Effects of Soil and Chemical Properties on the Partitioning of Organophosphate Esters (OPEs) at the Soil–Water Boundary

The differentiation of the partitioning behavior of various organophosphate esters (OPEs) at the soil–water boundary remains unexplored. This study demonstrated the effects of soil properties and physicochemical properties of the OPEs on the desorption of the OPEs from artificial OPE-contaminated soils in the lab. Equilibration time varies among the classes of the OPEs, with shorter equilibration times observed for chlorinated OPEs compared to those of aryl OPEs. The soil–water partitioning coefficients (Kd) of chlorinated OPEs relative to aryl OPEs demonstrate their increased propensity for porewater distribution at soil–water interfaces. Soil type has a more significant impact on the aryl OPEs than on tris(2-chloroethyl) phosphate (TCEP) and tris[(2R)-1-chloro-2-propyl] phosphate (TCIPP), reflected by the higher relative standard deviation of log Kd values of aryl OPEs than TCEP and TCIPP among soils. Significant positive correlations were observed between the Kd values of target OPEs and total organic carbon (TOC) and dissolved organic carbon (DOC). Furthermore, fulvic acid and polyaromatic-type humic acid promoted the retention of aryl OPEs in soils, while tyrosine/tryptophan in dissolved organic matter correlated negatively with the Kd of various OPEs. The findings of this study enhance our understanding of the fate of OPEs at the soil–water boundary and inform evaluations of OPE bioavailability in contaminated soils.