Antioxidant Oxidation Leads to Greater Accumulation of Novel Organophosphate Esters (OPEs) than Traditional OPEs in soil and Groundwater.

Government agencies have implemented stringent regulations on directly used organophosphate esters (OPEs), such as triphenyl phosphate (TPhP). However, it remains unclear to what extent NOPEs derived from high production volume Organophosphite antioxidants (OPAs) contribute to contamination and environmental risks in industrial-park soil and groundwater. Here, we integrated field investigations of soil and groundwater from a representative industrial park with soil incubation experiments, in vitro rat liver S9 biotransformation assays, and hazard assessment modeling. In industrial soil, the median total concentration of Σ4NOPEs reached 4.0 × 103 ng g-1, which was 3.1-fold higher than that of traditional Σ20OPEs, with tris(2,4-di-tert-butylphenyl) phosphate (TDtBPP) identified as the predominant compound. In industrial groundwater, the median concentration of Σ4NOPEs was 7.5 × 103 ng L-1, approximately 13.2-fold higher than that of traditional Σ20OPEs (564 ng L-1). The transformation potential of OPAs was strongly dependent on molecular structure, with TDtBPPi undergoing the highest conversion potential. Relative to traditional TPhP, TDtBPP exhibited 72.1-fold greater persistence, 4.10-fold higher resistance to biotransformation, and 94.0-fold greater human exposure risk. This study demonstrates that the transformation of high production volume OPAs represents an overlooked pathway contributing to OPE contamination. OPA-derived NOPEs can accumulate to elevated levels and substantially increase contaminant burdens and associated exposure risks in industrial soil and groundwater.