Method Development for a Short-Term 7-Day Toxicity Test with Unionid Mussels.

The US Environmental Protection Agency's short-term freshwater effluent test methods include a fish (Pimephales promelas), a cladoceran (Ceriodaphnia dubia), and a green alga (Raphidocelis subcapitata). There is a recognized need for additional taxa to accompany the three standard species for effluent testing. An appropriate additional taxon is unionid mussels because mussels are widely distributed, live burrowed in sediment and filter particles from the water column for food, and exhibit high sensitivity to a variety of contaminants. Multiple studies were conducted to develop a relevant and robust short-term test method for mussels. We first evaluated the comparative sensitivity of two mussel species (Villosa constricta and Lampsilis siliquoidea) and two standard species (P. promelas and C. dubia) using two mock effluents prepared by mixing ammonia and five metals (cadmium, copper, nickel, lead, and zinc) or a field-collected effluent in 7-day exposures. Both mussel species were equally or more sensitive (more than two-fold) to effluents compared with the standard species. Next, we refined the mussel test method by first determining the best feeding rate of a commercial algal mixture for three age groups (1, 2, and 3 weeks old) of L. siliquoidea in a 7-day feeding experiment, and then used the derived optimal feeding rates to assess the sensitivity of the three ages of juveniles in a 7-day reference toxicant (sodium chloride [NaCl]) test. Juvenile mussels grew substantially (30%-52% length increase) when the 1- or 2-week-old mussels were fed 2 ml twice daily and the 3-week-old mussels were fed 3 ml twice daily. The 25% inhibition concentrations (IC25s) for NaCl were similar (314-520 mg Cl/L) among the three age groups, indicating that an age range of 1- to 3-week-old mussels can be used for a 7-day test. Finally, using the refined test method, we conducted an interlaboratory study among 13 laboratories to evaluate the performance of a 7-day NaCl test with L. siliquoidea. Eleven laboratories successfully completed the test, with more than 80% control survival and reliable growth data. The IC25s ranged from 296 to 1076 mg Cl/L, with a low (34%) coefficient of variation, indicating that the proposed method for L. siliquoidea has acceptable precision. Environ Toxicol Chem 2021;40:3392-3409. © 2021 SETAC.

Evaluation of Juvenile Freshwater Mussel Sensitivity to Multiple Forms of Florpyrauxifen-Benzyl.

ProcellaCOR® (active ingredient [ai], florpyrauxifen-benzyl) is an aquatic herbicide registered for use in 2018 for managing invasive and nuisance macrophyte species. Registration studies evaluating its acute toxicity revealed a favorable environmental profile; however, prior to this study, no information existed on the toxicity of florpyrauxifen-benzyl to native freshwater mussels (Family Unionidae), one of the most sensitive and imperiled faunal groups globally. We followed standard acute (96 h) toxicity test guidelines and exposed juvenile Fatmucket (Lampsilis siliquoidea) and Eastern Lampmussel (Lampsilis radiata) to the following formulations or compounds: ProcellaCOR SC and EC formulations, technical grade active ingredient (TGAI, florpyrauxifen-benzyl), and an analytical-grade sample of the weaker florpyrauxifen acid (FA). In all tests, the estimated median lethal concentrations to produce 50% mortality (LC50) were greater than the highest concentration tested of each formulation or compound. The no observable adverse effect concentrations (NOAEC, based on analytical recoveries measured at the highest concentration tested where no toxicity was observed) were TGAI = 26 µg/L, FA = 100,000 µg/L, ProcellaCOR® SC = 193 µg ai/L ProcellaCOR® EC = 585 µg ai/L and the NOAEC values for the registered commercial formulation products (ProcellaCOR® SC and ProcellaCOR® EC) were orders of magnitude greater (3.9× and 11.7×, respectively) than the maximum application rate (50 µg/L). Our results show that the herbicide formulations and compounds tested were not acutely toxic to juveniles of these two species of freshwater mussels, indicating minimal risk of short-term exposure from florpyrauxifen-benzyl applications in the environment for aquatic weed control. However, potential chronic or sublethal effects remain uncharacterized and warrant additional investigation.

Acute toxicity of polyacrylamide flocculants to early life stages of freshwater mussels.

Polyacrylamide has become an effective tool for reducing construction-related suspended sediment and turbidity, which are considered to have significant adverse impacts on aquatic ecosystems and are a leading cause of the degradation of North American streams and rivers. However, little is known about the effects of polyacrylamide on many freshwater organisms, and prior to the present study, no information existed on the toxicity of polyacrylamide compounds to native freshwater mussels (family Unionidae), one of the most imperiled faunal groups globally. Following standard test guidelines, we exposed juvenile mussels (test duration 96 h) and glochidia larvae (test duration 24 h) to 5 different anionic polyacrylamide compounds and 1 non-ionic compound. Species tested included the yellow lampmussel (Lampsilis cariosa), an Atlantic Slope species that is listed as endangered in North Carolina; the Appalachian elktoe (Alasmidonta raveneliana), a federally endangered Interior Basin species; and the washboard (Megalonaias nervosa), a common Interior Basin species. We found that median lethal concentrations (LC50s) of polyacrylamide ranged from 411.7 to >1000 mg/L for glochidia and from 126.8 to >1000 mg/L for juveniles. All LC50s were orders of magnitude greater (2-3) than concentrations typically recommended for turbidity control (1-5 mg/L), regardless of their molecular weight or charge density. The results demonstrate that the polyacrylamide compounds tested were not acutely toxic to the mussel species and life stages tested, indicating minimal risk of short-term exposure from polyacrylamide applications in the environment. However, other potential uses of polyacrylamide in the environment (e.g., wastewater treatment, paper processing, mining, algae removal) and their chronic or sublethal effects remain uncertain and warrant additional investigation. Environ Toxicol Chem 2017;36:2715-2721. Published 2017 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.