PAHs associated with the leaves of three deciduous tree species. I - Concentrations and profiles

Results for the concentrations of total polycyclic aromatic hydrocarbons (S igma PAH) and the PAH profile in leaves from three deciduous tree species f rom the same woodland are presented, and discussed with reference to enviro nmental and leaf-related variables. There were significant differences betw een oak, ash and hazel leaves in their Sigma PAH concentrations (sum of 23 PAHs), and in the relative contribution of individual PAHs to the sum. Leav es exhibiting pubescence (hairiness) were found to have significantly highe r Sigma PAH concentrations than hairless leaves, regardless of their positi on in the vegetation strata of the wood. Hazel leaves from the understorey had a PAH profile consisting of a greater proportion of the 4-, 5- and 6-ri ng PAHs than oak or ash from the canopy. This was concluded to be the resul t of the filtering effect of the main canopy on the air passing over and th rough it, with subsequent transfer of particles and attendant PAHs to the u nderstorey below. The proportion of Sigma PAH contributed by the 6-ring PAH in hazel leaves was negatively correlated with distance from the southern edge of the canopy. It is proposed that the predominantly windward edges of the woodland, where atmospheric turbulence is likely to be greatest, favou red the deposition of particle-bound PAHs to leaves. (C) 2000 Elsevier Scie nce Ltd. All rights reserved.