Impact of exotic and inherent dissolved organic matter on sorption of phenanthrene by soils

The impacts of exotic and inherent dissolved organic matter (DOM) on phenanthrene sorption by six zonal soils of China, chosen so as to have different soil organic carbon (SOC) contents, were investigated using a batch technique. The exotic DOM was extracted from straw waste. In all cases, the sorption of phenanthrene by soils could be well described by the linear equation. The presence of inherent DOM in soils was found to impede phenanthrene sorption, since the apparent distribution coefficients (Kd*) for phenanthrene sorption by deionized water-eluted soils were 3.13-21.5% larger than the distribution coefficients (Kd) by control soils. Moreover, the enhanced sorption of phenanthrene by eluted versus control soils was in positive correlation with SOC contents. On the other hand, it was observed that the influence of exotic DOM on phenanthrene sorption was related to DOM concentrations. The Kd* values for sorption of phenanthrene in the presence of exotic DOM increased first and decreased thereafter with increasing the added DOM concentrations (0-106 mg DOC/L). The Kd* values at a low exotic DOM concentration (≤28 mg DOC/L) were 14.7-48.4% larger than their control Kd values. In contrast, higher concentrations (≥52 mg DOC/L) of added exotic DOM clearly impeded the distribution of phenanthrene between soil and water. The effects of exotic and inherent DOM on phenanthrene sorption by soils may primarily be described as 'cumulative sorption', association of phenanthene with DOM in solution, and modified surface nature of soil solids due to DOM binding.