Effects of Dissolved Organic Matter on the Simazine Sorption in Different Soils

The effects of dissolved organic matter (DOM), derived from compost, on the sorption of simazine by soils were studied using a batch equilibrium technique. Six soils with different organic carbon contents were investigated in this study. Simazine sorption isotherms on soils were described by the linear equation, and the distribution coefficients without DOM (Kd) or with DOM (Kd*) were obtained. Generally, the values of Kd*/Kd were initially increased and then decreased with raising DOM concentrations of 0-65 mg DOC·L in the soil-solution system form. Critical concentrations of DOM (DOMnp) were obtained, and the value of Kd* was equal to Kd. The presence of DOM with concentrations lower than DOMnp promoted simazine sorption on the soils (Kd* > Kd), whereas the presence of DOM with concentrations higher than DOMnp tended to inhibit the simazine sorption (Kd* < Kd). Interestingly, DOMnp for the tested soils was negatively correlated to the soil organic carbon content, and the maximum of Kd*/Kd (Kmax) was correlated positively with the maximum of DOM sorption on the soil (Xmax). Further investigations also showed that the presence of the hydrophobic fraction of DOM evidently promoted the simazine sorption on soils, whereas the presence of hydrophilic DOM fraction obviously tended to inhibit the simazine sorption.