Passive sampling in brackish waters: Monitoring metals and organic pollutants in the Camargue and its application to phytoremediation

Abstract

The Camargue region in southern France, characterized by its unique brackish water ecosystems, faces significant contamination from agricultural runoff, introducing organic pollutants and metals into the environment. This study presents a four-seasonal monitoring program comprising nine sampling campaigns, using Polar Organic Chemical Integrative Samplers (POCIS) and Diffusive Gradients in Thin Films (DGT) to explore the temporal and spatial dynamics of contaminants. A comprehensive analysis was conducted on 483 organic pollutants, encompassing a broad spectrum of herbicides, fungicides, their degradation products, and a comprehensive list of heavy metals. By providing time-weighted average concentrations, these techniques allowed to track seasonal variations driven by agricultural cycles and hydrological processes. The results revealed persistent organic pollutants, such as 2-methyl-4-chlorophenoxyacetic acid (MCPA), atrazine metabolites, and metolachlor ethanesulfonic acid (ESA), exhibiting clear seasonal peaks aligned with crop applications. Heavy metals, including copper and barium, displayed temporal fluctuations influenced by both anthropogenic activities and natural geochemical processes. To demonstrate the applicability of this monitoring approach, passive samplers were also deployed within an existing phytoremediation system based on Phragmites australis, allowing to assess its effectiveness in contaminant removal. While organic pollutants were reduced by up to 95 %, metal removal remained variable. This study underscores the high suitability of passive sampling for long-term environmental monitoring in brackish water ecosystems, offering a robust methodology to track pollutant dynamics, support regulatory assessments, and evaluate remediation strategies. The findings provide critical insights for future monitoring programs aimed at balancing agricultural productivity with the protection of fragile aquatic environments.