Fate of triclosan and triclosan-methyl in sewage treatment plants and surface waters

The fate of triclosan in diverse stages of two sewage treatment processes has been determined. The elimination process differed considerably depending on the technology applied in the respective sewage treatment plant (STP). The plant operating with a two-stage biologic (activated sludge) process removed triclosan more efficiently than the STP with a combination of physical and activated sludge process. The treatment in the aeration basin was the dominant elimination mechanism, whereas the final biologic filter was not very effective. The elimination rates for triclosan were 87% and 95%, respectively. These data were compared with emissions of a multitude of STPs in the river Ruhr catchment area as well as triclosan and its known transformation product, triclosan-methyl, in the river. The concentrations of both compounds were between < 3 and 10 ng/L in true surface-water samples for triclosan and between 0.3 and 10 ng/L for triclosan-methyl. The STP effluents held higher concentrations (10 to 600 ng/L triclosan). The ratio of triclosan to triclosan-methyl did not change significantly within the longitudinal profile of the river, but diverse STPs discharging to the river exhibited individual triclosan-to-triclosan-methyl ratios. From the riverine concentration data, in-river elimination rates and half-life were estimated.