Pollution of the environment, particularly with persistent substances like heavy metals or some pesticides, is a serious problem nowadays. Measurements of concentrations of pollutants do not provide information on the impact of the toxicants on organisms. Parameters of organisms such as survival, function, activity of organisms, community structure are influenced both by anthropogenic and natural factors and discerning impacts of these two types of factors is very difficult or impossible.The concept of pollution-induced community tolerance (PICT) is a tool introduced into ecological and ecotoxicological studies to cope with this problem. The main principles of PICT are that organisms differ in their sensitivity to pollutants and that there is a causal relationship between the presence of pollutant and the effect in the community. Investigating of PICT encompasses two phases: selection phase and detection phase. In the first, usually long-term phase, organisms are treated with a toxicant. In the second phase, a short-term experiment is performed - organisms are subjected to different concentrations of the substance and a chosen biological parameter (or a few ones) is measured. It may be stated that there is a real influence of particular substance on a community when PICT is observed. Communities of soil, water and sediment microorganisms, nematodes, sediment macro- and meiofauna were usually studied. Different heavy metals and pesticides such as atrazine and tri- butyltin were the most often used substances in PICT studies. PICT can be a useful tool in ecological risk assessment and environmental protection but some problems with the interpretation of the results of PICT studies should be solved.
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