Toxicity tests single-species

U.S. EPA (U.S. Environmental Protection Agency) (1999) A review of single species toxicity tests Are the tests reliable predictors of aquatic ecosystem community responses EPA/600/R-97/114, U.S. EPA, Office of Research and Development, Washington D.C., 58 pp. 

Maltby, L., Clayton, S.A., Yu, H., McLoughlin, N., Wood R.M. and Yin, D. (2000) Using single species toxicity tests, community level responses and toxicity identification evaluations to investigate effluent impacts, Environmental Toxicology and Chemistry 19, 151-157. 

Microcosms and mesocosms are relatively expensive and time-consuming approaches, and thus may not always be appropriate to evaluate effects for many chemicals. Often, the only effects data that exist for a chemical are results from standardized laboratory single-species toxicity tests. In criteria setting there are 2... 

The concept of the most sensitive species relates the results of toxicity tests to the real world . In this way, certain species in a particular community are assessed as being most sensitive to pollutants the results of tests on single species in artificial situations are then extrapolated to predict the effects of pollutants on whole communities or ecosystems. The logic here is that if a pollutant is non-toxic to the most sensitive species, then it will be safe for the rest of the community. There are, however, some questions about the usefulness of extrapolating from simple, highly artificial, single-species toxicity tests to complex, multivariate ecosystems. 

There are two basic types of aquatic single-species toxicity tests acute and chronic. Acute toxicity tests have been the workhorse of aquatic toxicologists for many years. These tests are relatively simple, take little time, and are cost-effective. A large historical database exists for many chemicals and effluents. Acute toxicity tests are most often used to quickly screen toxicity or to determine the relative sensitivities of different test species. Mortality is the effect monitored during the test duration of 48 h (invertebrates) or 96 h (fish). In a typical acute toxicity test, 5-10 organisms are exposed under static conditions in glass test beakers to five test concentrations. A control is included. The experiments with test concentrations and control are conducted in triplicate. Daily observations are made on survival, and dead organisms are removed. 

The results of the traditional acute single-species toxicity tests conducted in the laboratory cannot be used alone to predict effects on natural populations, communities, and ecosystems. The cultural species in laboratory tests are different from those in most ecosystems. Conditions such as the size of the test species, its life stage, and nutritional state can have an effect on toxicity. Furthermore, the experimental conditions in laboratory tests cannot duplicate the complex interacting physical and chemical conditions of ecosystems, such as seasonal changes in water temperature, dissolved oxygen, and suspended solids. In addition to these environmental modifying factors, aquatic life is usually exposed simultaneously to numerous potential toxicants (mixtures). Although the toxicities of binary and ternary mixtures have been evaluated for some chemicals in laboratory toxicity tests, the resultant information has predictive limitations. 

Because of the deficiencies of single-species toxicity tests, alternative approaches are being evolved to address the structural and functional processes of an ecosystem. Multispecies tests include the use of laboratory microcosms, outdoor ponds, experimental streams, and enclosures. There are no standardized procedures for these tests. They are conducted with plant and animal species obtained from laboratory cultures and biota collected from natural sources. They can be conducted indoors or outdoors. The toxic effects, in addition to those used for single-species tests, are determined for structural parameters, such as community similarity, diversity, and density, and for functional parameters, such as community respiration and photosynthesis. Effects on these parameters are reported as the NOEC and LOEC. 

Design Parameters for Single-Species Toxicity Tests... 

The design of multispecies toxicity tests runs into a classical dilemma. If the system incorporates all of the heterogeneity of a naturally synthesized ecological structure, then it can become unique, thereby losing the statistical power needed for typical hypothesis testing. If multispecies toxicity tests are complex systems and subject to community conditioning, then the tests are not repeatable in the same sense as a single-species toxicity test or biochemical assay. 

The stressor-response profile is in some ways analogous to a dose-response curve in the sense of a single species toxicity test expanded to the community and ecosystem level. Since many of the responses are extrapolations and based on models from the molecular to ecosystem level it is important to delineate the uncertainties, qualifications, and assumptions made at each step. 

Cairns, J. 1984. Are single species toxicity tests alone adequate for estimating environmental hazard Environ. Monitor. Assess. 4 259-273. 

Selected Ecotoxicological Benchmarks for Energetic Materials Established in Standardized Single-Species Toxicity Tests with Terrestrial Plants... 

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