Effect of polar-dissolved organic matter fractions on the mobility of prometryne in soil

Using two fractions of dissolved organic matter (DOM) with different polarity, we carried out the experiments with standard batch equilibration, soil column leaching, and soil thin layer chromatography to investigate the behavior of the herbicide prometryne in soils. The purpose of the study was to: (1) separate DOM into hydrophilic matter and hydrophobic acid forms and characterize their chemical properties; (2) analyze interaction between the DOM fractions and prometryne in soils. The herbicide prometryne was tested on Eutric gleysols soils. Two forms of DOM were prepared from lake sludge (SL) and rice straw (ST), from which hydrophilic matter (HiM) and hydrophobic acid (HoA) were individually extracted. The sorption and desorption experiments were carried out using the standard batch equilibration method. Soil column leaching was performed with soil samples packed into PVC columns (30 x 4.5 cm i.d.) to a bulk density of about 1.27 g cm(-3). Soil thin layer chromatography was performed using soil (15 g) and water (10 mL) mixture that was spread as a 0.7 mm thick layer over 20 x 10-cm glass plates. Two DOM fractions, HiM and HoA, reduced prometryne sorption to soils and increased mobility of prometryne in soils. The results were supported by soil column and plate analyses. Composition and structure of the two DOM fractions were analyzed using Fourier-transformed infrared (FT-IR) and three-dimensional excitation-emission matrix fluorescence spectra. HiM fractions contained more unsaturated components and functional nitrogen groups and therefore appeared more effective on prometryne mobility than HoA. These results suggest that HoA and HiM differentially affect the environmental behavior of prometryne in soils. DOM extracted from either ST or SL can be grouped into HiM and HoA categories. HiM fractions contained more DOC than HoA fractions. Analysis using FT-IR and EEM fluorescence spectra revealed that HiM fractions contained more unsaturated components and functional nitrogen groups than HoA fractions. The apparent difference may explain the fact that the HiM fractions were more effective on mobility of prometryne in the soil than HoA.