New chemicals are produced in increasing numbers. In Finland every year about 28 000 different products are manufactured or imported which can be classified as harmful. These products contain about 5000 different harmful substances. We also receive harmful compounds in airborne emissions. Substances are further transformed in industrial processes, in waste management and in the environment by human activities and natural processes. However, only rather limited monitoring data is available about the environmental concentrations of these compounds (concerning about 20–40 substances). The environmental risks of harmful substances can be recognized, assessed and managed by : 1) measuring concentrations in the environment, 2) testing the effects on biota in toxicity tests and 3) monitoring ecosystem changes in the environment. Microbes have a key role in the environment as degraders in the carbon and nutrient cycles. They also have the capability to transform and degrade many harmful man-made substances. Microbes have a strong effect on the exposure of other biota to chemical substances. Hence they can be regarded as primary targets for harmful effects of chemicals or active transformers of chemicals in the environment.The objective of this study was to evaluate the usefulness and applicability of microbial toxicity tests, biodegradation tests and microbial biomass and activity measurements in the environment for the environmental hazard identification and risk assessment of chemicals, effluents and contaminated soils. The study considers both aquatic and soil environments. The effects of modern pulp mill bleaching effluents on biota were assessed by a set of different biotests and by chemical analysis. The effluents and their long term effects on aquatic microbial processes were also studied in outdoor mesocosms. In one part the biodegradation kinetics of carbon-14-labeled model compounds in standard tests and in environmental conditions were measured and compared. The effects of several pesticides on soil microbes were tested and assessed in laboratory tests and in field trials. The applicability of microbial toxicity tests in the assessment of soil pollution and bioremediation processes was also studied in comparison with chemical analysis. The results of the study can support the development and selection of test methods for environmental risk management and regulatory decisions
