Department of Science and High Technology, University of Insubria, Via Valleggio 11, 22100 Como, Italy.
Department of Sciences and Technologies, University of Sannio, Via F. De Sanctis SNC, 82100 Benevento, Italy.
Sci Total Environ. 2020 Oct 15;739:139893. doi: 10.1016/j.scitotenv.2020.139893. Epub 2020 Jun 6.
Urban trees provide important ecosystem services, including air quality improvement. Polycyclic aromatic hydrocarbons (PAHs) are among the most important pollutants in air, due to their elevated concentrations and toxicity. Plants can act as filters of PAHs and as "chemical reactors" for pollutant removal, therefore reducing air concentrations. Here, the first assessment of photo- vs. biodegradation of PAHs on leaves of urban trees is presented. A dynamic air-vegetation-soil model (SoilPlusVeg) was improved to simulate the fate of two representative PAHs with contrasting physico-chemical properties (phenanthrene and benzo[a]pyrene). Simulations were performed for two different environmental scenarios from Italy (Como and Naples), selected for their dissimilar meteorological parameters, plant species and emission levels. The effect of photo- and biodegradation on leaf concentrations and fluxes towards air and soil was investigated comparing deciduous (maple, cornel and hazelnut) and evergreen (holm oak) broadleaf woods. The results showed that biodegradation in the phyllosphere could not be neglected when evaluating the ecosystem services provided by urban trees, as this process contributed significantly to the reductions (up to 25% on average) in PAH leaf concentrations and fluxes to air and soil; however, the reductions revealed ample variations with time (up to more than two orders of magnitude) showing the dependence on meteorological parameters, air compartment structure, as well as type of woods. These findings permitted to improve the ecological realism of the simulations and obtain more accurate results when predicting organic contaminant uptake and release by plant leaves, including potential for food chain transfer and long-range transport.
城市树木提供了重要的生态系统服务，包括改善空气质量。多环芳烃（PAHs）是空气中最重要的污染物之一，因为它们的浓度高且毒性大。植物可以作为 PAHs 的过滤器和污染物去除的“化学反应器”，从而降低空气中的浓度。本研究首次评估了城市树木叶片上 PAHs 的光降解与生物降解。改进了动态空气-植被-土壤模型（SoilPlusVeg）以模拟两种具有不同物理化学性质的代表性 PAHs（菲和苯并[a]芘）的归宿。针对意大利的两个不同环境情景（科莫和那不勒斯）进行了模拟，这些情景因气象参数、植物物种和排放水平的不同而有所区别。通过比较落叶林（枫树、山茱萸和榛子）和常绿树（油橄榄）阔叶林，研究了光降解和生物降解对叶片中 PAHs 浓度以及向空气和土壤中迁移通量的影响。结果表明，在评估城市树木提供的生态系统服务时，不能忽视叶片生物降解对 PAHs 浓度和向空气及土壤中迁移通量的影响，因为该过程对 PAHs 浓度的降低（平均可达 25%）和向空气及土壤中的迁移通量有重要贡献；然而，随着时间的推移，这种降低幅度变化较大（高达两个数量级以上），表明其对气象参数、空气区室结构以及树木类型的依赖性。这些发现提高了模拟的生态现实性，并在预测植物叶片对有机污染物的吸收和释放时获得了更准确的结果，包括食物链转移和长距离传输的潜力。
