PRINCIPLES OF TOXICOLOGY - Biology East Borneo

488 EXAMPLE OF RISK ASSESSMENT APPLICATIONSTABLE 19.5 Arsenic Risk Assessment Example: Typical USEPA ReasonableMaximum Exposure Soil Exposure Parameters aExposure Parameter Value ReferenceABSgi 0.28 Freeman et al. (1995)ABSsk 0.001 USEPA (1995)AF 0.2 mg/cm 2 USEPA (1997)ATnc8760 days (adult); USEPA (1991)2190 days (child)ATc 25,550 days USEPA (1991)BW70 kg (adult);USEPA (1991)15 kg (child)CA 1.8 × 10 –7 mg/m 3 Modeled air concentrationCS 90 mg/kg Site-specific average arsenicconcentration in soilED24 years (adult); USEPA (1991)6 years (child)EF 350 days/year USEPA (1991)IR100 mg/day (adult) USEPA (1991)200 mg/day (child)SA2900 (adult)USEPA (1997)1000 (child)VR20 (adult)10 (child)USEPA (1997)a Note: USEPA typically assumes 80–100 percent bioavailability for arsenic in soil. Therefore, theUSEPA default value for ABS gi is 0.8–1.The calculated HI is rounded to one significant figure. Because the HI does not exceed one,arsenic exposure would be unlikely to cause noncancer effects. However, even if the HI valueslightly exceeded one, this is would be unlikely to be of significant health consequence. This isparticularly the case since the oral RfD for arsenic is based on a no-observed-adverse-effect level(NOAEL) in humans of 8 × 10 –4 mg/kg⋅day. As stated by the USEPA, a case can be made forsetting the oral RfD as high as the NOAEL. The USEPA adjusted the NOAEL downward usingan uncertainty factor of 3 to account for uncertainty associated with an incomplete databaseregarding the noncarcinogenic effects of arsenic.Note that if calculated for the adult, the HI for exposure to arsenic in soil would be lowerbecause a child is exposed to more soil than an adult when dose is calculated on the basis of bodyweight.TABLE 19.6 Arsenic Risk Assessment Example: Calculated Daily Exposure (in mg/kg) to Arsenic inResidential SoilChild ResidentAdult ResidentExposure Pathway ADI a LADI b ADI LADIIngestion 3.22 × 10 –4 2.76 × 10 –5 3.45 × 10 –5 1.18 × 10 –5Skin absorption *1.15 × 10 –6 *9.86 × 10 –8 ∗7.15 × 10 –7 *2.45 × 10 –7Inhalation 1.06 × 10 –7 9.05 × 10 –9 3.46 × 10 –8 1.19 × 10 –8a Average daily intake.b Lifetime average daily intake.c Expressed as an absorbed dose rather than a daily intake.