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Communication Dans Un Congrès Année : 2021

Monitoring of sediment contaminations in surface freshwaters: relevance of time-integrated sampling of suspended particulate matter (SPM)

Résumé

European directives require from each Member State to monitor the contamination of continental sediments and confirm that the concentrations of hydrophobic organic contaminants and trace metals in sediments do not significantly increase with time. In France, the Water Agencies do not have a fit-for-purpose methodology for correctly interpreting the data on sediment contamination monitoring. The main operational obstacle is the difficulty to compare surface sediment contamination data from year to year, due to the natural variability of sediments (such as grain size, which partially controls the variability of contaminant concentrations). Thus, the sampling of suspended particulate matter (SPM) that targets small-size particles (typically <200 µm) represents a promising alternative to surface sediments monitoring. To demonstrate this hypothesis, we used on the concentrations of several contaminants (trace elements and PAHs) measured in surface sediment and SPM (collected via continuous centrifuge sampling) provided by French Water Agencies from their monitoring programs in order to assess temporal trends of contamination. Trends analysis (Hype Software) highlighted the relevance of using SPM sampling compared to sediment monitoring, especially because of the greater homogeneity of the sampled particles. We notably highlighted that the sampling of SPM allows to better detect temporal trends despite a limited number of samples and avoid a concentration normalization step (e.g. using Fe or Al for metals), which is often required to assess temporal trends by using surface sediment. To collect SPM, particle traps represent an affordable alternative tool to obtain a sufficient amount of SPM for chemical analyses. In comparison to continuous centrifugation, particle traps have the advantage of providing integrative SPM sampling over a period of typically 2 to 4 weeks. Moreover, particle traps can be easily deployed on a monitoring network, without the need of expensive maintenance or highly qualified personnel. As part of the Rhône Sedimentary Observatory (OSR) program, particle traps (designed according to those from German Environmental Specimen Bank) are deployed since 2009 all along the Rhône River (from Lake Geneva to the Mediterranean Sea) and at the outlets of its main tributaries for the monitoring of particulate contaminants. In order to demonstrate the relevance and the representativeness of SPM collected by particle traps, grain size distributions, PCB (Polychlorinated biphenyls) and mercury concentrations were compared in SPM collected in parallel over 2-weeks periods by particle trap and by continuous centrifugation (considered as the reference sampling method) over a period of 4 years at Jons Station (Upper Rhône River). Results showed that SPM collected by particle trap are coarser than SPM collected by centrifugation. We showed that this shift was highly dependent on water discharge, without affecting PCB and Hg concentrations, which allows estimating accurate temporal trends or particulate fluxes of PCB and Hg at annual scale. Concentrations of Hg obtained on SPM collected on the Saône River displayed a seasonal trend with higher concentrations during low flow conditions, suggesting a higher proportion of organic-enriched autochthonous SPM during these hydrological conditions.
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hal-03594132 , version 1 (02-03-2022)

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  • HAL Id : hal-03594132 , version 1

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Aymeric Dabrin, Anice Yari, Matthieu Masson, Jérôme Le Coz, Marina Coquery. Monitoring of sediment contaminations in surface freshwaters: relevance of time-integrated sampling of suspended particulate matter (SPM). 2nd international conference on contaminated sediments, CONTASED 2021, 2021, Bern - Online, Switzerland. ⟨hal-03594132⟩
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