Effects of rice straw-derived dissolved organic matter on pyrene sorption by soil

The objectives of the present study were to elucidate the chemical and structural properties of dissolved organic matter (DOM) derived from aerobic decay of rice straw and to quantify the effect of the DOM on the sorption of pyrene on soil. The DOM samples were obtained from microcosms incubated at 0, 21, 63, and 180 d. The bulk DOM samples were fractionated to four fractions: hydrophilic matter (HIM), acid-insoluble matter (AIM), hydrophobic acid (HOA), and hydrophobic neutral (HON) fractions. The bulk DOM and the four DOM fractions were characterized for their elemental compositions and functionalities. The results showed that HIM had the highest H/C atomic ratios, whereas HOA and AIM had the lowest H/C atomic ratios. These DOM samples were used as the background DOMs in the initial aqueous solutions for measuring sorption of pyrene on a paddy soil. The results indicated that, among the four DOM fractions, HOA, HON, and AIM significantly lowered the pyrene sorption coefficients, but HIM had little or no effect on the pyrene sorption by the soil. It appears that less polar AIM and HON had stronger binding affinities for pyrene in water, reducing the sorption coefficient for the soil, whereas more polar and less aromatic HIM had much weaker binding affinity for pyrene in water, causing little or no effect on the pyrene sorption by the soil. The present study showed that rice straw-derived DOM may enhance desorption and transport of organic pollutants in soil-water systems.