Fate of organohalogens in US wastewater treatment plants and estimated chemical releases to soils nationwide from biosolids recycling

Abstract

This study examined the occurrence in wastewater of 11 aromatic biocides, pesticides and degradates, and their fate during passage through US treatment plants, as well as the chemical mass contained in sewage sludge (biosolids) destined for land application. Analyte concentrations in wastewater influent, effluent and sludge from 25 facilities in 18 US states were determined by liquid chromatography electrospray (tandem) mass spectrometry. Dichlorocarbanilide, fipronil, triclocarban, and triclosan were found consistently in all sample types. Dichlorophene, hexachlorophene, and tetrachlorocarbanilide were detected infrequently only, and concentrations of the phenyl urea pesticides diflubenzuron, hexaflumuron, and linuron were below the limit of detection in all matrixes. Median concentrations (±95% confidence interval) of quantifiable compounds in influent ranged from 4.2 ± 0.8 μg L⁻¹ for triclocarban to 0.03 ± 0.01 μg L⁻¹ for fipronil. Median concentrations in effluent were highest for triclocarban and triclosan (0.23 ± 0.08 and 0.07 ± 0.04 μg L⁻¹, respectively). Median aqueous-phase removal efficiencies (±95% CI) of activated sludge treatment plants decreased in the order of: triclosan (96 ± 2%) > triclocarban (87 ± 7%) > dichlorocarbanilide (55 ± 20%) > fipronil (18 ± 22%). Median concentrations of organohalogens were typically higher in anaerobically than in aerobically digested sludges, and peaked at 27 600 ± 9600 and 15 800 ± 8200 μg kg⁻¹ for triclocarban and triclosan, respectively. Mass balances obtained for three primary pesticides in six activated sludge treatment plants employing anaerobic digestion suggested a decreasing overall persistence from fipronil (97 ± 70%) to triclocarban (87 ± 29%) to triclosan (28 ± 30%). Nationwide release of the investigated organohalogens to agricultural land via municipal sludge recycling and into surface waters is estimated to total 258 000 ± 110 00 kg year⁻¹ (mean ± 95% confidence interval), with most of this mass derived from antimicrobial consumer products of daily use. This study addresses some of the data gaps identified by the National Research Council in its 2002 study on standards and practices of biosolids application on land.