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Section112(a)(8)oftheActdefinesan"electricutilitysteamgeneratingunit"as"anyfossilfuel!firedcombustionunitofmorethan25megawattselectric(MWe)thatservesageneratorthatproduceselectricityforsale."Aunitthatcogeneratessteamandelectricityandsuppliesmorethanonethirdofitspotentialelectricoutputcapacityandmorethan25MWeoutputtoanyutilitypowerdistributionsystemforsaleisalsoconsideredanelectricutilitysteamgeneratingunit(i.e.,utilityunit).  Section112(n)(1)(A)alsorequiresthat:  "0 ` TheEPAdevelopanddescribealternativecontrolstrategies  p forhazardousairpollutants(HAPs)thatmaywarrantregulationundersection112;and ` (#` (#   "0 ` TheEPAproceedwithrulemakingactivitiesundersection112 ` tocontrolHAPemissionsfromutilitiesifEPAfindssuchregulationisappropriateandnecessaryafterconsideringtheresultsofthestudy. ` (#` (# ES.2REGULATORYDETERMINATION  ThisreportdoesnotcontainadeterminationastowhetherornotregulationstocontrolHAPemissionsfromutilityunitsareappropriateandnecessary.TheAgencyhasdeferredtheregulatorydeterminationuntilalaterdate.ES.3OVERVIEWAPPROACHTOCOMPLETINGTHESTUDỲThestudyincludednumerousseparateandinterrelatedanalyses.First,HAPemissionstestdataweregatheredfrom52utilityunits(i.e.,boilers),includingarangeofcoal-,oil-,andnaturalgas-firedutilityunits.Second,theemissionstestdataalongwithfacilityspecificinformation(e.g.,boilertype,controldevice,fuelusage)wereusedtoestimateHAPemissionsfromall684utilityplantsintheUnitedStates(U.S.).Third,ascreeninglevelhazard/riskassessmentwascompletedtoprioritizetheHAPsforfurtheranalyses.Fourth,variouspriorityHAPswereanalyzedforinhalationandmultipathwayexposuresandrisksandotherpotentialimpacts.Inaddition,potentialcontrolstrategieswereanalyzedforthepriorityHAPs.TheoverallsummaryofthestudyispresentedinFigureES-1. l,'6 Ї  Thisreportpresentsthefindingsofthestudy.Theprimarycomponentsofthisreportare:(1)adescriptionoftheindustry;(2)ananalysisofemissionsdata;(3)anassessmentofhazardsandrisksduetoinhalationexposuresto67HAPs;(4)assessmentsofrisksduetomultipathway(inhalationplusnoninhalation)exposurestofourϢHAPs(radionuclides,mercury,arsenic,anddioxins);and(5)adiscussionofalternativecontrolstrategies.  Thestudywasbasedprimarilyontwoscenarios:(1)1990baseyearemissions;and(2)2010emissions.Inaddition,emissionsfor1994wereestimatedusingthemostrecentdata.The1990scenariowaschosensincethatwastheyeartheAmendmentstotheActwerepassedandwasthelatestyearforwhichutilityoperationaldatawereavailableatthetimethestudywasinitiated.The2010scenariowasselectedtomeetthesection112(n)(1)(A)mandatetoevaluatehazards afterimpositionoftherequirementsoftheAct.Primarily,thismeantassessingthehazardsaftertheacidrainprogramisinplace.The2010scenarioalsoincludedestimatedchangesinHAPemissionsresultingfromprojectedtrendsinfuelchoicesandprojectedincreasesinelectricpowerdemands.However,theeffectsofotherongoingorpotentialactivitiesthatwerenotfactoredintothe2010projections(e.g.,industryrestructuring,newozoneandparticulatematter[PM]standards,globalclimatechangeprograms)mayresultinthe2010projectionsbeingeitherunderestimatedoroverestimated.ES.4EMISSIONSDATAANALYSIS  Atotalof684utilityplants(i.e.,utilities)wereidentifiedasmeetingthecriteriaforthestudyin1990intheU.S.Theseutilitiesarefueledprimarilybycoal(59percentoftotalunits),oil(12percent),ornaturalgas(29percent).Manyplantshavetwoormoreunitsandseveralplantsburnmorethanonetypeoffuel(e.g.,containbothcoalandoilfiredunits).In1990,therewere426plantsthatburnedcoalasoneoftheirfuels,137plantsthatburnedoil,and267plantsthatburnednaturalgas.  Emissionestimatesfortheyears1990,1994,and2010werebasedonemissionstestdatafrom52unitsobtainedfromextensiveemissiontestsbytheElectricPowerResearchInstitute(EPRI),theDepartmentofEnergy(DOE),theNorthernStatesPowerCompany,andtheEPA.Thetestingprogramwasdesignedtotestawiderangeoffacilitytypeswithavarietyofcontrolscenarios;therefore,thedataareconsideredgenerallyrepresentativeoftheindustry.However,thereareuncertaintiesinthedatabecauseofthesmallsamplesizesforspecificboilertypesandcontrolscenarios. '@#0 TRP'3 Letter Landscape3' '3 Letter Landscape3'T  ?s[=-)h|^   ` E^a hdXsgbc3#` p0 G `:,R#E0*x0*x4*g ..                                        $"`( $?   #?   #TRY3' LetterP'3 Letter Landscape 3' Letter '3 Letter LandscapeT  Thesetestdataprovidedthebasisforestimatingaverageannual  emissionsforeachofthe684plants.Atotalof67ofthe188HAPslistedinsection112oftheActwereidentifiedintheemissionstestingprogramaspotentiallybeingemittedbyutilities.TablesES-1andES2presentestimatedemissionsfor,respectively,asubsetofpriorityHAPsfor1990,1994,and2010,andforasetofcharacteristicboilersfor1994.  AlthoughtheEPAusedaverageannualemissionsestimatesinassessinglongtermexposurestoindividualHAPsonanationalbasis,emissionstestdatawerenotavailableforeachutilityintheU.S.Therefore,estimatesforindividualplantsareparticularlyuncertain.Basedonanuncertaintyanalysis,theaverageannualemissionsestimatesareexpectedtoberoughlywithinafactorofplusorminusthreeofactualannualemissions.However,eventhisuncertaintyanalysishadlimitations.Forexample,theuncertaintyanalysisdidnotincludedataonpotentialupsetsorunusualoperatingconditions;therefore,therangeofuncertaintycouldbegreater.ES.5GENERALAPPROACHTOEXPOSUREANDRISKASSESSMENT  Mostoftheriskassessmentfocusedoninhalationexposure.All67HAPswereassessedforinhalationexposures,atleastatascreeninglevel.Formanyofthe67HAPs,inhalationexposureisbelievedtobethedominantexposurepathway.However,forHAPsthatarepersistentand/orbioaccumulate,andaretoxicbyingestion(orareradioactive),thenoninhalationexposurepathwayscouldbemoreimportant.Basedonascreeningandprioritizationassessment,whichisdescribedbelow,theEPAidentifiedfourhighpriorityHAPs(radionuclides,mercury,arsenic,Ϣdioxins)toassessfornoninhalationexposures.Inaddition,cadmiumandleadwereidentifiedasnexthighestpriority.Multipathwayassessmentsarepresentedforradionuclides,mercury,arsenic,andϢdioxins.TheothertwoHAPs(leadandcadmium)wereexaminedqualitativelyfortheirpotentialformultipathwayhazards.ES.6SCREENINGASSESSMENT  AsoutlinedinFigureES1,EPAinitiallyconductedascreeningassessmentthatconsideredinhalationandnoninhalationexposureroutesforall67HAPstoidentifypriorityHAPsformoredetailedassessment.Toscreenforinhalationexposures,theEPAusedtheHumanExposureModel(HEM)tomodelthe67HAPsfromall684utilityplantsutilizinggenerallyconservativeassumptions(i.e.,assumptionsthataremorelikelytooverestimateratherthanunderestimaterisks)toestimateinhalationrisksformaximallyexposedindividuals(MEIs).̀ x&!. TRP'3 Letter LandscapeY3' Letter '3 Letter Landscape 3' LetterT  s[=-)h|^   ` E^a hdXsXT X&&دTableES1.NationwideUtilityEmissionsforThirteenPriorityHAPsa#&د& hXT-#   &&دRF *qTU ddd Xdd Xdd X..q,'d4 ,D4",D4",D4",D4",D4",D4",D4",D4",Dd"+  7VVV& @ ^<<7ZRF@==HAP RVWV?04VVV  RNationwideHAPemissionestimates(tonsperyear)b J@-|" << ^ VWV  ><<J *WW l *Coal @WW1""WW @Oil DWWV1""WW DNaturalgas J@- " << > WWV n<<J JWWV9   @1990@J1990 WWVnA$ " @1990 @WWV (@1994(@1994 WWVnA$ " (@1994 (@WWV h@2010h@2010 WWVnA$ " h@2010 h@WWV @1990@1990 WWVnA$ " @1990 @WWV (@1994(@1994 WWVnA$" (@1994 (@WWV h@2010h@2010 WWVnA$" h@2010 h@WWV @1990@1990 WWVnA$" @1990 @WWV (@1994(@1994 WWVVnA$" (@1994 (@WWV h@2010h@2010 sVdL$" h@2010 << n h@WWVV .<<sArsenic PWA PV  N@61N@P61 gWX6 P  N@61 N@W  L@56L@g56 pWa6 P  L@56 L@W  Q@71Q@p71 dWU6 P  Q@71 Q@W  @5d5 ZWK* P  @5 W  @4@Z4 cWT5 P  @4 @W  @3c3 fWW* P  @3 W 333333?0.15333333?f0.15 kW\8 P 333333?0.15 333333?W  ףp= ?0.18 ףp= ?k0.18 mWVZ8 P  ףp= ?0.18  ףp= ?W ?0.25m0.25 QWVB8 P ?0.25 << . WV <<QBeryllium HWW9$ tWV ffffff@7.1ffffff@H7.1 iWWZ7$ t ffffff@7.1 ffffff@WW @7.9@i7.9 iWWZ7$ t @7.9 @WW ffffff @8.2ffffff @i8.2 jWW[7$ t  ffffff @8.2 ffffff @WW q= ףp?0.46q= ףp?j0.46 jWW[8$ t! q= ףp?0.46 q= ףp?WW ?0.4?j0.4 jWW[7$ t" ?0.4 ?WW q= ףp?0.23q= ףp?j0.23 IWW:8$ t# q= ףp?0.23 q= ףp?WW IТNMc 'WW$ t$WW 'NM +WWV$ t%WW +NM CWV4$ t& << WWV ><<CCadmium QWWBH 'WV ffffff @3.3ffffff @Q3.3 iWWZ7H ( ffffff @3.3 ffffff @WW  @3.2 @i3.2 rWWc7H )  @3.2  @WW ffffff@3.8ffffff@r3.8 gWWX7H * ffffff@3.8 ffffff@WW 333333?1.7g1.7 ^WWO,H + 333333?1.7 WW ?1.1?^1.1 gWWX7H , ?1.1 ?WW ?0.9g0.9 FWW7,H - ?0.9 WW FЄ 'WWH .WW 'Є 4WWV!H /WW 4Є HWV9!H 0 << > WWV ><<HChromium PWWAl 1WV  @R@73@R@P73 gWWX6l 2  @R@73 @R@WW  O@62O@g62 pWWa6l 3  O@62 O@WW  U@87U@p87 fWWW6l 4  U@87 U@WW @4.7f4.7 ^WWO,l 5 @4.7 WW 333333@3.9333333@^3.9 gWWX7l 6 333333@3.9 333333@WW 333333@2.4g2.4 FWW7,l 7 333333@2.4 WW FЄ 'WWl 8WW 'Є 4WWV!l 9WW 4Є HWV9!l : << > WWV ><<HLead PWWA ;WV  R@75R@P75 gWWX6 <  R@75 R@WW  O@62O@g62 pWWa6 =  O@62 O@WW  U@87U@p87 eWWV6 >  U@87 U@WW  &@11e11 ]WWN+ ?  &@11 WW !@8.9!@]8.9 rWWc7 @ !@8.9 !@WW @5.4@r5.4 sWWd7 A @5.4 @WW Q?0.43Q?s0.43 kWW\8 B Q?0.43 Q?WW Gz?0.47Gz?k0.47 xWWVe8 C Gz?0.47 Gz?WW (\?0.68(\?x0.68 \WVMC D (\?0.68 << > (\?WWV <<\Manganese HWW9 EWV d@164d@H164 iWWZ7 F d@164 d@WW e@168e@i168 iWWZ7 G e@168 e@WW `k@219`k@i219 iWWZ7 H `k@219 `k@WW "@9.3"@i9.3 iWWZ7 I "@9.3 "@WW 333333@7.3333333@i7.3 iWWZ7 J 333333@7.3 333333@WW @4.7@i4.7 HWW97 K @4.7 @WW HЄ 'WW LWW 'Є +WWV MWW +Є CWV4 N << WWV ><<CMercury PWWA( OWV  G@46G@P46 gWWX6( P  G@46 G@WW  I@51I@g51 pWWa6( Q  I@51 I@WW  N@60N@p60 gWWX6( R  N@60 N@WW ?0.25g0.25 _WWP-( S ?0.25 WW ?0.2?_0.2 hWWY7( T ?0.2 ?WW p= ף?0.13h0.13 kWW\-( U p= ף?0.13 WW ~jtX?0.0015~jtX?k0.0015 oWW`:( V ~jtX?0.0015 ~jtX?WW _Q[?0.0017_Q[?o0.0017 {WWVh:( W _Q[?0.0017 _Q[?WW ~jt?0.024~jt?{0.024 kWV\D( X ~jt?0.024 << > ~jt?WWV ><<kNickel PWWAL YWV  M@58M@P58 gWWX6L Z  M@58 M@WW  J@52J@g52 pWWa6L [  J@52 J@WW  @Q@69@Q@p69 qWWb6L \  @Q@69 @Q@WW `x@390`x@q390 iWWZ7L ] `x@390 `x@WW t@320t@i320 rWWc7L ^ t@320 t@WW i@200i@r200 rWWc7L _ i@200 i@WW @2.2@r2.2 iWWZ7L ` @2.2 @WW 333333@2.4333333@i2.4 kWWVX7L a 333333@2.4 333333@WW  @3.5k3.5 ^WVO7L b  @3.5 << > WWV ><<^Hydrogenchloride TWWE pcWV tA143000tAT143,000 oWW`: pd tA143000 tAWW [A134000[Ao134,000 xWWi: pe [A134000 [AWW A155000Ax155,000 kWW\: pf A155000 AWW @2900k2,900 `WWQ- pg @2900 WW h@2100h@`2,100 iWWZ8 ph h@2100 h@WW p@1500i1,500 GWW8- pi p@1500 WW GNM 'WW pjWW 'NM 4WWV! pkWW 4NM HWV9! pl << > WWV ><<HHydrogenfluoride SWWDDmWV @20000@S20,000 mWW^9Dn @20000 @WW v@23000v@m23,000 kWW\9Do v@23000 v@WW d@26000k26,000 ^WWO.Dp d@26000 WW a@140^140 ^WWO,Dq a@140 WW q@280q@^280 fWWW7Dr q@280 q@WW  @R@73f73 EWW6+Ds  @R@73 WW ENM 'WWDtWW 'NM 4WWV!DuWW 4NM =WV.!Dv << > WWV <<=ТAcrolein JWW;hwWV  9@259@J25 jWW[6hx  9@25 9@WW  ;@27;@j27 jWW[6hy  ;@27 ;@WW  A@34A@j34 JWW;6hz  A@34 A@WW JNM *WWh{WW *NM *WWh|WW *NM *WWh}WW *NM *WWh~WW *NM .WWVhWW .NM =WV.h << WWV n<<=ТDioxinsd PWWAWV  Om?0.000097 Om?P0.000097 uWWf<  Om?0.000097  Om?WW iUMu?0.00012iUMu?u0.00012 iWWZ; iUMu?0.00012 iUMu?WW -C6*?0.00020i0.00020 DWW50 -C6*?0.00020 WW D1x105 *WWWW *9x106 *WWWW *3x106 *WWWW *NM *WWWW *NM .WWVWW .NM <WVV+! << n WWV <<<Formaldehyde IWWV8WVV  A@35A@I35 iWWVX6  A@35 A@WWV  =@29=@i29 iWWVX6  =@29 =@WWV  F@45F@i45 iWWVX6  F@45 F@WWV  3@193@i19 jWWVY6  3@19 3@WWV "@9.3"@j9.3 kWWVZ7 "@9.3 "@WWV #@9.5#@k9.5 jWWVY7 #@9.5 #@WWV  B@36B@j36 iWWVX6  B@36 B@WWV  C@39C@i39 kWWVVX6  C@39 C@WWV  L@57L@k57#RFZ/#LB@  L@57 <<  L@WWVV L*XF` XX*aZRF0 F RadionuclidesaretheonepriorityHAPnotincludedonthistablebecauseradionuclideemissionsaremeasuredindifferentunits(i.e.,curiesperyear)and,therefore, H wouldnotprovidearelevantcomparisontotheotherHAPsshown.Radionuclideemissionsarepresentedinchapter9. F.F. b0 F Theemissionsestimatesinthistablearederivedfrommodelprojectionsbasedonalimitedsampleofspecificboilertypesandcontrolscenarios.Therefore,there  areuncertaintiesinthesenumbers(seesectionES.4fordiscussion). F.F. c F NM=Notmeasured. H d0 F Theseemissionsestimateswerecalculatedusingthetoxicequivalency(TEQ)approach,whichisbasedonthesummationoftheemissionsofeachcongenerafter  adjustingfortoxicityrelativeto2,3,7,8tetrachlorodibenzopdioxin(i.e.,2,3,7,8TCDD).#RFZVe#RXOXRFPXT XXRXOPF.F. . XXF` X(e. L TRY3' LetterP'3 Letter Landscape 3' Letter '3 Letter LandscapeT& 7 TableES2.EstimatedEmissionsforNinePriorityHAPsfrom  CharacteristicUtilityUnits(1994;tonsperyear)a  P  XPXTRF P*XY d d'd4 D4"D4"D4"D4"D4"D4"D4"D4"Dd"TU(#(#, d4 ,D4",D4",Dd"+  3VVW" ,| l23ZRFFuel: ;VWW*"VVW ;Coal ;VWW*"VWW ;Oil =VWWV*"VWW =Naturalgas SVVB*" 2 l VWWV \SRSUnitsize(MWe): \WVK8"VV Pt@325Pt@\325 }WVl@8 " Pt@325 Pt@WV d@160d@}160 WVVl@8 " d@160 d@WV n@240n@240 rVcK8 " n@240 SR \ n@WVV ,S"rArsenic TWEA  V {Gzt?0.0050{Gzt?T0.0050 xWi:A   {Gzt?0.0050 {Gzt?W a+ey?0.0062a+ey?x0.0062 qWV^:A  a+ey?0.0062 a+ey?W a2U0*3?0.0003q0.0003 aWVR:A  a2U0*3?0.0003 S" , WV <c"aCadmium TWWEr WV HPsb?0.0023HPsb?T0.0023 xWWi:r  HPsb?0.0023 HPsb?WW ǺV?0.0014ǺV?x0.0014 XWWVE:r  ǺV?0.0014 ǺV?WW XТNCb HWV9!r  c" < WWV <c"HChromium RWWC WV )\(?0.11)\(?R0.11 vWWg8  )\(?0.11 )\(?WW a+ey?0.0062a+ey?v0.0062 XWWVE:  a+ey?0.0062 a+ey?WW XNC HWV9!  c" < WWV <c"HLead SWWD $ WV /$?0.021/$?S0.021 vWWg9 $  /$?0.021 /$?WW y&1?0.014y&1?v0.014 WWWVD9 $  y&1?0.014 y&1?WW WNC HWV9! $  c" < WWV <c"HMercury GWW8U WV ?0.05G0.05 `WWQ-U  ?0.05 WW a2U0*S?0.0012`0.0012 MWWV:/U  a2U0*S?0.0012 WW MNC HWV9!U  c" < WWV <c"HHydrogenchloride FWW76 WV g@190F190 \WWM,6 ! g@190 WW "@9.4\9.4 JWWV7,6 " "@9.4 WW JNC HWV9!6 # c" < WWV <c"HHydrogenfluoride EWW6g $WV  ,@14E14 EWW6+g %  ,@14 WW ENC 4WWV!g &WW 4NC HWV9!g ' c" < WWV <c"HТDioxinsc XWWI (WV qr> 0.00000013qr>X0.00000013 WWr> ) qr> 0.00000013 qr>WW vԷ1X> 0.000000023vԷ1X>0.000000023 ]WWVJ? * vԷ1X> 0.000000023 vԷ1X>WW ]NC JWVV9! + c" < WWV lcRJNickel 2WWV!,WVV 2NC SWWVB-WWV 333333?1.7333333?S1.7%  mWWVVZ7. 333333?1.7 333333?WWV Mbp?0.004m0.004#RFZm#I?=/ Mbp?0.004 cR l WWVV IZRF*XF` XX*a0 F Thereareuncertaintiesinthesenumbers.Basedonanuncertaintyanalysis,theEPApredictsthattheemissions w0 estimatesaregenerallywithinafactorofroughlythreeofactualemissions. F(#F(# b0 F NC=Notcalculated.2F(#F(# c0 F SeefootnotedofTableES1#RFZ'~#.R&&RFl&د&&R&{3F(#F(# '7uk. XXF` XF~.P&د&&l&دIftheMEIriskwasaboveaminimummeasure(e.g.,exposuregreaterthanonetenththeinhalationreferenceconcentratio8 !?in[RfC] u#  a      ףorcancer _7 riskgreaterthan1chancein10million),thentheHAPwaschosenformorestudy.Fornoninhalationexposures,the67HAPswereprioritizedbyconsideringfivecriteria:(1)persistence;(2)tendencytoϢbioaccumulate;(3)toxicity;(4)emissionsquantity;and(5)radioactivity.  Basedonthisscreeningassessment,atotalof14HAPswereidentifiedaspriority.TwelveHAPs(arsenic,beryllium,cadmium,chromium,manganese,nickel,hydrogenchloride[HCl],hydrogenfluoride[HF],acrolein,dioxins,formaldehyde,andradionuclides)wereidentifiedasprioritypollutantsforfurtherstudybasedonpotentialforinhalationexposuresandrisks.Fourofthese12HAPs(arsenic,cadmium,dioxins,andradionuclides)plus2additionalHAPs(mercuryandlead)wereconsideredpriorityformultipathwayexposure);ofthese6ϢHAPs,4(arsenic,mercury,dioxins,andradionuclides)wereidentifiedasthehighestprioritytoassessformultipathwayexposuresandrisks.Overall,atotalof14ofthe67HAPswereconsideredpriority.Theother53HAPswerenotevaluatedbeyondthescreeningassessment. '"I ЇES.7INHALATIONRISKASSESSMENTLOCALANALYSIS  TheEPAestimatedinhalationexposuresandrisksduetodispersionofHAPemissionswithin50kilometers(km)ofeachofthe684plants(i.e.,localanalysis).For13ofthe14priorityHAPs,theHEMwasused;forradionuclides,theCleanAirActAssessmentPackage1993(CAP93)modelwasused.TheHEMexposuremodelingconductedfortheinhalationriskassessmentwasverysimilartothemodelingconductedforthescreeningassessment.Thesamedefaultoptionsandsameinputdatawereused.However,thereisoneimportantdifference.Fortheinhalationriskassessment,adistinctionwasmadebetweenurbanandrurallocations.Ifaplantislocatedinanurbanarea,itwasmodeledusingtheurbanmode(i.e.,dispersionisassumedtobecharacteristicofemissionsemittedbyafacilityinanurbanlocationwheretherearebuildingsnearby).Dispersionofthepollutantplumeinanurbanareaisexpectedtoexhibitgreaterturbulencebecauseofheattransferandobstacles(i.e.,largebuildings).Ifaplantislocatedinarurallocation,itwasmodeledusingtheruralmode(i.e.,dispersionisassumedtobecharacteristicofafacilitylocatedinarurallocation).Inthescreeningassessment,allplantsweremodeledusingtheurbandefaultbecauseusingtheurbandefaulttypicallyleadstomoreconservative(i.e.,higher)estimatesofhumanexposures,whichisappropriateforascreeningassessment.However,usingtheurbanandruraldistinctionisbelievedtoreflectmorerealisticconditions.  Thecancerrisksforallgasfiredplantswerewellbelowonechanceinonemillion(i.e.,<1x106)andnononcancerhazardswere  identified.Therefore,gasfiredplantsareomittedfromthefollowingdiscussions.  Incaseswheredataweremissingorincomplete,theEPAhadtomakevariousassumptions.Afewoftheseassumptionsaremorelikelytooverestimaterisks.Otherassumptionsusedarelikelytounderestimaterisks.Basedonanuncertaintyanalysisconductedforthisstudy,itisestimatedthattheseassumptionstakentogetherleadtoareasonablehighendestimate(i.e.,conservative,butwithintheboundsofreasonableestimates)oftherisksduetoinhalationexposurewithin50kmofplants.Withinthelimitsofcurrentscientificinformation,thisapproachis,therefore,mostlikelytooverestimatehealthrisksforthesepollutants.TheuncertaintyanalysissuggeststhatthemostlikelyestimatedinhalationMIRs(i.e.,centraltendencyMIRs)mayberoughly2to10timeslowerthanthehighendMIRspresentedbelow.TheaverageindividualrisksduetoinhalationexposuretoutilityHAPemissionsforthetotalexposedU.S.population(roughly200,000,000people)arepredictedtoberoughly100to1000timeslowerthanthehighendinhalationMIRs.ES.7.1InhalationCancerRisksforCoalFiredUtilitiesBasedonLocal 4'"/ Analysis(1990) '@#0   Thevastmajorityofcoalfiredplants(424ofthe426plants)areestimatedtoposelifetimecancerrisks(i.e.,increasedprobabilityofanexposedpersongettingcancerduringalifetime)oflessthan1x106 $*t%3 duetoinhalationexposuretoutilityHAPemissions.Onlytwoofthe426plantsareestimatedtopotentiallyposeinhalationrisksgreaterthan1x106(seeFigureES2). X,'6 Ї  TheincreasedlifetimecancerMIRduetoinhalationexposuretocoalfiredutilityHAPemissions,basedonthelocalanalysis,isestimatedtobenogreaterthan3x106.Arsenicandchromiumarethe (x ТHAPscontributingmosttotheinhalationrisks(seeTableES-3).AllotherHAPs,includingradionuclides,wereestimatedtopresentinhalationriskslessthan1x106forcoalfiredunits. \   ThecancerincidenceintheU.S.duetoinhalationexposuretoϢHAPs(includingradionuclides)fromall426coalfiredplants basedon   thelocalanalysis isestimatedtobenogreaterthanapproximately0.2 `   cancercaseperyear(cases/yr),or1caseevery5years.However,asdescribedinlatersections,theconsiderationoflongrangedispersionofHAPs(beyond50km)resultsinincreasedestimatesforcancerincidence.ES.7.2InhalationCancerRisksforOilFiredUtilitiesBasedonLocal ,  Analysis(1990)     Themajorityoftheoilfiredplants(125ofthe137plants)areestimatedtoposeinhalationcancerMIRslessthan1x106.However,up `  to11ofthe137oilfiredplantsareestimatedtopotentiallypresentinhalationMIRsabove1x106(seeFigureES3).Nickel,arsenic,  Тradionuclides,andchromiumaretheprimarycontributorstothesecancerrisks.  Foroilfiredutilities,thehighestcontributiontotheMIRsisfromnickel.However,therearesubstantialuncertaintieswiththenickelriskestimates.Nickelisemittedinseveraldifferentforms(e.g.,nickeloxides,solublenickel,sulfidicnickel)andthehealtheffectsofthesedifferentformsvary,andforsomeformsareunknownoruncertain.Nickelsubsulfide(whichisoneofthepossibleformsofϢsulfidicnickel)isaknownhumancarcinogenandappearstobethemostcarcinogenicformbasedonavailabledata.Basedonlimiteddata,3to26percentofthenickelemissionsarebelievedtobesulfidicnickel.ItisnotknownhowmuchofthesulfidicnickelemissionsarenickelϢsubsulfide.Severalothernickelspecies(e.g.,nickeloxides)arealsopotentiallycarcinogenicbutthepotenciesarenotknown.  H$ TRP'3Letter LandscapeY3' Letter '3 Letter Landscape 3' LetterT  sN[=-)h|^   ` E^a hdXsߢxeOB2.p|0p) `. E)N))e`6*x ...... ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ......P &P&دZ PNote:Thehighendmaximumindividualrisks(MIRs)arepresentedasexponentsinthisfigure.Forexample,anincreasedcancerriskofonechanceinonemillion "  (i.e.,1x106)isshownas1E6inthisFigure.Thefigureshowsthat91plantsareestimatedtoposeanMIRbetween1x107and1x106.#P Z##P&د& Pӕ# T#  o s`[=-)h|^   ` E^a hdXsߢxB2.p|0Cs)$ `.""Es)s)$s)ef *xx n..n.... n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. n..n..n..n.. ..n..n.. P &P&دZ PNote:TheMIRsarepresentedasexponentsinthisfigure.Forexample,anincreasedcancerriskof1x106isshownas1E6here.Thefigureshowsthereare9oil  p$ firedplantswithestimatedMIRsbetween1x106and1x105.#P Z##P&د& PӋ#  %. TRY3'LetterP'3Letter Landscape 3' Letter '3 Letter LandscapeTPXT X&P&دTableES3.SummaryofHighEndInhalationCancerRiskEstimates  fromLocalAnalysisforCoalFiredUtilitiesfortheYear1990#P&د& XPXT#z&&&P&دz>&z&*g d d d4 D4"D4"Dd"XY(#(#,Rd4 ,D4",_D4",` Dd"+  3VVV" d ,<<3#P z>g#Z PHAP ;VWV*T"VVV ;HighestCancerMIRa ;VWV*T"VWV ;Populationwithlifetimerisk P >1x106 =VWVV*T "VWV =Numberplantswith P  MIR>1x106 QVB*T " << , VWVV <<QArsenic 'W0  V '2x106 QWB0  W @850@Q850 iWVV70  @850 @W  @2i2 \WVM50   @2 <<  WV %<<\Chromium 'WWT WV '1x106 FWW7T WW [@110F110 ^WWVK,T  [@110 WW  ?1^1 ^WVVM5T   ?1 << % WWV U<<^ТTotalb(AggregateofHAPs) )WWVx WVV )3x106 SWWVBx WWV @850@S850 iWWVVV7x  @850 @WWV  @2i2#P Z#z> PE;9x   @2 << U  WWVV E*XF` XX*a#P z>≵#Z P0 F Estimatedlifetimemaximumindividualrisk(MIR)duetoinhalationexposureforthe highestriskcoalfiredplant.  ` Basedonanuncertaintyanalysis,theseestimatesareconsideredreasonablehighendestimates(seesectionES.7.4fordiscussion). F(#F(# b0 F EstimatedriskduetoinhalationoftheaggregateofHAPsassumingadditivityofriskfor26individualcarcinogenic d  ТHAPs.#P Z?##P&د& Pӆ# F(#F(# . XXF` X.  Toevaluatetherangeofpotentialrisksduetonickelemissions,theEPAestimatedrisksusingvariousassumptionsfornickelcancerpotency(presentedinchapter6).Forexample,assumingthenickelmixis50percentascarcinogenicasnickelsubsulfide,thehighestinhalationcancerMIRduetotheaggregateofHAPemissionsfromthehighestriskoilfiredutilityplantisestimatedtobe6x105. $ Assumingthenickelmixis10percentascarcinogenicasnickelϢsubsulfide,thehighestinhalationcancerMIRduetotheaggregateofHAPemissionsfromthehighestriskoilfiredutilityplantisapproximately3x105.ThevaluesinTableES4andFigureES3are ( basedontheconservativeassumptionthatthenickelmixis50percentascarcinogenicasnickelsubsulfide.  EstimatedrisksduetoinhalationexposureforasubsetofHAPsbasedonthelocalanalysisarepresentedinTableES4.AllotherHAPsanalyzedwereestimatedtoposeinhalationcancerrisksbelow1x106 8. forall137oilfiredplants.  ThecancerincidenceintheU.S.duetoinhalationexposuretoHAPemissions(includingradionuclides)fromall137oilfiredutilities,basedonthelocalanalysis,isestimatedtobenogreaterthan0.5cancercase/yr.ES.7.3InhalationCancerRisksBasedonLongRangeTransport "6   Inadditiontotheaboveanalyses,theEPAconductedlongrangetransportanalysestoassessemissionsdispersionandexposuresonanationalscalefor1990.TheRegionalLagrangianModelofAirPollution(RELMAP)wasusedtoestimatethedispersionofHAPemissionsfromthefacilitystackouttothebordersofthecontinentalU.S.ThisisincontrasttotheHEM,whichestimatesdispersionandairconcentrationswithin50kmofthesource.PXT X&P&د̜#  8*%@ #TableES4.SummaryofHighendInhalationCancerRiskEstimatesBasedonLocalAnalysisforOilFiredUtilitiesfortheYear1990#P&د& XPXTZ#  * ddRd4 D4"_D4"` Dd"g(#(#, d",)D",1D", D0"+  3VVV" d :L3&&&P&دZ&E(&&&Z(&Z&EHAP ;VWV*H"VVV ;HighestMIRa ;VWV*H"VWV ;Populationwithlifetimerisk  Ѐ>1x106 =VWVV*H "VWV =NumberplantswithMIR   >1x106 QVB*H " L : VWVV #PQТNickelb 9W*  V 95x105 TWE  W @110000@T110,000 xWVe:  @110000 @W  &@11&@x11 hWVYA   &@11 P # &@WV 3`hArsenic 9WW* WV 91x105 GWW8 WW @2400G2,400 _WWVL-  @2400 WW  @2_2 \WVM5   @2 ` 3 WWV 3`\ТRadionuclides 9WW* 8WV 91x105 GWW8 8WW @2400G2,400 _WWVL- 8 @2400 WW  @2_2 \WVM5 8  @2 ` 3 WWV 3`\Chromium 9WW* `WV 95x106 GWW8 `WW @2300G2,300 _WWVL- ` @2300 WW  ?1_1 ^WVWM5 `  ?1 ` 3 WWV C`,^Cadmium ;WWW*8 WVW ;2x106 GWWW68 WWW  F@45G45 ]WWWVJ+8   F@45 WWW  ?1]1 ^WVVM58   ?1 `, C WWWV c`L^ТTotalc(aggregate) ;WWV*p WVV ;6x105 VWWVEp !WWV @110000@V110,000 xWWVVe:p " @110000 @WWV  &@11&@x11#>Z#QGEp #  &@11 `L c  &@WWVV Q*XF` XX*a`>Z`Z&E(&ZZ(&Z&E0 F Estimatedlifetimemaximumindividualrisk(MIR)duetoinhalationexposureforthe highestriskoilfiredplant.Based h $ onanuncertaintyanalysis,theseestimatesareconsideredreasonablehighendestimates(seesectionES.7.4fordiscussion). F(#F(# b0 F TheestimatesfornickelandtotalHAPsarebasedontheassumptionthatthemixofnickelcompoundsis50percent l' ascarcinogenicasnickelsubsulfide. F(#F(# c0 F EstimatedriskduetoinhalationoftheaggregateofHAPsassumingadditivityofriskfor14individualcarcinogenic t) ТHAPs. F(#F(# #Z&E(&Z##&د&(&Z&En#. XXF` X!.P&د&&&د  TheRELMAPmodelingwasconductedforallcoalandoilfired D- utilities,butwaslimitedtomercury,cadmium,chromium,arsenic,nickel,lead,anddioxins.Onlyinhalationexposurestothe#&د&&P&د#P&د&&&دcarcinogenicHAPsarediscussedinthissection.Depositionand x0 Тmultipathwayconcernsarediscussedelsewhereinthisreport.ThelongrangetransportmodelingindicatesthatthelocalHEManalysisalonedoesnotaccountforasubstantialpercentageofthepopulationexposuresduetocoalfiredutilityemissions.AcomparisonoftheHEMresultstotheRELMAPresultsindicatesasignificantportionofemissionsdispersefurtherthan50km,aswouldbeexpectedfortheseϢHAPs,whicharemostlyfineparticulatesubstancesemittedfromelevatedstacks.PXT X&P&د X8 #Xʺ*X XPXT2##&د&*XXʺ#  TheRELMAPresultsforarsenic,cadmium,chromium,andnickel(whichareemittedmainlyasPM)wereusedtoestimatethepotentiallongrangetransportinhalationexposuresforothercarcinogenicHAPs.Usingthismethodology,thehighestcancerincidenceduetoinhalationexposuretoHAPsfromcoalfiredutilitiesconsideringbothlocalandlongrangetransportisestimatedtobeupto1.3cases/yr,whichisabout7timesgreaterthantheincidenceestimatedinthelocalanalysisalone.Thecancerincidenceforoilfiredutilitiesdidnotchange(seeTableES-5).  l'"C &   Xʺ*X&&دTableES5.SummaryofHighEndInhalationRiskEstimatesDueto  LocalandLongRangeTransport#&د&*XXʺ#*rv dd d")D"1D" D0"(#(#,d4 ,D4 ,D4 ,D4 ,Dd"+  9VVV& d ]~(9&&&&دZ&E(&&&Z(&Z&ELOCALIMPACTS(dispersionwithin50kmofeachutilityplant)d TWVE- ~( ] VVV =^(T =WW.WV =OILFIREDPLANTS DWWV1""WW DCOALFIREDPLANTS VVVVE-" ^( = WWV D~XVPollutant ;VWV*& v"VVV ;Maximumindividualrisk(MIR) ;VWV* " "VWV ;AnnualincreasedcancerIncidence ;VWV* " "VWV ;Maximumindividualrisk(MIR) =VWVV* ""VWV =Annualincreasedcancerincidence QVB* "" ~X D VWVV -N(QТRadionuclides 0W!$ tV 0  1x105 OW@$ t W ?0.2O  0.2 OW@5$ t  ?0.2 W O  2x108 SWV@$ t W ?0.1S0.1 ^WVO7$ t ?0.1 N( - WV =^(^ТNickela 0WW!V WV 0  5x105 ZWWKV  WW ?0.2?Z  0.2 ZWWK@V   ?0.2 ?WW Z  7x107 UWWVBV  WW {Gzt?0.005U0.005 `WVQ9V  {Gzt?0.005 ^( = WWV =^(`Chromium 0WW! WV 0  5x106 PWWA  WW {Gz?0.02P  0.02 PWWA6   {Gz?0.02 WW P  1x106 TWWVA  WW {Gz?0.02T0.02 _WVP8  {Gz?0.02 ^( = WWV =^(_Arsenic 0WW! WV 0  1x105 PWWA ! WW {Gz?0.04P  0.04 PWWA6 "  {Gz?0.04 WW P  2x106 TWWVA # WW ?0.05T0.05 _WVP8 $ ?0.05 ^( = WWV =^(_Cadmium 0WW!< %WV 0  2x106 QWWB< & WW {Gzt?0.005Q  0.005 QWWB7< '  {Gzt?0.005 WW Q  2x107 VWWVC< ( WW a2U0*C?0.0006V0.0006 aWVR:< ) a2U0*C?0.0006 ^( = WWV =^(aAllOthersb 0WW!n *WV 0  8x107 QWWBn + WW {Gzt?0.005Q  0.005 QWWB7n ,  {Gzt?0.005 WW Q  8x107 UWWVBn - WW Mbp?0.004U0.004 `WVQ9n . Mbp?0.004 ^( = WWV =^(`ТTotalc 0WW!P/WV 0  6x105 ZWWKP0 WW ?0.5?Z  0.5 ZWWK@P1  ?0.5 ?WW Z  3x106 ^WWVKP2 WW ?0.2?^0.2 qVVV^BP3 ?0.2 ^( = ?WWV ]~(qLOCALPLUSLONGRANGEIMPACTS(dispersionfromutilityemissionpointstobordersofcontinentalU.S.) KWV<$4 ~( ] VVV =^(K 4WW%$5WV 4  OILFIREDPLANTS DWWV1"$6 WW DCOALFIREDPLANTS VVVVE-$7" ^( = WWV D~XVPollutant ;VWV*&v8"VVV ;Maximumindividualrisk(MIR) ;VWV*":"VWV ;Annualincreasedcancerincidence ;VWV*"<"VWV ;Maximumindividualrisk(MIR) =VWVV*">"VWV =Annualincreasedcancerincidence QVB*"@" ~X D VWVV -N(QТRadionuclides 0W!$tAV 0  1x105 ZWK$tB W ?0.2?Z  0.2 ZWK@$tC  ?0.2 ?W Z  Notestimated ^WVK$tD W ffffff?0.7ffffff?^0.7 iWVZB$tE ffffff?0.7 N( - ffffff?WV =^(iТNickela 0WW!VFWV 0  Ӝ5x105 ZWWKVG WW ?0.2?Z  0.2 ZWWK@VH  ?0.2 ?WW Z  1x108 `WWVMVI WW ~jt?0.038~jt?`0.038 kWV\DVJ ~jt?0.038 ^( = ~jt?WWV =^(kChromium 0WW!KWV 0  5x106 [WWLL WW {Gz?0.02{Gz?[  0.02 [WWLAM  {Gz?0.02 {Gz?WW [  2x106 _WWVLN WW 333333?0.15333333?_0.15 jWV[CO 333333?0.15 ^( = 333333?WWV =^(jArsenic 0WW! PWV 0  1x105 [WWL Q WW ?0.05?[  0.05 [WWLA R  ?0.05 ?WW [  3x106 _WWVL S WW Gz?0.37Gz?_0.37 jWV[C T Gz?0.37 ^( = Gz?WWV =^(jCadmium 0WW!<UWV 0  2x106 \WWM<V WW ~jtx?0.006~jtx?\  0.006 \WWMB<W  ~jtx?0.006 ~jtx?WW \  3x107 `WWVM<X WW {Gzt?0.005{Gzt?`0.005 kWV\D<Y {Gzt?0.005 ^( = {Gzt?WWV =^(kAllOthersb 0WW!nZWV 0  8x107 \WWMn[ WW ~jtx?0.006~jtx?\  0.006 \WWMBn\  ~jtx?0.006 ~jtx?WW \  1x106 `WWVMn] WW y&1?0.028y&1?`0.028 mWVV\Dn^ y&1?0.028 ^( = y&1?WWV m^XmТTotalc 2WWV!P _WVV 26x105 \WWVKP `"WWV ?0.5?\0.5 \WWVK@P a" ?0.5 ?WWV \4x106 ^WWVVKP b"WWV ?1.3?^1.3#>Z#[QOP c" ?1.3 ^X m  ?WWVV [*XF` XX*aZ>0 F Assumesthatthenickelmixtureis50percentascarcinogenicasnickelsubsulfide."TdF(#F(# b0 F EstimatedrisksduetoexposuretoallremainingHAPsanalyzed(i.e.,excludingnickel,arsenic,chromium,cadmium, "e andradionuclides). F(#F(# c0 F Aggregaterisk(riskduetoinhalationexposuretoallcarcinogenicHAPs,assumingadditivityofrisks).$XgF(#F(# d0 F Thereareuncertaintiesassociatedwiththeseriskestimates.SeesectionsES.7.4fordiscussion.#>Z4#' `>&د&`$ hF(#F(# . XXF` X.P&د&&&د  AcomparisonbetweentheHEMlocaldispersionresultsandthe &("k longrangetransportmodelingresultsindicatesthatlongrangetransportismuchlessimportantfortheMIRthanitisforcancerincidence.Forexample,theMIRfromthelocalanalysesforcoalfiredutilities(i.e.,inhalationriskof3x106)ispredictedtoincreaseby )%o roughly10to20percenttoabout4x106whenambientconcentrations *%p  areaddedfromlongrangetransportofarsenicfromall @+&q #&د&&P&دr#P&د&&&دotherutilitiesinthecontinentalU.S.Foroilfiredutilities,the   longrangetransportofHAPshasnoimpactonthehighestinhalationMIRbecauseoftheremotelocationofthetwohighestriskoilfiredplants.ES.7.4UncertaintieswiththeInhalationCancerRiskAssessment    Thereareseveralareasofuncertaintyintheinhalationriskassessmentincluding:(1)theimpactsoflongrangetransport;(2)theemissionsandhealtheffectsofdifferentformsofchromiumandnickel;(3)theuseofalinearnonthresholdhightolowdose#&د&&P&د#   P&د&&&دextrapolationmodelforestimatingcancerrisksatlowexposure L   concentrations;(4)theimpactsofepisodicreleasesresultingfromupsetsorunusualoperatingconditions;(5)howresidencetimesandactivitypatternsimpacttheexposures;(6)theimpactsonsensitiveϢsubpopulations;(7)theimpactsofbackgroundexposures;and(8)theriskofcomplexpollutantmixtures.  TheuncertaintyanalysisindicatesthattheinhalationcancerMIRsandincidenceestimatespresentedabovearereasonablehighendestimatesoftherisksduetoinhalationexposurewithin50kmofeachplant.Thatis,theestimatesareconsideredgenerallyconservative(i.e.,predictedtoberoughlythe90thto95thpercentile).TheuncertaintyanalysissuggeststhatthemostlikelyestimatedinhalationϢMIRs(i.e.,centraltendencyMIRs)mayberoughly2to10timeslowerthanthehighendMIRspresentedabove.TheaverageindividualrisksduetoinhalationexposuretoutilityHAPemissionsforthetotalexposedU.S.population(roughly200,000,000people)arepredictedtoberoughly100to1,000timeslowerthanthehighendinhalationMIRs.ES.7.5SummaryoftheInhalationCancerRisks @   Forthemajorityofutilityplants(approximately671ofthe684plants),theestimatedinhalationcancerrisksduetoHAPemissionsarelessthan1x106.However,severalplants(2coalplantsandupto11 t #&د&&P&د#P&د&&&دoilplants)areestimatedtopotentiallyposeinhalationcancerrisks 0  above1x106.Oneoilplantisestimatedtoposeahighendinhalation <! cancerMIRofupto6x105.Basedontheassessment,nogreaterthan " 1.8cancercases/yrareestimatedtooccurintheU.S.duetoinhalationexposuretoHAPemissionsfromallcoalandoilfiredutilities.Furtherresearchandevaluationmaybeneededtomorecomprehensivelyassesstheinhalationcancerrisks,especiallytoreducetheuncertaintiesassociatedwiththenickelriskestimates.#&د&&P&د #P&د&&&د T!' #&د&&P&د} #P&د&&&دES.7.6InhalationNoncancerRisks ")   TheEPAalsoassessednoncancerrisks(i.e.,healtheffectsotherthancancer)duetoshortandlongterminhalationexposure.Manganese,HCl,HF,andacroleinwerefoundtobethefourHAPsofhighestpotentialconcernfornoncancereffects.  BasedonmodelingHAPsforall684plantswiththeHEM,estimatedlongtermambientHAPconcentrationsweregenerally100to10,000timesbelowtheRfCorsimilarbenchmark.ThehighestestimatedlongtermambientHAPconcentrationwas10timesbelowtheRfC.  Usingashorttermairdispersionmodelthatconsidersall reasonablemeteorologicalconditions,EPAmodeledmaximumonehour +&5 concentrationsforthreeHAPs(HCl,HF,andacrolein).Thehighestshorttermexposurewas140timesbelowtheacutereferencelevel.#&د&&P&د # l  ES.8MERCURYMULTIPATHWAYASSESSMENTES.8.1BackgroundDiscussionforMercury \   Mercurycyclesintheenvironmentasaresultofnaturalandhuman(anthropogenic)activities.Theamountofmercurymobilizedandreleasedintothebiospherehasincreasedsincethebeginningoftheindustrialage.Mostofthemercuryintheatmosphereiselementalmercuryvapor,whichcirculatesintheatmosphereforuptoayear,andhencecanbewidelydispersedandtransportedthousandsofmilesfromlikelysourcesofemission.Afteritdeposits,mercurycommonlyisemittedbacktotheatmosphereeitherasagasorassociatedwithparticles,toberedepositedelsewhere.Asitcyclesbetweentheatmosphere,land,andwater,mercuryundergoesaseriesofcomplexchemicalandphysicaltransformations,manyofwhicharenotcompletelyunderstood.    Mercuryisapersistentelementandbioaccumulatesinthefoodweb.Mercuryaccumulatesmostefficientlyintheaquaticfoodweb.Predatoryorganismsatthetopofthefoodwebgenerallyhavehighermercuryconcentrations.Nearlyallofthemercurythataccumulatesinfishtissueismethylmercury.Inorganicmercury,whichislessefficientlyabsorbedandmorereadilyeliminatedfromthebodythanϢmethylmercury,doesnottendtobioaccumulate.  Fishconsumptiondominatesthepathwayforhumanandwildlifeexposuretomethylmercury.TheEPAs1997MercuryStudyReporttoCongresssupportsaplausiblelinkbetweenanthropogenicreleasesofmercuryfromindustrialandcombustionsourcesintheU.S.andϢmethylmercuryinfish.However,thesefishmethylmercuryconcentrationsalsoresultfromexistingbackgroundconcentrationsofmercury(whichmayconsistofmercuryfromnaturalsources,aswellasmercurywhichhasbeenreemittedfromtheoceansorsoils)anddepositionfromtheglobalreservoir(whichincludesmercuryemittedbyothercountries).Giventhecurrentscientificunderstandingoftheenvironmentalfateandtransportofthiselement,itisnotpossibletoquantifyhowmuchofthemethylmercuryinfishconsumedbytheU.S.populationiscontributedbyU.S.emissionsrelativetoothersourcesofmercury(suchasnaturalsourcesandreemissionsfromtheglobalpool).Asaresult,itcannotbeassumedthatachangeintotalmercuryemissionswillbelinearlyrelatedtoanyresultingchangeinmethylmercuryinfish,noroverwhattimeperiodthesechangeswouldoccur.Thisisanareaofongoingstudy.ES.8.2MethylmercuryHealthEffects x&!.   EpidemicsofmercurypoisoningfollowinghighdoseexposurestoϢmethylmercuryinJapanandIraqdemonstratedthatneurotoxicityisthehealtheffectofgreatestconcernwhenmethylmercuryexposureoccurstothedevelopingfetus.Dietarymethylmercuryisalmostcompletelyabsorbedintothebloodanddistributedtoalltissuesincludingthebrain;italsoreadilypassesthroughtheplacentatothefetusandfetalbrain.Thereferencedose(RfD)isanamountofmethylmercury,whichwheningesteddailyoveralifetimeisanticipatedtobewithout X,'6 adversehealtheffectstohumans,includingsensitivesubpopulations.AttheRfDorbelow,exposuresareexpectedtobesafe.TheriskfollowingexposuresabovetheRfDisuncertain,butriskincreasesasexposurestomethylmercuryincrease.  ExtrapolatingfromthehighdoseexposuresthatoccurredintheIraqincident,theU.S.EPAderivedaRfDformethylmercuryof0.1microgramperkilogrambodyweightperday(g/kgbw/day).WhiletheU.S.EPAwasadvisedbyscientificreviewerstoemploythisRfDforthisanalysis,newdataareemerging.CurrentlyongoingaretwolargeepidemiologystudiesintheSeychelleIslandsandintheFaroeIslandsthatweredesignedtoevaluatechildhooddevelopmentandneurotoxicityinrelationtofetalexposurestomethylmercuryinfishconsumingpopulations.Becauseofvariouslimitationsanduncertaintiesinalloftheavailabledata,theU.S.EPAandotherFederalagenciesintendtoparticipateinaninteragencyreviewofthehumandataonmethylmercury,includingthemostrecentstudiesfromtheSeychelleIslandsandtheϢFaroeIslands.ThepurposesofthisreviewaretorefinetheestimatesofthelevelofexposuretomercuryassociatedwithsubtleneurologicalendpointsandtofurtherconsensusbetweenalloftheFederalagencies.Afterthisprocess,theU.S.EPAwilldetermineifachangeintheRfDformethylmercuryiswarranted.(Note:seethe1997EPAMercuryStudy l ReporttoCongressforfurtherdiscussionandassessmentofmercury 8 healtheffectsandpublichealthimpacts).& x ES.8.3MercuryMultipathwayExposureAssessment ,|   Mercurywasconsideredhighestpriorityformultipathway'x,r$Ԁexposureanalysis.Toassessthetransportanddepositionofmercuryemissionsfromutilitiesandtoestimateconcentrationsinenvironmentalmediaandbiota,threemodelingeffortswereundertaken:(1)longrangemodeling,(2)localscalemodeling,and(3)modelingofenvironmentalconcentrations.TheRELMAPwasusedtopredictlongrangedispersionanddepositionacrosstheU.S.Forthelocalanalysis,amodeldesignedtopredictdepositionofHAPswithin50km,theIndustrialSourceComplexVersion3(ISC3)airdispersionmodel,wasused.Next,theEPAsIndirectExposureModelVersion2M(IEM2M)wasusedtoestimatemercuryenvironmentalconcentrationsandhumanexposures.Hypotheticalexposurescenarioswereevaluatedforfourmodelplants(alargecoalfired,amediumcoalfired,asmallcoalfired,andamediumoilfiredutilityboiler).Theanalysisincludedthreetypesofplantlocations:(1)rural(agricultural),(2)nearlakes(lacustrine),and(3)urban.Threehumanfishconsumptionscenarioswereconsidered.  Themodelingprovidedinformationonwhetherlocaland/orlongrangetransportofmercuryissignificantinavarietyofscenarios.Themodelsindicatethatmostofthemercuryfromutilitiesistransportedfurtherthan50kmfromthesource.Thefateandtransportmodelsprovidedanassessmentofpotentialinhalationandingestionexposures.ES.8.4SummaryofMercuryAssessmentResultsforUtilities )$2   Recentestimatesofannualtotalglobalmercuryemissionsfromallsources(naturalandanthropogenic)areabout5,000to5,500tonsperyear(tpy).Ofthistotal,about1,000tpyareestimatedtobenaturalemissionsandabout2,000tpyareestimatedtobecontributionsthrough x,'6 thenaturalglobalcycleofreemissionsofmercuryassociatedwithpastanthropogenicactivity.Currentanthropogenicemissionsaccountfortheremaining2,000tpy.Pointsourcessuchasfuelcombustion;wasteincineration;industrialprocesses(e.g.,chloralkaliplants);andmetaloreroasting,refining,andprocessingarethelargestpointsourcecategoriesonaworldwidebasis.  Fortheyear1994,coalfiredutilitieswereestimatedtoemitapproximately51tpyofmercuryintheU.S.,whichisestimatedtobe33percentofthe158tpyofairborneanthropogenicemissionsofmercuryintheU.S.Ifoneassumesthatcurrentanthropogenicactivityrepresentsbetween40and75percentofthetotalairborneemissions(anthropogenicplusotheremissions[e.g.,naturalemissions]),onecancalculatethatU.S.utilitiesemitroughly13to26percentofthetotal(naturalplusanthropogenic)airborneemissionsofmercuryintheU.S.  Giventheglobalestimatesof5,000to5,500tpy(whicharehighlyuncertain),U.S.anthropogenicmercuryemissionsareestimatedtoaccountforroughly3percentoftheglobaltotal,andU.S.utilitiesareestimatedtoaccountforroughly1percentoftotalglobalemissions.  AcomputersimulationoflongrangetransportofmercuryemissionsfromallU.S.sourcesconductedfortheEPAs1997MercuryStudyReporttoCongresssuggeststhataboutonethird(~52tons)ofthe158tpyofU.S.anthropogenicemissionsaredeposited,throughwetanddrydeposition,withinthelower48States.Theremainingtwothirds(~107tons)istransportedoutsideofU.S.borderswhereitdiffusesintotheglobalreservoir.Inaddition,thecomputersimulationsuggeststhatanother35tonsofmercuryfromtheglobalreservoirisdepositedforatotaldepositionofroughly87tpyintheU.S.Althoughthistypeofmodelingisuncertain,thesimulationsuggeststhataboutthreetimesasmuchmercuryisbeingaddedtotheglobalreservoirfromU.S.sourcesasisbeingdepositedfromit.Whatisnotuncertainisthatadditionalemissionstoairwillcontributetolevelsintheglobalreservoiranddepositiontowaterbodies.  LongrangetransportmodelingconductedaspartofthisUtilityStudypredictsthatapproximately30percent(15tpy)oftheutilitymercuryemissionsdepositinthecontinentalU.S.Theestimatedannualdepositionratesresultingfromutilitymercuryemissionsrangefrom0.5togreaterthan10microgramspersquaremeter.LongrangetransportmodelingalsopredictsthatthehighestdepositionoccursintheeasternhalfoftheU.S.,particularlyareassuchassoutheasternGreatLakesandOhioRiverValley,centralandwesternPennsylvania,largeurbanareasintheeasternU.S.(e.g.,Washington,D.C.,NewYorkCity)andvariouslocationsinthevicinityoflargecoalfiredutilities.Basedonthelimitedavailablereceptormonitoringdata,theRELMAPmodelseemstobeaccuratewithinafactorofplusorminus2.Thatis,theϢRELMAPmodelseemstooverandunderestimatemercuryvalueswithinafactoroftwoandappearstoberelativelyunbiasedinitspredictions.  Themodelingassessmentinconjunctionwithavailablescientificknowledge,supportsaplausiblelinkbetweenanthropogenicP&د&&&دmercury#&د&&P&دp9# +&5 emissionsandmercuryfoundinfreshwaterfish.Asnotedabove,there X,'6 aremanysourcesofmercuryemissionsworldwide,bothnaturalandanthropogenic.Thecoalfiredutilitiesareonecategoryofthemercurysources.  MercuryisconsideredthehighestpriorityformultipathwayϢanalysesbecauseitisanenvironmentallypersistent,toxicelement.Mercuryisdepositedtosoilandterrestrialvegetationbutatlevelsthatdonotresultinhumanexposureslikelytobedetrimentaltohealththroughterrestrialexposurepathways.However,initsmethylatedformmercurybioaccumulatesinthefoodweb(especiallytheaquaticfoodweb).Modelingresultssuggestthatmostofthemercuryemittedtotheatmosphereisdepositedmorethan50kmawayfromthesource,especiallysourcesthathavetallstacks.Asstatedabove,themodelingassessmentfromtheMercuryStudyinconjunctionwithavailablescientificknowledge,supportsaplausiblelinkbetweenanthropogenicmercuryemissionsandmercuryfoundinfreshwaterfish.Additionalemissionstoairwillcontributetolevelsintheglobalreservoiranddepositiontowaterbodies.Asaresult,mercuryemissionsfromutilityunitsmayaddtotheexistingenvironmentalburden.  Atthistime,theavailableinformation,onbalance,indicatesthatutilitymercuryemissionsareofsufficientpotentialconcernforpublichealthtomeritfurtherresearchandmonitoring.TheEPArecognizesthattherearesubstantialuncertaintiesthatmakeitdifficulttoquantifythemagnitudeoftherisksduetoutilitymercuryemissions,andthatfurtherresearchand/orevaluationwouldbeneededtoreducetheseuncertainties.Remainingquestionsincludethefollowing:(1)whatisthequantitativerelationshipbetweenachangeinU.S.mercuryemissionsandtheresultingchangeinmethylmercurylevelsinfish;(2)whataretheactualconsumptionpatternsandestimatedmethylmercuryexposuresofthesubpopulationsofconcern;(3)whataretheactualmercurylevelsinastatisticallyvalidandrepresentativesampleoftheU.S.populationandsusceptibleϢsubpopulations;(4)whatexposurelevelsarelikelytoresultinadversehealtheffects;(5)whataffectstheformationofmethylmercuryinϢwaterbodiesanditsbioaccumulationinfish;(6)howmuchmercuryisemittedfromnaturalsourcesandpastanthropogenicsources;and(7)howmuchmercuryisremovedduringcoalcleaningandotherongoingpracticesforpollutioncontrol.Newdatathatcouldreducesomeoftheuncertaintiesarelikelytobecomeavailableinthenextseveralyears,andEPAplanstoreviewandconsiderthesedata,asappropriate,infuturedecisions.  Regardingpotentialmethodsforreducingmercuryemissions,theEPAhasnotidentifiedanydemonstratedaddoncontroltechnologiescurrentlyinuseintheU.S.thateffectivelyremovemercuryfromutilityemissions.(However,theremaybeaddoncontroltechnologiesusedinothersourcecategoriesthateffectivelyreducemercuryemissions.)Basedonavailabledata,totalmercuryremovalbyexistingPMcontroldevicesoncoalfiredutilitiesvariesconsiderably,rangingfrom0to82percentremoval(withamedianefficiencyof15percentremoval)forcoldsideelectrostaticprecipitators(ESPs),andfrom0to73percentremoval(withamedianefficiencyof8percentremoval)forfabricfilters.Also,hotsideESPsexhibitednomercurycontrol.Existingfluegasdesulfurization(FGD)unitsexhibitlimitedmercury X,'6 control,rangingfrom0to62percentremoval,withamedianremovalof23percent.ThemercurycontrolefficiencyofFGDunitsisafunctionofseveralfactorsincludingtemperature,plantconfiguration,andtypeofcoal.Pilotscalestudieshaveshownthatmercuryremovalcanbeenhancedthroughtheuseofactivatedcarboninjection.However,thelimitedresultstodateutilizingcarboninjectionareinconsistentandmoredataandresearchareneeded.Othervariouspollutionpreventionstrategies,suchascoalcleaning,haveshownsomeeffectivenessinreducingutilityemissionsofmercury.Conventionalcoalcleaningremoves,onaverage,approximately21percentofthemercurycontainedinthecoal.Also,fuelswitching,suchasswitchingfromcoaltonaturalgas,wouldresultindecreasedemissionsofmercury.ES.9SCREENINGLEVELMULTIPATHWAYASSESSMENTFORARSENIC  Arsenicisanaturallyoccurringelementfoundnormally,invariousconcentrations,insoil.Inaddition,arseniccanalsobenaturallypresentinothermedia(e.g.,variousfoodsourcesandwater).Arseniclevelshavebeenmeasuredinavarietyoffoods.Eventhoughshellfishandothermarinefoodscontainthegreatestconcentrationsoftotalarsenic,muchofthearsenicpresentinfishandshellfishexistsinthelesstoxicorganicform.Otherfoodproducts,suchasmeats,rice,andcereals,containhigherpercentages,andoftenhighertotalamounts,ofinorganicarsenic,whichistheformofprimarytoxicologicalconcern.  Arsenicisalsonaturallypresentintraceamountsincoalandoil.Whencoaloroilareburned,someofthisnaturallyoccuringarsenicisreleasedtotheatmosphere.Thequantityofarsenicreleasedfromanyutilityplantisdependentonmanyfactorsincludingtheconcentrationofarsenicinthefuel,controldeviceefficiency,andotherfactors.  Utilitiesemitabout62tpyofarsenicnationwide,about3to4percentofthetotalanthropogenicarsenicemissionsintheU.S.Becauseofitschemicalandphysicalcharacteristics,arsenicemittedtotheatmospheremaybetransportedtootherenvironmentalmedia(soilorwater),thusallowingnoninhalationexposurestooccur.&  ES.9.1ExposureModeling T!'   ItwasnotpossibletomodeleveryutilityplantforarsenicϢmultipathwayexposures.Therefore,ascreeninglevelmodelplantapproachwas'T!PԀused.Fourmodelplants(i.e.,alargecoalfired,amediumcoalfired,asmallcoalfired,andamediumoilfiredutilityboiler)weredesignedtocharacterizetypicalutilityplants.Intakingthemodelplantapproach,itwasrealizedthattherewouldbeagreatdealofuncertaintysurroundingthepredictedfateandtransportofarsenicaswellastheexposures.However,theassessmentwasusefulforestimatingpotentialrisksduetoutilityarsenicemissions.Threemodelswereusedtopredictenvironmentalarsenicconcentrationsandexposure:theRELMAP,theISC3,andtheIndirectExposureModelVersion2(IEM-2).Thesemodelswereusedtopredictthefateandtransportofarsenicemissionsandtoestimatehumanexposurestoarsenicthroughmultipleexposureroutes,includingfoodconsumption,wateringestion,andinhalation.Threebasicexposurescenarioswereconsidered:a X,'6 subsistencefarmer(adultandchild),asubsistencefisher(adultandchild),andapicachild(i.e.,achildthatingestssignificantquantitiesofsoil).Thesescenarioswereconsideredbecausetheyrepresentpossiblehighendscenariosforexposuretoarsenic.ES.9.2HealthEffectsofArsenic \   Inhalationexposuretoinorganicarsenichasbeenstronglyassociatedwithlungcancerinhumans.Humanexposuretoinorganicarsenic,viaingestion,hasbeenassociatedwithanincreasedriskofseveraltypesofcancer,includingskin,bladder,liver,andlungcancers.Oralexposuretoinorganicarsenichasalsobeenassociatedwithnoncancereffects,includingeffectstothecentralnervoussystem,cardiovascularsystem,liver,kidney,andblood.ES.9.3ApproachforEstimatingScreeningLevelArsenicRisks H    Increasedcancerriskswereestimatedforeachhypotheticalscenario,forthefourmodelplants,eachofwhichwasplacedintwodifferenthypotheticallocations(i.e.,aneasternhumidsiteandadrywesternsite).Foreachoftheexposurescenarios,exceptforthepicachild,itisassumedthatthehypotheticalpersonisexposedfor30years.Forthepicachild,itisassumedthatexposureoccursfor7years.RiskswereestimatedbymultiplyingtheestimatedintakesofarsenicbytheEPAscancerpotencyfactorforarsenic.& 4 ES.9.4ScreeningLevelArsenicRiskAssessmentResults P   Theresultsofthescreeninglevelmultipathwayarsenicexposureassessmentprovideanindicationofthepotentialhazards'4PZԀandrisksthatmayoccurduetoemissionsfromautilityplant.However,theresultsarenotapplicabletoanyparticularplant.Thereareuncertaintiesandlimitationstotheanalysis.  Exposurestoinorganicarsenicduetobackgroundlevelsandduetoemissionsfromthemodelutilityboilerswerepredictedtobemainlythroughtheingestionofgrains.Exposuretoinorganicarsenicthroughtheingestionoffishwasnotpredictedtobeamajorpathwayofexposurebecausethereisconsiderableevidencethatlittleofthetotalarsenicinfishtissueisinorganicarsenic.Soilingestionisthemajorrouteofexposuretoinorganicarsenicforthepicachild.  ES.9.4.1ArsenicCancerRisks.Thecancerrisksdueto T!' Тmultipathwayexposurestoinorganicarsenic,asestimatedinthemodelplantanalysisusinghypotheticalscenarios,duetoutilityemissionsalone(nobackground)wereestimatedtorangefrom4x107to1x104. #* Thehighestestimatedrisk(1x104)wasforapicachildassumedtobe D$+ livingatthepointofmaximumdeposition.Thearsenicemissionsfromthelargecoalfiredmodelutilityboilerattheeasternhumidsitewereestimatedtoposethishighestriskforthepicachild.Whentheriskfrombackgroundexposure(2x104)isaddedtothemaximumriskfrom 4'"/ utilityexposure,theriskforthepicachildisestimatedtobeupto3x104.The picachildisconsideredahighend,conservative (#1 scenario.  Backgroundexposureswereestimatedtodominatetheexposuresandrisksinallscenarios.Whenconsideringonlythearsenicemissionsfromthemodelutilityunits(notincludingbackground),inall X,'6 scenariositwasthelargecoalfiredunitthatwasestimatedtoposethegreatestmultipathwayrisksandthemediumcoalfiredunitwasestimatedtoposethenexthighestrisks.Thesmallcoalfiredunitandtheoilfiredunitwereestimatedtopresentlowerrisks.  ES.9.4.2UncertaintyDiscussion.Thereareuncertainties \ associatedwiththecancerriskestimatesfromarsenic.Theanalysiswasbasedonmodelplantsandhypotheticalconstructs;therefore,theresultsarenotapplicableforanyspecificutilityplant.FurtherϢanalysesareneededtobettercharacterizetherisksposedbyarsenicemissionsfromutilities.Afewuncertaintiesarediscussedhere.  Exposuretoarsenicthroughtheingestionoftaporwellwaterwasnotincludedinthisassessment.Theexposuremodelingassessmentwasbasedonamodelplantanalysis,hypotheticalscenarios,andincorporateddatawithvaryingdegreesofuncertainty.Also,thereareuncertaintiesassociatedwiththehealtheffectsdataforarsenic.Forexample,theanimalingestionstudieshavenotclearlyshownanassociationbetweenarsenicingestionexposureandcancer.ES.10DIOXINSCREENINGLEVELMULTIPATHWAYASSESSMENT  ThehighestMEIinhalationcancerriskduetodioxinemissionsfromanyutilityplantbasedontheHEManalysis(describedinsectionES.7)wasestimatedtobe1x107.TheEPAestimatesthatcoalfired P utilitiesemit0.2poundsperyear(lb/yr)ofdioxin(toxicequivalents,ϢTEQ)andthatoilfiredutilitiesemit0.01lb/yr.Theseestimatescombinedareroughly1percentofthenationwideanthropogenicdioxinemissions.However,dioxinemissionsdatawereonlyavailablefortwelveutilityplantsand42percentofthemeasurementswerebelowtheminimumdetectionlimit.Moreover,dioxinsarenotpartofthenaturallyoccuringfossilfuel.Theyareformedinhighlycomplicatedreactionswhichmayoccurwithunknownfrequencyduringcombustion.Therefore,theemissionsdatafordioxinsfromutilities,whicharethebasisofexposuremodeling,areconsideredmoreuncertainthantheemissionsdataformanyoftheotherHAPs.  Forthescreeninglevelmultipathwayanalysis,thetransport,deposition,multipathwayexposures,andhumancancerriskswereassessedforutilityemissionsofpolychlorinateddibenzopdioxins(PCDDs)andϢpolychlorinateddibenzofurans(PCDFs),collectivelyreferredtoasϢdioxins.Atmosphericdepositionofdioxinemissionscanbeimportantbecausedioxinstendtopersistintheenvironmentandbioaccumulateinthefoodweb.Environmentalpersistenceandbioaccumulation,coupledwithcarcinogeniceffectsatverylowlevels,makemultipathwayexposureanimportantconsiderationfordioxins.ES.10.1Methods 4'"/   Thebasicapproachforestimatingscreeninglevelmultipathwayexposurestodioxinswassimilartothemethodsdescribedaboveformercuryandarsenic.However,thereweresomedifferences.TheEPAsϢISCST3modelwasusedtopredictdepositionandairconcentrationsofϢdioxinswithin50kmofeachoffourmodelplants.Modelplantswereselectedtorepresentbothlargeandsmallcoalandoilfiredutilities.AmodifiedversionoftheIEMspreadsheetmodelwasusedto X,'6 estimateenvironmentalconcentrations,exposurestotheenvironmentalconcentrationsfor16hypotheticalhumanscenarios,andtheresultingcancerrisks.Pathwaysassessedincludeinhalation,dermalcontactwithsoil,andingestionofwater,soil,fish,plants,andanimals.ES.10.2Results \   Sincetheanalysiswasbasedonmodelplants,usinghypotheticalscenarios,theresultsarenotapplicabletoanyspecificplantandcontainsubstantialuncertaintiesabouttherisksduetodioxinemissions.Totalmodeledscreeninglevellifetimecancerrisksrelatedtomultipathwayexposuretodioxinsforthefourmodelplantanalysisrangedfrom1x1010to2x104.Theresultsofthisanalysisindicate    thattheexposuresandrisksduetofishconsumptionarethehighestofallpathwaysconsidered.Thehighestmodeledresultof2x104lifetime <  cancerriskwasobtainedforthesubsistencefisherexposurescenario.Inallmodeledscenarios,thenoninhalationexposureswereatleastoneorderofmagnitudelargerthantheinhalationexposures,thusdemonstratingthepotentialsignificanceofincludingmultipathwayexposureanalysisintheriskassessmentsforpollutantsthatareenvironmentallypersistentandtendtobioaccumulate.Also,unliketheresultsforarsenic,modeledexposurestodioxinsforeachpathwayexceedthebackgroundexposureestimatesfordioxins.ES.10.3UncertaintyDiscussion    Severalsensitivityanalyseswerecompletedforthescreeninglevelmultipathwayassessmentofutilitydioxinriskstoassessthereasonablenessoftheresults.Theassumptionswiththegreatestimpactonthepredictedrisktothesubsistencefisherwerethosemadeaboutthebiotasedimentaccumulationfactor.Thissensitivityanalysissuggeststhatthemodelingresultsarereasonableforascreeninglevelanalysis.& 4 ES.11MULTIPATHWAYASSESSMENTFORRADIONUCLIDES  Radionuclideemissionsfromutilitiesmayresultinhumanexposure'40_xfrommultiplepathwaysincluding:(1)externalradiationexposurefromϢradionuclidessuspendedinairordepositedontheground,and(2)internalexposurefromtheinhalationofairbornecontaminantsoringestionofcontaminatedfood.TheCAP93modelwasusedtoestimateϢmultipathwayexposuresandrisksduetoradionuclideemissionstohumanswithin50kmofall684utilities.However,thisassessmentdidnotusesitespecificdataforthenoninhalationexposureanalysis,butratherreliedonvariousgenericassumptionsandgeneralinputdata.  BasedontheCAP93modeling,667ofthe684plantsareestimatedtoposemultipathwayriskslessthan1x105.Thehighestestimated % !- ТmultipathwayradiationexposurefortheMEIduetoradionuclideemissionsfromutilitieswaspredictedtobe1.5millirems(mRems)peryear,whichisestimatedtoposeanincreasedcancerriskof3x105. '@#0 Seventeenplants(13coaland4oilfiredplants)wereestimatedtoposemultipathwayrisksbetween1x105and3x105.Theestimated h)$2 cancerincidenceintheU.S.,duetoemissionsanddispersionofϢradionuclideswithin50kmofeachutility,isestimatedtobe0.3cancerdeaths/yr.Thecancerincidenceappearstobemostlyduetoinhalationexposure.Thenoninhalationexposurescontributeonly X,'6 slightlytotheincidence.ThenoninhalationexposurepathwayshaveagreaterimpactontheMEIs,especiallyforcoalfiredplants.  Therisksduetoexposuretoradionuclidesfromutilitiesaresubstantiallylowerthantherisksduetonaturalbackgroundradiation.Theaverageexposuretonaturalbackgroundradiation(excludingradon)fortheU.S.populationhasbeenestimatedtoberoughlyabout100mRemsperyear,whichisabout67timeshigherthanthehighestexposureduetoutilityradionuclideemissions.ES.12QUALITATIVEMULTIPATHWAYEXPOSUREASSESSMENT  TheEPArecognizesthatnoninhalationexposurepathwayscouldbeimportantforadditionalHAPsthatarepersistentandtendtoϢbioaccumulate.AfewadditionalHAPsthatwerenotmodeledforϢmultipathwayexposuresarediscussedbelow.& 4 ES.12.1CadmiumandLead ,|    Cadmiumemissionsfromthevastmajorityofplants(683ofthe684plants'4,)areestimatedtoposeinhalationriskslessthan106,andthe   highestmodeledairconcentrationofleadwas200timesbelowthenationalambientairqualitystandard(NAAQS).Cadmiumandleadarepersistent,maybioaccumulate,andaretoxicbyingestion.However,sincetheemissionquantitiesandinhalationrisksarerelativelylow,theEPAdoesnotplantoconductfutureevaluationsofmultipathwayexposuresofcadmiumandleadfromutilities.ES.12.2NickelandChromium    Nickelandchromiumwerenotconsideredtobepriorityfornoninhalationexposures.Atrelativelyhighoraldoses,nickelandchromiumdocausenoncancertoxicity.However,thereareconsiderableuncertaintiesaboutthenoncancertoxicityofnickelandchromiumatrelativelylowingestiondoses(belowthetoxicthreshold).Also,itisuncertainwhethertheyposeacarcinogenicriskbyingestion.Hence,EPAdoesnotplantoassessmultipathwayexposuresfornickelandchromiumforutilities.& 4 ES.13POTENTIALIMPACTSOFHYDROGENCHLORIDEANDFLUORIDE  Noexceedancesofthehealthbenchmarks(e.g.,RfCs)forHCl'4ˆԀorHFwereidentifiedintheinhalationexposureassessment.However,emissionsofHCLandHFmaycontributetoaciddepositionand,toalesserextenttoPMfineandvisibilityproblems.Totheextentthattheseemissionsmaycontributetosuchproblems,theycouldbeaddressedthroughotherTitlesoftheAct.& 4 ES.14ALTERNATIVECONTROLANDPREVENTIONSTRATEGIES  Therearenumerouspotentialalternativecontrolstrategies'4x&ԀforreducingHAPs.Theseincludeprecombustioncontrols(e.g.,fuelswitching,coalswitching,coalcleaning,coalgasification),combustioncontrols,postcombustioncontrols(e.g.,PMcontrols,SO2controls), $*t%3 andapproachesthatpreventpollutionbyimprovingefficiencyinsupply(e.g.,promotingenergyefficiencyincombustion)ordemand(e.g.,demandsidemanagement[DSM],pollutionprevention,energy X,'6 conservation).Thedegreeoffeasibility,cost,andeffectivenessofeachofthesepotentialcontroltechnologiesvaries.Forexample,coalcleaningtendstoremoveatleastsomeofallthetracemetals,withleadconcentrationsbeingremovedtothegreatestextent(averagingapproximately55percentremoval)andmercurybeingremovedtheleast(averagingapproximately21percent).ExistingPMcontrolstendtoeffectivelyremovethetracemetals(withtheexceptionofmercury)whileFGDunitsremovetracemetalslesseffectivelyandexhibitmorevariability.Fuelswitching(e.g.,switchingfromcoaltonaturalgas)couldresultinsubstantialreductionsinHAPemissions.TherearefewexistingdatathatshowtheHAPreductioneffectivenessofDSM,pollutionprevention,andenergyconservation.Thesecontrolstrategiesneedtobeexaminedfurtherfortechnicalandeconomicconsiderations.&  ES.15OTHERISSUESANDFINDINGSES.15.1EmissionsandRisksfortheYear2010 p    Inadditiontothe1990analysis,theEPAalsoestimated'Ԁemissionsandinhalationrisksfortheyear2010.Therearesubstantialdatagapsanduncertaintiesintheprojectionstotheyear2010.However,theapproachutilizedisreasonablegiventhelimitationsofdatatocompletesuchprojections.  BasedonEPAsassessmentforthisreport,HAPemissionsfromcoalfiredutilitiesarepredictedtoincreaseby10to30percentbytheyear2010.Predictedchangesthatwereincludedinthe2010emissionsprojectionsincludetheinstallationofscrubbersforasmallnumberoffacilities,theclosingofafewfacilities,andanincreaseinfuelconsumptionofotherfacilities.However,basedonEPAsexposuremodelinganalysisfortheyear2010,theinhalationrisksin2010forcoalfiredutilitiesareestimatedtoberoughlyequivalenttothe1990inhalationrisks.Foroilfiredplants,emissionsandinhalationrisksareestimatedtodecreaseby30to50percentbytheyear2010.Multipathwayrisksfor2010werenotassessed.UtilizationofaddoncontrolstocomplywiththeacidrainprogramarenotexpectedtosignificantlyimpactonHAPemissionsduetotheirlimitednumbersandlimitedHAPcontrolefficiencyimprovement.However,ifadditionalactionsaretakentoreduceemissionsofcriteriapollutants,acidrainprecursors,orglobalwarmingcompounds(e.g.,useoffuelswitchingoraddoncontrolstoreduceSOx,NOx,and/orcarbondioxideemissions), T!' theseactionscouldresultinreductionsinHAPemissions.Forexample,ϢanalysesperformedtoassesscompliancewiththerevisedNAAQSforozoneandPMindicatethatmercuryemissionsin2010maybereducedbyapproximately16percent(11tpy)overthoseprojectedinthisreport.Otherpotential(butunknown)actions(e.g.,repowering,restructuring)mayhaveasignificantimpactonHAPemissions;however,theseunknownswerenotincludedinthe2010projection.ES.15.2PeerReview '@#0   DraftversionsofChapters1through9and13ofthisreportanddrafttechnicalsupportdocumentswerereviewedbymanynonEPAscientistsrepresentingindustry,environmentalgroups,academia,andotherparties.Chapters10,11,and12arenewchaptersproducedinresponsetomajorcommentsfromthereviewers.EPAheldascientificpeerreviewmeetingandalsoapublicmeetinginJuly1995toobtain X,'6 commentsfromreviewers.InFebruary,April,andSeptember1996,allsectionsofthedraftreportunderwentadditionalreviewbyEPA,StateandlocalAgencies,andotherFederalAgencies.Additionalreviewoccurredduring1997.TheEPAhasrevisedthereport,asappropriate,basedonthereviewerscomments.However,therewereseveralcommentsthatcouldnotbefullyaddressedbecauseoflimitationsindata,methods,andresources.Inaddition,thereweresomecommentsthatEPAdidnotagreewith.Also,thenewchapters(10to12)haveonlyundergonealimitedreview.Draftversionsofthisreport,alongwithallthecommentsreceived,havebeensubmittedtothepublicdocket(A9255)atthefollowingaddress:U.S.EPA,AirandRadiationDocketandInformationCenter,mailcode6102,401MStreet,S.W.,Washington,D.C.20460;telephonenumber(202)2607548.Materialsareavailableforpublicreviewatthedocketcenterorcopiesmaybemailed(forafee)onrequestbycallingtheabovenumber.ES.15.3IndustryReport p    IfalternativemethodsandassumptionswereusedtostudytheHAPemissionsfromutilities,theresultswouldlikelybesomewhatdifferent.Toassesstheimpactofusingalternativeassumptionsandmethods,itisusefultocomparetheEPAstudywithasimilarstudycompletedbytheEPRI.  TheEPRIpreparedareport,entitled ElectricUtilityTraceSubstancesSynthesisReport,(November1994)thatparalleledtheEPAsstudy.Manyofthesameemissionsdatawereusedandsimilarriskassessmentmethodswereutilized.TheEPRIstudyconcludedthatcancerinhalationrisksarebelow1x106forallutilities,andnoncancer  inhalationrisksarewellbelowFederalthresholdlevelsforallutilities.PopulationinhalationrisksweredeterminedbytheEPRItobeinsignificant(lessthan0.1cancercase/year).Casestudiesatfourplantsfoundthatmultimediarisks,includingmercury,arebelowlevelsofconcern.  TheEPRIsriskestimatesaregenerallysimilarto,butinseveralcaseslowerthan,thoseofEPA.Differencesbetweenthestudiesinclude:(1)EPAsuseofahigherunitriskfactorforarsenic;(2)EPAsassumptionthatnickelwascarcinogenic(EPRIassumednickelwasnotcarcinogenic);(3)EPAsevaluationofexposurebeyond50kmtoalllocationsintheU.S.(EPRIdidnotattemptthisanalysis);(4)EPRIsϢradionuclideanalysiswasbasedonseveralmodelplants,whiletheEPAevaluatedeveryplantintheU.S.;and(5)theEPRIassumedthatchromiumemissionswerefivepercentchromiumVI(thecarcinogenicform),whileEPAassumedthat11percent(forcoalfiredplants)and18percent(foroilfiredplants)werechromiumVI.Inaddition,theEPRImercurymultimediastudyconsideredonlythelocalimpactfromfourplants(notworstcase)anddidnotincludepotentialimpactsoftotalnationwideutilitymercuryemissionsandcontributionstototalenvironmentalloadings.& 4 ES.15.4PotentialEnvironmentalImpactsNotIncludedinStudy h)$2   Thereareotherpotentialenvironmentalissuesassociatedwithutilitiesnotassessedinthisreport.Theseinclude:(1)the'4h)-Ԁimpactsofcriteriapollutants(SO2,NOx,PM,carbonmonoxide,andozone)oracid +&5 rainprecursors(SO2andNOx),whicharestudiedandregulatedunder X,'6 othersectionsoftheAct;(2)anassessmentofecologicalimpactsofϢHAPs;(3)theimpactsofcarbondioxideemissionsandclimate;and(4)theimpactsresultingfromrestructuring,mining,drilling,solidwastedisposal,transmission,transportation,orotheractivitiesassociatedwithelectricpowergeneration.TheseissuesandpotentialimpactswerenotassessedbecausetheywereconsideredbeyondthescopeofthisstudyasmandatedbySection112(n)oftheAct.ES.15.5LinktoParticulateMatter     Arsenic,cadmium,chromium,lead,nickel,radionuclides,andseveralotherHAPsareemittedprimarilyasPM.Consequently,theseϢHAPsmaycontributetoPMemissionsandPMhealthconcerns,especiallyfrompoorlycontrolledcoalfiredunitsanduncontrolledoilfiredunits(abouttwothirdsofoilfiredunitsareuncontrolledforPM).ImpactsforPMwerenotaddressedinthisstudy,butarebeingstudiedunderTitleIoftheAct.IfadditionalcontrolsofPMemissionsareutilized,thiscouldresultinreductionsinHAPemissions.ES.16OVERALLTECHNICALSUMMARYANDCONCLUSIONS  Basedonavailableinformationandcurrentanalyses,theEPAbelievesthatmercuryP&د&&&دfromcoalfiredutilities#&د&&P&د#ԀistheHAPofgreatest l potentialconcernandmeritsadditionalresearchandmonitoring.Thereareuncertaintiesregardingtheextentofrisksduetomercuryexposuresincludingthosefromutilityemissions.Furtherresearchandevaluationareneededtogainabetterunderstandingoftherisksandimpactsofutilitymercuryemissions.Inaddition,furtherresearchandevaluationofpotentialcontroltechnologiesandstrategiesformercuryareneeded.  ForafewotherHAPs,therealsoarestillsomeremainingpotentialconcernsanduncertaintiesthatmayneedfurtherstudy.First,thescreeningmultipathwayassessmentsfordioxinsandarsenicsuggestthatthesetwoHAPsareofpotentialconcern(primarilyfromcoalfiredplants);however,furtherevaluationsandreviewareneededtobettercharacterizetheimpactsofdioxinsandarsenicemissionsfromutilities.Second,nickelemissionsfromoilfiredutilitiesareofpotentialconcern,butsignificantuncertaintiesstillexistwithregardstothenickelformsemittedfromutilitiesandthehealtheffectsofthosevariousforms.TheimpactsduetoHAPemissionsfromgasfiredutilitiesarenegligiblebasedontheresultsofthisstudy;therefore,theEPAfeelsthatthereisnoneedforfurtherevaluationoftherisksofHAPemissionsfromnaturalgasfiredutilities.& h ES.17AREASFORFURTHERRESEARCHANDANALYSIS  Therearemanyuncertaintiesanddatagapsdescribedthroughoutthisreport.Thissectionsummarizesseveralimportantareasinwhichfurtherresearchorscientificworkmaybeneeded.'hD$ES.17.1EmissionsDataforDioxins (#1   Emissionsdatafordioxincompoundswereavailablefromlessthan12utilityplants.Manyofthemeasurementswerenearthedetectionlimits.Therefore,therearegreateruncertaintieswiththedioxinemissionsthanfortheotherHAPs.Researchmaybeneededtogainabetterunderstandingofthedioxinemissionsfromutilitiesandthe X,'6 dioxinformation,ifany,invariousutilityboilertypes(e.g.,unitswithcoldsideorhotsideESPs).ES.17.2SpeciationofNickel 4   Therearesignificantuncertaintiesregardingtheformsofnickelemittedfromoilfiredutilitiesandtheirassociatedhealtheffects.Researchwouldbeusefultodeterminetheemissionsquantitiesofvariousnickelformsandthehealtheffectsofvariousnickelforms.ES.1.7.3MultipathwayRiskAssessment L     FurtherworkmaybeneededtobettercharacterizetherisksduetoϢmultipathwayexposuretocertainHAPs(e.g.,arsenicanddioxins).ES.17.4Local,Regional,andLongrangeTransportExposures <    Furthermodelingandevaluationmaybeneededtobettercharacterizetheimpactsoflocal,regional,andlongrangetransportofϢHAPsfromutilities.& x ES.17.5Mercury 8    Therearenumerousareasregardingmercurythatmayneedfurther'xresearch,study,orevaluation.Afewpotentialareasforfurtherstudyincludethefollowing:0  (1)0` (#(#additionaldataonmercurycontentofvarioustypesofcoal;` (#` (# 0  (2)0` (#(#improvedmethodsformeasuringmercurylevelsinwater; \` (#` (# 0  (3)0` (#(#theimpactofreducingmercuryemissionsfromcoal-fired  facilitiesonthebioaccumulationofmercuryinfish; ` (#` (# 0  (4)0` (#(#statisticallyvalidandreliableestimatesofmethylmercury  exposurelevelsintheU.S.populationandsusceptibleϢsubpopulations,asmeasuredinhumanhair; ` (#` (# 0  (5)0` (#(#theoccupational,dietaryandbehavioralfactorsthataffect " mercuryexposuresforpeoplewhoaredeterminedtobeexposedaboveathresholdofconcern; ` (#` (# 0  (6)0` (#(#thehumanhealthandenvironmentalbenefitsthatwouldbe  & expectedbyreducingmercuryemissionsfromU.S.utilities; ` (#` (# 0  (7)0` (#(#controltechnologiesorpollutionpreventionoptionsthatare ") available,orwillbeavailable,thatcouldpotentiallyreducemercuryemissionsandwhatarethecostsofthoseoptions; ` (#` (# 0  (8)0` (#(#howdootherregulations,programsandactivities(e.g.,acid x&!. rainprogram,electricityrestructuring,NAAQSs,andclimatechange)affectmercuryemissions;and ` (#` (# 0   (#(# 0  (9)0` (#(#additionaldataonmercuryemissions(e.g.,howmuchis h)$2 emittedfromvarioustypesofunits,howmuchisdivalentvselementalmercury,andhowdofactorssuchasconroldevice,fueltype,andplantconfigurationaffectemissionsandϢspeciation).X,'6` (#` (# Ї  Severaladditionaluncertaintiesandpotentialareasforfurtherresearchonmercuryarediscussedinothersectionsofthisreport.ES.17.6ProjectionstotheYear2010 4   Therearesignificantuncertaintiesandunknownsintheemissionsandriskprojectionsmadetotheyear2010(e.g.,impactofelectricityrestructuring;impactofStateeffortstoregulatesuchrestructuring;impactofanyclimatechangeabatementinitiatives).Researchandevaluationintheseareasmaybeneeded.ES.17.7EcologicalRisks  X    TheeffectsofHAPsonwildlife,endangeredspecies,andterrestrialandaquaticecosystemswerenotevaluatedinthisstudy.Althoughnotmandatedbysection112(n)(1)(A),furtherevaluationofecologicalrisksduetoHAPemissionswouldbeneededtofullyevaluatetheimpactsofutilityHAPemissions.& x ES.17.8CriteriaPollutantandAcidRainPrograms ,|    FurtherevaluationisneededtoassesstheimpactsoftheAcid'x,cRainandCriteriaPollutantprograms(e.g.,impactofrevisionstothePMfineandozoneNAAQS;impactofOzoneTransportAssessmentGroup[OTAG]activities)onHAPemissions,especiallyformercury.