Concentrations and Mass Fluxes of Chloroacetic Acids and Trifluoroacetic Acid in Rain and Natural Waters in Switzerland

Abstract

Chloroacetic acids (CAAs) and trifluoroacetic acid (TFA) are widely distributed environmental pollutants. The origin of CAAs is still under debate, while TFA is considered to be a major atmospheric degradation product of recently introduced hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs). Because of the phytotoxic potential of the CAAs, i.e., monochloroacetic acid (MCA), dichloroacetic acid (DCA), and trichloroacetic acid (TCA), and the persistence of TFA, these compounds are of considerable environmental concern. Hence, it is important to know their fluxes and their spatial and temporal distribution in the environment. In this study, the occurrence and mass fluxes of MCA, DCA, TCA, and TFA were assessed on a regional scale over Switzerland, based on more than 1000 concentration measurements in rain and snow, surface water, groundwater, and wastewater. Among different precipitation events, the measured concentrations varied significantly from <11 to 7100 ng/L. However, no statistically different average haloacetic acid (HAA) concentrations among six precipitation sampling sites located in various areas in Switzerland were observed (range of average concentrations: MCA 1430−2770 ng/L, DCA 390−1370 ng/L, TCA 95−380 ng/L, TFA 33−220 ng/L). The similar average HAA concentrations in precipitation at a remote site close to the free troposphere at an elevation of 3580 m above sea level (Jungfraujoch) and at a site that receives precipitation which scavenged the Earth's boundary layer (urban site Dübendorf/Zürich) suggests that HAAs are derived from well-mixed precursor(s) in the atmosphere. When moving from precipitation to surface waters (i.e., rivers), the TFA/CAA ratios increased by a factor of 10−11 for TFA/MCA and TFA/DCA and by a factor of 1.2 for TFA/TCA. Mass flux calculations show that precipitation is the dominant source of the HAAs, particularly of MCA, DCA, and TFA (>95%). In the case of TCA, wastewater effluents contributed 27% of the total input. The results further indicate that, as compared to the CAAs, TFA is quite persistent in the aquatic and terrestrial environment and may thus accumulate in soils and groundwater.