Current levels and composition profiles of emerging halogenated flame retardants and dehalogenated products in sewage sludge from municipal wastewater treatment plants in China

Occurrence of new toxic chemicals in sludge from wastewater treatment plants (WWTPs) is of concern for the environment and human health. Alternative halogenated flame retardants (HFRs) are a group of potentially harmful organic contaminants in the environment. In this study, a nationwide survey was carried out to identify the occurrence of HFRs and their potential dehalogenated products in sewage sludge from 62 WWTPs in China. Of all 20 target chemicals analyzed, decabromodiphenyl ethane (DBDPE), hexabromocyclododecane (HBCD) and 1, 2-bis (2,4,6-tribromophenoxy)-ethane (BTBPE) were detected in all sludge samples, and the concentrations were in the range of 0.82-215, 0.09-65.8, and 0.10-2.26 ng g^-1 d.w., respectively. Dechlorane Plus (DP) was found in 60 of 62 samples, and the concentration ranged from nd-298 ng g^-1 with a mean of 18.9 ng g^-1 d.w. The anti-DP fractional abundance f_anti (0.79) in the samples was much higher than the commercial DP composition (f_anti = 0.59), indicating a stereoselective degradation. Comparison with global sludge concentrations of HFRs indicate that China is at the medium pollution level in the world. Principal components analysis revealed that strong correlations existed between ln-transformed concentrations (natural logarithm) of the dominant BFRs and total organic carbon (TOC) as well as industrial wastewater proportion, influent volume and serving population. Significant linear relationships (R = 0.360-0.893, p < 0.01) were found among emerging brominated flame retardants (BFRs), suggesting their common commercial applications and release sources to the environment. Two kinds of dehalogenated products, pentabromocyclododecane (PBCD) and undecachloropentacyclooctadecadiene (Cl₁₁-DP), derived from HBCD and DP, were also identified in sewage sludge for the first time.