t E80 8 199# A Risk-Based Cleanup Criterion for PCE in Soft/67531/metadc1097151/m2/1/high_res_d/6040357.pdfA RISK-BASED CLEANUP CRITERION FOR PCE IN SOIL" J.l. Danlels, T.E. McKone,

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A Risk-Based Cleanup Criterion for PCE in Soft" .............

J. I. DanielsT. E. McKone

L. C. Hall

This paper was prepared for the Sixth _mnual DOE ModelConference on Waste Management and Environmental Restoration

October 29--November 2,1990Oak Ridge, TN

September 26,1990

This is a preprint of a paper intended for publication in a journal or proceedings, Since

changes may be made before publicition, this preprint is made available with the

understanding that it will not be cited or reproduced without the permission of theauthor.

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A RISK-BASED CLEANUP CRITERION FOR PCE IN SOIL"

J.l. Danlels, T.E. McKone, and L.C. HallEnvironmentalSciencesDivision

LawrenceLivermoreNational LaboratoryP.O. Box 5507, L-453

Livermore,CA 94550-0617415422-0910 (FT'S: 532-0910);

. FAX: 415-423-6785(FTS: 543-6785)

ABSTRACT

The most importantattrbJte o! a chemicalcontaminant at a hazardous-wastesite for decisionmakersto considerwithregardto itscleanupisthe potentialriskassociatedwithhumanexposure. Forthisreasonwe havedevelopeda strategy for establishinga risk-basedcleanup criterionfor chemicals in soil.We describe this strategy by presenting a cleanup criterion for tetrachloroethylene (PCE) in soilassociatedwitha representativeCalitomla landscape. We beginby discussingthe environmental late andtransport model, developed at the Lawrence Livermore National Laboratory (LLNL), that we used topredict the equilibriumconcentrationof PCE in five environmental media from a steady-state source insoil. Next, we explainthe conceptand applicationof pathway-exposurefactors (PEFs), the hazard index,and cancer-potency factors (CPFs) for translating the predicted concentrations of PCE into estimatedpotential hazard or risk for hypothetically exposed individuals. Finally, the relationship betweenconcentration and an allowable level of risk is defined and the societal and financial implications arediscussed.

INTRODUCTION

Currently, there are no Federal or State of California regulatory limits for concentrations ofchemical co_amlnants in soilanalogousto the maximum contaminant levels, MCLs, designed to protectagainst adversehealth effectsfrom the ingestionof drinkingwater. Therefore, governmentagencies andresponsibleparties accountablefor the mitigationof hazardous-wastesites in California cannot comparethe concentrationof a chemicaldetected in soilat a praticular siteto a regulatory limit for that chemical insoilto rapidlyascertainwhether the measuredsoilconcentrationmight pose an unacceptablelevel of dskto human health. To overcome this predicament confronting risk managers, we have developed astrategyconsisting of a six-stepprocedurefor establishinga rlsk-basedcleanup criterionfor chemicalsintroduced intosoil. Becausethis strategy accountsfor the multimedia and multiple-pathwayexposurecharacteristics of many soil contaminants, the resulting cleanup criterion for a soil contaminant isconsistentwith a complete assessment of potential riskto exposed populations.

We illustrate the six-stepprocedure for developing risk-based cleanup criterionfor _hemicais insoil withtt_eexampleof tetrachloroethylene(perchicroethylene,PCE) inthe soil of a 100-krn2 landscaperepresenting a typical regionof California. This organicchemical is a common contaminant of sell andgroundwater in many urban areas of Califomla because of its widespread use as an industrial solvent.Additionally, the U.S. Environmental Protection Agency (U.S. EPA, 1985) classified PCE as a PossibleHuman Carcinogen(Group C), and the State of Califomia includes PCE in a listof "Chemicals Knowntothe State to Cause Cancer or Reproductive"toxicity"(California Department of Health Services [CDHS],1990).

Work pedormed umler the auspices of th_)U.S. Department of Energy by the Lawrence LivermoreNational Laboratoryunder ContractW-7405-Eng-48 with funding provided by the State of CaliforniaDepartment of Health Services, Toxic Substances Control Program, Memorandum of UnderstandingNg. 87-T0102.

-l- DOCUME,,NT tS UNLIMITED

DLS'_'RIBUTtON OF TNI,._ C_...

MULTIMEDIA PARTITIONING OF PCE INTRODUCED INTO SOIL

Onceintroducedintosoil,chemicalssuchas PCEwill distrbuteintootherenvironmentalmediaincludingair,surfacewater,andgroundwater.Toestimatetheconcentrationsof PCEinair,water,andsoilresultingfromthesteady-stateinputof PCEtotheselllayerofa 100-km2 landscaperepresentingatyp¢_,regioninCalifornia,weusethemultimediatransportandtransformationmodelGEOTOX(McKone,1981;McK0neet al., 1983;McKoneandKastenloerg,1986;McKoneand Layton,1986;McKoneet al., 1987;andLaytonet al., 1986),whichis a computerprogramdevelopedat the LawrenceLivermoreNationall.aboratory(LLNL). Table 1 summarizestheprocessesbywhichcontaminantsareexchangedand lostamongcounts 04theGEOTOXmodel.

Thespedflclandscapeparameters(e.g.,meteorology,hydrogeoiogy,andsoilproperties)usedin• GEOTOXare basedon thenationalland-classificationsystemfordescribingecoregionsof the United

States developedfor the U.S. Departmentof the Interiorand the U.S. Departmentof Agriculture(Bailey,1980). Weestimatedorobtainedfromthe literaturethephysicochemicalpropertiesof PCE(e.g,solid/Ikluldand air/liquidpartitioncoefficientsandthediffusioncoefficientsof PCE inair and water)thatalsoare essentialinputto theGEOTOXmodel. Table2 showstheequilibriumconcentrationsot PCE indifferentenvimrm_entalmediapredictedbyGEOTOXfora 100-km2 Californialandscapeassuminga soil-basedsteady-statesourceof contamination.The predictedconcentrationsappearinginTable 2 arescaledtoa soilconcentrationof PCEof 1 ppm(rng/kg).

DEVELOPMENT OF PATHWAY-EXPOSURE FACTORS

Pathway-exposurefactors(PEFs)incorporateinformationon humanphysiology,human-behaviorpatterns,and environmentaltransportto linkenvironmentalconcentrationsof a chemicalto potentialexposurepathwaysand lifetimeaccumulations.Accordingly,we use PEFsdevelopedby McKoneandDaniels(1990)to translateenvironmentalconcentrationsof PCEintoquamitativeestimatesof theamountof PCEthat passesintothe lungsandgastrointestinaltract,andacrossthe sudaceof theskin andweexpresssuch intakesin unitsof rng/kg-d.Forexample,Equation1 is thePEF for ingestionof drinkingwater(Fww).

. I '

whereIw = the liletime-equivalentfluidintake(2 L/d);andBW . the liletime-equivalentbodyweight(58 kg).

Table3 containsthe numericalvaluesandunitsof the PEFsfor the nineexposurepathwaysand fiveenvironmentalmediaapplicableto PCE.

• EXPOSURE MATRIX

Weconstructa matdxcontainingmedium-andpathway-specifichumanexposuresby multiplyingthe PEFs in Table 3 by thecorrespondingmedium-specificconcentrationsof PCE shownin Table 2.Then,we totalmultimediaexposurefora particularpathwayby summingthe exposurevaluesfor thatpathwayacrossali media. Table4 showsthematrixof medium-and pathway-specificexposuresto PCE,the totalsfor multimediapathway-specificexposures(e.g., inhalation[Eh], ingestionIF.g],anddermalcontact[Ed]),and thetotalmultimediamultiple-pathwayexposure(i.e., Eh + Eg+ Ed),whichis a chronicdailyintake(CDI).

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Table 1. Summary of the Ixocesses by which contaminants are exchanged and lost among the sevencounts of the GEOTOX model. , ..... _

Gains Losses

Air (gas phase of the Diffusion from soil and Diffusion to soil;

troposphere) surface water, diffusion to surface water;

washol_t by rainfall; and

convection lossesl i I nun n inull nun n

• Air Particles(atmospheric dust) Resuspensionof depositedsoil Deposition from atmosphereto

particles, soil;

deposition from air to surface

water;, and

convective losses.- - ill

Upper-Soil Layer (surface-soU Diffusion from air; Diffusion to air;

layer) washout by rainfall; infiltration (leaching);

deposition of air particles; and resuspension of deposited soil

irrigation from groundwater, particles;

soil-solution runoff; and

erosion.L_ i i i ............

Lower-Soil Layer (vadose zone) Infiltration from upper-soil Infiltration to groundwater zone.

!r.............

Ground-Water Zone Infiltration from lower-soil. Discharge to surface-wat_

irrigati °n. ...................

Surface Water Diffusion from air; Sediment deposition;

washout by rainfall; diffusion to sediment; and

deposition of atmospheric surface-water outflow.

particles; soil-solution runoff;

erosion (mineral runoff);

diffusion from sediment; and

sediment.............. =.................................. 1

Sediment Layer Diffusion from surface water; and Diffusion to surface water; and

sediment deposition (from surface sediment resuspension.

water).

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Table 2. Concentrationsof PCE inthe al_icab_ environmentalmediaof a 100-knv?.landscape assuminga soU-basedstea0y-state sourceof contamination. Concentrations am predicted using the GEOTOXmodel_andare scaledto a _ concentrationof PCEof 1.0 _. ..........

Media labbm_akm;concentration units) ....... PCE concentrationSoil(cs; 1.oAir gases (Ca; illgt_) 1.4

Air particles(Cp;mg/rn3) - 0.0aPotablewater (Cw;mg/t.) 0.21Sudacewater tct; m_) , 0.27 ..........a There issomepattltlon_gof ICE to pint.lares inair; however,the majorityof PCE inthe air

. compartmerdisinthe gaseous phaseandthe very smallamount presemon particlesis insignificant.

Table 3. Matrixo(pathway-exposurefactors(PEFs) for PCE in specificenvironmentalmedia.PEFs associatedwith environmentalmedium

.... concentration,Ci, where i isthe type of mediumaAir Air Ddnking Sudace

(gas phase; (particles; Soil waterb waterm3/kg-d), m3/kg-d), (kg/kg-d), (L/kg-d), (L/kg-d),

Pathway C_ Cp C_ Cw . Cr

Inhalation Fah Fph Fsh Fwh -'-(0.39) (0.31) (9.2 x 10"9) (0.11)

Ingestion

Water -- -- -- Fww --(3.4 x 10"2)

Fruitsand

vegetables Fav Fpv Fsv -- ---: (1.6 x 10"4) (14.0) (1.1 x 10"3)

Grains Fag Fpg Fsg . -- ---(2.5 x 10"4) (22.0) (8.0 x 10"4)

Meat Fat Fpt Fst Fwt --(5.7 x 10 6) (2.8 x 10"2) (5.4 x 10"7) (1.9 x 10"6)

Milk Fak Fpk Fsk Fwk ---• (4.0 x 10"6) (2.9 x 10"2) (5.2 x 10"7) (1.2 x 10"6)

Fish .... Frf(2.1 x 10"2)

Soil -- -- Fss -- --(1.5 x 10-6)

Dermalcontact -- Fsd Fwd -- --

{2.6 x 10"6) (3.8 x 10"2)a Subscriptsrefer to the sourcemedia(a = air gases, p = air particles,s = soil, w - drinking water, and

r = surface water) and pathways (h = inhalation,w = water ingestion, v = vegetables, g = grain,t = meat, k = milk, t = fish, s - soll ingestion,and d = dermal contact).

b Drinking-waterconcentrations are obtainedby arithmeticallyaveraging the concentrations in surfaceandgroundwaterso as to reflectthe mix ina local-watersupply. Forcalculationof a cleanupcriterion,we assumehalfof the drinkingwatercomes fromgroundwaterand the other halffrom sudacewater.

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"5"

CARCINOGENIC POTENCY AND NONCARCINOGENIC THRESHOLD

The term carcinogenic"potency"is used here to refer to the quantitativeexpressionof increasedtumorigenicresponseper unl dose rate at very lowcloses. The noncarctnooen¢threshold appliesto thedailyexposureover the coumssof a lifetimethat is likely to be withoutappreciable riskof noncarcinogan¢deleteriouseffects;this safe levetis referredto as the reference dose (RfD).

Carcinogenic Potency

' We used the range of PCE cancer-potencyestimates calculated by Bogen et al. (1987) fromrodenttumor-incidence data publishedby the NCl (1977) and NTP (1986). These potency estimates

' were calculatedas a functionof metalxdlzeddose of PCE because there is evidence that it is a _ 04' PCE's metabolismthat 18responsl)le for PCE's ¢arctnogantcity(U.S. EPA, 1985; Bogen et al., 1987). We

reliedon these values instead 04those derived bythe U.S. EPA (1985 and 1986), because the potenciesderived by Bogen et al. (1987) were adjusted to include data on animal body weight, metabollteelimination,andother factorsnot addressedinthe calculationsbythe U.S. EPA (1985 and 1986). Bngenet al. (1987) used the term q_(M) to Specifythe 95% upper-confidancelimit (UCL) estimate of potency.Thisterm relateslow levels of metabolized©lose,M, to predicted upper-bound Increasedtumor risk,R*, bythe linear approximationR° --q; (M)x (M).

To estimate the carcinogenic potency of PCE in terms of human-applied dose, A, which isnecessary for calculation of an acceptable-exposure limit (because exposure is expressed in terms ofappliedand not metabolized dose),theterm q_(M) is multipliedby f, the fractionof the applieddose that ismetabolized(i.e., q_(A) = q_ (M) x f). We calculated the arithmetic means of the fractionmetabolizedofan orally-acquired dose of PCE, f'mo, or a respired or dermally-acquireddose of PCE, f*mr, usingtherespectiveranges of values forthese parametersdevelopedby Bogen and McKone (1988) fromthe dataof Ikeda et al. (1972) and Ohtsuldet al. (1983). Table 5 presentsthe highest and lowest estimates04thepathway-specificvalues of q; (A) basedon the lowestand highestvaluesof q_(M) calculated by Bogenetal. (1987) and based on the meanvaluesoff*mo (26%) and f'mr (20%).

• : Table5. Rangeof ca_c-potency estimatesfor PCE for ingestion,respiration, or dermal exposure.I,

Applied potency, ql(A)a

(nngA/kg-d) "1

Metabolized potency, Inhalation

q_(M)b or

. (ing M/k[_-d) "1 Inl_stion c derma!, uptake d ,,

0.095 0.025 0.019

o.42 o. z

a 95%-UCL potency of human applied dose, A, basedon surface-area,interspeciesdose-extrapolationIt. lt

method. Note that ql(A) = ql(M) x f, where f = f'mo or Pmr.

b Rangeof 95%-UCL potency of humanmetabolized dose, M, basedon surface-area,";nterspeciesdose-extrapolation method. Values from Bogenet al. (1987).

• c Calculated using the arithmeticmeanof Pine = 0.26.

d Calculated using the arithmetic mean of Pmr = 0.20. lt is assumed that the fraction of applied dosethat is metabolized is the samefor inhalation and dermal contact(seeBogen, 1988).

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Noncarclnogenlc Hazard Index

AccordingtotheU.S. EPA(1989)theratiooithetotalcalculatedmultimediaexposure,expressedasa CDI,tothe R;Disthehazardindex. Ifthisratioexceedsone,thenthereisa potentialfortl_eexposuretoyielda noncarcincge_adversehealtheffect.BecauseonlyanoralRfDforPCEof1× 10-2 mg/kg-dis available(U.S. EPA,1990a),weusethisvalueinourcalculatlons.

DERIVATION OF RISK-BASED SOIL CONCENTRATIONS FOR PCE

• To derivea rangeof risk-basedconcentrationsof PCEinsoilas Possiblecleanupcriterion,wefirstcalculatethetotalcarcinogenicriskandnoncarcinogenichazardindexassociatedwith1 ppmof PCEin

' soil.Wethenusethesevaluesin thederivationol alternativesas cleanupcriterionforPCEinsoil. TheaJterrmiveswe derivecorrespondto eachof threelevelsof excessindivldual-liletlmecancerdsk-1per10,00(_(i.e.,10-4],1 per 100,000[i.e., I0"5), andI per 1,000,000(i.e.,10"6),andto a hazardindexthatdoesnotexceedone. The threelevelsof excessindivldual-liletlmecancerriskwere selectedbecausetheyarecitedbyregulatoryagencies(seeU.S.EPA,19901)andCDH$, 1989)as beingacceptablelevelsofriskassociatedwithexpo_re to a carcinogenpresentInenvironmentalmedia.

C,81culatedTotal Risk for 1 PPM of PCE In SoU

Fora 100-km2 landscapein a typicalCaliforniaregion,the calculatedtotalriskassociatedwith1 ppmof PCEinsoil[RTC(1lc)m)]isdeterminedusingEquation2:

RTc(lppm) = (Eh, CPFh). (Eg. CPFg). (EdoCPFd), (2)where

RTc(lppm) = thecalculatedtotalriskassociatedwith1 ppmofPCEinsoil;

Eh = inhalationintakerelatedto multimediaexposureresultingfroma soil-basedPCEconcentrationof 1 ppm(mg/kg-d);

,. _,.

Eg = ingestionintakerelatedto multimediaexposureresultingfroma soil-basedPCEconcentrationof 1 ppm(Ir_Jkg-d);

. Ed = dermalcontactrelatedto multimediaexposureresultingfroma soil-basedPCEconcentrationofI ppm(mp)kg-d);

" CPFh = maximumorminimumcancer-potencyfactorfortheinhalationpathway(1/[mg/kg-d]);

CPf:g = maximumor minimumcancer-potencyfactorforthe ingastionpathway(1/[moJkg-d]);and

CPFd = maximumorminimumcancer-potencyfactorforthedermal-contact• pathway(1/[moJkg-d]).

Cleanup Alternativeso

Wecalculatea cleanupconcentrationof PCEin soil,Cs(cleanup)i,correspondingto a specifiedleveloftotalacceptablecarcinogenicrisk,RTA(e.g.,10"6),andtoa noncarcinogenichazardindexofone

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by scalingthe steedy-stateconcentrationof PCEin soil,Cs(1ppm),bythe ratioof RTA(cleanup)toRTC(1pprn)as showninEq.3 (wherei- c),orbytheraL_oof I to CDI/RfD_ _ inEq.4 (wheret. h).

Cs(cleanup)c - Cs(lppm)x [RTA(Cleanup)/RTC(lppm)],and (3)

Cs(_anuP)h.Cs(1ppm)x [_ 1., (4)• i

r

Table6 showsalternativecleanupconcentrationsforPCEcorrespondingto lowandhighcancer-poteno/' estimatesandao(:_otal_levelsofcarcinogenicriskthatrangefrom10-4to 10-6, andcorrespondingtoa

hazardIndex04one.

CONCLUSlCN

The PCEconcentrationspresentedinTable6 constitutea rangeof risk-basedcleanuplevelsforconsiderationbyriskmanagersfora 100-km2 Californialandscape.However,themethodologydescribedherecanbeusedtodevelopothermoreor lessconservativevaluesforconsideration.Nevertheless,it is 'apparentthattheconcentrationsof PCEin Table6 thatcorrespondtocarcinogenic_ rangingfrom10-4to 10-6 arealilowerthantheconcentrationof PCEassoc"ia,edwitha noncar_nlc hazardindexequalto one. Consequently,theconcentrationof PCEcorrespondingto a hazardindexof onemaybe rejectedfromconsiderationbecauseit isassociatedwitha carcinogenicdskabovetherangeof acceptability(i.e.,10-4 to 10"6),althoughit is likelyto bewithoutappreciableriskof noncaminogenicdeleteriouseffects.Nothwithstanding,selectionof a la_specitlc cleanupcriterionforanychemicalin soilshouldalsoincludeconsiderationofcriteriasuchas likelihoodofpublicexposure,sizeandoverallsusceptibility04thepopulation=risk,andtheprincipalexposurepathway,aswellasuncertaintiesintheinputparametersandfinalresults.

Finally,adoptinga scientificallycrediblelandscape-specificrisk-basedcleanupcriterionfor achemicalin sollwiflbenefitsociety'by servingas a mechanismto protectpublichealthwhilejustifyingdecisionsaboutcleaningup or notcleaningupcontaminatedsites. Suchdecisionsare importantto our

..; societybecausetheywill reducetheenormousoverallcostthat is now contemplatedfor cleaningupeverycontaminatedsitecompletelyandthatthreatensto cripplethenation'seconomiccompetitiveness.

Table6. Risk-basedconcentrationsofPCEinsoilforconside,'ationasa cleanupcriterionfora 100-km2" landscaperepresentincjatypicalCaliforniaregion.

Acceptablelevelofriska SoilConcentration(Cs[cleanup];rng/kg)t i

or noncarcirmgenichazard Low Potencyb High Potencyb

10-4 9 x 10-3 2 x 10-3

10-5 9 x 10-4 2 x 10 -4

10-6 9x 10 -5 2x 10-5

Hazardindex.(CDI/F_fD).1 2 x 10" 2, a Risk is the incrementalprobabilityof an individualdevelopingcancer over a 7(),y lifetimeas a

consequenceofmuitipathwayexposure(i.e.,fromingestion,inhalation,and dermalcontact)to soil-basedconcentrationsof PCEinmultipleenvtrornentalmedia(i.e.,soil,air,andwater).bTheterms"low"and"high"refertothe rangeofcancer,potencyestimatesforPCElistedinTable5.

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