Assessment of damage to ecosystems: a major issue in ecotoxicological research

The assessment of the environmental impact of pollutants at the ecosystem level raises theoretical and methodological problems of substantial magnitude. Despite the usefulness of a more reductionist approach related to the measure of the effects of pollutant on populations, such as specific toxicity testing or--regarding the assessment of impact of chronic exposure--the use of various biomarkers, these measures do not provide data relevant to conclusions at the community and ecosystem level. The assessment of effect on entire ecosystems requires two kinds of information: (1) What are the consequences of pollutant exposure on the community structure, and (2) what is its impact on fundamental ecological processes that control the ecosystem functioning? Disturbances of structure may be appraised in terms of the major parameters that currently describe it at the community level, such as species richness, ecological diversity, and dominance. The assessment of pollutant effect on ecosystem biodiversity, though underestimated for a long time, is a major issue in applied ecotoxicological research. Accurate attention must be given to keystone species, which in both terrestrial and aquatic ecosystems control the diversification of the whole trophic web in a community. Therefore, if induced by a given pollutant, the decline of the populations of a keystone species may lead to a major destructing of the community. The second major issue in ecotoxicological research is assessment of damage to ecosystem functioning. Because productivity is of such practical importance, appraising changes in primary and secondary productivity is acutely needed. Indeed, chronic pollutant exposure is a permanent threat to biological natural resources as it impedes their production and renewal. Another major point in the assessment of effects at the ecosystem level is the effect of pollution on natural biogeochemical cycles, as well as the study of the ways through which a number of various and often common contaminants, some of them acting at global scale, interact with such cycles. It is also fundamental to assess the effects of pollutants on decomposer activity in both soil and natural waters and on its interaction with biogeochemical processes such as element recycling. In a larger context, though still almost unexplored, ecotoxicology is related to assessment of effects on complex ecosystem assemblages on a regional scale (i.e., landscape ecology and its relationship to functional ecotoxicology).