Elevated contaminations and risks of novel organophosphate esters and their transformation products in paddy soils

The contamination characteristics and associated risks of traditional organophosphate esters (TOPEs), novel OPEs (NOPEs), and their transformation products of diesters (di-OPEs) and hydroxylated derivatives (OH-OPEs), remain poorly understood in grain-producing regions. In this study, the occurrence and distribution of OPEs were investigated in paddy soils from the Dongting Lake Basin, the largest rice-producing region in China. The results showed that the median concentration of all measured OPEs (Σ₃₄OPEs) was 783 ng/g. Among these, the median concentration of Σ₃NOPEs (434 ng/g) was substantially higher than that of Σ₁₅TOPEs (166 ng/g) (p < 0.05). Additionally, the median concentrations of Σ₇OH-OPEs and Σ₉di-OPEs were 0.112 ng/g and 184 ng/g, respectively, suggesting active in situ transformation processes. Notably, the NOPE compound tris(2,4-di‑tert-butylphenyl) phosphate (AO168=O) and its transformation product bis(2,4-di‑tert-butylphenyl) phosphate (B2,4DtBPP) were identified as the predominant contaminants in these paddy soils. Spatial analysis revealed distinct regional distributions, with the West Dongting Lake Basin exhibiting the highest median concentration of Σ₃₄OPEs (1090 ng/g), followed by East (750 ng/g) and South (641 ng/g) basins. Ecological risk assessment using risk quotient (RQ) and toxicological priority index (ToxPi) approaches highlighted the high-risk priority of AO168=O (RQ, 7395; ToxPi, 0.81) and B2,4DtBPP (RQ, 6.87; ToxPi, 0.79). These findings provide critical insights into the occurrence, distribution, and environmental risks of NOPEs and their transformation products in rice-producing regions.