Degradation of bisphenols, halogenated flame retardants, and pesticides in wastewater and biosolids samples during frozen storage.

Wastewater and biosolids are important pathways of chemicals to the environment and thus are often included in monitoring programs. Wastewater samples are often stored frozen when insufficient resources prevent immediate analysis or when samples are included as part of environmental specimen banks. However, the stability of chemical substances in frozen samples is not well known. The objective of this study was to evaluate the stability over a one-year period of three substance groups: bisphenols, halogenated flame retardants (HFRs), and pesticides in frozen (-20 °C) wastewater media. Influent, effluent, and biosolids samples were collected from two wastewater treatment plants (WWTPs) and target analytes were spiked into each sample. Three influent, effluent, and biosolids samples from both WWTPs were immediately chemically analyzed and triplicate influent, effluent, and biosolids samples from both WWTPs were analyzed after approximately 30-70, 180, and 365 days of frozen storage. The bisphenols (except bisphenol E), all but one HFR (pentabromobenzyl bromide), and pesticides in the organochlorine, organonitrogen, and pyrethroid groups were highly or moderately stable during frozen storage. Although most organophosphates and triazines were also highly or moderately stable, there were seven analytes in these pesticide groups, namely chlorpyriphos-oxon, diazinon-oxon, disulfoton sulfone, malathion, phosmet, ametryn, and metribuzin that were not stable. Consistent differences in chemical stability were not observed between the different wastewater matrices or time frozen. This study indicates that wastewater and biosolids samples can be stored frozen with confidence that concentrations of bisphenols, HFRs, and pesticides are not affected by chemical transformation, with a few exceptions.