Effects Of Dissolved Organic Matter On Sorption Of Benzotriazole To Typical Soils

Dissolved organic matter(DOM) plays an important role in affecting the environmental behaviors of organic contaminants. DOM is ubiquitous in the environment. So far, the effects of DOM on sorption of the emerging organic contaminants(e.g., benzotriazole(BTA)) to soil have not been well understood. In this study, the North China Plain soil(GSS13) and the Pearl River Delta soil(GSS16) were selected as sorbents. Two types of DOM, i.e., dissolved humic acid(HA) and tannic acid(TA), with different functional groups were chosen to investigate the effects of DOM and HA fractions on BTA sorption to Chinese reference soils by batch experiments. The main conclusions are as follows:(1) The sorption of BTA to the soil is fast at the beginning stage and becomes slowly due to the decrease of sorption sites. There is not significant effect of solution p H on BTA sorption. The influence of Na+(0.01-0.05 M) on BTA sorption to the soil is not obvious. However, Ca2+(0.01-0.05 M) promotes BTA sorption to the soil and the promoting effect is dependent on concentration of Ca2+ ion.(2) The mechanisms of DOM sorption to soil include electrostatic attraction and ligand exchange, etc. HA and TA show a stronger sorption in Na Cl solution than that in Na2SO4 solution. This is because electrostatic interaction is an important mechanism for HA and TA sorption to soil GSS13 under the experimental conditions. Compared with Cl-, SO42- exhibites a stronger competition with DOM for positively charged sorption sites. The ligand exchange between carboxylic groups of DOM and phenolic groups of minerals in the soil is an important mechanism. This may be the reason why a higher sorption capacity for TA than that for HA to the soils is observed in the experiments.(3) The addition of DOM increased the sorption of BTA to soil. With increasing concentration of DOM, the sorption ability increased. Sorption of BTA would be facilitated by the previously sorbed DOM through hydrogen bonding. The polarity effect contributes to increase sorption nonlinearity. When the equilibrium solution p H ranged from 6.5 to 10.5, carboxylic groups of HA became progressively deprotonated. As a result of hydrogen bonding ability between the sorbed DOM and BTA declined with increasing solution p H.