Sulphate Toxicity to Freshwater Organisms: A Re-Examination of the British Columbia Sulphate Water Quality Guidelines for the Protection of Aquatic Life

摘要

The current ambient water quality guidelines for sulphate in British Columbia are largely based on studies that are flawed and do not accurately assess the toxicify of sulphate. The principal studies in sulphate toxicity to organisms, representing a number of trophic levels, including the amphipod Hyalella azteca, the cladoceran Daphnia magna, the striped bass Morone saxatilus, and the aquatic moss Fontinalis antipyretica, were repeated and reassessed. This assessment and other studies, indicate thatorganisms exhibit reduced toxicity from sodium sulphate exposure in waters of increasing hardness and more specifically, waters with increasing calcium content. In consideration of the relatively low toxicity of sulphate shown by these studies, the current guideline is overly conservative and proposes unnecessarily strict discharge limits. A new guideline for the protection of ecosystem integrity is proposed, which takes into consideration the hardness of the receiving waters. A maximum allowable level of sulphate in industrial discharges in waters of hardness (as CaCO_3) less than 50 mg/L should be 200 mg/L sulphate; 300 mg/L in waters having hardness from 50 to 100 mg/L; and 400 mg/L in waters having hardness over 100 mg/L.