Zinc toxicity in stormwater runoff from sawmills in British Columbia

Samples of stormwater runoff from three sawmills on Vancouver Island, BC, were tested for acute toxicity with juvenile rainbow trout. All except one of the 27 samples tested exhibited toxicity. Causes of toxicity were investigated using toxicity identification evaluation techniques; specifically, treatment with the chelating agent EDTA. Toxicity was attributed to divalent cations, particularly zinc, in 24 of these samples. The very low hardness associated with most of the samples increased the potential for metals toxicity. Zinc toxicity showed a strong dependence on hardness, with a range of LC50s of 72–272 μg/L between hardnesses of 9–100 mg/L.