Assessing Trifluoroacetate Accumulation and Transport in Agricultural and Forested Areas in a Mountainous Catchment

Trifluoroacetate (TFA) is an emerging contaminant that originates from various human sources. The degradation of fluorinated gases in the atmosphere leads to an ubiquitous input through precipitation. Degradation of agricultural pesticides and pharmaceuticals in waste water add to the amount of TFA pollution. Once released into the environment, the TFA molecule is nearly conservative due to its negative charge, high solubility in water, and absence of degradation pathways. Consequently, TFA concentrations in the environment are constantly increasing, following the industrial production of fluorinated precursor substances. Previous studies suggested accumulation of TFA in plants or retention in organic soil. This knowledge, however, is based on a small number of samples or laboratory labelling experiments. Catchment-scale studies are so far missing. In particular, hydrological processes controlling adsorption and desorption are poorly understood. We therefore analyzed a two-year dataset of weekly major ion and isotope tracers together with TFA in the mountainous Dreisam catchment (Black Forest, Germany). We sampled precipitation, the discharge of three nested catchments and a hillslope spring. A balancing approach suggested that TFA was not permanently retained in forested headwaters. In agricultural parts, we found a surplus of TFA which added up to an annual input of 11 kg km^-2 on arable land. Major ions suggested that previously retained TFA was flushed from soils under wet conditions following large precipitation events. This was true both for agricultural and non-agricultural areas. These findings indicate that TFA concentrations in soils may be higher than average concentrations found in rain or streamflow. Therefore, future research should focus on the unsaturated zone.