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Evaluation of Chronic Sensitivity of a Freshwater Mussel Using Partial Life-Cycle Toxicity Tests and Long-Term Toxicity Tests
Citation:
Wang, N., J. Kuntz, J. Stevens, Sandy Raimondo, T. Augspurger, AND C. Barnhart. Evaluation of Chronic Sensitivity of a Freshwater Mussel Using Partial Life-Cycle Toxicity Tests and Long-Term Toxicity Tests. SETAC NA, Fort Worth (Virtual), Texas (Virtual), November 15 - 19, 2020.
Impact/Purpose:
The research presents extensions to mussel toxicity test protocols to measure impacts on reproduction and determine if test duration influences species sensitivity. The work represents the first year of research under the RARE project "Development of a Long-Term Toxicity Test and a Partial Life-Cycle Toxicity Test: Filling Data Gaps of Conservation Significance in Freshwater Mussel Ecotoxicology" (RARE trancking number 2044). The results of the work demonstrate that test duration influences effects concentrations, and incorporating longer term exposures into mussel toxicity test protocols will reveal sensitive test endpoints not measurable using current test protocols.
Description:
ASTM E2455 standard recommends a 4-week duration for chronic toxicity test with juvenile mussels. Because mussels can live for decades, concerns have been expressed whether the responses of survival and growth over a 4-week exposure are adequate to assess long-term impacts. Additionally, no standard method is available to determine mussel reproduction endpoints. The objectives of this 2-year study were to (1) refine methods for a long-term 12-week toxicity test and a partial life-cycle toxicity test with a commonly tested unionid mussel (fatmucket, Lampsilis siliquoidea) and (2) evaluate the sensitivity of the different endpoints from these tests. A reference toxicant (KCl) was used in the first-year study. Gravid female fatmucket brooding mature glochidia were exposed to five KCl concentrations (50% dilution series) and a control water for 6 weeks in the partial life-cycle test. A subsample of glochidia was isolated from each adult mussel to determine the glochidia viability at the end of the adult exposure. Another subsample of glochidia were collected for a 24-h exposure in the same KCl solution for their adults. Preliminary results based on nominal concentrations showed that the EC20 (~15 mg K/L) for the viability of glochidia at the end of the adult exposure was similar to EC20 (~14 mg K/L) from the 24-h glochidia exposure, indicating that the KCl toxicity to glochidia after the adult exposure did not change with the additional exposure with free glochidia. In the long-term test, 2-month-old juveniles were used for 4- and 12-week exposures. The 12-week EC20 for survival (~6.4 mg K/L; growth measurements are ongoing) was 4-fold lower than the 4-week EC20 (~27 mg K/L), indicating that increasing chronic test duration from 4 to 12 weeks substantially increased the KCl toxicity. In addition, the survival endpoint from the 12-week juvenile test was more sensitive than the reproduction endpoint from the partial life-cycle test. The ongoing second-year study will repeat the first-year study with a second toxicant (nickel) and additional reproduction endpoints (e.g., juvenile metamorphosis success).
