An investigation of the application of the Canadian water quality guidelines

The Canadian water quality guidelines for the protection of aquatic life as sume that (1) the external water concentration is an effective measure of t he concentration at the active sire in organisms, which is ultimately respo nsible for a toxic response, and that (2) the safety factor accounts for an y differences between laboratory and field conditions as well as the extrap olation from the effect concentration to a long-term no-effect concentratio n. This study examines these assumptions and assesses potential errors that environmental managers can make when applying the guidelines. The methodol ogy is based on assessing the probability that internal concentrations of s everal contaminants are greater than or less than the "safe" concentration, assumed by the guideline, when the water concentration is at the water qua lity guideline. Results derived from empirical observations and a food-web bioaccumulation model show that a high probability (62-100%) exists that sa fe internal concentrations are exceeded for polychlorinated biphenyls, 1 2 4,5-tetrachlorobenzene, and hexachlorobenzene in Lake Ontario when the aque ous concentrations are at the water quality guideline values. This is due t o field bioaccumulation factors bring greater than the bioaccumulation fact ors in laboratory toxicity tests used for the water qualify guideline devel opment. Factors contributing to the exceedence of safe internal concentrati ons at the water quality guideline values are identified. Recommendations f or improvement of the water quality guideline process are provided.