Acute toxicity of six freshwater mussel species (glochidia) to six chemicals: implications for daphnids and Utterbackia imbecillis as surrogates for protection of freshwater mussels (Unionidae)

One of the overarching goals of this study was to examine the appropriateness of using the freshwater mussel Utterbackia imbecillis and the standard test organisms Ceriodaphnia dubia and Daphnia magna as surrogates for testing lethal dose limits for acute exposure to pesticides in different chemical classes and with different modes of action. The researchers performed 24 hour acute toxicity tests in order to compare lethality responses in the test organisms mentioned above and also in the freshwater mussels Leptodea fragilis, Lampsilis cardium, Lampsilis siliquoidea, Megalonaias nervosa, and Ligumia subrostrata. The chemicals tested were carbaryl (insecticide), copper (molluscicide), 4-nonylphenol (used in various compounds and known to cause endocrine disruption in some organisms), pentachlorophenol (fungicide defoliant/ general herbicide), permethrin (broad spectrum pyrethroid insecticide), and 2,4-D (a systemic herbicide).

2,4-D and carbaryl were shown to generally be the least toxic of the tested chemicals to all species tested. The most toxic substance tested overall was copper, with 4-nonylphenol being the most toxic organic compound. Comparing the LC50 values to published expected environmental concentrations of these chemicals indicated a low risk of acute mortality to glochidia, though effects of chronic exposure are unknown and the potential for over-application or spills of these chemicals to be detrimental are high. While Daphnia magna was shown to potentially be a good surrogate for testing lethality of chemicals on freshwater mussels, U. imbecillis did not always qualify as a sufficient surrogate because its LC50s were greater for most contaminants.

Milam, C.D., J.L. Farris, F.J. Dwyer, and D.K. Hardesty
Archives of Environmental Contamination and Toxicology
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