Shad Mosher

Acute and chronic toxicity of glyphosate compounds to glochidia and juveniles of Lampsilis siliquoidea (unionidae)

Native freshwater mussels (family Unionidae) are among the most imperiled faunal groups in the world. Factors contributing to the decline of mussel populations likely include pesticides and other aquatic contaminants; however, there is a paucity of data regarding the toxicity of even the most globally distributed pesticides, including glyphosate, to mussels. Therefore, the toxicity of several forms of glyphosate, its formulations, and a surfactant (MON 0818) used in several glyphosate formulations was determined for early life stages of Lampsilis siliquoidea, a native freshwater mussel. Acute and chronic toxicity tests were performed with a newly established American Society of Testing and Materials (ASTM) standard guide for conducting toxicity tests with freshwater mussels. Roundup, its active ingredient, the technical-grade isopropylamine (IPA) salt of glyphosate, IPA alone, and MON 0818 (the surfactant in Roundup formulations) were each acutely toxic to L. siliquoidea glochidia. MON 0818 was most toxic of the compounds tested and the 48-h median effective concentration (0.5 mg/L) for L. siliquoidea glochidia is the lowest reported for any aquatic organism tested to date. Juvenile L. siliquoidea were also acutely sensitive to MON 0818, Roundup, glyphosate IPA salt, and IPA alone. Technical-grade glyphosate and Aqua Star were not acutely toxic to glochidia or juveniles. Ranking of relative chronic toxicity of the glyphosate-related compounds to juvenile mussels was similar to the ranking of relative acute toxicity to juveniles. Growth data from chronic tests was largely inconclusive. In summary, these results indicate that L. siliquoidea, a representative of the nearly 300 freshwater mussel taxa in North America, is among the most sensitive aquatic organisms tested to date with glyphosate-based chemicals and the surfactant MON 0818.

Acute and chronic toxicity of pesticide formulations (atrazine, chlorpyrifos, and permethrin) to glochidia and juveniles of Lampsilis siliquoidea

Freshwater mussels are among the most imperiled faunal groups in North America; approximately 67% of the nearly 300 native freshwater mussel species (family Unionidae) are listed as endangered, threatened, or of special concern. Despite evidence that glochidia and juvenile life stages are highly sensitive to some chemical contaminants, the effects of pesticides on early life stages of unionid mussels are largely unknown. In the United States, pesticide registration is based on toxicity data of the active ingredient, not formulations as they are sold and applied. Some pesticide formulations, however, are more toxic than their active ingredient (technical-grade pesticide) alone because of the presence of surfactants, adjuvants, or other ingredients in the formulation. The objective of the present study was to compare the toxicity of active ingredients of several current-use pesticides (atrazine, chlorpyrifos, and permethrin) to the toxicity of pesticide formulations to glochidia and juvenile life stages of a freshwater mussel (Lampsilis siliquoidea). The atrazine formulation (Aatrex) was more toxic than technical-grade atrazine in chronic tests with juvenile L. siliquoidea. For other pesticides, acute and chronic toxicity of technical-grade pesticides were similar to the toxicity of pesticide formulations. Median effective concentrations for chlorpyrifos were 0.43 mg/L for glochidia at 48 h, 0.25 mg/L for juveniles at 96 h, and 0.06 mg/L for juveniles at 21 d. Atrazine and permethrin as well as their formulations did not cause significant acute toxicity in glochidia or juveniles at exposure concentrations approaching water-solubility limits. Additional research is needed on other pesticides with different modes of action, on the role of different routes of exposure, and with other species of unionid mussels to evaluate similarities of toxic response.

Fluoxetine alters adult freshwater mussel behavior and larval metamorphosis.

We used acute and partial-lifecycle tests to examine the effects of the pharmaceutical fluoxetine on freshwater mussels (Unionida). In acute tests lasting 24-48 h, we determined median effective concentrations (EC50s) for fluoxetine with larval (glochidia viability) and juvenile (survival) life-stages of fatmucket (Lampsilis siliquoidea) and black sandshell (Ligumia recta). In a 28-d behavioral test we exposed brooding adult female wavy-rayed lampmussels (Lampsilis fasciola) to 0.37 and 29.3 μg/L fluoxetine to determine effects on adult behavior (foot protrusion, mantle lure display and glochidia parturition). We also assessed the effects of 24-h exposure of 1 and 100 μg/L fluoxetine on glochidia viability duration and metamorphosis success for the wavy-rayed lampmussel. Fluoxetine EC50s ranged from 62 μg/L for juveniles (96 h) to 293 μg/L for glochidia (24 h). In adults, statistically significant increases were observed in foot protrusion at 0.37 and 29.3 μg/L fluoxetine and lure display rates at 29.3 μg/L; glochidia parturition was not significantly affected at any test concentration. Twenty-four hour exposure of glochidia to fluoxetine did not affect viability duration, but likelihood of metamorphosis to the juvenile stage significantly increased with 1 and 100 μg/L treatments. Our results demonstrated effects of fluoxetine to unionid mussels at concentrations less than previously reported and approaching concentrations measured in surface waters.

Partial life-cycle and acute toxicity of perfluoroalkyl acids to freshwater mussels

Freshwater mussels are among the most sensitive aquatic organisms to many contaminants and have complex life-cycles that include several distinct life stages with unique contaminant exposure pathways. Standard acute (24-96 h) and chronic (28 d) toxicity tests with free larva (glochidia) and juvenile mussels are effective at generating data on contaminant effects at two discrete life stages but do not incorporate effects on brooded glochidia. We developed a novel partial life-cycle assay that incorporates exposures to brooding adult female mussels and used this method in combination with acute toxicity tests to assess adverse effects of perfluoroctanesulfonic acid (PFOS) and perfluoroctanoic acid (PFOA) on freshwater mussels. Fatmucket (Lampsilis siliquoidea) were exposed to PFOS at two life stages: brooding glochidia (in marsupia) for 36 d and free glochidia in water for 24 h. In standard acute tests with glochidia (24-48 h exposures) and juveniles (48-96 h exposures) of fatmucket and black sandshell (Ligumia recta), glochidia were 8 to 25 times more sensitive than juveniles. Perfluoroctanesulfonic acid significantly reduced the duration of glochidia viability and reduced probability of metamorphosis at concentrations 3,000 times lower than the most sensitive acute endpoint (24-h EC50). The partial life-cycle test is adaptable to a variety of endpoints and research objectives and is useful for identifying adverse effects at contaminant concentrations below those required for an acute lethal response.

Effects of lead on Na+, K+‐ATPase and hemolymph ion concentrations in the freshwater mussel Elliptio complanata

Freshwater mussels are an imperiled fauna exposed to a variety of environmental toxicants such as lead (Pb) and studies are urgently needed to assess their health and condition to guide conservation efforts. A 28‐day laboratory toxicity test with Pb and adult Eastern elliptio mussels (Elliptio complanata) was conducted to determine uptake kinetics and to assess the toxicological effects of Pb exposure. Test mussels were collected from a relatively uncontaminated reference site and exposed to a water‐only control and five concentrations of Pb (as lead nitrate) ranging from 1 to 245 μg/L in a static renewal test with a water hardness of 42 mg/L. Endpoints included tissue Pb concentrations, hemolymph Pb and ion (Na+, K+, Cl−, Ca2+) concentrations, and Na+, K+‐ATPase enzyme activity in gill tissue. Mussels accumulated Pb rapidly, with tissue concentrations increasing at an exposure‐dependent rate for the first 2 weeks, but with no significant increase from 2 to 4 weeks. Mussel tissue Pb concentrations ranged from 0.34 to 898 μg/g dry weight, were strongly related to Pb in test water at every time interval (7, 14, 21, and 28 days), and did not significantly increase after day 14. Hemolymph Pb concentration was variable, dependent on exposure concentration, and showed no appreciable change with time beyond day 7, except for mussels in the greatest exposure concentration (245 μg/L), which showed a significant reduction in Pb by 28 days, suggesting a threshold for Pb binding or elimination in hemolymph at concentrations near 1000 μg/g. The Na+, K+‐ATPase activity in the gill tissue of mussels was significantly reduced by Pb on day 28 and was highly correlated with tissue Pb concentration (R2 = 0.92; P = 0.013). The Na+, K+‐ATPase activity was correlated with reduced hemolymph Na+ concentration at the greatest Pb exposure when enzyme activity was at 30% of controls. Hemolymph Ca2+ concentration increased significantly in mussels from the greatest Pb exposure and may be due to remobilization from the shell in an attempt to buffer the hemolymph against Pb uptake and toxicity. We conclude that Na+, K+‐ATPase activity in mussels was adversely affected by Pb exposure, however, because the effects on activity were variable at the lower test concentrations, additional research is warranted over this range of exposures.