The scientific basis of bioassays

Abstract

The ultimate goal of ecotoxicological testing is to predict ecological effects of chemicals and other stressors. Since damage should be avoided rather than corrected after it occurs, the predictive value of such tests is crucial. A modest base of evidence shows that, in some cases, extrapolations from bioassays on one species to another species are reasonably accurate and, in other cases, misleading. Extrapolations from laboratory bioassays to response in natural systems at the population level are effective if the environmental realism of the bioassay is sufficiently high. When laboratory systems are poor simulations of natural systems, gross extrapolation errors may result. The problem of extrapolating among levels of biological organization has not been given the serious attention it deserves, and currently used methodologies have been chosen for reasons other than scientific validity. As the level of biological organization increases, new properties are added (e.g., nutrient cycling, energy transfer) that are not readily apparent at the lower levels. The measured responses (or end points) will not be the same at all levels of biological organization, making the validation of predictions difficult. Evidence indicates that responses of ecologically complex laboratory systems correspond to predicted and documented patterns in stressed ecosystems. The difficulties of improving the ecological evidence used to predict adverse effects are not insurmountable since the essence of predictive capability is the determination of effects thresholds at all levels of organization. The dilemma between basing predictive schemes on either traditional or holistic methods can only be solved by facing scientific and ethical questions regarding the adequacy of evidence used to make decisions of environmental protection.'When very little is known about an important subject, the questions people raise are almost invariably ethical. Then as knowledge grows, they become more concerned with information and amoral, in other words more narrowly intellectual. Finally, as understanding becomes sufficiently complete, the questions turn ethical again. Environmentalism is now passing from the first to the second phase, and there is reason to hope that it will proceed directly on to the third.' E. O. Wilson, 'The Conservative Ethic ', 1984

Comparative ecotoxicity of suspended sediment in the lower Rhone River using algal fractionation, Microtox® and Daphnia magna bioassays

“…It is recognized that ecotoxicological testing needs to be based on standard test organisms and to be supplemented by the use of some ambient bioassay. Furthermore a battery of tests should be used in order to ensure that the 'no effect level' in one test will also be discriminated at several trophic levels (Nebecker et al, 1984;Cairns & Pratt, 1989;Dutka et al, 1989;Sloterdijk et al, 1989;Giesy & Hoke, 1989). In this paper we concentrate on the ecotoxicity associated with suspended sediments of the Rhone River as determined by three acute bioassay procedures.…”

Freshwater Invertebrate Toxicity Tests

“…filtration rate, respiration, behaviourl and the conventional test criteria (reproduction, survival, growth) can be established. If a scientific framework (Cairns & Pratt, 1989) for the development of new bioassays is followed, we feel that biochemicallGeisy & Graney, 1989) and physiological (Calow & Sibly, 1990) test criteria in bioassays with invertebrates (as well as with vertebrates) could become very important in toxicity evaluations. This is especially so for the monitoring of industrial effluents and waste waters, where speed is (sometimes) very important.…”

Simplified models to analyse time- and dose-dependent responses of populations to toxicants

“…Given that the internal dose of a chemical is what determines its toxicity, and since it takes time for the compound to penetrate into the organism, time of exposure is a factor essentially linked to effective toxic doses (Newman 1998). Although this principle is well understood, ecotoxicologists have interpreted it in a curious way in order to standardise toxicity bioassays: the time of exposure is arbitrarily fixed and suited to the various kinds of organisms tested (Buikema et al 1982;Cairns and Pratt 1989). Thus, by removing the time variable, toxicity has practically been redefined by the median lethal (LC 50 ) or effective concentrations (EC 50 ) and other endpoints (e.g.…”