Review of concentrations and chemistry of trichloroacetate in the environment.

This paper reviews the concentrations of trichloroacetate (TCA) in the atmosphere-plant-soil system. Data originate mainly from Europe. The median TCA concentration in rainwater and canopy drip decreased until 1995. From then the median TCA concentration in rainwater remains rather constant while for canopy drip later data are not available. The same seems to hold for concentrations in air although a very limited data set is available. The median concentrations in coniferous needles and groundwater are constant for the period observed. The median TCA concentrations in soil decreased until 1992 and then remained constant.The TCA formation from chlorinated solvents in the atmosphere may explain a substantial percentage of the TCA amount in the atmosphere. The TCA concentrations in rainwater and canopy drip indicate that there will be other sources contributing to 10-50%. Waste incineration, biomass burning and natural formation in the marine boundary layer are potential candidate sources of TCA, but nothing can be said as yet on their TCA emission rates. Anthropogenic emissions of chlorine could also be a source.TCA can be formed from chlorinated solvents by biota. However, for coniferous trees the uptake of TCA from soil may be the predominant route. Biotic and abiotic reactions can cause to formation of TCA in soil, but also formation of TCA from chlorinated solvents by biota that excrete TCA, may contribute. Mass balance calculations of the bioactive soil top layer show that the production rate of TCA in certain soil types could be substantial. The mass balance calculations could not distinguish between natural and anthropogenic sources in soil.