Effect of sediment test variables on selenium toxicity to Daphnia magna

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Abstract
The effects of three test method variables (spiking method, sediment storage and sediment: water ratio) on solid‐phase sediment toxicity of selenite‐spiked sediments were investigated using Daphnia magna 48‐h acute exposures. Spiking methods compared stirring and shaking of selenite with sediments followed by toxicity testing from 4 to 72 h. The two methods produced similar LC50 values; however, significant toxicity changes occurred over time. The effect of mixing spiked sediments from 0.5 to 48 h showed decreased toxicity after 24 and 48 h of shaking. Storage of selenite‐spiked sediments at 4 and 25°C revealed significant differences in LC50 values between storage temperatures and with time of storage. Toxicity tended to decrease faster in sediments stored at 25°C. Sediment: water comparisons varied the volume of sediment and water used in test beakers and the sediment surface area. In general, only extreme sediment: water ratios affected survival. Varying the sediment surface area while maintaining a constant 1:4 ratio did not alter survival. An increased surface area and a decreased sediment: water ratio (1:8) decreased survival.

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