Occurrence of Dechlorane series flame retardants in sediments from the Pearl River Delta, South China

Dechlorane series flame retardants (DECs), e.g. Dechlorane plus (DP), have reportedly showed an increase in consumption since the phase-out of traditional brominated flame retardants (BFRs). Here we investigated DP and 7 structural analogues, as well as its 2 dechlorinated products in 76 surficial sediments from the Pearl River Delta (PRD), one of the three important manufacturing bases of China. The concentration of Σ₈DECs varied from 28.1 to 38,000 pg g^-1 dw in the PRD sediments, dominated by DP and Mirex. Spatially, sedimental DP concentrations were significantly and positively correlated with the municipal gross domestic product (GDP), population and sewage discharge of the PRD cities, but were insignificantly related to their industrial outputs. This indicates that DP in the PRD sediments mainly originated from urban activities instead of industrial ones. Although Mirex has been restricted for several decades, it demonstrated ubiquity in the PRD and considerably high levels in several termite control hot-spots (up to 34,200 pg g^-1), implying its massive historical use in this subtropical region. Other DECs, however, exhibited quite low abundances, implying their limited applications in this region. In comparison to the historical data, sedimental DP concentrations presented an increasing trend in most rivers in the PRD except the West River. The fractions of anti-DP (f_anti) showed insignificant deviations from its technical value, suggesting that no obvious anti-DP transformation occurred in most PRD sediments. However, anti-Cl₁₁-DP, an important dechlorination product of anti-DP, was ubiquitously found in the PRD sediments, and its concentrations were significantly and positively associated with those of anti-DP. Therefore, anti-Cl₁₁-DP in the PRD sediments was deemed as the impurity co-emitted with anti-DP rather than its dechlorination byproduct. Considering its ubiquity, increasing trend and persistence, DP in the PRD environments merits continuous concerns.