Effects of sulfate on the acute toxicity of selenate to freshwater organisms

This study evaluated the relationship between ambient sulfate concentration s and acute selenate toxicity to freshwater aquatic life. Previous studies indicated that increasing sulfate concentrations reduced selenate bioconcen tration and toxicity. However, these studies generally were not conducted i n a manner that was conducive to their use in deriving a water quality crit erion. We compiled results from previous studies and generated additional d ata to help define a selenate-sulfate relationship for acute toxicity. Sele nate toxicity was determined in standardized test waters with varying sulfa te concentrations using Ceriodaphnia dubia, Gammarus pseudolimnaeus, Hyalel la azteca, and Pimephales promelas as the test organisms. Analysis of test results indicated that a significant relationship does exist between acute selenate toxicity and ambient sulfate concentrations. Data from these tests and previous studies were combined to develop a statistical relationship s ufficiently robust to derive a sulfate-dependent water quality criterion fo r selenate. The relationship is similar to those commonly derived between d ivalent metals and hardness to adjust water quality criteria.