Extending the toxicity-testing paradigm for freshwater mussels: Assessing chronic reproductive effects of the synthetic estrogen 17α-ethinylestradiol on the unionid mussel Elliptio complanata.

Surface water concentrations of the synthetic estrogen 17α-ethinylestradiol (EE2) as low as 1ng/L can cause adverse reproductive effects in fish under acute and chronic exposure conditions, whereas higher concentrations (> 5ng/L) in acute studies are necessary to elicit adverse effects in freshwater mussels. Prolonged chronic exposures of freshwater mussels to EE2 remain un-evaluated. An extended duration testing paradigm was used to examine reproductive and biochemical (carbohydrate, lipid, protein) effects of EE2 on the unionid mussel, Elliptio complanata, throughout its reproductive cycle. Mussels were exposed to a control and EE2 concentrations (5 and 50ng/L) in six discrete and sequential 28 d tests, and in one discrete and simultaneous 180 d test, from February through August. Foot protrusion and siphoning behavior were recorded daily, along with conglutinate releases and larval (glochidia) mortality. Gonad, hemolymph, and gonad fluid samples were taken for biochemical and vitellogenin-like protein (Vtg) analysis post-exposure. Female mussels released eggs and conglutinates during the months of April to June, indicating sexual maturation during this time. Conglutinates released in the 5ng/L treatment in 28 d exposures contained fewer glochidia and more eggs, and increased concentrations of Vtg in hemolymph were observed from April to August in the 5ng/L treatment during the 180 d exposure. Results indicate that the 180 d test approach, concurrent with the sequence of 28 d tests, enabled a more robust evaluation of mussel behavior and physiology than would have been possible with a single short-term (28 d) test.