Trace elements and polycyclic aromatic hydrocarbons remediation by soil-plant infiltration systems: a way to decrease environmental impact of cities?
Résumé
City development to support population growth results in water cycle disturbance due to impervious surface area increase, water runoff pollutant fluxes [1] , and roadside soil pollutant accumulation [2] that may drive to groundwater contamination. To prevent potential long-term risks for the environment, Low Impact Development Technologies (LIDT) have been widely implemented in the past few years due to combined ecological and economic advantages. However, poor is known about the role of plants and their associated microorganisms on pollutants remediation in such green infiltration systems. Thereby, six representative large-scale outdoor mesocosms planted with Juncus effusus, Iris pseudacorus, Phalaris arundinacea as monospecies were co-contaminated with Polycyclic Aromatic Hydrocarbons (PAHs, i.e. phenanthrene, pyrene and benzo[a]pyrene), and Trace Elements (TEs, i.e. zinc, lead, and cadmium). Mesocosms were studied two years for plant biomass production, PAHs soil dissipation, and metal uptake by plants. PAHs were extracted from soils by microwave assisted extractions and analysed by gas chromatography (GC-MS) while microwave-acid digestion was used to extract metals from soil and plants, which were then analysed by ICP-AES. A special attention was paid to soil microbial community structure through total, fungal and bacterial biomasses using Q-PCR, 16S rDNA and 18S rDNA and total microbial activity. TEs uptake varies considerably with plant species and the TE considered. The sequence of TEs availability to plant was determined. PAHs concentrations in soil were drastically reduced after six months and divided by 10 to 100 for low molecular weight PAHs and by 2 to 7 for benzo[a]pyrene depending on plant species. In order to compare this approach at mesocosm scale to LIDT performance and apply our results to a real case study, grass and vegetated swales receiving laterally road runoff water were also investigated for pollutant remediation and microbial characterization. The results show similar conclusion as those obtained with experimental mesocosms. Through this study, application of analytical chemistry to environmental purpose is illustrated and the need of a multidisciplinary approach to study ecological technologies benefits is pointed out.