An ecological effects assessment includes a description of ecotoxicological benchmarks used in the assessment, toxicity profiles for contaminants of concern, and results of the field sampling efforts. The field data may include field survey information and toxicity test results.
Ecotoxicological benchmarks represent concentrations of chemicals in environmental media (i.e. water, soil, sediment, biota) that are presumed not to be hazardous to biota. There may be several benchmarks for each medium and each endpoint species, which allows for estimation of the magnitude of effects that may be expected based on the contaminant concentrations at the site. For example, there may be a benchmark for a “no‐effect level,” a “low‐effect level,” “chronic‐effect level,” a “population‐effect level” and an “acute‐effect level.” Using all of these benchmarks will provide more information for decision makers than any one of the above.
There are few federal or state benchmarks currently available in the United States or elsewhere. Criteria that are used as benchmarks are the National Ambient Water Quality Criteria for the Protection of Aquatic Life (NAWQC) (USEPA 1986). These are ARAR, and are used as benchmarks for the fish community and other water‐column species (e.g. invertebrates such as daphnids). However, not all contaminants have these criteria. Therefore, other benchmarks are needed. Benchmarks for the fish, benthic, soil invertebrate, and plant communities, and wildlife are described briefly in Sections 5.3.3.1–5.3.3.4. The primary source of toxicity information used in the development of these benchmarks is the open literature (Risk Assessment Forum 1996, 1999).
Fish Community
The acute and chronic NAWQC or state water quality criteria are ARARs and must be used as benchmarks. However, these were developed as broadly applicable values, and thus it may be more appropriate to determine benchmarks for the geographical location and species present at the site. The literature should be reviewed for chronic values in systems similar to that at the site, whether it be a freshwater, estuarine, marine, hard‐water, or soft‐water system. Laboratory toxicity tests have been conducted on many different aquatic species for many contaminants. In fact, the aquatic system currently has the largest readily available database of contaminant concentration/effects data.
Benthic Community
There are several methods that may be used for calculating sediment benchmarks for the benthic community. For nonionic/nonpolar organic contaminants, the equilibrium partitioning approach is often employed. For inorganic contaminants, existing bulk sediment toxicity values from the literature may be used, or pore water concentrations of contaminant may be compared to existing NAWQC. Unfortunately, the database of single‐contaminant exposure/effects data for sediments is limited. The majority of the data come from contaminated sites and, therefore, multiple contaminants were present. However, sediment contamination is receiving more attention, and risk assessors and managers must stay current with respect to advances in the areas of sediment toxicology and policy.
Soil Invertebrate and Plant Communities
The plant community plays a dominant role in energy flow and nutrient cycling in ecosystems. Soil invertebrates and plants form the bases of many food webs. There is an extensive database for soil contaminants. However, the majority of endpoints used by researchers have been food crop species. While this information is crucial to human health risk assessors, it is not directly applicable to ecological risk issues. The primary literature will be the major source of toxicity information that must be used in the development of toxicity benchmarks. Soil contamination impacts on plant, invertebrate, and even microbial communities are recent important issues. Again, this is an area within ERA in which it is imperative to remain current.
Wildlife
Wildlife benchmarks are particularly complicated because wildlife may be exposed to contaminants in their drinking water, the soil around them, and in their diet (from both plant and animal sources). Therefore, wildlife benchmarks must account for these multiple exposure routes. Benchmarks may be derived for each exposure route separately (for cases where exposure is through only one route) and also for total exposure. In the case of exposures from multiple routes, a benchmark such as NOAEL or LOAEL (no/lowest observed adverse effects level) is selected and expressed as a dosage, such as milligrams of contaminant per kilogram of body weight (per day). Benchmarks for wildlife are species specific, in order to account for different species sensitivities, body weights, foraging habits, and diets. In the selection of appropriate benchmark values, the toxicological literature must be consulted, with emphasis on reproduction endpoints. Contaminant toxicity profiles assist risk assessment readers to clearly understand the toxic effects of contaminants in the environment. Toxicity profiles in a risk assessment can provide a concise summary of relevant toxicity information. It is worth repeating that the information must be relevant to the waste site and endpoints of concern. That is, the profile should not simply be a list of median lethal doses (LD50s) for rats and mice. Dose–response information should be compiled for the contaminants that are found at the site, and for the receptor species of interest there.
Toxicity profiles and biological effects data for the species of interest are also useful for helping risk assessors and risk managers evaluate the extent and magnitude of risk. Contaminant concentrations at which lethal and sublethal effects (including behavioral modifications) are observed should be presented (i.e. dose–response information). Information such as the mobility of the chemical (e.g. water solubility, soil sorption, octanol–water partition coefficient), persistence in the environment, and interactions with other contaminants will help risk managers make an informed decision and educate the public.
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