Review on Degradation Behavior and Transformation Products of Organophosphorus Flame Retardants

Organophosphorus flame retardants (OPFRs), as widespread alternatives to brominated flame retardants, are now ubiquitous in the environment and generate a large number of uncharacterized transformation products (TPs) through abiotic and biotic transformation. However, a comprehensive description of OPFR TPs is still lacking. This review systematically integrates current knowledge on the environmental fate of OPFRs, focusing on the formation, occurrence, and toxicity of TPs. We compiled 463 TPs derived from 25 parent OPFRs identified in laboratory studies, involving 1338 reaction pathways, among which hydrolysis (>29%) and hydroxylation (>30%) were the dominant reaction pathways in microbial, plant, and animal metabolism. To date, 19 TPs have been confirmed in multiple environmental matrices, among which diester metabolites (e.g., diphenyl phosphate (DPHP) and bis(1,3-dichloro-2-propyl) phosphate (BDCIPP)) are most frequently detected in human urine, blood, and breast milk. Importantly, accumulating toxicological data indicate that TPs such as hydroxylated triphenyl phosphate (OH-TPHP), BDCIPP, and di-n-butyl phosphate (DnBP) exhibit greater endocrine-disrupting, developmental, and metabolic toxicity than their parent compounds. Given the evidence presented, heightened emphasis should be placed on incorporating TPs into environmental risk assessment.