Revisiting the avian Eco-SSL for lead: Recommendations for revision

The avian ecological soil screening level (Eco-SSL) for lead (11 mg/kg) is within soil background concentrations for >90% of the US. Consequently, its utility as a soil screening level is limited. Site-specific ecological risk-based remedial goals for lead are frequently many times greater. Toxicity reference values (TRVs) play a major role in defining Eco-SSLs. The lead Eco-SSL TRV is driven by reduced egg production in Japanese quail (Coturnix japonica), which displays effects at doses both substantially lower and greater than other tested species. High variability in egg production in Japanese quail has also been observed for other contaminants. Japanese quail egg production may therefore be to variable and unreliable an effect endpoint upon which to base regulatory screening criteria. Toxicity data supporting the Eco-SSL were re-evaluated and only studies reporting both no and lowest observed adverse effect levels (NOAELs and LOAELs) for reproduction, growth, or survival were considered. Dose-response data were extracted from 10 studies both as concentrations and doses. Dose-response relationships were developed using the USEPA Benchmark Dose Software for dietary concentrations and doses for egg production in Japanese quail and chickens. Effect levels (of 10%, 20%, and 50%) were extracted from the dose-response analyses. Species sensitivity distributions and dose-response data indicated reproduction was most sensitive to lead and survival was least sensitive, with growth intermediate. Limited data for ringed turtle doves (Streptopelia risoria) and American kestrels (Falco sparverius) suggests lower sensitivity than chickens to lead. ED10 and ED20 thresholds for chickens were 4.4 and 9.8 mg/kg/d, respectively. Avian lead Eco-SSLs were recalculated based on the chicken ED10 and ED20, with and without a bioavailability adjustment. Revised avian lead Eco-SSLs for the most highly exposed species (American woodcock), based on the ED10 and assuming 100% and 50% bioavailability, were 36.3 mg/kg and 43.7 mg/kg, respectively.