[en] [phenyl-¹⁴C]Sulfometuron methyl is stable in water at pH 7 or 9, but hydrolyzes readily (half-life 2 weeks) to [¹⁴C]methyl 2-(aminosulfonyl) benzoate and [¹⁴C]1,2-benzisothiazol-3-one, 2,3-dihydro 1,1-dioxide (saccharin), at pH 5.0. [¹⁴C]Sulfometuron methyl was completely photolyzed to ¹⁴CO₂ under aquatic photolysis conditions. [¹⁴C]Methyl benzoate was identified as an intermediate in this photolytic degradation. [¹⁴C]Sulfometuron methyl was mobile on soils when tested using soil thin-layer plates and soil columns; this mobility agreed reasonably well with Freundlich soil isotherm constants. [¹⁴C]-Sulfometuron methyl has a low partition ratio (0.31) between n-octanol and 0.01 M phosphate buffer, pH 7.0. It does not accumulate in fish tissue when fish are exposed to 0.01 ppm or 1.0 ppm [¹⁴C]-sulfometuron methyl in their environment