Single-species testing

Pontasch et al. [182] summarize the shortcomings of single species tests as follows ... 

Extrapolation from individuals in single species tests to populations... 

In discussing the developments and applications of bioassays to liquid media and to sediments, we have placed some emphasis on the types of chemicals and environmental samples that have been appraised, on the types and frequency of biotic level(s) employed, as well as on the relative use of single species tests as opposed to test battery approaches. 

Whether TT (toxicity testing with single species tests at the same biotic level) or TBAs are performed, some test organisms have been more frequently used than others (Tab. 5). Invertebrates have been the most commonly employed, as had been pointed out in an earlier literature survey conducted between 1979 and 1987 (Maltby... 

Total number of single species tests reported in the 188 papers classified in Tables 1-3 (= sum of number of A, B, Bi, F, Fc, I, L, P, PI, S tests indicated in the Biotic levels employed column). 

Environment Canada (1999) Guidance document on application and interpretation of single-species tests in environmental toxicology, Report EPS l/RM/34, Environment Canada, Ottawa, 203 pp. 

Traunspurger, W., Schafer, H. and Remde, A. (1996) Comparative investigation on the effect of a herbicide on aquatic organisms in single species tests and aquatic microcosms, Chemosphere 33 (6), 1129-1141. 

Environment Canada. (1999) Guidance Document on Application and Interpretation of Single-species Tests in Environmental Toxicology. Environmental Protection, Conservation and Protection, Environment Canada. Ottawa, Ontario, Reference Method EPS l/RM/34. 

Single-species-tests (single-species-testing, both traditional tests and tests modified to include ecosystem and pollutant realism are needed). 

The physiological responses of species related to the presence of the chemical. (This Is traditional single-species testing (14) but with some additional tests to improve ecological and pollutant realism.)... 

Single species tests and tests using bioassay batteries are called lower-tier tests.19 But in order to carry out a more stringent examination of the complex interactions between potentially toxic chemical compounds and organisms inhabiting specific ecosystems, experiments are sometimes carried out in microcosms and mesocosms the literature describes these as higher-tier tests.19... 

On a higher level, laboratory single-species tests can provide useful information to predict effects on natural populations because they describe how toxicological effects are translated into ecological currency (maturation, reproduction, and mortality). Many major taxa, however, remain poorly studied (e.g., soil fauna and snails), and the role of tested species for the ecosystems to be protected is generally unknown. 

Given the reviewed data, the first issue relevant for mixture extrapolation is whether extrapolation can be justified at all over no mixture extrapolation, in which separate responses only are assumed. In our opinion, the single-species test data are sufficiently clear to suggest that mixture extrapolation is preferred over no extrapolation. Although some exceptions exist (e.g., low effect range and specific compound mixtures), the majority of studies (aquatic and terrestrial) generally concluded that concentration addition is a reasonable conservative approximation of mixture responses. Indeed, the species-level experimental data we have reviewed clearly... 

Single-species test result to population Populations to community Risk quotient concentration addition Empirical... 

Prediction of responses Single-species test result Complex models (life stage, IBM, 4.3.2... 

There is a wide spectrum of these microcosm and mesocosm higher-tier test systems available, from laboratory microcosms to outdoor mesocosms, enclosures, and artificial streams (ECETOC 1997). Fish are usually not included, and this is a problem if single-species tests suggest that fish are more sensitive than algae or invertebrates (Girling et al. 2000). 

Historically, the United Kingdom and some other regulatory authorities have based EQS values on single-species tests and only used mesocosm data as corroborative evidence. Under the WFD, however, mesocosm no-effect data have recently been used directly to set a freshwater EQS for chlorpyrifos in the European Union, and similar action has been taken for atrazine in the United States (USEPA 2003a). It is clear that such data are more relevant to the natural environment than laboratory-based single-species tests. 

The fact that chemicals can be so selective makes it difficult to extrapolate toxicity data from one species to another. For practical reasons, it is possible to perform toxicity tests only on a very limited number of species. Multiple-species tests represent a more sophisticated approach to ecotoxicity testing than do single species tests, but they are at an early stage of development. 

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