Association of tribenuron-methyl with colloidal and particulate materials

Abstract

Sorption of [ 14C]tribenuron-methyl to whole soil and isolated clay minerals was studied in batch and ultrafiltration experiments. The extent of sorption varied among the different soil types, decreasing in the order silt and clay, organic rich, and sand soil. The extent of sorption increased with decreasing pH, especially for the silt and clay rich soils. Different size classes separated from a loam soil showed different extents of sorption of tribenuron-methyl, higher for the silt and the clay fraction compared to the whole soil. Tribenuron-methyl showed a relatively stable K ow-value of ∼4 in the pH range 4–12. The low K ow-value indicates that hydrophobic sorption is of minor importance for tribenuron-methyl. Clay suspensions (10–1000 mg illite or smectite per litre) spiked with [ 14C]tribenuron-methyl were ultrafiltered by the use of hollow fibres. Results showed that a major part of tribenuronmethyl was associated with clay colloids (> 3 kDa). The degree of association was inversely related to pH, and higher for smectite than illite at the same pH values. Clay suspensions spiked with [ 14C]tribenuron-methyl were diafiltered by the use of hollow fibres. The results showed that the rate of sorption was very fast (pseudoequilibrium obtained within 100–200 min).