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Rapid microscale toxicity tests make it possible to screen large numbers of compounds and greatly simplify toxicity identification evaluation and other effect directed chemical analyses of effluents or environmental samples. Tests using Vibrio fischeri (such as Microtox®) detect toxicants that cause non-specific narcosis, but are insensitive to other important classes of contaminants. The microbial assay for risk assessment (MARA) is a 24 h multi-species test that seeks to address this problem by using a battery of ten bacteria and a fungus. But there has been little independent evaluation of this test, and there is no published information on its sensitivity to pesticides. Here, we assess the performance of MARA using a range of toxicants including reference chemicals, fungicides and environmental samples. Mean MARA microbial toxic concentrations and ICs (20% Inhibitory concentrations) indicate the toxicant concentrations affecting the more sensitive micro-organisms, while the mean IC (50% Inhibitory concentration) was found to be the concentration that was toxic to most MARA species. For the two fungicides tested, the yeast ( Pichia anomalia) was the most sensitive of the ten MARA species, and was more sensitive than the nine other yeasts tested. The test may be particularly valuable for work with fungicides. Mean MARA ICs were comparable to values for nine other yeast species and the lowest individual ICs for each toxicant were comparable to reported ICs for Daphnia magna, Selenastrum capricornutum and Microtox® bioassays. MARA organisms exhibited more variable sensitivities, with the most sensitive organism being different for different samples, enhancing the likelihood of toxicity detection and giving a toxicity 'fingerprint' that may help identify toxicants. The test, therefore, has great potential and would be valuable for ecotoxicological testing of pollutants. [ABSTRACT FROM AUTHOR]

Luoma suggested 25 years ago that tolerant populations could be used to detect adverse ecological effects of pollution. Despite the apparent attractiveness of the idea, there have been few successful examples of its use and a number of failures. Pollution-tolerant populations are limited almost entirely to areas that are grossly contaminated with one or a small number of substances and have flora and fauna that are severely impoverished. Tolerance does provide strong evidence of impact by a particular contaminant but is of limited value as a monitoring tool. Instances of evolved tolerance do, however, have a valuable role to play in environmental risk assessment. They provide model systems for understanding the impact of pollutants on the physiology and performance of individuals and in consequence how they produce effects at the population and community level, in the way that metal tolerance in plants has been used as a model system for the study of evolution. Pollution-induced community tolerance has more promise than population tolerance as a tool for monitoring the effects of pollution, and already has a much longer list of successful applications despite its shorter history. [ABSTRACT FROM AUTHOR]

Pollution-induced community tolerance (PICT) has been proposed as an indicator of the deleterious effects of pollutants on communities in the field. Nematode assemblages were sampled at 10 estuarine sites that ranged from uncontaminated to grossly contaminated with metals. Relative tolerance of these assemblages to Cu was quantified using acute toxicity tests. There were large differences between sites in tolerance to Cu, and copper tolerance was strongly correlated with severity of contamination. Enhanced Cu tolerance occurred at two sites where Cu concentration in sediment was around 180 µg/g but not at a third site, where Cu concentration was 214 µg/g. This implies a threshold of effects on these nematode communities at ∼200 µg/g Cu. Comparison with studies of nematode community composition in these same estuaries indicates that PICT is at least as sensitive as the best available ecological monitoring methods. It is, however, faster to carry out and requires much less taxonomic expertise. The PICT appears to be a sensitive indicator of ecological effects of pollution and has considerable promise as a monitoring tool. [ABSTRACT FROM AUTHOR]