Poster presentado en the SETAC Europe 31st Annual Meeting from 2–6 May 2021 in Seville, Spain.
Improving the air quality in cities is currently one of the main challenges for the European Union. Many studies showed that urban trees could be “Nature Based Solutions” that, providing important ecosystem services, can contribute to air pollution reduction. For example, plants can uptake organic contaminants from air including Polycyclic Aromatic Hydrocarbons (PAHs). Moreover, these compounds can be used as carbon source by phyllosphere microorganisms contributing to their degradation. Few studies focused on the quantification of the actual contribution of these microorganisms to the natural attenuation of airborne PAHs in urban areas. Existing studies focused mainly on the composition of the phyllosphere microbial communities and on the isolation of PAH degraders rather than on the estimation of biodegradation half-lives for these chemicals. In this study we measured the partitioning of 14C-pyrene (14C-PYR) on leaves of an urban holm oak (Quercus ilex), and its mineralization by indigenous phyllosphere microorganisms and by a PAH degrader (i.e., Mycobacterium gilvum) inoculated on leaves. Mineralization was investigated in two environments (i.e., water vs. air) using two different experimental systems. Moreover, to evaluate the influence of traffic generated particulate matter (PM) (deposited on leaf surface) on partitioning and mineralization of pyrene, both unwashed and washed leaves were considered. Partitioning was evaluated by measuring leaf-water partition coefficient (KLW) and estimating leaf-air (KLA) partition coefficient. Moreover, pyrene mineralization rate (k) and biodegradation half-lives (HL) were calculated under different experimental conditions. The partition experiments provided a leaf-water partition coefficient (Log KLW ~3.5 L kg-1) and a leaf-air partition coefficient (Log KLA ~1 m3 g-1) for holm-oak which were in the range of those reported in literature for otherplant species. The mineralization experiments showed that degradation was faster on unwashed leaves resulting in biodegradation half-lives of 14 days and 127 days for unwashed and washed leaves respectively. The results highlighted that plant-PM-microbe interactions could have a role in air quality improvement. The data obtained in the current study are among the few data available on PAH mineralization on leaves and are important input parameters for multimedia fate models aiming at quantifying the “air quality improvement” ecosystem service provided by urban trees.