Occurrence of Methyl Triclosan, a Transformation Product of the Bactericide Triclosan, in Fish from Various Lakes in Switzerland

The bactericide triclosan and methyl triclosan, an environmental transformation product thereof, have been previously detected in lakes and a river in Switzerland. Both compounds are emitted via wastewater treatment plants (WWTPs), with methyl triclosan probably being formed by biological methylation. Passive sampling with semipermeable membrane devices (SPMDs) showed the presence of methyl triclosan in some lakes, suggesting some potential for bioaccumulation of the compound. In this study, we report the presence of methyl triclosan in fish (white fish, coregonus sp.; roach, rutilus rutilus) from various lakes in Switzerland receiving inputs from WWTPs. Identification of the compound was based on mass spectral (MS) evidence including MS/MS data. The concentrations of methyl triclosan in the fish were up to 35 ng g-1 on a wet weight basis and up to 365 ng g-1 on a lipid basis with concentrations in a relatively narrow range for fish from the same lake (Thunersee, 4−6 ng g-1; Zürichsee, 32−62 ng g-1; Pfäffikersee, 43−56 ng g-1; Greifensee, 165−365 ng g-1, lipid basis). No methyl triclosan (<1 ng g-1, lipid basis) was detected in fish (lake trout, salmo trutta) from a remote lake in Sweden (Häbberstjärnen) and in fish (roach) from a small lake in Switzerland with no input from WWTPs (Hüttnersee, <2−<5 ng g-1, lipid basis). The concentrations of methyl triclosan in fish correlated (r2 = 0.85) with the ratio of population in the watershed to water throughflow of the lakes (P/Q ratio), which is considered to be a measure for the domestic burden from WWTPs to a lake. Passive sampling with SPMDs confirmed the presence of methyl triclosan in lakes and a river (Zürichsee and Greifensee; Limmat) but not in a remote mountain lake (Jörisee) and in Hüttnersee. The bioconcentration factor (BCF) of methyl triclosan estimated from the fish data and SPMD-derived water concentrations was in the order of 1−2.6 × 105 (lipid basis) and thus in the range of other persistent organic pollutants. SPMDs were found to be reliable for monitoring low concentrations of methyl triclosan in surface water. Methyl triclosan appears to be a suitable marker for WWTP-derived lipophilic contaminants in the aquatic environment and fish.