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

Available measurements of organochlorine concentrations in some biological matrices from the Baltic Sea stress the need for proper sampling and knowledge about biological matrices. To properly evaluate any analyte in biota, it is imperative to select and scrutinise the representativeness of the matrix and to select a relevant matrix. This article describes the importance of biological parameters in explaining the variation in concentrations of contaminants found in field-collected material. To disclose spatial and temporal variation in contaminant concentrations, annual analyses are required. Studies based on pooled samples are generally not recommended. The unexplained between-year variation found even in rather well-defined biological samples often implies that time trends showing changes of less than 5-10% are impossible to detect in experiments shorter than 10 years. Examples demonstrate the effect of this variation when interpreting temporal trends and spatial distribution. Normally most of this variation is due to biological factors. Any attempt to define spatial or temporal trends or differences between various ecological matrices with respect to contaminant concentrations requires a large number of chemical analyses, which often are very expensive. The development of methods for simplified chemical analysis would thus permit more individual analyses which will improve the utilisation of available resources.