Evaluation of the impact of volatile chlorinated hydrocarbons on forest trees based on air and needle measurement data and the detoxification capacity of spruce needles.

Although sound data bases on the emission rates, atmospheric lifetimes and photolytic degradation processes of volatile chlorinated hydrocarbons (VCH) in the air are available, there is still a lack of information on the uptake of these xenobiotics by plant canopies, on their fate and on the ecotoxicology of this pollution load. At the study sites in Achenkirch, VCH concentrations between 0.2 and 2.0 mu g m(-3) have been determined. The deposition on conifer needle surfaces has been described as to proceed at low velocities below 1 mm s(-1) and uptake rates have been determined for few compounds. All VCHs exhibit a high potential to accumulate in the cuticles of conifer needles and accumulation factors between 50 and 500 times above ambient concentrations have been reported. However, internal concentrations and resuspension data are not available. Furthermore, detoxification data have mostly been determined with model compounds like chlorobenzenes. These compounds seem generally to be detoxified at conjugation rates of 0.2 to 1.5 nkat mg protein(-1) in the spruce trees of the Christlum profile. In the present paper evidence is provided that detoxification of dichloromethane and tetrachloroethene proceeds at considerably lower rates in the range of pkat/mg protein, while for other aliphatic chlorocarbons, like trichloroethene, it may be lacking in trees from several stands. This may contribute to the overall stress of spruce trees by air pollutants and the conditions of the stands