TRICHLOROACETIC-ACID AS A PHYTOTOXIC AIR POLLUTANT AND THE DOSE-RESPONSE RELATIONSHIP FOR DEFOLIATION OF SCOTS PINE

Various ubiquitous volatile organic air pollutants (VOCs), especially C-2-halocarbons, may be converted to secondary air pollutants that are phytotoxic and known as herbicides. One of these is trichloroacetic a cid (TCA), found in concentrations ranging from 10 to 130 ng/g in the foliage of forest trees in northern Finland. TCA has been used as a he rbicide against monocotyledonous weeds. It has formative effects, inhi bits growth, and induces chlorosis and necrosis of light-exposed leave s, including those of woody plant species. Twenty Scots pine trees in an experimental stand 50 km southeast of Rovaniemi were sampled for co rrelation of TCA levels and needle loss. The trees located at the nort hwesterly edge of the stand could be divided into two groups, one more resistant to the phytotoxicant TCA than the second, The range of TCA concentrations in needles was 8-65 ng/g. The extent of defoliation (ra nge 25-90%) was lower in the TCA-resistant group, with a gradient of 0 .32% defoliation per unit TCA concentration; in the sensitive group, t he correlation line had a steeper slope of 0.78% defoliation per unit TCA concentration. These two groups serve as a basis for further studi es on morphological, anatomical, and biochemical parameters.