• bioaccumulation;
  • bioassay testing;
  • decision-making;
  • toxicity;
  • water quality

Abstract Bioassay testing includes both toxicity (one or more effects is measured) and bioaccumulation (the phenomenon of tissue accumulation is measured) tests. Both types of bioassay tests have an important place in water quality assessment programmes, ideally beginning with initial screening and as part of tiered testing that includes contaminant analyses and field studies. Both have advantages (e. g. measure bioavailability, provide quantitative data, experimental manipulations can address cause-effect relationships) and disadvantages (e. g. laboratory exposures do not necessarily reflect field conditions, not all organisms can be tested). Both provide essential, but not all, information necessary for holistic water quality assessments. This paper provides a review of the use of bioassays including definitions, applications, advantages and disadvantages, utility and relevance. The utility of bioassays in monitoring programmes is illustrated by two case studies. The first case study, involving novel toxicity studies conducted in the high Arctic, illustrates the versatility of bioassays such that testing conducted in a tent on the ice resulted in new knowledge and a change in industrial discharge limits. The second case study further illustrates the importance of bioassays in decision making. In this case, a decision not to immediately spend hundreds of millions of dollars for sewage treatment, but rather to concentrate on source control, was made based in large part on bioassay testing conducted as part of an integrated environmental assessment.