Biomarkers: useful tools for the monitoring of aquatic environments

The approaches for monitoring environment quality can be classified in two different categories : (1) the detection and/or quantification of stressors in both physical and biological compartments of the ecosystems (physicochemical approach), and (2) the evaluation of exposure of living organisms and subsequent effects at the individual, population and/or community levels (biological approach). Indices have been defined for both approaches. Threshold levels for pH, temperature, conductivity, oxidizable matter content, oxygen saturation, nitrogen, phosphorus and ion concentrations, organic contaminant and metal levels are used as physico-chemical indices to assess the quality of aquatic environments and water resources. Similarly, biological indicators have been developed to evaluate the impact of environmental stress on aquatic organisms at various levels of biological organisation. Among these biological indicators, biomarkers are used as tools to assess molecular, biochemical, cellular, physiological or behavioural changes that may reveal exposure of organisms to environmental chemicals. In some cases, biomarkers are able to indicate that chemicals specifically affect metabolic pathways or physiological functions in exposed individuals. Therefore, biomarkers can be used as both diagnostic and predictive tools. A number of case-studies demonstrated that biomarkers are useful tools to detect the presence of xenobiotics in living organisms and to diagnose individual health. However, interference with natural environmental factors or endogenous parameters may complicate the interpretation of biomarker responses, and sampling and measurement procedures must be properly designed and accurately followed. A more recent and fairly promising way to use biomarkers is based on mechanistic links that can be established between effects revealed in individuals and subsequent changes in populations and communities. Though rarely applied to natural ecosystems, the use of such an approach should be able to predict the effects of stress on populations and/or communities from measurements of biomarkers in individuals of selected species sampled in the field.