Riverine transport dynamics and historical trends of emerging and legacy flame retardants in an urbanized coastal zone: Pollutant management effectiveness in China.

Environmental pollution caused by the widespread use of flame retardants has been a major concern. To examine the state of emerging and legacy pollution and effectiveness of controlling measures, water samples were collected from eight major river outlets and five coastal sites in June, August, and December 2022 and sediment samples were from eight major river outlets in June 2022 in the Pearl River Delta, China. These samples were analyzed for organophosphorus flame retardants (OPFRs) and polybrominated diphenyl ethers (PBDEs). Due to widespread bans on PBDEs and replacement by OPFRs in the past decade, the concentrations of OPFRs were significantly higher than those of PBDEs (p<0.05), by two to three orders of magnitude. For example, the average concentrations of ∑8OPFR and ∑26PBDE in water samples from the eight major river outlets were 41.1 and 0.37 ng L-1, respectively; while those in sediment samples were 27.0 and 3.08 ng g-1, respectively. This difference reflects the effectiveness of China's environmental policies over time. At the same time, the annual riverine fluxes of OPFRs decreased from 72,000 kg year-1 in 2017 to 14,100 kg year-1 in 2022, whereas those of PBDEs decreased from 2140 kg year-1 in 2005 to 137 kg year-1 in 2022. Flooding diluted the concentrations of OPFRs but elevated those of PBDEs by freshly flushed particulate matter, due to different hydrophilicities. Although most OPFRs and PBDEs pose minimal ecological risks in water, the overall risk should not be overlooked, especially as BDE-209 may induce extremely high ecological risk in water. Overall, continuous monitoring of OPFRs and PBDEs in the Pearl River Delate remains crucial.