This project aims to address critical knowledge gaps related to the toxicity of common components of military effluents/base surficial runoff to federally threatened, endangered, and at-risk (TEA) freshwater mussels. The project team will evaluate the acute and chronic effects of ammonia, one of the most common aquatic pollutants in the U.S., with and without a co-stressor of either an elevated temperature or a mixture of metals that are likely deposited into the environment through military training activities (e.g., munitions-related metals). It is well known that juvenile mussels are sensitive to ammonia and several individual metals. However, limited information is available on the effects of multi-stressors on mussels, and thus there remains a need to evaluate the effects of co-stressors on TEA species under environmentally relevant conditions.

Two TEA mussel species (Green Floater, Lasmigona subviridis; Pink Mucket,Lampsilis abrupta) and a commonly tested freshwater mussel (Fatmucket, Lampsilis siliquoidea) are selected for toxicity testing. Female mussels brooding mature larvae will be collected for the propagation of juveniles. Ammonia toxicity tests will be conducted with one-week-old juveniles following the ASTM International standard test method E2455-22 in acute 96-h and short-term chronic 7-d exposures (1) at three temperatures (a standard test temperature and two elevated temperatures) and (2) with a mixture of metals at a standard temperature. The elevated temperatures will be selected at the environmentally relevant level for the regions the mussels typically inhabit and at a temperature that has been previously shown to be stressful for juvenile mussels. At least three metals will be selected from those of interest to SERDP and/or local military collaborators. Acute effect concentrations for ammonia based on the endpoints of mortality plus immobility and chronic effect concentrations based on survival, growth, and biomass with and without a co-stressor of elevated temperature or metal mixture will be determined and used to evaluate whether and how the co-stressor affects ammonia toxicity to organisms.

This study will provide data to evaluate the interactions and effects of multiple stressors and to predict the cumulative risk to TEA species from exposure to the multiple stressors. While the U.S. Environmental Protection Agency’s ambient water quality criteria (WQC) are available for ammonia alone or for individual metals, the results of the work will provide additional environmental guideline values to protect TEA species and other Department-of-Defense-relevant aquatic species from exposures to multiple common pollutants. In addition, this project will ultimately gauge the relative sensitivities of the two TEA species for protection under existing WQC and provide critical data to the Department of Defense for the protection of mollusks on military installations.