Environmental effects of saline oil-field discharges on surface waters

Ambient water samples from streams receiving discharges of coproduced brines from the Salt Creek oil field in Wyoming were collected and tested for toxicity from 1988 to 1990. Exposure to waters downstream from the oil field significantly (P < 0.05) reduced survival and reproduction of Ceriodaphnia dubia compared to the upstream control, but fathead minnows (Pimephales promelas) did not appear to be sensitive to the test conditions. Toxicity to Ceriodaphnia dubia increased as stream flow decreased. Toxicity could not be attributed to H2S, trace metals, or nonpolar organic compounds based on toxicity identification evaluation (TIE) methods. Major inorganic ions (Na+, K+, Cl−, HCO−3, and CO23) appeared to account for the observed toxicity.