Transcript RECAP
RECAP Addressing Exposure to Multiple Constituents that Elicit Noncarcinogenic Effects on the Same Target Organ/System Assumption of Dose Additivity: Carcinogens 1. Multiple chemicals: RiskT = Riski 2. Multiple exposure pathways: Total Exposure Cancer Risk = Riskpathway1 + Riskpathway2 + … + Riskpathwayi RAGS-A EPA 1989 Carcinogens and the RBCA Approach • A target risk level of 10-6 for individual chemicals and pathways generally will lead to a cumulative risk within the 10-6 to 10-4 range (SSG 1996) • Total Exposure Cancer Risk should be < 10-6 to 10-4 • Risk = EC1/RS1 + EC2/RS2 + … + ECi/Rsi X TR Assumption of Dose Additivity: Noncarcinogens 1. Multiple chemicals: Hazard Index = E1/RfD1 + E2/RfD2 + … + Ei/RfDi 2. Multiple exposure pathways: Total Hazard Index = HIpathway1 + HIpathway2 + … + HIpathwayi RAGS-A EPA 1989 Assumption of Dose Additivity: Noncarcinogens • Simultaneous subthreshold exposures to multiple noncarcinogenic chemicals could result in an adverse health effect • Only applicable to noncarcinogenic chemicals that affect the same target organ/critical effect (RfD) RAGS-A EPA 1989 Noncarcinogens and the RBCA Approach • No acceptable risk “range” • When multiple chemicals and/or pathways are present, target HQ should be adjusted so that the Total HI < 1.0 • Total HI = EC1/RS1 + EC2/RS2 + … + ECi/RSi MO-1 and MO-2 RS • Represent an acceptable exposure level for exposure to a single chemical via a single medium • Do not address additivity due to exposure to multiple chemicals or multiple exposure media • RS do address exposure via multiple pathways MO-1 and MO-2 RS • Risk-based RS must be adjusted to account for potential additive effects » Soilni, Soili, Soiles » GW1, GW2, GWes • Not applicable to SoilGW, Soilsat, GW3, Watersol, background levels, quantitation limits, MCLs, ceiling values MO-1: Accounting for Additivity Modification of risk-based MO-1 RS: » group noncarcinogenic chemicals by target organ/critical effect MO-1: Accounting for Additivity 1. Identify the target organ/critical effect for each noncarcinogenic chemical (RfD) » http://www.epa.gov/iris/subst/index.html 2. Group the chemicals by target organ/critical effect 3. Divide the RS by the number of chemicals affecting the same target organ MO-1: Accounting for Additivity Example Chemical A B C D Target Organ kidney kidney, liver CNS kidney RS 24 15 10 60 Adjusted RS 8 5 20 Divide the RS for A, B, and D by 3 (kidney) (Same as calculating a RS using a THQ of 0.33) Additivity - MO-1 If many noncarcinogenic COC are present: Adjust NC RS to account for additivity Compare adjusted NC RS to C RS and choose the lower of the two NC RS presented in Appendix I Worksheets MO-2: Methods for Accounting for Additivity Modification of risk-based MO-2 RS: » group by target organ/critical effect » site-specific apportionment of RS or THQ » calculation of a total HI for each target organ MO-2: Additivity Example: Site-specific apportionment COC Target THQRS THQRS A B C 0.33 0.33 0.33 kidney 1.0 kidney 1.0 kidney 1.0 Total HI 3.0 2 90 120 1.0 THQRS 0.67 0.8 30 0.1 40 0.1 1.0 1.6 9 12 MO-2 Additivity Example: Calculation of a THI for Each Target Organ THIkidney = ECA/RSA + ECB/RSB + ECc/RSc where: EC = exposure concentration RS = RECAP Standard THIkidney = 1/1.6 + 0.5/9 + 3/12 = 0.93 THI must be < 1.0 MO-3B: Accounting for Additivity Modification of risk-based MO-3 RS: » site-specific apportionment of RS or THQ » calculation of a total HI for each target organ/effect » group by target organ/critical effect Additivity Exposure to Multiple Media • If there is exposure to chemicals via more than one medium, then RS must be modified to account for additivity • Applicable only to MO-2 and MO-3 • MO-2 Example: a receptor is being exposed to chemicals via drinking water (GW1 or GW2) and soil Additivity: TPH Fractions Aliphatics C>6-C8 Aliphatics C>8-C16 (C>8-C10, C>10-C12, C>12-C16) Aliphatics C>16-C35 Aromatics C>8-C16 (C>8-C10, C>10-C12, C>12-C16) Aromatics C>16-C35 Additivity: TPH Additivity - TPH RS based on 10,000 cap Do not adjust 10,000 cap Identify risk-based value in Appendix I worksheets or calculate Adjust risk-based RS to account for additive effects If adjusted risk-based RS < 10,000, use risk-based RS If adjusted risk-based RS > 10,000, use 10,000 cap Additivity: TPH Fractions Example Soil: ethylbenzene, aliphatics C>8-C10, C>10-C12, C>12-C16 Id of targets: ethylbenzene: liver, kidney, developmental aliphatics C>8-C10: liver, hematological system aliphatics C>10-C12: liver, hematological system aliphatics C>12-C16 : liver, hematological system C>8-C16 Additivity - Liver: ethylbenzene and aliphatics C>8-C16 Adjustment factor: 2 NOT 4 Additivity: TPH Fractions Example (cont’d) Adjustment of MO-1 Soilni: ethylbenzene: 1500/2 = 750 mg/kg aliphatics C>8-C10: 1100/2 = 550 mg/kg aliphatics C>10-C12: 2100/2 = 1050 mg/kg aliphatics C>12-C16 : 3100/2 = 1550 mg/kg MO-1 Additivity Example for Soil Table 2 - Gasoline release COC MO-1 Soilni benzene --ethylbenzene 1500 toluene 690 xylene 12,000 aliphatics C6-8 --aliphatics C8-10 1100 aliphatics C10-12 2100 aromatics C8-10 610 aromatics C10-12 1000 Target Organ/Effect --liver, kidney, develop. liver, kid., CNS, nas.epi. activity, bw,mort. kidney liver, hematol. sys. liver, hematol. sys. bw bw MO-1 Additivity Example for Soil Table 2 - Gasoline release Summarize by target organ: (3) liver: ethylbenzene, toluene, aliphatics C8-12 (3) kidney: ethylbenzene, toluene, aliphatics C6-8 (1) developmental: ethylbenzene (1) CNS: toluene (1) nasal epithelium: toluene (1) hyperactivity: xylene (2) bw: xylene, aromatics C8-12 (1) mortality: xylene (1) hematological system: aliphatics C8-12 MO-1 Additivity Example for Soil Table 2 - Gasoline release COC benzene ethylbenzene toluene xylene aliphatics C6-8 aliphatics C8-10 aliphatics C10-12 aromatics C8-10 aromatics C10-12 Adjusted MO-1 Soilni --1500 3 = 500 (liver) 690 3 = 230 (liver) 12,000 2 = 6,000 (bw) --1100 3 = 367 (liver) 2100 3 = 700 (liver) 610 2 = 305 (bw) 1000 2 = 500 (bw) MO-1 Additivity Example for Soil Table 2 - Gasoline release Identification of the limiting soil RS: COC benzene ethylbenzene toluene xylene aliphatics C6-8 aliphatics C8-10 aliphatics C10-12 aromatics C8-10 aromatics C10-12 *based on a DF3 of 440 Soilni 1.5 500 230 6000 10,000 367 700 305 500 SoilGWDW* 4.8 29,040 52,800 79,200 10,000 10,000 10,000 10,000 10,000 Soilsat 900 230 520 150 NA NA NA NA NA MO-1 Additivity Example for GW Table 3 - Gasoline release COC MO-1 GW1 benzene --ethylbenzene --toluene --xylene --aliphatics C6-8 32 aliphatics C8-10 1.3 aliphatics C10-12 1.4 aromatics C8-10 0.34 aromatics C10-12 0.34 Target Organ/Effect --liver, kidney, develop. liver, kid., CNS, nas.epi. activity, bw, mortality kidney liver, hematol. sys. liver, hematol. sys. bw bw MO-1 Additivity Example for GW Table 3 - Gasoline release Summarize by target organ: (3) liver: ethylbenzene, toluene, aliphatics C8-12 (3) kidney: ethylbenzene, toluene, aliphatics C6-8 (1) developmental: ethylbenzene (1) CNS: toluene (1) nasal epithelium: toluene (1) hyperactivity: xylene (2) bw: xylene, aromatics C8-12 (1) mortality: xylene (1) hematological system: aliphatics C8-12 MO-1 Additivity Example for GW Table 3 - Gasoline release COC benzene ethylbenzene toluene xylene aliphatics C6-8 aliphatics C8-10 aliphatics C10-12 aromatics C8-10 aromatics C10-12 Adjusted MO-1 GW1 --------32 3 = 11 (kidney) 1.3 3 = 0.43 (liver) 1.4 3 = 0.47 (liver) 0.34 2 = 0.17 (bw) 0.34 2 = 0.17 (bw) MO-1 Additivity Example for GW Table 3 - Gasoline release Identification of the limiting GW RS: COC benzene ethylbenzene toluene xylene aliphatics C6-8 aliphatics C8-10 aliphatics C10-12 aromatics C8-10 aromatics C10-12 GW1 0.005 0.7 1 10 11 0.43 0.47 0.17 0.17 Watersol 1800 170 530 160 NA NA NA NA NA Additivity: GW1 and GW2 Include all NC COC when identifying targets If no current exposure: Adjust GW1 or GW2 RS based on NC effects Do not adjust GW1 or GW2 RS based on MCL Additivity: GW1 and GW2 If exposure is occurring: Adjust GW1 or GW2 RS based on NC effects For GW1 or GW2 RS based on MCL: 1. Calculate GW1 or GW2 RS for NC effects (Appendix I or J) 2. Adjust RS to account for additivity