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Historical records of airborne polycyclic aromatic hydrocarbons by analyzing dated corks of the bark pocket in a Longpetiole Beech tree.

Historical monitoring of airborne polycyclic aromatic hydrocarbons (PAHs) pollution levels was novelly demonstrated by analyzing the dated corks of a bark pocket formed from 1873 to 2003 in a Longpetiole Beech (Fagus longipetiolata) tree trunk sampled from southeastern China. The fundamental studies indicated that the PAHs of log K(oa) < 8.5 are primarily accumulated through interactions with lipid substances in cork and log K(oa) dependent, while the PAHs of log K(oa) > 8.5 existing as particle-phase dependent on log Vp are accumulated through stochastic entrapment by the lenticels on the surface of the cork. The translocation of PAHs by xylem flow and phloem stream as well as radial diffusion from the cork to the inner tissues was not significant, and the cork is most effective for accumulating airborne PAHs. The total concentrations of 16 EPA PAHs (sumPAHs) in the dated corks progressively increased from 43.5 ng/g recorded in the earliest available cork in 1873-1875 to the maximum 345.7 ng/g in 1956-1961, and then gradually decreased to 267.0 ng/g in 2003, while the concentration of perylene (PER) was slightly fluctuating at 0.178 +/- 0.033 ng/g. Moreover, the concentration ratio of sumPAHs to PER increased from 193 to 2431 from 1873 to 2003, indicating a progressive increase in PAH pollution in southeastern China.