CADDIS Volume 2: Sources, Stressors & Responses
Unspecified Toxic Chemicals
A causal analysis of toxic chemicals may benefit from information concerning the characteristic effects of commonly occurring toxic chemicals and the concentrations at which they occur, even if there is uncertainty about the identity of the specific chemicals involved. U.S. EPA's ambient water quality criteria documents provide access to high quality data and narrative summaries for many chemicals that have caused adverse effects on aquatic life.
Since the early 1980's, U.S. EPA has been developing ambient water quality criteria designed to protect aquatic organisms from harmful exposure to chemicals. These water quality criteria documents are valuable sources of exposure-response information for aquatic organisms, and each contains a comprehensive review of the aquatic toxicity literature for that particular chemical at the time of publication. The aquatic toxicity data used to derive the criteria are screened to ensure they meet certain toxicity test practices and data quality objectives. More information on how data are screened can be found in U.S. EPA (1991). Finally, the toxicity data contained in the criteria documents are arrayed from least sensitive to most sensitive, which is useful for comparing the effects on species in the field to relative sensitivities in the laboratory. Additional attributes of these documents include:
- Acute and chronic toxicity data conforming to standard test durations and endpoints in separate tables for freshwater and saltwater animals. [Acute toxicity data usually reflect severe endpoints from short-term exposures (e.g., 2- to 4-day LC50s or EC50s). Chronic toxicity data usually reflect exposure over all or part of an organism's life cycle and include sublethal (e.g., growth, reproduction, development) and lethal (survival) endpoints.]
- Data on chemical toxicity to aquatic plants (algae, macrophytes) and on bioaccumulation in aquatic organisms.
- Discussions of the environmental chemistry of the chemical, speciation, best measures of the chemical in water, and relative sensitivities of species.
Since most of the toxicity data contained in the criteria documents reflect exposures to a single chemical under standardized conditions in the laboratory, caution should be exercised when comparing such data to effects on organisms in the field, because other factors may increase or decrease a chemical's toxicity in the natural environment. Older criteria documents should be supplemented by more recent publications.