Bound or absorbed methabenzthiazuron residues in soil

The extractability of methabenzthiazuron residues from soil decreases with time after application. Employing a two-step extraction procedure (acetone/chloroform/water followed by 0.1N NaOH), 93% of the 14C-labelled methabenzthiazuron residues could be removed from the soil. According to the results of TLC and cochromatography, more than 94% of the extracted radiocarbon represented unaltered methabenzthiazuron. In an additional experiment, 14C-labelled methabenzthiazuron was incubated with two humic acid-like melanin-producing soil fungi. The melanins contained only small amounts of radioactivity. The results indicate that the non-extractable residue portion of methabenzthiazuron seems to be rather strongly adsorbed by soil organic matter binding sites than incorporated into or assimilated by soil organic matter. (author)