In the aerobic route of degradation study, metrafenone was observed to degrade slowly at 20°C, such that 66.2 – 69.0% AR was still present as the parent material at 120 DAT; calculated first order DT50 was 257 – 258 days. Very low levels of identified metabolites were found, with combined levels of CL 197675 and CL 197676 reaching maximum of 0.15% AR at 210 DAT, but not detected at 120 DAT. Unidentified radioactivity comprising a number of compounds in various extracts reached a maximum of 8.7% AR at 60 DAT. No information on metabolite formation was available from the aerobic rate of degradation study. Information on mineralisation and formation of unextracted residues was available from both aerobic 20°C studies. Mineralisation was relatively low with 1.5 - 5.3% AR as CO2 at 120DAT, with unextracted radioactivity reaching up to 17.4 - 24.8% AR at 120 DAT. Mass balance was acceptable throughout both studies. There appeared to be little indication of differences in metabolite, CO2 or unextracted residue formation with either radiolabel. A further aerobic study was conducted at 10°C. This demonstrated that degradation proceeded at a slower rate than at 20°C, with 82.0% AR remaining as parent at 120 DAT. Whilst radioactivity as ‘others’ reached a peak of 11.5% AR, no defined peak or fraction could be identified on analysis, and it likely that this category comprised numerous small components. CO2 and unextracted residues accounted for 1.4% AR and 8.2% AR respectively at 120 DAT.