Effect of dissolved organic matter on adsorption and desorption of mercury by soils

Effects of dissolved organic matter (DOM) on adsorption and desorption of Hg were investigated in two kinds of soils, Xanthi-Udic Ferralosols (XUF) and Typic Purpli-Udic Cambosols (TPUC). The DOM was obtained from humus soil (DOMH), rice straw (DOMR), and pig manure (DOMP). The presence of DOM obviously reduced Hg maximum adsorption capacity with up to 40% decreases over the control, being an order of DOMH (250.00 mg/kg) < DOMR (303.03 mg/kg) < DOMP (322.58 mg/kg) < CK (control 416.67 mg/kg) for the XUF and DOMH (270.27 mg/kg) < DOMR (312.50 mg/kg) < DOMP (324.23 mg/kg) < CK (476.11 mg/kg) for the TPUC, respectively. The inhibition of DOM on Hg adsorption was slightly weaker in XUF than in TPUC. Meanwhile, the DOM promoted Hg desorption from the soils. The kinetic models, the Two-constant equation and Elovich equation, were applicable to describe the adsorption and desorption processes of Hg in soils. The speed of Hg adsorption was consistently slowed down by the existence of DOM.