The disadvantages of current biodegradation tests are examined. These problems include need for high substrate concentrations, lack of parent compound concentration measurements and estimation of sediment effects, failure to indicate compounds to which microbial populations must adapt to degrade, and lack of site specificity in innocula selection. A modified river die-away test is proposed for determining biodegradability of organic compounds and testing for toxic degradation products. The chemical abatement test uses shake flasks containing sterile and nonsterile site water, both with and without site sediment. Concurrent toxicity testing with mysids or daphnids provides a sensitive assay for the detection of toxic metabolities.