Freshwater ecosystems in Central Appalachia experience increased concentrations of manganese (Mn) and total dissolved solids from the runoff of surface mines and valley fills. Biological communities have been impacted by these surface mining operations and it has been suggested that the increase in total dissolved solids may contribute to these negative effects, but standard laboratory toxicity tests have not found increased concentrations of total dissolved solids to have such negative effects as seen in the field. The elevated total dissolved solids in mining influenced streams may only be toxic in conjunction with another toxicant that is presence in these systems such as manganese. This study’s primary goal was to determine the toxic effects of a simulated mine water representative of elevated ionic conditions in mining influenced streams of Central Appalachia on the fathead minnow (Pimephales promelas) and examine potential cumulative effects with manganese. Breeding colonies were exposed to different concentrations of the simulated mine water then toxicity tests were performed with manganese on the embryos and larvae. The adverse effects of the combination of toxicants were determined using traditional and non-traditional toxicity testing endpoints. This study found that fathead minnow larval growth was decreased in a concentration of 10 mg Mn/L in conjunction with a 50% dilution of the simulated mine water, but no effect was observed at higher simulated mine water concentrations most likely because of the increased water hardness that is known to reduce both sulfate and manganese toxicity. The concentration of sulfate in the simulated mine water was more toxic when combined with manganese in comparison to historic data for sulfate toxicity. These findings could be applied to mitigation and restoration efforts for streams affected by mountaintop mining operations in Central Appalachia
