PBDEs versus NBFR in wastewater treatment plants: occurrence and partitioning in water and sludge

This study evaluates the occurrence of flame retardants (FR) in five wastewater treatment plants (WWTPs) located close to Barcelona (NE Spain), an area with high urban and industrial pressures. Compounds studied include eight polybromodiphenyl ethers (PBDEs) and eight New Brominated Flame Retardants (NBFRs), for which little information regarding their presence, partitioning and fate within the WWTPs is available. In unfiltered influent samples, PBDEs were not detected and bis(2-ethyl-1-hexyl)tetrabromophthalate was the only NBFR detected, and all WWTPs were efficient in eliminating this compound as no residues were found in the effluents. However, primary sludge contained from 279 to 2299 ng/g dry weight of ΣFR and the concentration increased in secondary (biological) sludge. NBFRs accounted for the main FR detected in sludge, representing a 63-97% of the total load, and among PBDEs, BDE-209 was the most ubiquitous congener. Considering the amount of sludge generated in each WWTP, it was estimated that 0.34-17.2 kg of FR are released annually through the sludge, which can have negative environmental and health implications if sludge is used as biosolid in agriculture. Overall, this study provides a sampling design and analytical protocol to be used to determine the evolution of FR in WWTPs and compares the levels detected, considering that PBDEs are being phased out to be substituted by other compounds which also have high accumulative and recalcitrant properties.