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(170) Relative Ionic Contribution of a Coal-processing Effluent to Biotic Impairment.
Kennedy, Alan*,1, Cherry, Donald1, Currie, Rebecca1, Zipper, Carl1, 1 Virginia Tech, Blacksburg, VA, USA
ABSTRACT- Water quality criteria (WQC) protecting aquatic life from discharges into surface waters have predominately been established for pollutants toxic at low levels. However, the concentrations of ordinarily benign ions without WQC, such as sulfate (3671.76 mg/L) and sodium (1952 mg/L), were elevated from sulfur removal in a coal-processing effluent (conductivity: 8,750 S/cm) to the extent that severe impairment of sensitive aquatic biota was evident in the Leading Creek watershed, Meigs County, Ohio. For instance, mean in situ growth of Corbicula fluminea, relative EPT minus Hydropsychidae abundance and relative mayfly abundance were reduced 76.2, 94.8, and 99.9% respectively, below the effluent compared to reference sites. This study provided evidence for a causal relationship between biotic impairment and the effluent, and isolated its ionic components with a series of mock solutions. Using Ceriodaphnia dubia in 48-h and 7-d toxicity tests, our findings indicated the toxicity of the effluent (48-h LC50: 6818; 7-d LOAEC: 3710 S/cm) was represented by the 12 ions analyzed (LC50: 7038; LOAEC: 3730 S/cm). Of those ions, sulfate, sodium, calcium and magnesium accounted for the majority of the acute toxicity of the effluent (LC50: 7165 S/cm). Additionally, water hardness was inversely related with conductive toxicity caused by sulfate and sodium, with substantial amelioration observed at hardness values of 110 mg/L (LC50: 5760 S/cm) and 508 mg/L (LC50: 6829 S/cm), compared to the toxicity at a hardness of 80 mg/L (LC50: 4827 S/cm). This suggests neutralization of acidified water from high sulfur containing coal washings with CaO, rather than NaOH, would be more protective of aquatic fauna. Thus, acute and chronic WQC should be considered for conductivity, sulfate and sodium in coal-processing effluents, contingent on hardness.
Key words: conductivity, sodium, sulfate, coal
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