(VCCEP) Tier 1 Pilot Submission for BENZENE - Tera

Table 8.2. Toxicity values for benzene: EPA default approach
Calculation of absorbed-dose noncancer reference values and cancer slope factors for benzene. Table demonstrates the range of values obtained from various
assumptions and modeling approaches.
Benzene VCCEP Submission
March 2006
Cancer Slope Factors
Noncancer Reference Values Lower-Bound Lower-Bound Upper-Bound
Unit IRIS default Alternative 3 a
TLV-Based b
Nonlinear Model Linear Model Linear Model
Initial value (air concentration) ppm -- -- 0.5 -- -- --
Initial value (air unit risk) ppm –1
-- -- -- 8.6E-05
Conversion factor 1 mg/m 3 per ppm -- -- 3.19 3.19 -- --
Initial value (air concentration) mg/m 3
0.03 0.9 1.6 -- -- --
Initial value (air unit risk) (µg/m 3 ) –1
-- -- -- 2.7E-08 2.2E-06 7.8E-06
Conversion factor 2 µg/mg -- -- -- 1,000 1,000 1,000
Inhalation rate m 3 /day 20 20 10 20 20 20
Absorption factor % 50% 50% 50% 50% 50% 50%
Body weight kg 70 70 70 70 70 70
Reference Dose [RfD] (absorbed) mg/kg-day 0.004 0.1 0.1 -- -- --
Cancer Slope Factor [CSF] (absorbed) (mg/kg-day) –1
-- -- -- 1.9E-04 1.5E-02 5.5E-02
Note: Because both the reference dose and the cancer slope factor were calculated on an absorbed-dose basis, the same value is used
Note: for all pathways (inhalation, ingestion, and dermal).
a See Table 8-1 and text for details.
b Value for adult occupational exposures, based on the ACGIH threshold limit value (TLV).
Reference Dose (absorbed) =
Cancer Slope Factor (absorbed) =
Converting units on air unit risks from ppm –1 to (µg/m 3 ) –1
8.6×10 –5
ppm
1 ppm
× × =
3.19 mg/m 3
1
1,000 µg/mg
Initial Value × Inhalation Rate × Absorption Factor
Body Weight
Initial Value × Conversion Factor 2 × Body Weight
Inhalation Rate × Absorption Factor
2.7×10 –8
µg/m 3
175