Effect Of Dissolved Organic Matter On The Sorption Of Oxytetracycline In Soils

Antibiotics, as a common type of chemical contaminant, are widely used in human life and animal disease prevention. A large amount of parent antibiotics and their metabolites are released into the environment through feces, giving rise to serious environmental pollution in the process of land application of manure and sewage sludge, hence the widespread of antibiotic resistance genes in water, sediment, soil and other environmental medium.Manure, acting as the main carrier of antibiotics, contains high concentrations of dissolved organic matter (DOM) which is important carrier for the transfer of organic contaminants in soils; thereby the occurrence of DOM may have great effect on the environmental behavior of antibiotics and the pollution of resistance genes. Therefore, based on the key roles of DOM in the antibiotics pollution, the study evaluated the impact of exogenous DOM on the sorption of oxytetracycline (OTC) on soils, which will provide basic data for the risk evaluation of antibiotics.In this paper, Aldrich commercial humic acid (HA) and manure-extracted DOM were selected as typically exogenous DOM, montmorillonite and four soils were screened as adsorbents, to study the distribution behavior of OTC. Meanwhile, a three-phase adsorption theoretical model was developed to distinguish the contribution of the interaction between DOM and OTC in the presence of DOM. According to the results, we drew three main conclusions are as follows:(1) The adsorption of OTC reduced significantly in the presence of HA, and the effect involved three possible mechanisms:the competition of HA for the active sites on montmorillonite surface, the binding interaction between humic acid and OTC, and the hindrance of HA coverage to the interlayer diffusion of OTC.(2) The adsorption of OTC was dependent on the type of soil and the pH value of solution. The presence of HA also decreased the soiption capacity of soil for OTC, and the extent of reduction was related to the adsorption-desorption characteristics of HA on soils. Therefore, the coverage of HA on the surface of sorbent may be the primary limiting factors.(3) The addition of manure-extracted DOM also reduced the adsorption amount of OTC on soils, but less than that of Aldrich HA, that may ascribe to the weaker binding of manure source DOM to OTC. The chicken manure-extracted DOM and pig manure-extracted DOM significantly enhanced the leaching risk of OTC. Therefore, in the forecast of antibiotics transference behavior, the effects of manure derived DOM should be considered.