Dames & Moore, 1999 - USDA Forest Service

Concentrations of PCOCs in other media, such as vegetation, aquatic insects.
earthworms, and small mammals, were accounted for by modeling.
In summary, the exposure pathways that are potentially complete at these sites and that will be
quantitatively considered in this ERA are:
Surface water to benthic organisms and fish
Sediment to benthic organisms and fish
Soil to terrestrial vegetation
Soil to other terrestrial receptors
Vegetation to terrestrial herbivores and omnivores
Terrestrial and aquatic biota to upper trophic level consumers
7.2.2.4 Sentinel, Indicator, and Surrogate Species - The Guild Approach
Receptor guilds (organisms with similar life histories or niches in the environment) have been used rather
than individual species for.this assessment because the general characteristics of each guild will provide risk
estimates that are representative of the entire guild. As such, these can be extrapolated more broadly than
single species estimates. The underlying concept is that each receptor of particular concern falls into a
group of potential receptors that function in similar ecological niches ("guilds"). For example, many species
of hawk feed on small mammals and require trees or cliffs for roosts. As such, each of these hawks display
similar life-histories and would be anticipated to have similar exposures to PCOCs at the sites. A single
surrogate, for example the red-tailed hawk, for which good life-history information, or toxicological data is
available, may be used for modeling purposes and results may be extrapolated to the "mammal-eating hawk
guild" as a whole. This allows the risk assessment models to directly evaluate species for which the best
exposure information is available, but allows results to be extrapolated to a broader range of potential
receptors, thereby maximizing data usage and applicability of results.
Representatives in each identified receptor guild and trophic level are selected below. The fundamental
assumption is that if the surrogate receptor is protected, the entire guild is protected. Deviations from this
assumption are discussed further in the uncertainty section of this report.
7.2.2.5 Selection of ROCs: Guild Representatives
The broadest classifications of receptors selected for this ERA are aquatic and terrestrial plants and animals.
Of the animals, fish, mammals, and birds are the three most prominent general groups at the site. Fish,
using salrnonids as representative species, were selected as an ROC because they are an important valued
resource and because they may provide food for certain birds and mammals, as well as recreation for
humans. Benthic insects were also selected as ROCs because they are important food items for fish and
some birds. Although periphyton is an important component of aquatic food chains, there are only a few
reports of the effects of metals on these communities. Therefore, this trophic level will only be discussed
briefly and qualitatively.
Although amphibians may exist at the site, and may be at risk from metals contamination, there is very little
toxicological data for these animals. The available mean toxicity data for amphibians exposed to cadmium,
& MOORE
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17693-005-019Uuly 27.1999,5:16 PM;DRAFT FlNAL RI REPORT
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