Concentrations of hydrophobic organic pollutants in U.S. wastewater treatment plants and in receiving surface waters modeled from EPA Biosolids monitoring data

Organic microcontaminants such as pharmaceuticals and personal care products (PPCPs) are currently not regulated with regards to wastewater treatment removal. To provide a basis for risk assessment, the U.S. Environmental Protection Agency (EPA) conducted a nationwide sampling campaign at seventy-four publicly owned treatment works, to assess contamination of biosolids with 145 different pollutants. However, a similar nationwide study of PPCPs contained in treated effluent of such a large number of wastewater treatment plants has never been conducted. In this study, a published empirical model was modified, and applied, to estimate from the biosolids concentrations reported by the EPA, the concentrations in raw and treated wastewater of pharmaceuticals and other organic contaminants. Target chemicals included eight organic compounds: (benzo(a)pyrene, beta-estradiol-3-benzoate, fluoranthene, miconazole, norgestimate, pyrene, triclocarban and triclosan. These compounds were selected based on the hydrophobicity range for which the model previously had been validated. The results of the mass loading estimations are compared to measured concentrations in treatment plant influent and effluent and also are put in relation to contaminant concentrations found in effluent receiving U.S. surface waters. Potential impacts on sensitive environmental receptors as well as potentially effective treatment methods for wastewater are identified and discussed. The removal efficiencies predicted by the model ranged from ≥13% for triclosan to ≥82% for benzo(a)pyrene. Modeled contaminant concentrations in treatment plant influent ranged from 0.025 to 12 μg/L whereas modeled contaminant concentrations in effluent ranged from 0.0062 to 10 μg/L. A comparison of predicted and observed removal efficiencies for triclosan and triclocarban indicated that the model predictions are conservative in nature and comparable to actual measurements made at sewage treatment plants. This study produced the first concentration estimates for beta-estradiol-3-benzoate, miconazole, and norgestimate in surface waters and identified important information gaps concerning ambient concentrations of microcontaminants and associated ecotoxicological effects.