The development of media-specific ecological values for risk assessment includes the derivation of acceptable levels of exposure for terrestrial wildlife (e.g., birds, mammals, reptiles, and amphibians). Although the derivation and subsequent application of these values can be used for screening purposes, there is a need to identify toxicological effects thresholds specifically for making remedial decisions at individual contaminated sites. A workshop was held in the fall of 2012 to evaluate existing methods and recent scientific developments for refining ecological soil screening levels (Eco-SSLs) and improving the derivation of site-specific ecological soil clean-up values for metals (Eco-SCVs). This included a focused session on the development and derivation of toxicity reference values (TRVs) for terrestrial wildlife. Topics that were examined included: methods for toxicological endpoint selection, techniques for dose-response assessment, approaches for cross-species extrapolation, and tools to incorporate environmental factors (e.g., metal bioavailability and chemistry) into a reference value. The workgroup also made recommendations to risk assessors and regulators on how to incorporate site-specific wildlife life history and toxicity information into the derivation of TRVs to be used in the further development of soil cleanup levels.
Behavioral responses of the common stream‐dwelling operculate snail Elimia clavaeformis were used to provide information about streamwater quality in in situ tests. These snails were found to be advantageous for such tests because they can be collected easily, individually marked, and transferred to other stream sites for release and recapture experiments.
In noncontaminated stream sites, Elimia tended to disperse upstream. The rate of net movement was variable, but typically ranged from 0.5 to 5 m/d. Water velocity and food level influenced the movement patterns of the snails in 24‐ and 48‐h field experiments in noncontaminated stream sites. Rates of movement in the laboratory were temperature dependent, and increased from about 1.0 cm/min at 9°C to 2.2 cm/min at 24°C.
In contaminated streams, snails showed clear evidence of stress: They moved downstream, and in some sites either withdrew into the shell or were unable to retract the foot or attach to a substrate. The maximum distance that Elimia traveled downstream in 24 h in a contaminated stream site was 17.5 m.
In laboratory streams, Elimia moved downstream when exposed to 0.02 mg/L total residual chlorine (TRC); the time required to immobilize these snails declined rapidly as TRC concentration increased. Behavioral characteristics of snails that may be useful for water quality assessments include turnover time (the time needed for a snail to right itself after being turned onto its back), the rate and direction of dispersal or immobilization.
Field studies, laboratory experiments and theoretical calculations were used to estimate the ecological risk caused by the release of toxic organic compounds from the Baird and McGuire Superfund hazardous waste site to the Cochato River, a small river in eastern Massachusetts. The results from the field studies, which included (a) direct measurements of chemical concentrations in sediments and fish tissues; (b) direct measurements of chemical concentrations in dialysis bags filled with hexane and placed in the river; and (c) taxonomic surveys at stations upstream of, adjacent to and downstream of the site, were compared to the results from laboratory tests and computer models, which included (d) toxicity bioassays, (e) toxicity quotients based on the U.S. Environmental Protection Agency's interim sediment quality criteria, and (f) estimates of bioaccumulation using equilibrium and fugacity models. The resulting patchwork of confirmatory and contradictory findings highlights the limitations of available theoretical and laboratory methods and cautions against reliance on any single method of quantifying stress to aquatic ecosystems.
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