FRACTIONATION OF THE ORGANIC-MATTER IN SOILS AND SEDIMENTS AND THEIR CONTRIBUTION TO THE SORPTION OF PESTICIDES

The organic matter of several soils and sediments was extracted by a gross fractionation procedure designed to dissolve specific classes of organic compounds. The sorption of napropamide, a nonionic herbicide, was measured on the original and extracted soils. It was found that soils contained a higher percentage of cellulose and hemicellulose materials whereas the lipid-like fraction was greater in the sediments. Sorption of the test chemical was greater in the sediments, even on an organic carbon basis, than in the soils. Removal of specific fractions slightly affected the K(oc) of the sediments but not of the soils while acid extraction resulted in large increases in sorption by both soils and sediments; this effect was only partially reversible upon readjusting the pH.