Nontarget Discovery of Organophosphite Antioxidant (OPA) Methyl Analogues in the Pearl River Estuary Sediments: Source Tracking to Commercial OPA Byproducts

Recent nontarget analyses have uncovered numerous novel organophosphate esters (OPEs) and organophosphite antioxidants (OPAs) in the environment, yet the origins of most newly identified contaminants remain elusive. In this study, we applied suspect and nontarget screening utilizing high-resolution mass spectrometry to identify eight novel OPA analogues (including parent OPAs along with mono- and dioxidized derivatives) structurally related to the commercial antioxidants AO626 and AO168, in sediments from the Pearl River Estuary. Their concentrations showed strong correlations with oxidation products of AO626/AO168. Further analysis revealed that seven of these compounds, termed OPA methyl analogues (OPAMAs), were present in commercial AO626 and AO168 products as OPAs and mono-oxidized derivatives, collectively accounting for 12-15% by mass. Laboratory photolysis experiments demonstrated that these OPAs and mono-oxidized derivatives can be oxidized in river water to form the corresponding mono- and dioxidized derivatives. Thus, sediment OPAMAs may originate from byproducts formed during industrial OPA synthesis using trimethyl phosphite and phenols via transesterification reaction. Retrospective screening confirmed OPAMA presence in food contact materials, corroborating a commercial-to-environment pathway. This study underscores that impurities and byproducts from commercial OPA products, together with environmental transformation, represent a significant source of emerging OPE contaminants in aquatic systems.