Sorption and desorption of organophosphate esters with different hydrophobicity by soils

Organophosphate esters (OPEs) are ubiquitous contaminants with potentially hazardous effects on both the environment and human health. Knowledge about the soil sorption-desorption process of organic chemicals is important in order to understand their fate, mobility, and bioavailability, enabling an estimation to be made of possible risks to the environment and biota. The aim of this study was to use the batch equilibrium technique to evaluate the sorption-desorption behavior of seven OPEs (TCEP, TCPP, TBEP, TDCP, TBP, TPhP, and EHDP) in soils with distinctive characteristics (two unamended soils and a soil amended with sewage sludge). The equilibrium concentrations of the OPEs were determined by high performance liquid chromatography coupled to a triple quadrupole mass spectrometer (HPLC-MS/MS). All the compounds were sorbed by the soils, and soil organic carbon (OC) played an important role in this process. The sorption of the most soluble OPEs (TCEP, TCPP, and TBEP) depended on soil OC content, although desorption was ≥ 58.1%. The less water-soluble OPEs (TDCP, TBP, TPhP, and EHDP) recorded total sorption (100% for TPhP and EHDP) or very high sorption (≥ 34.9%) by all the soils and were not desorbed, which could be explained by their highly hydrophobic nature, as indicated by the logarithmic octanol/water partition coefficient (K_ow) values higher than 3.8, resulting in a high affinity for soil OC. The results of the sorption-desorption of the OPEs by soils with different characteristics highlighted the influence of these compounds' physicochemical properties and the content and nature of soil OC in this process.