Derivation of acceptable concentrations for the protection of aquatic organisms.

Derivation of quality standards to protect aquatic ecosystems demands a minimum set of toxicity data to allow the risk assessor to take some account of: (1) variable responses to toxicants; (2) variable environmental characteristics; (3) interactions between duration of exposure and effects; and (4) ecological significance of impacts. Extrapolation from limited experimental data to predict a concentration protective in diverse ecosystems can employ either statistical models (consistent but rather rigid and may not protect all species) or empirical factors (more flexible and possibly more protective, but require expert judgment in their application). However derived, quality standards must be tailored to the specific conditions of release and environmental fate which influence a chemical's impact in aquatic ecosystems. It must also be recognised that protection of all individuals and even of all aquatic species may not be achievable or necessary to maintain a healthy ecosystem. Some possible future advances in the determination of water quality standards are suggested.