Selenium - The Risk Assessment Information System

5.2 Estimation of Dose and Calculation of the Eco-SSL
Three separate Eco-SSL values were calculated for avian wildlife, one for each of three surrogate
receptor species representing different trophic levels. The avian Eco-SSLs were calculated
according to the Eco-SSL guidance (U.S. EPA, 2003) and are summarized in Table 5.2.
Surrogate Receptor
Group
Avian herbivore
(dove)
Avian ground
insectivore
(woodcock)
Avian carnivore
(hawk)
Table 5.2 Calculation of the Avian Eco-SSLs for Selenium
TRV for
Selenium
(mg dw/kg
bw/d) 1
Food Ingestion
Rate (FIR) 2
(kg dw/kg bw/d)
Soil Ingestion
as Proportion
of Diet (P s) 2
0.290 0.190 0.139
0.290 0.214 0.164
0.290 0.0353 0.057
Concentration of
Selenium in Biota
Type (i) 2,3
(B i)
(mg/kg dw)
ln(B i) = 1.104 *
ln(Soil j) - 0.677
where i = plants
ln(B i) = 0.733 *
ln(Soil j) - 0.075
where i = earthworms
ln(B i) = 0.3764 *
ln(Soil j) - 0.4158
where i = mammals
Eco-SSL
(mg/kg dw) 4
1 The process for derivation of wildlife TRVs is described in Attachment 4-5 of U.S. EPA (2003).
2 Parameters (FIR, Ps, B i values, regressions) are provided in U.S. EPA (2003) Attachment 4-1 (revised February 2005).
3 Bi = Concentration in biota type (i) which represents 100% of the diet for the respective receptor.
4 HQ = [FIR * (Soilj * P s + B i)] / TRV solved for HQ=1 where Soil j = Eco-SSL (Equation 4-2; U.S. EPA, 2003).
6.0 ECO-SSL FOR MAMMALIAN WILDLIFE
The derivation of the Eco-SSL for mammalian wildlife was completed as two parts. First, the
TRV was derived according to the Eco-SSL guidance (U.S. EPA, 2003; Attachment 4-5).
Second, the Eco-SSL (soil concentration) was back-calculated for each of three surrogate receptor
species based on the wildlife exposure model and the TRV (U.S. EPA, 2003).
6.1 Mammalian TRV
The literature search was completed according to the Eco-SSL guidance (U.S. EPA, 2003;
Attachment 4-2) and identified 1,734 papers with possible toxicity data for selenium for either
avian or mammalian species. Of these studies, 1,532 were rejected for use as described in
Section 7.5. Of the remaining papers, 132 contained data for mammalian test species. These
papers were reviewed and the data were extracted and scored according to the Eco-SSL guidance
(U.S. EPA, 2003; Attachment 4-3 and 4-4). The results of the data extraction and review are
summarized in Table 6.1. The complete results are provided as Appendix 6-1.
Eco-SSL for Selenium 14
July 2007
2.2
1.2
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