Dames & Moore, 1999 - USDA Forest Service

Small Mammals
TRVs for representative mammals were obtained by scaling surrogate toxicity data by body size (EPA.
1993; Sample et al., 1997):
where
w = wildlife
s = surrogate
NOAELw = NOAEL (Body Weights /Body weightw)02' 7- 15
This method was used for calculating the TRVs (Table 7.2.3-48) for the little brown bat (0.055 kg body
weight), deer mouse (0.022 kg body weight) and dusky shrew (0.021 kg body weight) fiom the mouse and
rat data given in Sample et al. (1996).
Large Mammals
The scaling method works well for animals, such as bats, mice, and shrews that are approximately of the
same size, but it fails when very large differences in size exist between the surrogate and site-specific ROC.
For example, the logical extension of scaling is that shrews can withstand the highest exposures, while
elephants will be killed by the smallest exposures.
Therefore, an alternative toxicity data set was needed to supplement that provided by Sample et al. (1996) in
order to estimate TRVs for larger animals. These data sets are shown in Table 7.2.3-48 for mink (1 kg body
weight), and mule deer (60 kg body weight). For cadmium and lead, where only LOAEL values were
available as mammalian benchmarks, the NOAEL was estimated by dividing the LOAEL by 5 based on the
rationale discussed above.
7.2.33 Exposure Assessment
Aquatic ROCs
The primary aquatic ROCs are trout, benthic macroinvertebrates, and the birds and mammals that feed
upon these lower animals. NAWQC were not exceeded for arsenic, manganese, mercury, or nickel.
Therefore, these metals and organic compounds were not considered COCs for the baseline risk
assessment for aquatic ROCs.
Trout and Benthic Invertebrates
Exposure to trout and benthic invertebrates are predominated by the concentrations of metals &rid pH in the
creek surface waters.
Although trout could acquire metals through the ingestion of contaminated prey, such as benthic
invertebrates, previous studies have shown that the assimilation efficiency of the fish gut for metals is very
low (Spry et al., 1988; Handy, 1992). Therefore, toxicity was only judged by comparison with site-specific
surface water metal concentrations and the estimated toxicity values for metals concentrations causing
adverse effects on trout species (Table 7.2.3- 1 B 1, B2, and B3) such as are found in Railroad Creek.
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