Sorption of dissolved organic matter and its effects on the atrazine sorption on soils

The dissolved organic matter (DOM), water soluble organic matter derived from sewage sludge was separated into hydrophobic fraction (Ho) and hydrophilic fraction (Hi). The sorption of DOM and its fractions on soils and the effects of DOM sorption on a nonionic pesticide (atrazine(2-chloro-4-ethylamino-6-isopropylamino-1,3,5-trazine)) distribution between soil and water were investigated using a batch equilibrium technique. The total DOM sorption on soils described by the Langmuir equation reached saturation as the DOM concentration increased. The sorption of Ho fit the Freundlich model. In contrast, a negative retention evidently occurred as adding Hi at higher level in tested soils. The sorption of Ho dominated the total DOM sorption and the release of soil organic matter (SOM). Effects of DOM on the atrazine sorption by soils were DOM-concentration dependent and dominated by the interaction of atrazine, DOM, and soil solids. Generally, the presence of DOM with lower concentration promoted atrazine sorption on soils, namely the apparent partitioning constant (Kd) for atrazine sorption in the presence of DOM was larger than the distribution constant (Kd) without DOM; whereas the presence of DOM with higher concentration inhibited atrazine sorption (i.e., Kd < Kd). The overall effects of DOM on atrazine sorption in soils might be related to the DOM sorption and the release of soil intrinsic organic matter into aqueous solution. The sorption of Ho on soils promoted the atrazine sorption on soil, while the release of SOM by Hi and the competitive sorption between Hi and atrazine on soil surface led to a decrease of atrazine sorption. Information provided in this work may contribute to a better understanding of the DOM sorption and its impacts on the contaminant soil-water distribution.