Polycyclic aromatic hydrocarbons (PAHs) pollution recorded in annual rings of gingko (Gingko biloba L.): Translocation, radial diffusion, degradation and modeling Hui Yin a,b , Qing Tan b , Yong Chen b , Guibin Lv b , Dahua He c , Xiandeng Hou a, ⁎ a College of Chemistry, Sichuan University, Chengdu, Sichuan 610064, China b Chengdu Environmental Monitoring Center, Chengdu, Sichuan 610072, China c College of Mathematics, Sichuan University, Chengdu, Sichuan 610064, China abstract article info Article history: Received 8 August 2010 Accepted 13 August 2010 Available online 27 August 2010 Keywords: Polycyclic aromatic hydrocarbons Gingko Translocation Radial diffusion Degradation 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 D z and D r is in agreement with the structure of trunk tissue, suggesting that the radial diffusion is much difficult. Although the estimated D z and D r 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. © 2010 Elsevier B.V. All rights reserved. 1. Introduction It is commonly recognized that plants can act as a global and regional contamination indicator of anthropogenic toxic persistent organic pollutants (POPs) in air and its host soil [1]. However, there has been so far no evidence that organic contaminants in plants could be historical tracer with exception of the bark [2,3] and isotope information in tree-rings [4,5]. To further explore organic contami- nants in plants as historical tracers, it has significant meaning to clearly describe the organic contaminants accumulation behavior in plants. The accumulation behavior of organic contaminants in plants has been documented, including the following processes: (a) uptake, (b) translocation, (c) metabolism degradation (rhizodegradation and phytodegradation), (d) sorption and desorption between stream and biomass, and (e) transpiration of volatile organic compounds through leaves [1]. There are several uptake pathways for organic pollutants to enter plants as described in a previous paper of this issue. Uptake of organic contaminants has been investigated in numerous previous studies by empirical models, controlled exposure experiments in greenhouse, and field experiments [6–8]. For PAHs, it could be found in our previous work in this issue and Dietz [9] that the main uptake pathway might be gaseous and particles-bound deposition via foliage with the exception of two-ring compounds from root. Metabolism and degradation have been evaluated by 14 C-labeled experiments of atrazine [10], and a fuller review of this process can be found in Burken [11]. To the best of our knowledge, there are few works focused on the process of PAHs translocation into the trunk. The organic contaminant accumulation behaviors in plants are controlled by the factors of physical–chemical properties of pollu- tants, plant species, environment parameters and pollutants concen- trations in surrounding [1,6–8]. Many models have been developed to describe the accumulation processes [12–20]. Trapp and colleagues constructed a simple four compartments (air, soil, roots, and shoots) model from fugacity which indicated the escaping tendency of a chemical substance from a compartment or named phase [17]. One of the most comprehensive equilibrium and dynamic (steady-state) models by Trapp described roots uptake and translocation behaviors of neutral and ionized chemicals based on molecular level [18]. The model approach combines the processes of lipophilic sorption, electrochemical interactions, ion trap, advection in xylem and dilution by growth. Although Trapp declared the model predicted uptake and translocation with high accuracy for non-electrolytes, this model ignored a basic fact that the main uptake pathway is via foliage, not from roots, for the lipophilic organic compounds, especially PAHs. These kinds of models are not specific for not considering the dynamic process, such as translocation and diffusion. This led to unreasonable result that the concentration of a certain contaminant is the same in anywhere in the trunk. Microchemical Journal 97 (2011) 131–137 ⁎ Corresponding author. E-mail address: houxiandeng@yahoo.com.cn (X.D. Hou). 0026-265X/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.microc.2010.08.004 Contents lists available at ScienceDirect Microchemical Journal journal homepage: www.elsevier.com/locate/microc