthe older the house the gieater the amountof exterior lead trapped inside (61) Interiorhouse dust lead concentrations often reflectexterior soil lead concentrations (33) whichin turn generall) reflect the historic use oflead in gasoline and its increase widi trafficdensity rather than with the age of housingOlder housing associated with high PbB levels reflects exterior gasoline contaminatedsoil lead that accumulated in the interior ofthe dwelling when it was tracked in overtime and became available to very youngchildren through hand to mou"th activit)(14) In short variations in the contnbutions of sources to house dust appear to beunrelated to the age of homes (62) The following information supports this idea

Lead Tonnage Equivalent in Gasolineand Paint From a gross tonnage perspective approximately equal quantities of leadwere used in leaded gasoline between 1929and 1989 as were used in white lead paintpigments between 1884 and 1989 (3 4)(Figure 1) All die lead emitted from automobile exhaust pipes wis in the form of afine lead dust In conti ist most lead bisedpaint still exists as a thin mass on walls andstructures and is not readily accessible tochildren It is estimated that the use ofleaded gasoline left a residue of 4 to 5 million metric tons of lead in the environm e n c which poses i risk to sens i t ivepopulations (67)

Geographic Pattern of Gasoline LeadEmissions and Blood Lead The dispersion of lead from the combustion of leadedgasoline resulted in a distinct geographicpattern through die various environmentalmedia (air to soil to house dust to bloodlead) This pattern demonstrates the massive contribution of leaded gasoline to leadin the air subsequent deposition of leaddust from the air onto soil the tracking of

lead soil dust into structures o contaminate interior house dust and most importantly subsequent uptake of lead dust fromeither or both interior and exterior envir o n m e n t s b y > o u n g c h i l d r e n th roughhand to mouth act ivi ty These processesare discussed below

AIR Air lead concentrations were highestwhere lead exhaust was greatest Accordingto the U S LPA (5) air lead levels werehighest in the inner city lower in die outercity lower still in suburban areas and lowest m rural areas A distinct concentrationgradient occurred in air lead concentrationsaway from the downtown areas of mostmajor urban areas Lead in the air settles tothe ground and contaminates the soil

SOIL N u m e r o u s researchers haveshown a decreasing p a t t e r n of soil leadconcentrations similar to air lead concent ra t ions i e highest in the inne r citylower in the outer cit) krwer still in suburban areas and lowest in rural areas (12)This pattern was clearly demonstrated inmaps showing decreasing soil lead concentrations in foundation soils away from thedowntowns of Minneapolis and Saint PaulMinneso ta (}9) and in New OrleansLouisiana (75) even though communitiesaway from the inner city -were as old as theinner city communities Foundation soilsreflect the accumulated impact and washdown ot both air lead dust and exteriorlead based paint dust

HOUSE DUST Numerous studies havedemonstrated diat a large portion of interiorhouse dust lead is due to leaded gasolineFergusson and Kim (61) demonstrated thathouse dust lead concentrations increase as afunction of bui lding age indicating thatstructures act as traps for leid dust Theyalso found that house dust lead concentrations increase as a function of traffic densityi e decreasing house dust lead concentration gradients with increasing distancesfrom areas of high lead traffic similar to geographic patterns found for air lead and soillead concentrations Bornschem et al (33)found that soil lead concentrat ions andhouse dust lead concentrations are closelycorrelated [^=0 57] Fergusson et al (60)found that house dust is at least 50% soildust Research has demonstrated that soildust lead en te r s a s t ruc tu re by be ingtracked in (64-66) Chemical compositionstudies of house dust have revealed that thesource of lead in house dust is pr imar i lyleaded gasoline Such studies consists ofapport ioning sources of house dust leadbased on the ratio of chemical elements inthe original dust sources (e g paint or soil)

Environmental Health Perspectives Vol 106 Supplement I February 1998 223

MIELKE AND REAGAN

or the l i k e l y c o n t r i b u t i o n of lead fromorganic and inorganic sources or gravimetric and microscopic measurement in f inef rac t ions compared to possible sourcesSturges and Harnson (67) using gravimetric and microscopic measurement of finefractions reported that 85% of house dustlead was from leaded gasoline Fergussonand Schroeder (68) after examination ofthe organic and nonoiganic cont r ibut ionof sources to house dust reported that diesource of 95% of house dust lead wasleaded gasoline in newer housing and atleast 50% was from leaded gasoline inolder housing

BLOOD LEAD The geographic distubuuon of PbB levels follows the same patterns as lead in air soil and house dust andchanges as a function of the a\ailabihry oflead in gasoline Lead in food water andpaint do not exhibit specific geographic patterns In the case of lead based paint oldhouses everywhere old iarm houses smallcities and inner cities alike contain similaramounts of lead in paint The NHANFS IIand III studies and the ATSDR stud) on1984 lead screening data showed that PbBlevels were highest in the inner city lower inthe outer city lower in small communitiesand lowest in rural areas (19 35 37 45)Numerous reports in the literature supportthis pattern (15)

Does Lead Abatement AffectPbB Levels'Intervention does improve environmentalconditions and lower PbB levels in exposedp o p u l a t i o n s The U S EPA (69) in areview of 16 studies addressing lead abatemenr efFectiveness found that intervention did reduce exposed children s bloodlead c o n c e n t r a t i o n s on the order of18-34% 6-12 months following a %anety of intervention strategies Four studiesthat used PbB levels as a biologic markerconcluded

The Milwaukee Retrospective Educat ional Study (70) results indicate a13 6°/ decline 2 to 15 months followingi n t e rven t ion as the effect of their inhome educational outieach efforts Dustcont ro l measures conducted in theBaltimore Dust Control Study (54)were associated with a \f> 1% effect 12months following initiation Soil abatements performed in the Boston 3 CitySoil Abatement Study (71-72) exhjbited an 11 5% effect b) 11 months postintervention Finally the 1990 St LouisPaint Aba tement Study (73) alsoreported an 11 5% effect on the bloodlead levels of resident children 10 to 14

months f>Howmg the abateine it of damaged lead based paint (recall that a mukipie l inear regression model predicted a13% effect) Though the diia are limited ihese results suggest that rhese intervention stiategies are compa able in theireffect on blood lead concentrations

The Boston portion of the U S EPA3 City Soil Abatement Study addressed soillead abatement This study consisted ofthree different groups involv ing childrenwhose PbB levels were in the 7 to 24 ug/dlrange the study group that received abatement of soil house dust and loose paintcomparison group A which received abatement of house dust and loose paint andcomparison group B which on!) recededabatement of loose paint Only the studygroup that included soil abatement had asta t is t ical ly significant reduction in PbBl e v e l s (2 44 ug /d l ) 11 m o n t h s postabatement (71) In a follow up stud) PbBle\els continued to decline (3 03 ug/dl) inthe study group indicating a persistentintervention effect at least over the shortterm (2 years) (72) Moreover soil leadabatement performed in a subset of companson groups A and B resulted in a reduct ion in PbB l e v e l s of 41 and 13%respectively (69) The combined reductionin comparison groups A and B was 3 63ug/dl as a consequence of the subsequentsoil abatement (72) The U S EPA analysis of the Boston port ion of the 3 CityStudy concluded that blood lead werereduced by approximately 1 86 ug/dL at10 mo[nths] after soil lead abatementadd i t iona l reduct ions in blood lead ofabout 2 0 |Jg/dL (relative to non abated)were observed at 22 mo[nths] postabatement (74) One other soil abatementstud> is worth noting Soil lead abatementin the smelter town of Rouyn Norandaand the c o m m u n i t y of St Jean surRicheher Quebec resulted m decreases mPbB levels of about 30% (3 2 ug/dl) and50% (5 1 ug/dl) respectively (75)

The U S EPA Urban Soi l LeadDemons t ra t ion Project (3 City Study)integrated conclusion was that when soilis a significant source of lead in the chJd senvironment under certain conditions theaba tement of tha t soil wi l l resul t in areduct ion in exposure that will cause areduction in childhood blood lead concentrauons (74) The U S EPA furtherconcluded that

in the first year after soil abatement atmost 40 to 50 percent of a child s existingblood lead burden may be removed by

soil abatement or an) other combinationof abatements and intervent ions apartfrom medical t r ea tmen t by chelat ionThere may be a much greater effect orlead abatement in preventing lead exposure in future residents

Additional Risk Information on LeadBased Paint and Other Sources!Pathways A n u m b e r of o t h e r factorsshou ld be considered in d e t e r m i n i n gwhether lead paint is the principal source ofchildhood lead poisoning These factorsinelude the number of children at risk forlead exposure b) lead source the role ofseasonally in the child lead pioblem andihe role of pica in the child lead problem

First ATSDR estimated that nearl) 12million children under 7 years of age are atnsk from lead in paint and 12 million children are at risk from urban soil and oust(19) Clearly since the e are onl) IS million children under age 7 in the UnitedStates there exists considerable over l apbetween the two groups The U S EPA(16) also concluded that about 12 millionchildren were exposed to lead based paint+ u r b a n background i e lead irt soilHence both lead in soil and paint pose arisk separately or in combination to aboutan equal number of children roughl) twothirds of all children in the United Statesunder 7 >ears of age H

Second one of the s t r ik ing featuresabout the distribution of lead in populationsis that if PbB levels are monitored tempolally f-hey change as a function of the seasonsof the year The NHANES II survey showedthat PbB levels in the summer were about 20to 30% higher than in the winter (46)Hunter (7677) has reported that the prevalence of lead poisoning cases (defined as aPbB level > 40 ug/dl at the time) was 5 to 10times greater in the summer than the winterAt first it was thought that these seasonal differences were due to the effect of increasedsunlight on 1 25 CC vitamin D metabolismand its effect on calcium t ranspor tSubsequent research however showed diatthe seasonal change in vitamin D metabolism is too small to explain changes in PbBlevels (78)

The accepted explanation for seasonaldifferences in PbB levels and the prevalenceof lead poisoning cases are that in the summer there is a greater risk of geophagia(pica for soil) increased access and resuspension of soil dust lead increased deposition of lead m air through open windowsand most importantly increased trackingin of lead laden dust into dwellings from

224 Environmental Health Perspectives Vol 106 Supplement I February 1998

SOIL AN IMPORTANT PATHWAY OF HUMAN LEAD EXPOSUfY

he extenor by people and pels Both intenor hous dust lead and exterior soil dustlead conc( n t r a t ions are associated withincreases in PbB levels by season If PbBlevels were associated wi th nterior leadbased paint then PbB le\els should rise inthe win ter when children are more oftenconfined indoors Instead PbB levels arehigher when children have iccess to extenor sources of lead le soil and thereforeexterior lead dust

F ina l ly what about pici children' Ifchildren are categorized into three groups(those that never mouth fingers or objectsthose that do and those that cat nonfooditems [pica]) then the key to lead intake isaccessibility to lead sources I he mere presence of lead will not affect those childrenwho never engage in m o u t h i n g or picabeha\ior For those children who do engagein mouthing behavior but not pica the key\ar iables are the frequenc) of mouth ingbehavior and the size of the lead dust particle Rabmowitz and Bel lmger (79) haveshown that ehildren who mouth more thanothers have 2 to 3 times higher PbB levelsThe U S EPA (5) concluded that dustsources are important because of children s

and to mouth activities and because a sin;le gsam of dust can contain 10 times more

lead than the total diet of a child Fmall)children who have pica for soil or paint runthe nsjc of ingesting high doses of leadSome data suggest that pica children areabout five times more likely to eat soil dianpaint chips (80) Lead pain t chips easilycontain 5000 to 20 000 ug of leadChildren with pica for soil may ingest 5 g ormore per day At a soil concentration of1000 pg/g (typical of the inner city) a childcould ingest 5000 ug of lead in 1 dav Eithersource is more than enough to cause leadpoisoning As Houk (44) noted a childwho ingests as litde as 1/6 g of soil daily canbe lead poisoned [PbB > 30 pg/di] in a fewmonths Indeed smelter communities havesuffered epidemics of lead poisoning in theabsence of lead paint with soil and housedust concentrations comparable to those ofinner city neighborhoods (40 41)

Biological and EcologicalCausality Soil Leadto Blood LeadThe evidence presented above argues thatlead contaminated soil is a pathway ofhuman lead that is equally as important asexposure to lead based paint Critics of therole of lead contaminated soil may assertthat causality has not been proven How iscausality determined' Two centuries ago

David Hume stued that causality is a concept not susceptible to empirical demonstrat i o n Epidemiologis t s and sc i en t i s t scontribute to tlu incremental ac icnon ofdata that one hopes can be assembled into acoherent picture and from which lawfulnesscan be inferred (81)

If causality is not susceptible to empiricaldemons t r a t i on how then do we knowwhen causality is likely' Hill (82) delmeated a series of parameters that are import int in de te rmin ing whether causality isl ikely in a biological sense These parameters include consistency of effeet biologica l g rad ien t s of effect b i o l o g i c a lp l a u s i b i l i t y of effects cons i s t tnc ) ofbiological function and strength and specifieity of association To determine causaluy one must fust frame the question asvi as done by R u t t e r (53) on w h e t h e rlow level lead exposure exerts adversehealth effects

In the discussion prior to this sectionthe case was made that the overwhelmingcontributor to lead in soil \\as depositiondue to the combustion of leaded gasolineSchwartz (49) argued for the causal relationship between gasoline lead and PbB byciting the following factors

Expenmennl evidence found in theinvest igat ion of the con t r ibu t ion ofgasoline lead to PbB in isotopic studiesindicated a magnitude similar to thatfound in the NHANES II dataset i ethat in the late 1970s about 9 ug/dlof blood lead resulted from lead ingasoline (49)Cause preceded effect because giventhat the half l ife of lead in blood is 30days the NHANES II dataset revealedthat a 1 month lag between PbB levelsand gasoline air lead concentrationswas most significant on PbB with current or 2 month lag period being lesssignificantThe analys is was repeated in o therlocalities by other investigators and thesame patterns of gasoline lead emissions were found to be s ignif icant lyrelated to PbB levels this p rov idesreplicabihty and consistenc)Addit ional anal)ses revealed a l ineardose-response relat ionship betweengasoline lead and PbBGiven that gasoline lead produced 90%of U S air emissions in the 1970s andwas therefore a major source of cont ammat ion in the env i ronment airinhalation and ingestion of street dusthouse dust and soil contamination byhand to mouth activity demonstrate

hit absorption fnm the lung and gutis biologically possible1 o avoid Type I errors (accept ing aspurious relationship as real) confounding factors were controlled for in \ inous anal>ses these included age nees x income season degree of urbanization and region of the count)Other sources of lead exposure did notchinge during the NRANES II examimtion period in any significant v.aythis externally validates the conclusionThe following argument extends the

causal argument of Sch\\arcz (49) by examinmg the predominant intermediate pathway between gasoline lead and PbB i elead contaminated soil It must be remembered that soil is the sink for lead of allsources The essential causa] question is thisIs exposure to lead contaminated soil that isaccessible to young children a significantand impor tan t contributor to chi ldren sPbB levels'

Consistency of EffectCausal inference can be concluded if theassociation has been observed in differentinves t iga t ions us ing d i f fe rent researchstrategies A review of the literature as awhole (5 84 85) has consistently shownthat exposure to lead in soil has an effecton PbB levels

Biological Gradients of EffectWith regard to the effects of biologicalgradients i e dose-response relationshipsmost i nves t i ga t i ons do show a doseresponse relationship within the study butscal ing d i f f i c u l t i e s obscure the t ruedose-response relationship in man) studies(735) A reanalysis b> Burgoon et al (51)of 11 studies estimated a dose-responserelationship between soil lead and PbB of6 8 pg/dl per 1000 ug/g

Biological Plausibility of EffectsThe coherency between exposure and healtheffect is a necessary criterion for causality(86) It is well established that gasolineemissions resulting in increasing soil leadconcentrat ions beyond background arestrongly associated with PbB le\els (a surtogate measure of health effects) There is nobiological difference between soil lead exposure and exposures b) different pathwaysonce lead is absorbed after adjusting for relevant bioavailability issues it exerts its effects

Consistency of Biological FunctionCausality occurs if the association makesbiological sense i e that a likely biological

Environmental Health Perspectives Vol 106 Supplement I February 1998 225

MIELKE AND REAGAN

mechanism ex is t s by which the causaleffect can be mediated Paint and soil leadare absorbed through the gut after mgestion due to pica or mou th ing behav io rThere is no difference in biological effectafter adjusting for relevant b ioavai lab i l i t )issues because of the pathway of exposure

Strength and Specificity of AssociationAre the associations statistically trong andspecific' Lead in soil is stron^h associatedwith PbB le\els (the specific effect) becauseit can occur in the absence of Icid paint orother sources (5)

Ecological Causality RelativeRole of Lead Based Paintand Leaded GasolineThe central issue is w h e t h e r the mostimportant lead source is paint (intact orpeeling) or soil and dust The causalityquestion then is this What is the relativecontribution of gasoline contaminated soiland lead based paint exposures to the childlead problem' To answer the ciusal question noted above we first rewrite Hill s (82)delineation of biological parameters ofcausality in to ecological parameters ofcausality These parameters would includeconsistency of exposure ecological gradientsof exposure ecological plausibility of exposure consistency of ecological function andstrength and specificity of exposure

Consistency of ExposureDoes exposure to lead in soil/dust and/orpaint correlate with population PbB le\els'Exposure to lead contaminated soil housedust lead or street dust lead has consisrently shown a positive correlation betweensoil/dust lead concentrations and populat ion PbB levels (Table 5) In contrastexposure to lead paint is inconsis tent lycorrelated with population PbB levels

Ecological Gradients of ExposureDo population PbB level studies show ageographic gradient of effect and does leadin any pathway show this same effect' Boththe NHANES II (45) study (a survey of 64U S cities) and the ATSDR (19) study (asuney of 318 SMSAs) clearly and stronglyshowed that PbB levels vary as a function ofdistance The larger the city or the closer tothe center of the citv. the greater the number and percent of children above selectedPbB levels Does any lead pathway matchthe pattern found in these large scale PbB

I surveys' Again Table 5 shows that soilhouse dust street dust air and atmosphericdeposition exhibit a distance gradient in

concentrat ion s i m i l a r to that found w i t hlead in children s blood In contrast foodwater and paint pa\lvwa)s exhibit no suchdistance relationship It appears thereforethat exposure to lead in dust is an impoitantpredictor of lead in children s blood

Ecological Plauiibdity of ExposureHas the lead based paint or gasoline beenused in a manner tint would exphm theobserved PbB level pattern' Environncntalheilth issues can be analyzed through theecological method (87) The ecologicalapproach has many ad\antages a) Becauseexposure and heal th are analyzed on agroup basis very large populations ordersof m a g n i t u d e l a rger t h a n the t yp i ca lprospective cohort design of a few hundredcan be analyzed in a cost effective mannerb) This approach has the practical advantage of using existing databases c) Studiescan be completed in a relatively short timed) Because large databases are used thes tudies can measu re r e l a t i v e ! ) smal lincreases in risk e) Ihese t>pes of studiesare useful in investigating suspicious elusters of disease in relative!) small geographiclocations When the ecological method isused in conjunction w i t h other types ofresearch (case-control investigations ammal research prospective epidemiologicalstudies) and diere is consistency of evidencebetween the studies of different designs itadds to the plausibility of health hazards suggested bv the ecological data (88) Theadvantages of the ecological method is that itlends itself to the discussion of the causalnature of the subject being investigated Anecological approach has often been used toobserve that lead paint exposure is oftenfound in older deteriorated or recent!) renovated housing Because of the way citiesgrow and renew themselves this pattern oflead paint exposure reflects the nature of aneighborhood wi th older deter iora ted

neighborhoods providing greater access tolead paint chips and lead paint dust Whenont moves beyond an individual izedcase-control investigation and examines thePbB level pattetns observed in populationsd u r i n g the NHANES II and ATSDRstudies one finds that it icfiects a pattern ofthe c i ty 01 metropoli tan area as a w h o l e(1945) Tha t pattern reflects an incidencerate based upon cit) MZ.C or communi tylocation Similar to this cit) or metropolitanpattern are the patterns of traffic flow andleaded gasoline usage Lead concentrationsobserved in soil and house dust also matchtraffic flow patterns (12) Nearly equalamounts of lead were used in gasoline andwhite leid paint pigment (Figure 1) Mostgasoline lead was emitted as a dust jet mostlead pa in t is still intact as a th in mass onstructures Hence gasoline contaminatedsoil/dust provides a coherent explanation foipopulation PbB level patterns

Schwaru (49) argued that the citywidepattern does not point to lead based paintas h a v i n g an effect on PbB levels becausethe adul t decrease in PbB levels (37%) during the NHANES II study was similar tothat for children (42%) and adults- do noteat paint In addition mgestion of leadpajnt causes large increases in PbB levels Ifthere were a drop in lead paint exposure itwould only affect people whose PbB levelis*"above the mean Ho-wever the decreasein PbB d u r i n g the NHANES I I s t u d yshifted the entire distribution dramaticalheven low PbB groups showed ma jo rdeclines This would not occur if paint leadwere the major determinant Furthermorethe decline in PbB also occurred in suburbia which has a low percentage of pre1950 h o u s i n g and therefore less leadpaint yet both cities and suburbia showedthe same drop in PbB and the same gaslead coefficient Finall) o n l ) 0 2 % o f t h ehousing stock were included in lead paint

Table 5 Summary of the relationship between sources and pathways of lead exposure with blood lead levels anddistance s

Source /Pathway

SoilHouse dustStreet dustAirAir depositionFoodWaterPaint

Number ofstudy areas

4o45165012132839

Positive correlationwith PbB levels

424014281232

14

Positive correlationwith distance6

30 of 3017 of 188 of 8

27 of 279 of 9O o f OO o f OO o f O

Data from Reagan (9/| 'In this column the first number represents how many studies were positively associatedwith distance i e had a decreasing concentration gradient with distance The second number indicates how manystudies attempted to correlate the source/pathway with distance

226 Environmental Health Perspectives Vol 106 Supplement I February 1998

SOIL AN IMPORTANT PATHWAY OF HUMAN LEAD EXPOSURE

removal programs during this penod sop a i n t exposure r i tes were u n l i k ly tochange during this period

Consistency of Ecological FunctionDoes the d e t e r i o r a t i o n of p a i n t or thecombustion of gasuhne occur in a minnerihat best explains observed PbB pa t te rns 'When paint deteriorates it presents a leaddi st that settles onto the floor and elsewhereHouse dust floor loadings of more t h i n 200ug/ft hav e been of concern Soil dust loadings of 100 ppm conta in o v e r 139 000ue/ft2 in the uppei centimeter and soil leadconcentrations often exceed 1000 ppm inin ler city areas resulting in loadings of morethin 1 000 000 ug/ft' in the upper centimeter Foundation soil lead can be found atsuch concentrations iround brick 01 stoneb u i l d i n g s in the bsence of leid p a i n t(59 89) Man) studies shov, that sod leadcan be tracked into the house and result insevere contamina t ion (63 65 67 CS 90)Hence leaded gasol ine con tamina tedsoil/dust provides a consistent ecologicalexplanation for observed patterns of humanPbB lev els

Strength and Specificity of Exposure „ave studies that considered exposure to

ead in soil/dust and paint togethei foundtha t one or more p a t h w a y s consistent!)explain PbB resul t s ' Of the 161 s tudiessummarized in Table 5 26 considered leadboth in soil and paint Of these PbB levelswere positively associated with lead in soil in22 studies where is paint was only positivelycorrelated in 9 studies When one pathwaywas positive and the other negative 14 werepositive for soil and not paint and only 1was positive for paint and not so 1 (91)Generally then lead in soil is strongl) associated vvith population based PbB levels

The discussion ibove clearl) reveals anassociation between two variables—soil lead

concentutions and childl jod PbB levels—beyond v,hat could be atuibuted to chanceBoth biologically and ecol ->gically diis association can be interprets 1 as causal In thewords of Needleman and Bellmger (81) weare well aware that miking causal connect ions in the real world is not a puu\alue free enterprise Nevertheless it is rcisonable to draw die causal conclusion abovIn our view there is sufficient evidence to icton the conclusion that soil is equally imporrant as a pathwa) for lead as paint The maintask remaining for regulatory agencies andothers is to take this conclusion seriously

ConclusionThe purpose of the above discussion is2 fold to e\aluate the question of whetherlead based paint (intact or deteriorating inplace) is a more important pathway for leadaccumulation in young children than leadin soil from leaded gasoline and lead basedpaint (sanded or sandblisted) and to setthe stige for determining appropriate leada b a t e m e n t pol ic) As phi losopher Ku IPopper noted the wiy of science does notconsist of any proof of a hypothesis ratherit consists of a series of fulures to disprovethe hypothesis By this standard it is clearthat lesearch has failed to disprove ihehypothesis that soil lead exposure in younj,chi ldren is at least as impor t an t as leidpaint exposure Even if one argues that thework is incomplete that does not confeiupon us a freedom to ignore the knowledgewe already ha\ or to postpone the actiontt appears to demand at a given time (92)If HUD or an) other regulatory agencyrejects the need to treat soil as an equallyi m p o r t a n t pathway for lead as e q u a l l yimportant as paint the\ may be making aType II error (rejecting a \alid associationas spurious) in judgment or interpretationI e in this case rejecting as spurious theimportance of regulating lead in soil as well

as lead pami We must not continue to relyon the false eiusal model thit lead basedpaint is the only significant source of leadexposure in v umg children

Based on the arguments above leadbased paint i not a greater risk to youngchildren thin lead in soil "While lead basedpaint is a hi^h dose source the biologicaJl)relevant dos if c is not much if any greaterthan lead a\iilable in soil While lead basedpaint is cleai I) associated with severe leadpoisoning so too is lead in soil Lead ingasoline and I ad in food but not lead inpaint are stiongly associated with population PbB levels in both young children andadults Furthei lead in soil and house dustbut not lead based paint is associated withpopulation PbB levels in young childrenThe overwhelming majority or lead in soiland house dust is associated w ith lead fromgasoline Leid based paint dust is associatedwith cases of renovation of either exterior orinterior environments where the paint waspulverized into a lead dust or where leadcontaminated bare soil is low Abatement oflead c o n t a m i n a t e d soil may be moreeffective than abatement of lead paint inreducing PbB levels of young childrenbased upon the l imi ted data avai lableApproxim itely equal numbers of_childrenunder 7 )ens of age are exposed to lead insoil dust and intact or deteriorating leadbased pain t Seasonality studies strongl)point to lead in soil as a significant sourceof population PbB levels Studies of picachildren suggest that lead in soil is a greaterrisk factor than lead in paint In summar)lead in soil may well be the p r imarycausative agent for concern in addressingthe population of children at risk of leadpoisoning If so what does this mean forpublic pohc)? It means that equal regulatory attention must be given to lead contammaced soil as to lead based paint to solvethe child lead problem

REFERENCES

Mielke HW U r b a n e Geochemie Prozesse Mus te r undAuswirkungen auf die Menschliche Gesundheit In Geochemieund Umwelt (Matschullat J Tobschall HJ Voigt HJ eds)Berlin Springer Verlag 1997 169-179 [German]Nnagu JO Pacyna JM Quant i tau e assessment of worldwide contaminat ion of air water and soils by trace metalsNatute333 134-139(1988)Weaver JC A white paper on white lead ASTM StandardizationNews April 1989 34-38U S EPA EPA Approved Model Curriculum Lead AbatementTraining for Supervisors and Contractors Washington U SEnvironmental Protection Agencj 1992U S EPA Environmental Criteria and Assessment Office Air

Qualit) Criteria for Lead Rpt no EPA/600/8 83/028aF ResearchTriangle Park NC U S Environmental Protection Agency 1986NAS Measuring Lead Exposure in Infants Children and OtherSensit ive Populat ions Washington Nat iona l Academy ofSciences 1993Xintaras C Analysis Paper Impact of Lead Contaminated Soilon Public Health Atlanta Agency for Toxic Substances andDisease Registry 1992Statement of the Ethyl Corporation S 2609 A Bill to Amendthe Clean Air Act with Regard to Mobile Source EmissionControl Hearings before the Committee on Environment andPublic Works U S Senate 98th Congress 2nd Session June22 1984

Environmental Health Perspectives Vol 106 Supplement 1 February 1998 227

MIELKE AND RFAuAN

9 Mielke HW And rson ]C Berry isj Mielke P^X Chancy RLI ead concentriinns in inner city S D i l s as a factor in the childlead problem Am j Pub Health 73 1366-1369 (1983)

10 Mielke HW El i te B Burroughs S Hassmger N Urban lead 32levels in Mmne \ ohs the case of ill Hmong children hnvironRes 34 64-76 (U84) 3^

11 Mielke HW Bi rroughs S Wad S Yarrow T Mielke PWUrban lead in Minnesota soil ti Tsects of four cities MinnAcadSci50( l ) 19-24(1984/85)

12 Mielk HW A Inms JL Reagan PI Mielke PW Soil lust lead 34and childhood 1 d exposure as i function of city size and community traffic flo v the case for lei I abatement in MinnesotaIn Lead in Soi l (Da\ ies BE ^ V i x s o n B G eds) h n v i r o nGeochem Health Suppl 9 233-271 (U89)

13 Mielke HW Lead dust contammu d USA cities comparison 35of L o u i s i a n a and Minneso ta ^pp l Geochem 2 ( S u p p l )257-261(1993)

14 Davies BE Lead in the urban ind home en\ ironmems ofBr i ta in an ovei lew Trace Subsnn Envi ron Health XXVI131-144(1992) 36

15 Mielke HW Du^as D Mielke 1 \V Smith KS S m i t h SLGonzales CR Absociations bervw n soil lead and chi ldhoodblood lead in urban New Orleans ind rural Lafourche parishes ofLouisiana USA t-miron Health In ecr 105 950-954 (1997) 37

16 US EPA Strategy for Reducing 1 eid Exposures WashingtonU S Enuronmemal Protection Ag ncy 1991 38

17 B r u n e k r e e f B Veenstra SJ B i e i s t c k e r K Boleij JSM TheArnhem lead stud) 1 Lead uptake by 1 3 >ear old children Ining in the vicinit) of a secondary lend smelter in Arnhem TheNetherlands Em iron Res 2> 415-448 (1981) 39

18 Reagan PL Anal) sis of HUD s Pi nposed Paint Regulations andStandards St Paul MN Midwesi Environmental Education 40and Research Association (MEERA) 1996

19 ATSDR. The Nature and Extent of J ead Poisoning in Childrenin the United States A Report to Congress Atlanta Agency forToxic Substances ind Disease Registry 1988 41

20 CDC P r e v e n t i n g Lead P o i s o n i n g in Young ChildrenAtlanta Centers for Disease Control 1991

21 HUD Cornprel ensive and Workable Plan for the Abitemem ofLead Based Pimt in Privately Owned Hous ing Report ro 42Congress Washington Housing and Urban Development 1990

22 Reagan PL Direct Quotations of Government Reports on Leadin Dust of All Types St Paul MN Midwest Emuonmenta lEducation and Research Association (MEERA) 1997 43

23 US EPA Goldman LR Guidance on Residential Lead BasedPaint Lead Contaminated Dust ind Lead Contaminated Soil 44Washington U S Environmental Protection Agency 1994

24 OECD Risk Reduct ion Monograph No 1 Lead Rpt noEnviron Mono 65 OCDE/GD9367 Paris Organization forEconomic Cooperation and De\elopment 1993 45

25 CDC Strategic Plan for the El iminat ion of Childhood LeadPoisoning Atlanta Centers for Discise Control 1991

26 Alliance To abate or debate that is the question Mealey sLitigation Reports LEAD 3(13) 16-20 (1994)

27 Alexander FW DeKesHT Clavton BE The uptake and excre 46t ion by c h i l d r e n of lead and o ther c o n t a m i n a n t s InE n v i r o n m e n t a l Hea l th Aspects of Lead Proceeding ofanln terna t ional Symposium (Barth D Ber l in A Engel R 47Recht P Smeets J eds) Amsterdam Commission on EuropeanCommunities 1973319-331

28 Roberts TM Hutchmson TC Paciga J Chattopadh>ay A 48Jervis RE Van Loon J Parkmson DK Lead contaminationaround secondary smelters estimation of dispersal and accumulation by humans Science 186 1120-1123(1974)

29 US EPA Criteria and Standards Division The Environmental 49Lead Problem An Assessment of Lead in Drinking Water froma Mul t imedia Perspective Rpt no EPA 570/9 79 003Washington U S Environmental Protection Agencs 1979 50

30 OME Lead in Soil Committee Review and Recommendationson a Lead in Soil G u i d e l i n e Onta r io M i n i s t r y of theEnvironment 1987

31 Chancy R Mi Ike HW Sterrett SB Speciation mobility and

Lead jn Soi l I s sues andf eds) Environ Geochem

b i o a s a i l a b i h t ) of soi l lead InGuidelines (DaMes BE Wixson 1Health Suppl 9 105-109(1989)Angle CR Mcfn t i r e MS Children the barometer of environmental lead J 1 oucol Environ He Ith 5 853-870 (19S2)Bornschein RL Succop PA Ki rCt KM Clark CS Peace BHammond PB fxtenor surface <i ist lead, interior house dustlead and childhood lead exposur in an urban env i ronmentTrace Substan 1 nviron Health XX 322-3^2 (1986)Crocetti AF MushakP Schwair?J Determination of numbersof lead exposed U S children b) <i eis of the United States anintegrated sumirnry of a report to the U S Congress on childhood lead poisoning EnMron He 1th Petspect 89 109-120(1990)Brody DJ P i r k l e J L Kramet RA Flegal KM Mine TDGunter EW P is,chal DC Blood lead le els in the US population Phase 1 of ihe Third Nati mil HeaJth and Nutr i t ionalE x a m i n a t i o n Survey NHANES 111 1988 to 1991 JAMA272(4)277-283(1994)P i r k l e J L Brod) DJ Gunter F\V Kramer RA Pa rha! DCFlegal KM Matte TD The decline in blood lead le\els in theUnited States 1 he National Health and Nutritional ExaminationSurveys NHANLS JAMA 272(4) 284-291(1994)Centers for Disease Control Update Blood Lead LevelsUnited States 1991-1994 MMWR46(7) 141-146(1997)Mushak P Crocetti A Methods for reducing lead exposure in>oung children and other risk groups an integrared summanof a report to the U S Congress on childhood lead poisoningEmiron Health Ptrspect 89 125-135 (1990)Rabmowitz MB Stable isotopes of lead for source idennfication dm Toxicol 33(6) 649-655 (1995)YankelAJ Lmdcrn IH ^ al ter SD The Silver Valley leadstudy The relat ionship between childhood blood lead levelsand e n v i r o n m e n t a l exposure J Air Pollut Cont Assoc 27763-767(1977)Landngan PJ Cehlback SH Rosenblum BF S h o u l t s J MCandelana RM Barthel WF Liddlc JA Srnrek AL StaehhngNW Sanders JF Cpidemic lead absorption near an ore smelterN Engl J Med 292 123-129 (1975)RoelsHA BuchctJP Lauwerys RR Bruaux P Clae)S fhoreauF Lafontame A Verdu\n G Exposure to lead by the oral andthe pulmonary routes of children l iving in the \icimt) of a primary lead smelter Environ Res 22 SI-94 (1 980)Sachs H Effect of a screening pro^iam on changing patterns oflead poisoning Environ Health Perspect 7 4 1-4} (1974)Sta tement of Vernon Houk ]n Lead in Gasoline Publ icHeaJth Dangers Before the Subcommittee on the EnvironmentC o m m i t t e e on G o \ e r n m e n t Opera t ions House ofRepresentatives 97th Congress 2nd Session 198237-58Annest JL Trends in thetlood le-id levels of the US population the second national health and nutr i t ion examination sur\ey NHANES II 1976 1980 In Lead Versus Health Sourcesand Effects of Low Level Lead Exposure (Rutter M Jones RReds) New York John Wiley 198333-58National Center for Health Statistics Blood Lead Levels forPersons Ages 6 Months 74 \ears United States 1976 1980Vital Health Stat 11 233(1984)Bolger PM Carnng ton CD Caper SG A d a m s MAReductions in dietary lead exposure in the United States ChemSpeciat Bioavail 3(3/4) 31-36 (1991)Statement of Vernon Houk In Aitbotne Lead Reduction Actof 1984 [S Hrg 98 978] Before the Committee on Environment and Public Works US Senate 98th Congress 2ndSession 198423-25 87-94SchwartzJ Human exposure to lead from gasoline In HealthEffects of Lead (Hocz MCB ed) Ottawa Ro>al Society ofCanada 1986 151-180Menton RG Burgoon DA Marcus AH Pathways of lead contanimation for the Bngham and Women s Hospital longitudinallead study In Lead in Pa in t Soil and Dust Health RisksExposure Studies Measurement Methods and Quality Assurance(Beard ME Iske SDA eds) Philadelphia ASTM 199592-106

228 Environmental Health Perspectives Vol 106 Supplement I February 1998

SOIL AN If 1PORTANT PATHWAY OF HUMAN LEAD EXPOSUrE

>1 Burgoon DA Rust SW llogan KA Rehnonships among Ic id 73le\els in blood dust and soil In Lead 1 oisoning ExposureAbatement Regulation (Breen JJ Stroup CA eds) Boca RatonFL Le vis Publishers 1995 255-264

52 HUD Lead Based Pa in t Hazard Reduct ion and F i n a n c i n g 74Task Force Put t ing the Pieces Together Controll ing Lei IHazaids in rhe Nation s Housing Rp: no HUD 1547 LBPWashington Housing and Urban Developm nt 1995 75

5.5 Sayre JW Charney E Vo tiJ ] Pless IB House and hand dustas a po ten t i a l source of c h i l d h o o d lead exposure AJDC127 16/-170 (1974) 76

54 Charncy F Sayre J Coi I ter M Increased lead absorption ininner city children whe c does the lead crime from5 Pediatrics65226-231(1980) 77

55 Hammond PB Clark CS Gartside PS Buger O Walkei AMichael LW Fecal lead xcietion in young children as rehteel 78to souices of lead in ih it en \ i ronmcn Int Arch OccupEmiron Health 46 191-202 (1980)

56 H a m m o n d PB Exposu c to lead In I ad Absorpt ion inChildren (Chisolm JJ O ' lara DM eds) Baltimore Urban V 79Schwarzenberg 198255-61

57 Angle CR M c I n n r e M S Stelmak KL HiDh urban lead inddeer jsed red cell s u r \ i il Conf Heavy Metals En \ i on 9 8087-104(1975)

58 Duggan M Temporal ind patiaJ variation of lead in air and insurnce dust—implications for monitoring Sci Total Envinn 8133^7-48(1984)

39 Mielke HW Adams JL rnvironmental Lead Risk in the TwinCities Minneapolis University of Minneson 1989

60 RSC Commiss ion on L ad in the F n v n o n m e n t Lead inGasoline A Review of the Canadian Policy Issue ( I n t e r i m 82Report] Ottawa Ontario Ro>al Society of Canada 1985

61 FergussonJE kim ND J race elements in street and house 83dust souices and speciation Sci "PotaJ Einnon 100 125-130(1991)

62 Hunt A Johnson DL Ihovton I Watt JM Apportioning thesources of lead in house dus ts in the London Borough of 84Richmond England Sci Total Environ 138 183-206 (1993)

63 FergussonJE Forbes EA Sehroeder RJ Kyan DE Lead petrollead in the environment and its contr ibut ion to human blood 85lead levels Sci Total Envnon 50 1-54 (1986)

64 Harnson RM Toxic metals in street and household dusts SciTotal Enwron 11 89-97 (1979) 86

65 Roberts JW Warren GR Sources of toxics in house dust Int JBiosoc Res 9(1) 82-91 (1987)

fa6 Ott WR Roberts JW Fver> day exposures to toxic substances 87Sci Am 278 (2)82-87(1998)

67 Sturgcs WT Harnson RM An assessment of the contributionfrom paint flakes to the lead content of some street and house 88hold dusts Sci Total Environ 44 225-234 (1985)

68 FergussonJE Schroeder RJ Lead in housedust of ChnstchurchNew Zealand sampling levels and sources Sci Total Environ 894661-72(1985)

69 US EPA Review of Studies Addressing Lead AbatementEffectiveness Rpt no EPA 747 R 95 006 Washington US 90Environmental Protection Agency 199?

70 Schultz BD Persona] communication71 Weitzman M Aschengrau A Bellmger D Jones R Hamlm JS 91

Beiser A Lead contaminated soil abatement and urban children s blood lead levels JAMA 269(13) 1647-1654 (1993)

72 Aschengrau A BieserA Bellmger D Copenhafer D WeitzmanM The impact of soil abatement on urban children s blood 92lead levels phase II results from the Boston lead in soil demonstration project Environ Res 67 125-148 (1994)

Staes C M a t t T Cople) G Fla i d e r s D Binder iRetrosp ctive study of ihc impact of lejd based paint ha??idr e m e d i a t i o n on c h i l d r n s blood lead levels in St LouMissouri AmJEpidemio l 139(10) 1016-10^6(1994)US MA Urban Soil Lrid Demonstracion Project Volume 1EPA I n t e g r a t e d R e p o i t Rpt no EPA/f 00/P 93/00 1 IWashington U S Envmmnemal Prore tion Agenc) 1996Gagne D Blood lead Ic els in Rouyn N i t a n d a children following icmo\aJ of smelt contaminated yard ioils Can J PublicHealth 85 163-166(1994)Hunter JM The summer disease an integr-itive model of setsenility aspects of chi ldhood lead poisoning Soc Sci Med 11691-703(1977)Hunter JM The summer disease some fie'el evidence on seasonality in childhood lead poi onmg Soc Sci Med 12 85-94 (1978)M a h a f f y K R Rosen JF Chesne) RW Peeler JT Smith CMDeLuciHF Association between age bloo I lead concentrationand strum 1 25 dih>drox)cholecalciferol I vcls in children ArnJ C l m N u t r 3 5 1327-1331 (1982)Rabmowitz MB Belling r DC Soil lead —blood lead relationships imong Boston children Bull Envu m Contam Toxicol4l7;i-797(1988)S h e l l s h e a r ID J o r d a n LD Hogan DJ S h a n n o n FTEnvironmental lead exposi re in Christchur h children soil leidas a potential hazard N 7 Med J 81 382-3S6 (1975)Needleman HL Bellmger DC Type II f HILICS in the srud) ofchildhood exposure to lead at low dose i ntical and quantuative review In Lead F \posure and Child Development AnIntermtionaJ Assessment (Smith MA Grain LD Sors AI eds)New York KJuwar Academic Publishers 19o9 293-304H i l l B A Short Textbook on Medical S ta t i s t i cs LondonHoddcr & Strou0hton 1J77Rutter M Low level lead exposure sources effects and implications In Lead Versus Health Sources and effects of Low LevelLead Exposure (Rutter M Jones RR eds) New York JohnWiley&Sons 1983333-370Brunekreef B Exposure of Chi ldren 10 Lead Moni to r ingAssessment Research Center Lonoon Univers i ty of London1986Reagan PL Silbergeld E Establishing a health based standardfor lead in residential soils Trace Substan Environ Heal thXXIII 199-238 (1989)Botti C Comba P Forastiere F Settimi J Causal inference inenvironmenta l epidemiology the role of implicit \a lues SciTotil Fnviron 184 97-101 (1996)Walter SD The ecological method in the study of enwronmental heilth I Overview of the method Environ Health Perspect9461-65(1991)Walter SD The ecoloyeal method in the studj of environmental health II Methodological issues and feasibility EnvironHealth Perspect 94 67-73 (1991)Solomon RL Hartfoid JW Lead and cadmium in dusts andsoils in i small urban communi t ) Environ Sci Tech 10(8)773-777 (1976)Fergusson JE Lead petrol lead in the environment and its contnbution to human blood lead levels Sci Total Enwron 50217-221 (1986)Reagan PL Blood Lead Levels Pathways and Parameters ofExposure to Lead A Summary of 161 Studies in 10 Tables StPaul MN Midwest Environmental Education and ResearchAssociation (MEERA) 1986Hill B The environment and disease association or causationProc R Soc Med 58 29 5-300 (1965)

Environmental Health Perspectives Vol 106 Supplement I February 1998 229