Polycyclic aromatic hydrocarbons (PAHs) pollution recorded in annual rings of gingko (Gingko biloba L.): Translocation, radial diffusion, degradation and modeling

Burken's “donut ring” model was solved correctly, which was developed based upon the anatomy structure and the flow patterns of the tree. The correction of the model solution was validated by our field experimental data statistically. The vertical PAHs in sapwood is described as a carbon–nitrogen–water interaction process, which is companied with the allocation of photosynthate and other non-structure carbon. It could be found that the vertical translocation is related to the height of the sampling position closely. The anisotropy result of the estimated Dz and Dr is in agreement with the structure of trunk tissue, suggesting that the radial diffusion is much difficult. Although the estimated Dz and Dr are confirmed to depend upon Kow (the partition coefficient of PAHs in octanol/water), the different dominant factors are demonstrated in our result. Although the metabolism and degradation in Burken's model were neglected, the evidence of degradation presents in this work. 2-Chloro-Nap might be the degradation product of Nap by adding Cl to Nap rings, for 2-chloro-Nap only contains in trunk samples. This result was validated by the first-order degradation equation. The initial degradation reaction mechanism was also discussed briefly.