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Elucidating the role of microplastics as reservoirs of brominated flame retardants in river sediment
Summary
This study measured brominated flame retardant chemicals — persistent and toxic pollutants — on microplastics isolated from river sediments collected over 12 months above and below a wastewater treatment plant. Microplastics carried less than 1% of the total flame retardant load in sediments, suggesting they play a minor role as pollutant vectors compared to the sediment itself. However, higher microplastic and chemical concentrations were consistently found downstream of the treatment plant, pointing to wastewater discharge as a key contamination source.
Microplastics (MPs) are emerging contaminants in aquatic ecosystems and have been suggested to act as vectors of organic pollutants such as brominated flame retardants (BFRs). In this study, river sediments were collected upstream and downstream of a wastewater treatment plant (WWTP) over a 12-month period. Concentrations of eight polybrominated diphenyl ethers (PBDEs) and eight novel brominated flame retardants (NBFRs) were determined. In addition to bulk sediment analysis, BFRs were - for the first time - measured in the MPs isolated from each sediment sample, and the residual sediment remaining after MP removal. The proportion of BFRs associated with MPs was very low, typically < 1 % of total sediment loading. Consistent with this, MP mass and BFR concentrations were not significantly correlated, except for BDE-183 (r = 0.405, p = 0.049). Partition coefficients (K) reveale significant differences among BFRs, with BDE-209 and DBDPE differing from several lower-brominated congeners, consistent with logKow. Downstream of the WWTP, higher MP and BFR concentrations were observed, with significantly elevated ΣPBDE and BDE-209 levels (p = 0.034). Month-to-month fluctuations were evident, with spikes in November 2022, but no clear seasonal trend. Overall, MPs likely play a limited role as reservoirs of BFRs in this urban UK river system.