A comprehensive review of contents, toxic effects, metabolisms, and environmental behaviors of brominated and organophosphorus flame retardants

As emerging contaminants, flame retardants are ubiquitous in water, soil, the atmosphere, and organisms. Brominated (BFRs) and organophosphorus flame retardants (OPFRs) dominate as primary replacements for brominated diphenyl ethers, yet their comparative ecotoxicity and environmental behavior remain critically understudied. This study comprehensively summarizes environmental levels, toxicities, metabolism, and environmental behaviors between BFRs and OPFRs. It is showed that OPFRs have surpassed BFRs by 1 - 2 orders of magnitude in concentration becoming dominant contaminants across environmental matrices. OPFRs exhibit similar toxicity targets yet more complex metabolic pathways than BFRs, indicating that they are not environmentally safer alternatives. Meanwhile, they undergo microbial degradation as carbon substrates, photolysis as photosensitizers, and hydrophobic adsorption onto organic matrices (e.g., dissolved organic matter). These environmental behaviors may enhance or inhibit toxicity risk of flame retardants. In addition, the removal technologies and regulatory measures for flame retardants still require continuous refinement. Future studies should prioritize combined risk assessment of mixtures especially metabolites, environmental behaviors, and identification of the key environmental factors of flame retardants.