Effects of low dissolved oxygen on organisms used in freshwater sediment toxicity tests

Minimum dissolved oxygen requirements are part of standard guidelines for toxicity testing of freshwater sediments with several benthic invertebrates, but the data underlying these requirements are somewhat sparse. We exposed three common test organisms to ranges of dissolved oxygen concentrations to determine their responses in 10-d exposures, relative to published guidelines for sediment toxicity tests. The oligochaete, Lumbriculus variegatus, showed 100% survival in all exposures down to the lowest concentration tested, 0.7 mg O₂ l^-1. Midge (Chironomus dilutus) larva showed a more pronounced response; while survival was less than 90% only below 1.0 mg O₂ l^-1, the biomass endpoint showed EC₅₀, EC₂₀, and EC₁₀ values of 1.00 (0.91-1.10), 1.41 (1.16-1.71), and 1.67 (1.25-2.24) mg O₂ l^-1. The amphipod, Hyalella azteca, showed no adverse effects at concentrations as low as 2.12 mg O₂ l^-1. The combination of these data with other literature data suggest that DO minima in current North American 10-d sediment test guidelines are reasonable.