Effects of dietary organic selenium on growth, survival, and reproduction in Hyalella azteca and Chironomus dilutus

Chronic selenium toxicity thresholds are based primarily on dietary organoselenium exposure and subsequent reproductive effects in fish. Available chronic selenium toxicity data suggests 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. Selenized yeast was mixed with control yeast to achieve target concentrations of dietary selenium. This work was conducted in 3 phases. First, we performed a Diet/ration study, in which we evaluated the performance of the test organisms in yeast-only, 50:50 yeast:fish flake food, and 50:50 yeast:diatom diets fed under two different ramped ration regimes. The diet composition and ration regime designed in this preliminary study was then used during the subsequent studies. Next, we performed a Rangefinder study, which used 4 widely-spaced dietary selenium concentrations to evaluate the potential toxicity of dietary selenium to Hyalella azteca over 28 days and to Chironomus dilutus over 11 days. We then performed a Chronic study using Hyalella azteca for 28 and 42 days, to evaluate growth, survival, and reproduction endpoints. Ultimately, these data will be used to assess whether fish tissue-based toxicity thresholds for selenium will be protective of invertebrates, particularly in fishless waters.