Accumulation of airborne hexachlorocyclohexanes and DDT in pine needles

The accumulation of alpha- and gamma-hexachlorocyclohexanes (HCHs) and p,p'-DDT in Scots pine needles was measured simultaneously with the concentrations in the surrounding air. All three compounds accumulate during the entire life span of the needles. For p,p'-DDT the general accumulation is overlaid by a concentration peak during winter, probably related to particle deposition. For the HCHs the accumulation is overlaid by a seasonal pattern with rapid accumulation during spring and summer months and constant concentrations during winter months. The concentrations of alpha-HCH in the air were more or less constant during the whole sampling period, whereas gamma-HCH shows an air concentration peak in spring and early summer. Air concentrations of p,p'-DDT were for the most part below the detection limit. There is little evidence of revolatilization from the needles, with the exception of a small decline of gamma-HCH concentration in summer after the peak air concentrations. The high accumulation rate of the HCHs during the warm season correlates with high levels of volatile organic compounds (VOCs) in the needles. We suggest that the variation of VOC content in the needles cause seasonal variation of the air-plant partitioning coefficient. An additional complicating factor is that the dry weight of the needles has to be corrected for the yearly variation of starch content. The results presented here question models of uptake of airborne contaminants by plants that assume rapid equilibria between the air and plants.