Understanding the environmental fate and risks of organophosphate esters: Challenges in linking precursors, parent compounds, and derivatives.

Organophosphate esters (OPEs) have emerged as a global environmental and health concern due to their persistent, bioaccumulative, and toxic (PBT) properties. Recently, their precursors-organophosphite antioxidants (OPAs)-and transformation products, which may exhibit greater persistence and toxicity, have gained attention as critical contributors to OPE-related contamination. This critical review examines the transformation mechanisms of "OPAs → OPEs → OPE derivatives" across environments, sources and emission inventory methodologies, and the environmental occurrence, persistence, and toxicity of these chemicals. Key findings include: 1) the prevalence of certain novel OPEs derived solely from OPAs; 2) the significant role of OPAs in OPE emissions; 3) higher OPA detection frequencies and concentrations near emission sources; and 4) increased persistence of some OPE derivatives compared to parent compounds. However, critical knowledge gaps remain: 1) limited understanding of transformation mechanisms and products; 2) rough and incomplete emission factors without consideration of specific chemicals and emission via abrasion; 3) insufficient attention to a broader range of OPEs and OPAs beyond well-known examples like tris(2,4-di-tert-butylphenyl) phosphite (AO168) and its oxidized form tris(2,4-di-tert-butylphenyl) phosphate (AO168 =O); 4) lack of simultaneous studies concerning all three chemical categories simultaneously within a single gauging work for better understanding their association and therefore sources and fate; and 5) inadequate toxicity and degradation data for novel OPE and derivatives, hindering a comprehensive risk assessment of OPEs. Addressing these gaps is crucial for accurate risk assessment of OPE ecological and human health risks, enabling better management strategies for OPEs and their relevant chemicals.