Triflusulfuron-methyl is significantly degraded in soil by both chemical and biological processes. In sterile soil, degradation mainly occurs by hydrolysis of the sulfonylurea bridge to give IN-D8526 = triazine amin (50% after 6 months) and IN-W6725 = methyl saccharin (75-80% beyond 1 month) resulting from cyclisation of postulated transient methyl sulphonamide. In viable soil, degradation of trisulfuron-methyl is faster. Degradation still involves cleavage of the sulfonylurea bridge to give IN-D8526 (max. 55.2% after 21 d) and IN-W6725 (max. 83.7% after 29d) but these metabolites are further degraded. IN-D8526 undergoes N-demethylation to give IN-E7710 = N-desmethyl triazine amine (max. 34.1% after 90 d, slow decline observed) and then IN-M7222 = N,N-bis-desmethyl amine (max. 10.9% after 14 d, no clear decline observed). No significant metabolites are derived from IN-W6725. Bound residue is the main final degradation product (48.8% for the ester carbonyl moiety and 46% for the triazine moiety after 90 d). Mineralisation is moderate for the ester carbonyl moiety (17.5% after 90 d) and negligible for the triazine moiety (3.6% after 368 d).