Roles of dissolved humic acid and tannic acid in sorption of benzotriazole to a sandy loam soil

To clarify the role of dissolved organic matter (DOM) in sorption of organic pollutants, batch experiments on effects of two representatives of DOM (dissolved humic acid (HA) and tannic acid (TA)) on sorption of benzotriazole (BTA) to a sandy loam soil were conducted. Both HA and TA promoted BTA sorption to soil. Strong positive correlation between sorbed amount of BTA and DOM confirmed the contribution of cumulative sorption by HA or TA in enhancing BTA binding. TA promoted BTA sorption more obviously than HA by providing more sites. For HA with complex structure composed of heterogeneous fractions, its high molecular weight (>3200 Da) fraction could be preferentially sorbed by soil, and it can enhance BTA sorption more obviously than the low molecular weight fraction. The promoting effect of HA on BTA sorption decreased with pH increasing from 6.5 to 10.5 due to reduced sites and electrostatic repulsion between anionic BTA, HA and soil. Sorption of neutral BTA to soil affected by DOM could be well predicted by a modified Freundlich model with K-d (L kg(-1)) deviations less than 0.2 log unit.