Simulation of the Migration and Release Characteristics of Organophosphate Esters in Fluctuation Zone Soil of the Three Gorges Reservoir During Flooding

Abstract

In this study, we investigated the effects of organophosphate ester (OPE) concentrations, temperature, soil organic matter, and microorganisms on the migration and release of several common OPEs from fluctuation zone soil in the Three Gorges Reservoir (TGR) to the overlying water by simulation experiments in the lab. The results indicate that the release of OPEs is determined based on their concentrations in the soil. The release of OPEs from soil to the overlying water decreases with increasing organic matter content, which indicates that the presence of organic matter could inhibit the migration of OPEs. However, the inhibition of the release of OPEs of organic matter is not significantly enhanced when the organic content (dry weight) is greater than 30 g·kg-1. The average migration amount of OPEs is 1077.3 ng·mL-1 at 27℃, which was higher than that at 7℃, indicating that high temperature promotes the release of OPEs. The effect of microorganisms is not notable. Chlorine-based OPEs including Tris(2-chloroethyl) phosphate (TCEP), Tris(1-chloro-2-propyl) phosphate (TCPP), and Tris(1,3-Dichloro-2-Propyl) phosphate (TDCP) are the main monomers in the overlying water, mainly because both the Octanol-Water Partition Coefficient (Kow) and Organic Carbon Partition Coefficient (Koc) of chlorine-based OPEs are lower than that of alkane-based OPEs and aromatic-based OPEs. Thus, chlorine-based OPEs are more easily dissolved in water and are not easily adsorbed by organic matter in the soil. Therefore, chlorine-based OPEs are more likely to migrate from the soil and to be released into the overlying water than other OPEs and become the main OPE monomers in the overlying water of the TGR.