Fluxes of trichloroacetic acid between atmosphere, biota, soil, and groundwater

Trichloroacetic acid (TCA), in former times used as a herbicide in agriculture, is now ubiquitous and almost evenly distributed in precipitations of the Northern and Southern Hemisphere, despite larger emissions of the possible precursors tetrachloroethene and 1,1,1-trichloroethane in the Northern Hemisphere. The permanent input of a herbicidal compound into most vulnerable ecosystems might lead to adverse effects to biota (plants, microorganisms, etc.). TCA soil levels of coniferous forests in mountainous regions of Central Europe are significantly elevated. Mass balance calculations show that precipitation as sole source of TCA in soil seems to be of minor importance and provide evidence for a natural formation of TCA within soil itself. In addition, the isolation of a chlorinating enzyme in soil and laboratory experiments with humic acid, iron and halide point to an omnipresent chlorinating capability of nature producing polyhalogenated organic compounds such as TCA. In this paper we present an overview of TCA levels in the environment and provide a new estimate about the extent of a natural TCA formation, especially in soil.