In guideline laboratory studies on 2 soils there was some mineralisation to carbon dioxide of the phenyl ring (1.9 and 6.9%AR at 91 and 100 days respectively in each soil). The formation of unextracted residues was a significant route of dissipation representing 43.2 %AR at 91 and 100 days in each soil. In the reliable study on a single soil the metabolites metazachlor acid BH479-4 (max 16.2%AR at 91 days) and the sulfonic acid derivative BH479-8 (max 21.6%AR still increasing at study end) were found to be major metabolites in soil with concentrations greater than 10% AR. BH479-9 and BH479-11 reached concentrations of 5.3 and 7.5% AR respectively, the other metabolites identified were detected in smaller amounts. All metabolites identified contained both ring systems, (both the phenyl and the pyrazol rings). Cleavage of either of the ring systems is not a significant route of breakdown. The metabolic pathway of metazachlor proposed on the basis of the reliable route of degradation study in 1 soil is outlined in figure B.8.6. Almost all metabolites can be explained to be formed by glutathione (GSH) conjugation of metazachlor and subsequent degradation of the amino acid oligomer of the GSH side chain.