Effects of DOM on sorption of polar compounds to soils: Sulfapyridine as a case study

Sorptive behavior of sulfapyridine (SPD) in three organic-poor soils having different mineral compositions was investigated. The effects of adding biosolids-derived compost extract (dissolved organic matter, DOM) on SPD sorption to soil were evaluated. The primary goal was to discern between effects caused by DOM, pH, and ionic composition. SPD sorption in the three-phase (soil-DOM-SPD) systems was shown to decrease relative to non-DOM amended soils, when DOM and SPD were co-introduced to soil. This trend intensified with increasing pH as well as with increasing ionic strength. However, when DOM was applied prior to SPD, allowing for DOM sorption onto soil, only slight reduction in SPD sorption was observed with two of the soils. For the soil representing the weakest sorbent, the DOM pretreatment significantly increased SPD sorption. Finally, compost extract application was clearly demonstrated to affect the chemical properties of both SPD and its sorbents. Therefore, it may be necessary to consider soil chemical conditions in any attempt of assessing the effects of organic amendment on the sorption of polar contaminants.