PAHs associated with the leaves of three deciduous tree species. II: uptake during a growing season

Leaves from three species of deciduous tree (oak, ash and hazel) were sampl ed at intervals through a growing season in a mature, mixed-deciduous woodl and. Polycyclic aromatic hydrocarbon (PAH) concentrations remained within a small range for all species between May and September, deviating significa ntly only when increases in atmospheric concentrations of PAHs (notably fro m the 'Bonfire night' festival in early autumn) have been shown. We conclud ed that the influence of air concentrations was more important than meteoro logical conditions (temperature, humidity and rainfall) in determining plan t concentrations of PAHs over a growing season. Concentrations of 4-, 5- an d 6-ring PAHs were positively correlated with time for all species, but the re were significant differences in the PAH profile between species sampled from the canopy (oak and ash) compared with the understorey (hazel). Oak an d ash had similar PAH profiles, while hazel leaves had proportionally great er concentrations of the heavier molecular weight (4-, 5- and 6-ring) PAHs, and the ratios of these compounds to 3-ring PAHs was positively correlated with time. This affirms earlier work conducted on the same species in the same woodland, where we concluded that the canopy was filtering particles a nd attendant PAHs from air passing over or through it, and that these parti cles were transferred to the understorey and the woodland floor. (C) 2001 E lsevier Science Ltd. All rights reserved.