Chapter 7 Ecotoxicity testing

Abstract

Ecotoxicity tests are required in the context of national legislation and regulation of pesticides, other chemicals and environmental quality. Among the OECD (Organisation for Economic Cooperation and Development) countries the requirements differ only marginally as do also the current guidelines for the conduct of ecotoxicity tests. Ecotoxicity testing can be divided in lower-tier and higher-tier testing. In lower-tier tests single cohorts of a test species from different trophic levels and environmental compartments are examined in the laboratory under standardised conditions. International standards and guidelines have been developed by CEN (Comité Européen de Normalisation), ISO (International Organization for Standardization) and OECD. Depending on the selected test, the effect of the test material on one to several endpoints is investigated, mainly variables of survival, reproduction, growth and metabolism. The special characteristics , endpoints considered and problems of current lower-tier tests are described and discussed. Mainly two statistical designs are performed: the point-estimation approach to compute the EC x (effective concentration for an effect of x%) as toxicity parameter and the hypothesis-testing approach to determine the NOEC (no-observed effect concentration). Sometimes a so-called limit test is conducted, in which the effect of only one high concentration is investigated and statistically tested. Hypothesis testing is problematic since there is often the danger of a false-negative result, i.e. statistical test reveals “no effect” but there is one. Therefore, the hypothesis-testing approach has been increasingly criticised during the past decade, so that OECD and ISO decided on a phasing-out of the NOEC as toxicity parameter, which at this point appears to be not followed unequivocally. In higher-tier testing more flexible and complex ecotoxicity tests are performed, a standardisation of which is impossible. They are required if a chemical substance fails to meet the trigger values in lower-tier risk assessment. These tests range from experiments with additional species, populations, small communities in the laboratory to larger-scaled outdoor mesocosms. The general aim is to research fate and effects of a test substance under more realistic environmental conditions, i.e. fate processes can take place and the tested populations of the test community undergo biotic and abiotic interactions.