INTERACTIONS OF HERBICIDES WITH WATER-SOLUBLE SOIL ORGANIC-MATTER

Interactions of water-soluble soil organic matter (WSSOM) with the herbicides bromacil, metribuzin, alachlor, diquat, and paraquat were examined to determine if these interactions can improve predictions of herbicide leaching potential. A high-performance liquid chromatography gel filtration column was used to separate WSSOM extracts from four mineral agricultural soils into fractions with approximate log molecular weights of 4.96 to 6.82. WSSOM fractions were predominantly anionic in nature with some hydrophobic character. The amount of paraquat bound by WSSOM ranged from 1.1 to 2.1 mmol g-1DOC-1 with K(DOC) (partition coefficient for dissolved organic carbon) values from 0.050 to 0.187 L kg-1. Diquat was bound at 0.9 to 1.5 mmol g-1DOC-1 by the extracts with K(DOC) values from 0.044 to 0.143 L kg-1. Bromacil, metribuzin, and alachlor did not bind to the extracts tested. WSSOM did not increase paraquat solubility in the presence of soil. Binding of these herbicides to WSSOM in the soils used in this study would not be a significant mechanism for increased mobility and groundwater contamination potential.