Are there readily available data sources that would provide additional benchmark values?
The SIS Technical Plan identifies the most reliable benchmark values (i.e., those listed in IRIS and HEAST, interim values derived by NCEA, as well as toxicity benchmark values derived by ATSDR and CalEPA). When discussing toxicity benchmarks as part of the Phase IA screening (Section 2.2.1.2, page 2-6), EPA also proposes using the provisional approach developed by HWIR to develop interim toxicity benchmark[s] for screening purposes. This methodology should be referenced. Section 3.2.3.4 (Human Health Effect Benchmark) presents the typical hierarchy for choosing toxicity values for use in risk assessment and is therefore appropriate. The proposed benchmarks (page 3-24) for several of the 25 chemicals without benchmark values are reasonable based on chemical characteristics and erring on the side of conservatism in each case. For fluoride, using the RfD for fluorine (0.06 mg/kg/day) is valid; it is consistent with ATSDR’s MRL of 0.05 mg/kg/day for sodium fluoride (which does not appear
