Degradation of organophosphate flame retardants by white-rot fungi: Degradation pathways and associated toxicity

The environmental persistence of organophosphate flame retardants (OPFRs) in water is becoming and environmental concern. White Rot Fungi (WRF) have proven its capability to degrade certain OPFRs such as tributyl phosphate (TBP), tris(2-butoxyethyl) phosphate (TBEP), tris(2-chloroethyl) phosphate (TCEP) and tris(2-chloroisopropyl) phosphate (TCPP). Despite this capability, there is limited knowledge about the specific pathways involved in the degradation. In this study, three different WRF were paired with individual OPFRs, and potential transformation products (TPs) were identified by UHPLC-HRMS. Some compounds structures were further validated by NMR. From these data degradation pathways were proposed. TBP was degraded by successive hydroxylation and hydrolysis reactions, with a novel dehydrogenation step suggested. Both TCEP and TCPP underwent oxidative dechlorination, with TCEP experiencing subsequent hydrolysis. Uncommon reductive dehalogenation was also observed. TCPP further underwent hydroxylation and environmentally relevant methylation. TBEP generated numerous TPs, mainly by successive dealkylations, along with hydroxylation. Notably, demethylation in TBEP degradation was proposed for the first time. Additional secondary products were formed through hydroxylation and oxidation of the initial metabolites. Finally, in vivo and in silico toxicity assessments were conducted, identifying certain TPs as potentially toxic.