Sediments contaminated by human activities usually contain a mixture of chemicals that produce unforeseen combined toxic effects in organisms. Thus, traditional risk assessments based on the concentrations of chemicals are unlikely to produce realistic data on toxicity. In the CONTEST project, 19 biotests were evaluated using a model contaminated sediment from the Baltic Sea. Most of the biotests applied showed concentration-dependent toxicity related to the degree of chemical pollution measured in the test sediment with some variability in the sensitivity of the test organism and the endpoint. The different biotests were analysed according to specially designed assessment criteria, and the results are foreseen to be useful for end-user groups including environmental authorities, private companies and industries, environmental laboratories, consultants, and the scientific community.

A baseline study on the concentrations of contaminants in the Baltic Sea surface sediments was carried out in 1993. The study was initiated by the International Council for the Exploration of the Sea as a response to the request by the Helsinki Commission. All subareas of the Baltic Sea were covered. In addition to surface sediment samples for contaminant analyses, sedimentation rates were determined and a mineralogical study as well as a sediment characterization of the sediment cores were carried out. A recommendation is given on the use of sediment studies in relation to the monitoring of the state of the Baltic Sea.