The relevance of the community approach linking chemical and biological analyses in pollution assessment

The Water Framework Directive of the European Union requires achievement of good chemical and ecological status in river systems. Risk assessment for toxicants is mostly based on individual single-species tests, though extrapolation of such results to ecosystem evaluation is often afflicted with uncertainties. Advances include higher-tier testing, which comprises use of multi-faceted ecotoxicity tests, and community (multi-species) tests. Including several trophic levels in pollutant testing shows that both direct and indirect effects occur in biological communities. Direct effects are expressed as changes in community composition, growth rates, metabolism and death rate. Indirect effects at other trophic levels (primary producers, consumers, predators) are exerted through trophic links. Biofilm-grazers comprise a simple food chain, where potential and negative effects affecting one of them could be magnified through the food web (bottom-up versus top-down effects), thus reinforcing or decreasing the ability of biofilms to be indicators of the effects of toxicants in aquatic ecosystems.