Histological evaluations of organ tissues reveal sublethal effects in a freshwater mussel (Villosa iris) exposed to chloride and potassium concentrations below benchmark estimates.

Salinization of freshwater ecosystems due to anthropogenic sources will increasingly impact biodiversity. An example of point-source industrial salinization has occurred from historical activities at a U.S. Environmental Protection Agency Superfund Site near Saltville, Virginia USA and its associated chemical waste ponds adjacent to the North Fork Holston River. These point source discharges are documented contributors to mussel declines, partially due to high concentrations of chloride (Cl-, ≤ 26,000 mg Cl-/L) and potassium (K+, ≤ 97 mg K+/L). During a chronic 61-day laboratory study, Rainbow mussels, Villosa iris, were exposed to concentrations of Cl- (0, 416, 831, and 1,663 mg/L) and K+ (0, 4, 8, and 17 mg/L) to determine effects on survival and organ tissues. All test mussels died by day-2 in the 1,663 mg Cl-/L exposure, and 50% of mussels died by day-13 in the 17 mg K+/L concentration. Significantly greater abundances of tissue abnormalities were observed in digestive glands and kidneys with exposures to the 4 and 8 mg/L concentrations of K+ versus the control, and significantly greater abundances of lesions in kidneys were observed in the 416 and 831 mg Cl-/L concentrations compared to the control. The sublethal effects to digestive glands and kidneys were below reported effect (EC50, 20, 10 and LOEC) concentrations. Significant histological differences between control and baseline (day-0 sample) mussels were observed, suggesting the need for further study on the effects of captivity during longer-term laboratory experiments.

Assessment of growth, survival, and organ tissues of caged mussels (Bivalvia: Unionidae) in a river-scape influenced by coal mining in the southeastern USA.

The Clinch River contains one of the most diverse freshwater mussel assemblages in the United States, with 46 extant species, 20 of which are listed as federally endangered. In a 91 km section of the Clinch River, mussel densities have severely declined at key sites from 1979 to 2014 (zone of decline), compared to other river sections that support high density and stable mussel populations (zone of stability). Coal mining has occurred in tributary watersheds that drain to the zone of decline since the late nineteenth century. To determine differences in survival, growth, and organ (gills, digestive glands, kidneys, and gonads) tissue health between the river zones, laboratory-propagated mussels were deployed to cages for one year at four sites each within the zones of mussel stability and decline. Means of growth and survival of mussels in the zone of stability were significantly greater than in the zone of decline, and mean fractions of kidney lipofuscin in mussels in the zone of decline was significantly greater than in the zone of stability. Water concentrations of K+, Na+, Al, and Mn were significantly greater in the zone of decline than in the zone of stability. Statistical correlation results indicated that mussel survival was positively associated with concentrations of Mn in water, and kidney lipofuscin was negatively associated with concentrations of dissolved K+, SO42-, and Mg2+. Most concentrations of contaminants were below published benchmark criteria, yet our results suggest that conditions continue to exist in the zone of decline that promote impacts to mussels that are at least partially associated with low concentration coal-related contaminants. More research is needed to determine the additive, synergistic, or antagonistic effects of these complex ionic mixtures on freshwater mussels from river environments, such as in the Clinch River, where constituent concentrations are relatively low.