The state of the aquatic environment as deducted from bioassays-quantitated ecosystem risks

Bioassays represent powerful tools for the assessment of environmental quality. This report focuses on the measurement of the toxicity of surface water samples towards a battery of several differing aquatic organisms. The toxicity is determined by isolating toxic organic chemicals from the surface water by use of a concentration procedure, and by exposing the organisms to the concentrates thus obtained. Subsequently this method evaluates the results statistically, to yield a measure for the degree to which the water represents a risk for the aquatic ecosystem. This risk is expressed in terms of 'toxic potency' which represents the fraction of the ecosystem that is affected in any way by the environmental conditions.