Toxicity of thiocyanate, phenol and their mixtures to freshwater aquatic organisms: A mixture modeling approach

Thiocyanate and phenol are two environmentally significant constituents of wastewater streams from coke production plants and coal conversion facilities. The objective of this research project was to study the toxic effects of thiocyanate and phenol as individual constituents and as a mixture on the survival and reproduction of freshwater aquatic organisms.; Acute and chronic toxicity experiments were conducted for thiocyanate and phenol with Daphnia magna at 20{dollar}spcirc{dollar}C and Ceriodaphnia affinis/dubia at 25{dollar}spcirc{dollar}C in hard water to study their individual toxic effects on survival and reproduction. Statistical analysis of the dose response relationships for the individual chemicals indicated the type of combined effects that occur when thiocyanate and phenol are present simultaneously. Mixture models for toxicant interaction were used to predict joint toxic effects on survival and reproduction. The applicability of the mixture model was tested by performing joint toxicity experiments for specific thiocyanate and phenol mixtures to verify the model for toxic effects on specific whole organism performances.; The acute toxicity of thiocyanate with D. magna and C. affinis/dubia was 6.9 and 2.8 mg SCN{dollar}sp{lcub}-{rcub}{dollar}/L, respectively, based on the 48-hour LC{dollar}sb{lcub}50{rcub}{dollar}. The chronic toxicity of thiocyanate based on the MATC was (0.25-0.39) and (0.32-0.47) mg SCN{dollar}sp{lcub}-{rcub}{dollar}/L for the 21-day D. magna and the seven-day C. affinis/dubia experiments, respectively. Dose response relationships were statistically analyzed for survival and reproduction.; Lethal dose response curves for thiocyanate and phenol toxicity to D. magna and C. affinis/dubia were established using probit analysis. Lethal dose response curves for thiocyanate and phenol mixtures were predicted using the concentration addition model. The model was verified to accurately predict the strictly additive joint lethal toxicity of thiocyanate and phenol mixtures.; Neonate production and hatchability, two indices of reproduction, were selected to evaluate the chronic toxic effects of thiocyanate and phenol on D. magna and C. affinis/dubia. The resulting dose response curves for thiocyanate and phenol mixtures were compared to curves predicted on the basis of the mathematical model for concentration addition.; Low concentrations of thiocyanate, phenol and their mixtures generally caused a stimulation effect on D. magna and C. affinis/dubia reproduction. (Abstract shortened with permission of author.)...