A comparative ecological and toxicological investigation of a secondary wastewater treatment plant effluent and its receiving stream

摘要

AbstractA comparative ecological and toxicological investigation was conducted on a secondary wastewater treatment plant point—source discharge and the receiving system, a fourth—order freshwater stream in the Kentucky River basin. Biological, chemical, hydrological and on—site toxicological studies were performed at 10 monitoring stations, including reference sites. The principal objectives were to assess downstream persistence of aquatic contaminants, to quantify their effects on structure and function of aquatic communities and to evaluate the 8—d fathead minnow embryo—larval test for measuring instream toxicity and estimating chronic effects on aquatic biota. The principal ecological endpoints included species richness, diversity (H'), density and dominance (D) of macroinvertebrates and diversity of fish species. Macroinvertebrates were further analyzed by trophic groups. Marked downstream gradients existed for effluent dilution, decreasing concentration of selected chemicals, improvement in ecological conditions and decreasing toxicity, as measured in on—site static—renewal tests. A good predictive correlation was found between embryo—larval survival and independent ecological parameters, especially species richness of macroinvertebrates. In addition, static—renewal and flow—through toxicity tests were performed with effluent dilutions to determine LC50 and toxicity threshold values (LC1), expressed as percent effluent by volume. The estimated toxicity thresholds correlated closely with the actual percent instream effluent dilution observed at the first downstream station at which no ecological imp