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BackgroundPaper BP-395E
LAUNDRY DETERGENT: THE TOXICOLOGYAND CARCINOGENICITY OF NTA
William MurrayScienceandTechnologyDivision
January1995
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~LAUNDRY DETERGENT: THE TOXICOLOGYAND CARCINOGENICITY OF NTA
iNTRODUCTION *
American oncology studies during the mid-1970sindicateda link betweena
commoncomponentoflaundrydetergent,nitrilotriaceticacid(NTA), andanincreasedincidence
of urinarytracttumoursin testmiceandrats.~This finding raisedconcernwith respectto human
exposureto NTA, which haswidespreaddomesticandindustrialuse,andpromptedextensive
investigationson the effectsOf NTA on mammalianandenvironmentalsystems. This paper
briefly describesthe chemicalpropertiesof NTA, its role asa detergentcomponent,and the
environmentalandtoxicologicalassessmentsconductedso far.
CHEMISTRY
NTA, first synthesizedin 1862, is an aminotricarboxylicacidthatcan sequester
*~*~ metalionsaswatersolublecomplexes.It isarelativelylargemoleculewith a molecularweight
of 191. 14 g. Its chemicalformulais N(CH2COOH)3. Physically,thecentralnitrogenatomhas
a moleculeof aceticacid attachedat eachof its threebondingsites. Chemicalmanufacturers
synthesizeNTA in its sodiumsalt form, in which thehydrogenatomof theaceticacidcarboxyl
group (COOll) is replacedby sodium(COONa) ~TheNTA sodiumsalt hasbindingproperties
which make it useful in detergentsasa watersoftener When NTA is dissolvedin water the
sodiummoiety easily dissociatesaway from theNTA giving free Na~~ions.~This leavesa
negativelychargedbonding site at the endof eachcarboxylgroup (COO) which attractsand
tightly bonds calcium (Ca~)andmagnesium(Mg~)ions More simply put, sodiumions
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detachfrom the NTA moleculeand are replacedby the causativeagentsof “hard” water
(calciumandmagnesiumions), thereby“softening” thewater.
DETERGENTS
~ A detergentis any materialthat increasest1~c~aning~effect of wateron soiled
objects. Laundry detergentsareroutinelycomposedof 15-25% surfactants,30-40% builders,
5 % anti-corrosionsilicates, and 1% auxiliary agents (optical brighteners,foam stabilizers,
enzymesandantiredepositioncompounds),with the balanceconsistingof inert inorganicsalts
to give the driedproductgoodphysicalandmechanicalproperties.
Surfactants,alsocalledsurfaceactiveagents,greatlylowerthesurfacetensionof
water. Many substancesthat can adhereto a fabric exhibit hydrophobicity; thatis, they repel
water. Reducingsurfacetensionreduceshydrophobicityandallowswaterto comeinto contact
with thesoiledspot. Many surfaceactiveagentsdo not workwell in eitherhardwateror water
with a low pH value.
Builders, compoundsthat act as water softenersand deflocculants,contribute
greatly to the overall detergenteffect. Only threebuildersareusedextensivelyin detergents:
NTA, condensedphosphates(sodiumtripolyphosphate,STP), andzeolites. NTA softensthe
wash water, making the surfactantmoreactive, and it alsoactsasa deflocculant. Its strong
ability to bond with calciumallows it to excisecalcium from soil clumps,breakingthecalcium
* bridgesthatbind soil to itself and to fabrics.
STP used to be the builder compoundof choice in detergentformulations.
However,the STP releasedin laundrywastewaterswas found to degradeto phosphate(P04),
an essentialplant nutrientusuallypresentin naturalwatersat concentrationslow enoughto limit
vegetativegrowth. The increaseddischargeof phosphateinto streamsandlakesreversedthis
naturalgrowth limitatio~nd~stimtdatedalgae~growth;thus~severely~upsettingthe ecological
balancein water bodies. Canadianregulationsthat limited the maximum concentrationof
elementalphosphorousin laundrydetergentsto 2.2% (ona weightbasis)appearedin theCanada
Gazette,Part 11, on 8 November1989
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Such stringentregulationsto limit the concentrationof phosphorousin laundry
detergentshaveforced detergentmanufacturersworld-wide to useeither NTA or zeolitesas
buildersin their products. Naturalzeoliteis hydratedalkali-aluminumsilicate;*i~hasa porous
structureandiscapableofexchangingalkali ionsfor calciumandmagnesiumbutit is nothighly
valuedasabuilding agent Variousformsof syntheticallyproducedzeolitedo exhibit excellent
deflocculantandwater-softeningproperties Syntheticzeolitemanufactureis apatentedprocess
controlledby onechemicalcompany,however;asaresult,manydetergentmanufacturersprefer
to useNTA astheir builderagent.
TOXICOLOGY AND ENVIRONMENT STUDIES
A. Toxicity and Teratology
The minimum lethal oral doseof NTA sodiumsalt for ratsis 4 g per kg body
weight.°~Assumingthat thetoxicity of NTA is constantfor all mammals,it would requirethe
ingestionof 227g (halfa pound)of NTA to kill a 57 kg (125 lb.) humanbeing. Thus, NTA
is not a very toxic substance.
Chronicdosingof rats andmice with NTA was found to causedose-dependent
healthproblemsandbirth defects. This is not unexpected;regularlargedosesofNTA would
continuallyextractcalcium andmagnesium,andotherpositively chargedionsfrom bodycells
anddisrupttheir function. ~In regardto birth defects,inducedcalciumdeficiencyin a pregnant
mammalwould arrestnormal foetal bonedevelopment. Becausea high doseis requiredto
induce such effects in animals, NTA is poorly absorbedby humans,and there is a low
environmentalconcentrationof NTA, the InternationalJointCommission,in its reportto The
Great Lakes ResearchAdvisory Board (1972), concludedthat NTA representsa low health
hazardto humans.
(1) M. Windholz, Ct a!. editors, TheMerck Index,An Encyclopediaof ChemicalsandDrugs, 9th edition,Merck & Co., Inc., Rahway, N.J., 1976,p. 854.
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B. Carcinogenicity
ThepotentialofNTA to causecancerin miceandratswasexaminedby a number
of American laboratoriesduring themid-197Os.~In its assessmentof the carcinogenicityof
NTA, baseduponexperimentsconductedat two differentlaboratories,theUnitedStatesNational
CancerInstitutereportedthatdaily ingestionofdietscontainingNTA ataconcentrationof0.258
g/kg body weight,for periodsofup to 24 months,i~sultedin urinarytract tumours~inmiceand
rats. Thesestudiescannotbe regardedas having definitively establishedNTA as a human
carcinogen,however,asthetestingproceduresdid not simulatereal-lifeconditions.
Assuming that humanshavethe samecancerresponseto NTA asdo rats and
mice, daily NTA consumptionof 0.258 g/kg body weightperday (14.7 gperday for a 57 kg
adult) shouldinduceurinarytract tumours. In Canada,the only non-deliberatesourceof NTA
is drinking water, which, accordingto the CanadianWaterQuality Guidelines,hasan average
concentrationof NTA of 2.8 microgramsper litre. Therefore,a 57 kg adult would haveto
drink 5,252,937litres of Canadiantapwaterdaily to receivea doseof NTA equivalentto the
onethat causedcancersin ratsandmice.
Suchcancerdataservelittle real-worldpurposeandraisethequestionofwhy they
were generated.The internationalstandardsfor cancerresearchandcarcinogenclassification
havebeenestablishedby the InternationalAgency for Research(IARC). Canceroccurrences
can bevery rareanddifficult to correlatewith a particularsubstancein normalenvironmental
or occupationalconcenfratióñ~In testing,theentireprocedurecan Usuallybe speededup by
subjectinganimals “to a maximumtolerateddoseof a substanceover their lifetimes.“(3) In
cancerstudies, such “heroic dosing” can saveboth time and money; however, it can also
producedataof questionableutility when, asin the caseof NTA, massivedosesof a mildly
toxic sUbstanceareadministered.
(2) R.L. Anderson, eta!. , “A Reviewof theEnvironmental and Mammalian ToxicologyofNitrilotriaceticAcid, “ CRC Critical Reviewsin Toxicology, Vol. 15, p. 1-101, 1985.
(3) R.J. Moolenaar, “Overhauling Carcinogen Classification,” Issuesin Scienceand Technology,Vol. 8,1992,p. 70-75.
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Thisaberrationin theTARC cancer-testingmethodologyisa recognizedproblem
and efforts~are being made to change either the methodologyOr the IARC carcinogen
classificationsystem.~4~Reformis hamperedbecausethe world needsa standardizedcancer-
testingregimeandthepresentsystemhasbeenin placefor sometime. Theoretically,theIARC
~systemshouldnotcauseproblems,for non-real-worlddataareusuallyignoredby knowledgable
professionals The United StatesEnvironmentalProtectionAgency (EPA), however, stnctly
adheresto the IARC classificationsystem.~5~Once the EPA lists a chemicalas a possible
carcinogen,environmentalgroupsand the mediaareat liberty to describethat chemicalas
cancer-causingor aslinked to cancer.
On a positivenote, the EPA recentlyannouncedthat it hasbegunto revise its
guidelines for carcinogenicrisk assessmentwith plans to take into consideration“realistic
exposurescenariosand mechanisms[of action] when calculating a chemicals’shazard to
humans.,~(6)
Following the AmericanNTA carcinogenicityinvestigation,a large numberof
independentstudieswereinitiated. All thesestudiesindicatedthatNTA posesno humanhealth
risk at the concentrationsto which humansarenormally exposed. According to Dr. Robert
Squire,Professor,JohnsHopkinsUniversity and former AssociateChief of Pathologyat the
NationalCancerInstitute,“At thelevelsthat I understandNTA humanexposurewill occuras
a result of detergentuse, it [NTA] is completely safein all respects. In fact the risk of
* * carcinogeniceffectat humanexposurelevels mustbeconsideredasvirtually zerobasedon the
scientificevidenceavailable.“~
(4) Ibid.
(5) Ibid.
(6) D.J. Hanson,“EPA to ReviseCancerGuidelinesto IncorporateMoreThanTumours,”Chemicaland
EngineeringNews, 26 September1994,p. 21-22.(7) MonsantoCanadaInc., “NTA PreparednessStatementsRe: CanadianPressStory - March 15/93,”
MonsantoNews Release,p. 6, March1993.
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C. EnvironmentalConsiderations
The environmentaleffectsof NTA havealsobeenwell investigated. Although
NTA is alargemolecule,it isnotacomplexsubstance.Its molecularstructure,anitrogenatom
andthreemoleculesof aceticacid(vinegar),is easilybiodegraded.
A Germanresearchscientist,Dr H Bernhardt,publisheda study in 1984which
showedthat theNTA concentrationin wastewaterwasreducedby over 95% afterthewater’s
normal passagethrougha sewagetreatmentplant. Lower levels of NTA destructionwere
observedin sewagetreatmentplantsonly (i) at temperaturesbelow 5-7°C,(ii) in instancesof
high sewagetreatmentplant loadings (wheredilution or sewagewashoutresultedfrom heavy
storm runoff), or (iii) where bacterial acclimation to NTA had not been established.~
Bacterialpopulationsacclimatedto NTA degradationhavebeenisolatedin thevicinity ofsewage
plantoutfalls, in groundwater,lakesandrivers. Accordingly,nearlyall oftheNTA thatpasses
througha sewagetreatmentplantcan be expectedto be degradedin thenaturalenvironment.
DISCUSSION
The toxicology, carcinogenicityandenvironmentalfate of NTA havereceived
extensiveinvestigation. This chemicaldegradesrapidly in theenvironmentand is found asa
contaminantof drinking wateronly at very low concentrations.Humanexposureto NTA is so
limited as to poseno identifiable healthrisk. Indeed,~NTA is so safeandenvironmentally
benign that EnvironmentCanadahas awardeda numberof detergentscontainingNTA its
environmentalchoice “Eco-logo” label.
(8) H. Bernhardt,et a!., Studie uber die aquatischeUmweltvertraglichkeitvon Nitrilotriacetate (NTA),VerglaghansRicharz,SanktAugustan,1984