Freshwater Mussel Sensitivity to Polyacrylamide, Sediment, and Turbidity.

BUCZEK, SEAN B. Freshwater Mussel Sensitivity to Polyacrylamide, Sediment, and Turbidity (Under the direction of W. Gregory Cope and Richard A. McLaughlin). Human activities have significant impacts on aquatic ecosystems and the organisms that occupy them. Anthropogenic activities cause environmental degradation by altering land-cover and leading to increased runoff, soil erosion, and reduced biodiversity. Polyacrylamide (PAM) has become an effective chemical tool for mitigating some of the adverse impacts of erosion and suspended sediment on aquatic ecosystems. However, little is known about the effects of sediment and turbidity on many freshwater organisms, and prior to this study, no information existed on the toxicity of sediment, turbidity, and PAM compounds to native freshwater mussels (family Unionidae), one of the most imperiled faunal groups globally. To characterize the risk of both PAM and environmentally relevant sediment exposure to freshwater mussels, acute toxicity tests were conducted following standard guidelines for the early life stages (glochidia larvae and juveniles) of freshwater mussels. Toxicity of 5 different anionic PAM compounds and 1 non-ionic compound was evaluated for juveniles (test duration 96-h) and glochidia (test duration 24-h) of three freshwater mussel species Lampsilis cariosa, Alasmidonta raveneliana, and Megalonaias nervosa. The mussels were exposed at PAM concentrations of 5, 50, 100, 200, 500, and 1000 mg/L and assessed for survival and viability. We found that median lethal concentrations (LC50) of PAM ranged from 412 to greater than 1000 mg/L for glochidia and from 129 to over 1000 mg/L for juveniles. All LC50s were orders of magnitude greater (2– 3) than concentrations typically recommended for turbidity control in the field (1–5 mg/L). Our results demonstrate that the PAM compounds tested were not acutely toxic to the mussel species and life stages tested, at concentrations relevant to turbidity control, indicating minimal risk of short-term exposure from PAM applications in the environment. To further inform the risk assessment, juvenile (test duration 96-h) Lampsilis siliquoidea were exposed to three different experimental conditions (settled sediment, suspended sediment, and PAMflocculated settled sediment), as well as a range of treatment turbidity concentrations (50, 250, 1250, and 3500 nephelometric turbidity units; NTU) and assessed the exposed mussels for survival and sublethal oxidative stress to elucidate potential toxicity. No effects were found on mussel survival, suggesting a high level of tolerance of L. siliquoidea for these conditions and treatments in short-term exposures. In contrast, there were significant reductions in protein concentration, ATP production, and oxidized proteins in mussels exposed to suspended sediment, indicating adaptive plasticity of physiological protective responses that limit energy production and reactive oxygen species accumulation under unfavorable environmental conditions. The results suggest that anionic PAM applied to reduce suspended sediment may be effective at minimizing the effects of short-term turbidity exposure and possess minimal risk of acute toxicity with a 24to 126-fold margin of safety to juvenile freshwater mussels. These findings provide valuable information with direct implications for the conservation of freshwater mussels and their habitat. © Copyright 2015 by Sean B. Buczek All Rights Reserved Freshwater Mussel Sensitivity to Polyacrylamide, Sediment, and Turbidity