Effects of Exogenous Organic Matter on the Migration of Organic Contaminants with Different Polarities in Soil

Exogenous DOM (dissolved organic matter) plays an important role in the co-migration of organic pollutants, which controlled by many factors. To evaluate the effect of DOM on contaminants migration and reveal the controlling factors, batch sorption experiment was conducted with carbamazepine (CBZ) and sulfamethoxazole (SMX) as two typical pollutants and montmorillonite as medium. Use humic acid to represent DOM. Fourier-transform infrared spectroscopy and dual-beam UV-Vis spectrophotometer was used for sample characterization. The results showed great differences. DOM can reduce the adsorption capacity of SMX by 4.5 times when the SMX concentration reaches 40 mg/L. But for CBZ, its sorption changed from inhibition to promotion as concentration increases. DOM can increase its adsorption capacity by 2.3 times with the increase of CBZ concentration. Contaminant polarity was proved to be the most important factor. The saturated solubility of SMX is low and the K-ow is high, indicating that CBZ is more hydrophobic than SMX. DOM has solubilization and competitive adsorption effects on SMX. While for CBZ, competitive adsorption is dominated between low-concentration CBZ and DOM; high-concentration CBZ mainly cause co-adsorption or cumulative adsorption. The molecular weight and concentration of DOM also have a certain influence on co-migration. The higher the molecular weight of DOM, the greater the effect on pollutants sorption. Furthermore, as DOM concentration increases, the lower the inhibition of SMX and low-concentration CBZ sorption, the stronger the promotion of high-concentration CBZ sorption. In a word, the polarity of pollutants can determine whether DOM promotes or inhibits the co-migration. But the nature of DOM only can change the magnitude of that impact.