ASSOCIATION OF TRIBENURON-METHYL WITH COLLOIDAL AND PARTICULATE MATERIALS

Sorption of [C-14]tribenuron-methyl to whole soil and isolated clay mi nerals was studied in batch and ultrafiltration experiments. The exten t of sorption varied among the different soil types, decreasing in the order silt and clay, organic rich, and sand soil. The extent of sorpt ion increased with decreasing pH, especially for the silt and clay ric h soils. Different size classes separated from a loam soil showed diff erent extents of sorption of tribenuron-methyl, higher for the silt an d the clay fraction compared to the whole soil. Tribenuron-methyl show ed a relatively stable K(ow)-value of approximately 4 in the pH range 4-12. The low K(ow)-value indicates that hydrophobic sorption is of mi nor importance for tribenuron-methyl. Clay suspensions (10-1000 mg ill ite or smectite per litre) spiked with [C-14]tribenuron-methyl were ul trafiltered by the use of hollow fibres. Results showed that a major p art of tribenuron-methyl 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 wi th [C-14]tribenuron-methyl were diafiltered by the use of hollow fibre s. The results showed that the rate of sorption was very fast (pseudoe quilibrium obtained within 100-200 min).