BIOLOGICAL VARIATION - AN IMPORTANT FACTOR TO CONSIDER IN ECOTOXICOLOGICAL STUDIES BASED ON ENVIRONMENTAL-SAMPLES

Available measurements of organochlorine concentrations in some biolog ical matrices from the Baltic Sea stress the need for proper sampling and knowledge about biological matrices. To properly evaluate any anal yte in biota, it is imperative to select and scrutinise the representa tiveness of the matrix and to select a relevant matrix. This article d escribes the importance of biological parameters in explaining the var iation in concentrations of contaminants found in field-collected mate rial. To disclose spatial and temporal variation in contaminant concen trations, annual analyses are required. Studies based on pooled sample s are generally not recommended. The unexplained between-year variatio n found even in rather well-defined biological samples often implies t hat time trends showing changes of less than 5-10% are impossible to d etect in experiments shorter than 10 years. Examples demonstrate the e ffect of this variation when interpreting temporal trends and spatial distribution. Normally most of this variation is due to biological fac tors. Any attempt to define spatial or temporal trends or differences between various ecological matrices with respect to contaminant concen trations requires a large number of chemical analyses, which often are very expensive. The development of methods for simplified chemical an alysis would thus permit more individual analyses which will improve t he utilisation of available resources.