Occurrence and distribution of oligomeric organophosphorus flame retardants in different treatment stages of a sewage treatment plant

Oligomeric organophosphate esters (OOPEs) like 2,2-bis(chloromethyl)-propane-1,3-diyltetrakis (2-chloroethyl) bisphosphate (V6), resorcinol bis(diphenylphosphate) (RDP) and bisphenol A bis(diphenylphosphate) (BDP), are widely used as alternatives of Deca-BDE in plastic and electronic consumer products. However, studies on the environmental occurrence and fate of OOPEs are very scarce. This work studied the occurrence, distribution and fate of V6, BDP and RDP during the different treatment stages of a sewage treatment plant (STP) in Beijing, China. To accomplish this, a method to analyze trace V6, BDP and RDP in suspended solids samples and aqueous samples of sewage and sludge was developed by using liquid chromatography tandem mass spectrometry (LC-MS/MS). Using this method, BDP and RDP were detected for the first time in suspended solids of sewage and sludge with a concentration of 2.06–5.82 ng/g dry weight and 0.44–3.45 ng/g dry weight, respectively, whereas their concentration level in the aqueous phase of these samples were below the detection limits of the method. However, V6 was detected in all treatment stages of the STP, with concentrations in the range of 10.2–27.1 ng/L in aqueous phase and 0.40–1.73 ng/g dw in solid phase. Mass balance results indicated that 75.6% of the original V6 mass flow was discharged along with effluent, while 83.3% and 72.2% of the initial RDP and BDP mass flow were lost due to biodegradation, respectively. Nevertheless, compared to the 14 widely used monomeric organophosphate esters (MOPEs), the concentration levels of OOPEs in this studied STP were relatively low. - Highlights: • An analytical method to measure trace 3 OOPEs in sewage and sludge was developed by using LC-MS/MS. • BDP and RDP were detected for the first time in suspended solids of sewage and sludge. • Mass flow and mass balance were applied to study the fate of 3 OOPEs in STP. • 75.6% of the initial V6 mass flow was discharged along with effluent. • 83.3% and 72.2% of the initial RDP and BDP mass flow were lost due to biodegradation, respectively.