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MA4 Biotic Ligand Model
(036) Influence of acute copper exposure on whole-body sodium levels in larval fathead minnows.
van Genderen, Eric1, Tomasso, Joseph1, Klaine, Stephen1, 1 Clemson University, Pendleton, SC, USA
ABSTRACT- Surface waters of low hardness ( ≤ 40 mg/L as CaCO3) may inherently present significant stress to aquatic biota. For example, freshwater fish must continually regulate internal concentrations of ions (i.e., Na+, K+, Cl-) in order to survive. As ambient concentrations of these ions decrease, the concentration gradient between the plasma and the environment increases. Since metals, such as copper, inhibit ionoregulation, the increased energy requirement to counter passive diffusive losses in soft water may translate into increased sensitivity to metal exposure. We developed a method to determine whole-body sodium concentrations of larval fathead minnows as a physiological indicator of health. This method was used to characterize net rates of sodium flux from fish exposed to copper in the presence of varying levels of hardness and alkalinity. Organisms exposed to copper at acutely lethal levels had significantly less whole-body sodium than control fish by 6 hours following test initiation. By 12 hours, sodium flux had diminished and whole body sodium remained relatively constant at low levels until mortality occurred. Hardness dependent rates of sodium loss showed evidence of saturation-type kinetics. Competitive inhibition of copper by hardness cations was not demonstrated below hardness of 50 mg/L as CaCO3, when alkalinity was held constant. However, rates of whole-body sodium loss decreased as alkalinity increased from 10 to 100 mg/L as CaCO3 (constant hardness), which was attributed to carbonate complexation. Consequently, current hardness-based water quality regulation for copper may be accurate only when alkalinity is co-varied with hardness. Further characterization of the mechanism of metal toxicity in soft water, and the resulting physiologic response in larval fish, may better explain observed sensitivity in this environment.
Key words: fathead minnow, whole-body sodium, copper, cation competition
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