Probabilistic assessment of environmental exposure to the polycyclic musk, HHCB and associated risks in wastewater treatment plant mixing zones and sludge amended soils in the United States

Abstract

The objective of this work was to conduct an environmental risk assessment for the consumer use of the polycyclic musk, HHCB (CAS No. 1222-05-5) in the U.S. focusing on mixing zones downstream from municipal wastewater treatment plants (WWTPs) and sludge amended soils. A probabilistic exposure approach was utilized combining statistical distributions of effluent and sludge concentrations for the U.S. WWTPs with distributions of mixing zone dilution factors and sludge loading rates to soil to estimate HHCB concentrations in surface waters and sediments below WWTPs and sludge amended soils. These concentrations were then compared to various toxicity values. Measured concentrations of HHCB in effluent and sludge from a monitoring program of 40 WWTPs across the U.S. formed the basis for estimating environmental loadings. Based upon a Monte Carlo analysis, the probability of HHCB concentrations being below the PNEC (predicted no effect concentration) for pelagic freshwater organisms was greater than or equal to 99.87% under both mean and low flow regimes. Similarly, the probability of HHCB concentrations being less than the PNEC for freshwater sediment organisms was greater than or equal to 99.98%. Concentrations of HHCB in sludge amended soils were estimated for single and repeated annual sludge applications with tilling of the sludge into the soil, surface application without tilling and a combination reflecting current practice. The probability of soil HHCB concentrations being below the PNEC for soil organisms after repeated sludge applications was 94.35% with current sludge practice. Probabilistic estimates of HHCB exposures in surface waters, sediments and sludge amended soils are consistent with the published values for the U.S. In addition, the results of these analyses indicate that HHCB entering the environment in WWTP effluent and sludge poses negligible risk to aquatic and terrestrial organisms in nearly all exposure scenarios.