Quantification of triclosan, chlorinated triclosan derivatives, and their dioxin photoproducts in lacustrine sediment cores

Abstract

Triclosan (TCS) is an antimicrobial agent commonly detected in wastewater effluent. During water and wastewater disinfection with free chlorine, TCS can be transformed to a series of chlorinated triclosan derivatives (CTDs). When discharged into surface waters, TCS and CTDs may be photochemically transformed via a cyclization reaction to a series of polychlorinated dibenzo-p-dioxins (PCDDs). Because PCDDs are a class of compounds known to be toxic and carcinogenic in the environment, tracking their formation from TCS and CTDs in aquatic ecosystems is necessary.To evaluate the historical exposure of surface waters to TCS, CTDs, and their derived PCDDs, sediment cores were collected from an array of wastewater-impacted Minnesota lakes. Following radiometric dating, TCS and CTDs were extracted from core sections and quantified by liquid chromatography-tandem mass spectrometry (LC-MS-Q3). PCDDs were extracted from the same core sections and quantified by high resolution gas chromatography-high resolution mass spectrometry (HRGC-HRMS). The concentrations and temporal trends of TCS, CTDs, and their PCDDs in aquatic sediments were found to be a function of historical wastewater treatment operations and lake system scale. Cores collected from large-scale riverine systems with many wastewater sources recorded increasing concentrations of TCS, CTDs, and their derived PCDDs since the patenting of TCS in 1964. In small-scale lakes with a single wastewater source, the depositional trends of these analytes were directly attributed to increased TCS use, local improvements in treatment, and changes in wastewater disinfection since the 1960s. Overall, concentrations of TCS, CTDs, and their PCDDs were higher in small-scale systems, reflecting a greater degree of wastewater impact. Although specific PCDD congeners are known photoproducts of TCS and CTDs, the same PCDDs were also found at very low concentrations in northern Minnesota lakes with little or no wastewater impact. Background levels of these PCDDs were attributed to a secondary, region-specific source in the 19th and 20th centuries.To evaluate the potential risk that TCS and CTDs pose to aquatic environments, the contribution of their derived PCDDs to the total PCDD pool, in terms of mass and toxicity, was determined for each sediment core. In heavily impacted systems, the PCDD contribution from TCS and CTDs accounted for up to 70% of total PCDD mass and 32% of total PCDD toxicity in recent sediment. Thus, the discharge of TCS and CTDs may pose a substantial threat to wastewater-impacted lakes in Minnesota.