Assessing Sub-Lethal Effects of Chloride and Potassium on Adult Rainbow Mussels Villosa iris Using Histological Evaluations of Vital Organs

Mussel abundance has drastically declined in the North Fork Holston River downstream of Saltville, VA.  Historical industrial activities at Saltville, and continued pollution of the river, are believed to be significant causes of these declines.  Seepage waters from waste holding ponds adjacent to the river add high concentrations of chloride (Cl^-) and potassium (K⁺) and are suspected of negatively impacting mussel populations.  Two laboratory studies were conducted to assess sub-lethal histological impacts to tissues of adult Villosa iris exposed to environmentally relevant concentrations of Cl^- and K⁺.  Treatments consisted of low (203 mg/L and 4 mg/L) and high (705 mg/L and 8 mg/L) concentrations of Cl^- and K⁺, respectively in a three-month study in 2012.  We subsequently exposed mussels to low (705 mg/L and 8 mg/L), mid (1410 mg/L and 16 mg/L), and high (2820 mg/L and 32 mg/L) concentrations in a two-month study in 2013.  Histological evaluations in the 2012 study indicated no significant differences among treatments and control (p>0.05); however, effects of captivity were suspected of influencing results.  The increased concentrations of both Cl^- and K⁺ in the 2013 study significantly impacted mussel survival and tissue condition.  Effects of captivity, toxicological mechanisms, and management implications will be discussed.