Effects of dietary selenium on the amphipod <i>Hyalella azteca</i> and the midge <i>Chironomus dilutus</i>

Chronic selenium (Se) water quality criteria are based primarily on dietary organoselenium exposure and subsequent reproductive effects in fish. Available chronic Se toxicity data suggest that invertebrates are less sensitive than fish, but chronic invertebrate studies are limited. We evaluated yeast-based diets for chronic toxicity studies with Hyalella azteca and Chironomus dilutus. Growth and survival were similar among C. dilutus fed a yeast-only diet, a mixture of yeast and fish flake food, and a mixture of yeast and diatoms. Survival and growth of H. azteca were best in the yeast + diatom diet, so this diet was used for subsequent tests. In rangefinder tests, H. azteca 28-day survival, growth, and biomass and C. dilutus 11-day survival were all significantly reduced at a dietary Se concentration of 49 µg/g dry weight, whereas C. dilutus growth and biomass were affected only at 200 µg/g dry weight Se. Hyalella azteca had similar sensitivity to dietary Se in a 28- to 42-day chronic test: survival, growth, and biomass were significantly reduced at 44.5 µg/g dry weight Se. Dietary Se reduced H. azteca reproduction by 75% to 100% relative to controls, but differences were not significant. Tissue Se 10% effect concentrations (EC10s) were lower for H. azteca (9.0-23 µg/g dry wt) than for C. dilutus (11-56 µg/g dry wt). However, model evaluations suggest that the C. dilutus 11-day survival and H. azteca 42-day EC10s were less reliable than other endpoints. When tissue EC10s were converted to equivalent Se concentrations in fish tissue with a food web model, H. azteca (18 µg/g dry wt) and C. dilutus (68 µg/g dry wt) ranked 6th and 12th of 13 freshwater genera, respectively. Overall, these results suggest that the current U.S. Environmental Protection Agency tissue-based Se water quality criteria would be protective for fish and invertebrates and could be used for management of fishless waters.