Seasonal Influence on Pesticide Transfer and Bioaccumulation in Native Wetland Vegetation in an Agricultural Critical Zone

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Wetlands are acknowledged for their significant role in mitigating contaminant fluxes to aquatic environments. However, the contribution of intrinsic vegetation to the efficacy of wetlands in dispersing pesticides remains a subject of debate. This study seeks to quantify: (1) the ability of native wetland plants to bioaccumulate pesticides in distinct compartments (roots, stems, leaves), and (2) the transfer of pesticides from sediments and water to plants, as well as within plants. Two field campaigns were conducted in a pond located in an agricultural area during two contrasting seasons: autumn and the subsequent summer. Six pesticides (metolachlor, boscalid, epoxiconazole, tebuconazole, aclonifen and pendimethalin) typical of arable farming practices and with different chemical properties were analysed in samples taken from five native plant species: Salix alba L., Carex pendula Huds, Mentha aquatica L., Typha latifolia L. and Juncus inflexus L. A new method was developed to analyse pesticides by using thermo desorption GC-MS which allowed a sensitive quantification in all plant compartments. Pesticides were found in all the plants, but Salix alba and Carex pendula proved to be the most effective accumulators of pesticides compared to other species, and showed perennial accumulation over time. The most hydrophobic molecules were mainly found in leaves, partly due to translocation. The impact of flood events, which introduced a significant amount of pesticides from the upper drainage catchment into the pond between the two sampling campaigns, was evident in terms of storage by plants. This study highlights the importance of revegetating ponds with native species as part of a wetlands remediation plan.