§ 250.306. Ingestion numeric values.
(a) For a regulated substance which is a systemic toxicant, the ingestion numeric value for that substance was calculated using the appropriate residential or nonresidential exposure assumptions from subsection (d) according to the following equation:
(b) For a regulated substance which is a carcinogen, the ingestion numeric value for that substance was calculated using the appropriate residential or nonresidential exposure assumptions from subsection (d) according to the following equation:
(c) For a regulated substance that has both an oral reference dose and an oral cancer slope factor, the ingestion numeric value is the lower of the two numbers as calculated by the equations in subsections (a) and (b).
(d) The default exposure assumptions used to calculate the ingestion numeric values are as follows:
| Residential | Nonresidential | |||
| Term | Systemic1 | Carcinogens2 | (Onsite Worker) | |
| THQ | Target Hazard Quotient | 1 | N/A | 1 |
| RfDo | Oral Reference Dose (mg/kg-day) | Chemical-specific | N/A | Chemical-specific |
| BW | Body Weight (kg) Soil Groundwater | 15 70 | N/A | 70 70 |
| ATDC | Averaging Time for systemic toxicants (yr) Soil Groundwater | 6 30 | N/A N/A | 25 25 |
| Abs | Absorption (unitless)3 | 1 | 1 | 1 |
| EF5 | Exposure Frequency (d/yr) Soil Groundwater | 250 350 | 250 350 | 180 250 |
| ED | Exposure Duration (yr) Soil Groundwater | 6 30 | N/A N/A | 25 25 |
| IngR | Ingestion Rate Soil (mg/day) GW (L/day) | 100 2 | N/A N/A | 50 1 |
| (Footnotes on next page) | ||||
| CF | Conversion Factor Soil (kg/mg) GW (unitless) | 1 x 10-6 1 | 1 x 10-6 1 | 1 x 10-6 1 |
| TR | Target Risk | N/A | 1 x 10-5 | 1 x 10-5 |
| CSFo | Oral Cancer Slope Factor (mg/kg-day)-1 | N/A | Chemical-specific | Chemical-specific |
| Atc | Averaging Time for carcinogens (yr) | N/A | 70 | 70 |
| Ifadj4 | Ingestion Factor Soil (mg-yr/kg-day) GW (L-yr/kg-day) | N/A | 57.1 1.1 | 17.9 0.4 |
Notes:
1Residential exposure to noncarcinogens is based on childhood (ages 1-6) exposure for soil, and adult exposure for groundwater, consistent with USEPA (1991).
2Residential exposure to carcinogens is based on combined childhood and adult exposure.
3The oral absorption factor takes into account absorption and bioavailability. In cases where the oral RfD or CSF is based on administered oral dose, the absorption factor would be limited to bioavailability. The default value is 1.
4The Ingestion Factor for the residential scenario is calculated using the equation Ifadj = EDc x IRc/BWc + EDa x IRa/Bwa, where EDc = 6 yr, IRc = 100 mg/day for soils and 1 L/day for groundwater, BWc = 15 kg, EDa = 24 yr, IRa = 50 mg/day for soils and 2 L/day for groundwater, and BWa = 70 kg. The ingestion factor for the nonresidential scenario is calculated using the equation Ifadj = ED x IR/BW, where ED = 25 yr, IR = 50 mg/day for soils and 1 L/day for groundwater, and BW = 70 kg.
5In cases where the inhalation RfD or CSF is based on absorbed dose, this factor can be applied in the exposure algorithm. The default value is 1.
(e) The residential ingestion numeric value for lead in soil was developed using the Uptake Biokinetic (UBK) Model for Lead (version 0.4) developed by the EPA (U. S. Environmental Protection Agency. (1990). Uptake Biokinetic (UBK) Model for Lead (version 0.4). U. S. EPA/ECAO. August 1990, in lieu of the algorithms presented in subsections (a) and (b). Default input values are identified in Appendix A, Table 7. Because the UBK model is applicable only to children, the nonresidential ingestion numeric value was calculated according to the method developed by the Society for Environmental Geochemistry and Health (Wixson, B. G. (1991)). The Society for Environmental Geochemistry and Health (SEGH) Task Force Approach to the Assessment of Lead in Soil. Trace Substances in Environmental Health. (11-20), using the following equations:
Table 7 identifies each of the variables in this equation.
This section cited in 25 Pa. Code § 250.304 (relating to MSCs for groundwater); 25 Pa. Code § 250.305 (relating to MSCs for soil); and 25 Pa. Code § 250.310 (relating to minimum threshold MSCs).
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