The route of degradation of prosulfuron, radio-labelled in either the triazine or phenyl-ring has been studied in laboratory soils under aerobic, anaerobic, and aerobic-sterile conditions at 20 and 25°C. In the original DAR of prosulfuron, two studies were reported by Atkins in 1993 and two studies in 1994. Two studies were reported by Reischmann in 1995. All studies are considered to be acceptable. Two additional laboratory soil degradation studies were conducted to address degradation over a wider range of pH values, as required under guidance 1107/2009 due to pH dependance for hydrolysis and its potential impact on the route of degradation. In summary, aerobic degradation of prosulfuron in soil mainly occurs via a biological process and is enhanced by temperature and moisture. Under anaerobic conditions degradation of prosulfuron is similar than under aerobic conditions, at least in poorly active soils. Photolysis is not a major route of degradation. The degradation of prosulfuron proceeds via formation of several metabolites and the same metabolic pathway is followed for all of the main metabolites, irrespective of soil characterisation. Degradation proceeds via cleavage of the sulfonylurea bridge yielding CGA159902 (phenyl sulfonamide) - maximum 47.4 % after 12 months (Atkins, 1993a, 1994a) and CGA150829 (triazine amine) - maximum 40.6 % after 62 days (Fahrbach, 2011a). Another pathway involves O-demethylation of prosulfuron yielding CGA300406 (maximum 24.0 % after 30 days (Reischmann, 1995). This metabolite may be further degraded to CGA325025 (demethoxy amino prosulfuron) reaching a maximum of 17.4 % after 274 days (Atkins, 1993b); or undergoes either opening of the triazine ring leading to CGA349707 reaching a maximum of 22.6 % after 12 months (Reischmann, 1995), SYN542604 (previously also known as M5) reaching 30.8 % after 62 days (Fahrbach, 2011) and minor metabolites (CGA325028 and CGA325027 (<10 %)) or cleavage of the sulfonylurea bridge to give G28533 (dihydroxy triazine; <10 %). A minor pathway involves hydroxylation of prosulfuron yielding small amounts of CGA300408. During aerobic degradation of prosulfuron, two unknown soil metabolites M17 and M18 were detected, which would trigger a risk assessment for groundwater contamination according to SANCO/221/2000. In Fahrbach (2011) study, metabolite M17 reached 6.1% of the applied radioactivity (on day 120; study end) in soil 18 Acres after application of phenyl-labelled prosulfuron. In Fahrbach (2011a) study, metabolite M18 accounted for 9.9% of the applied radioactivity (on day 120; study end) in soil Vétroz treated with triazine-labelled prosulfuron. Despite of a significant amount of work by the Notifier, identification of these metabolites was not possible and therefore no information of their properties or concentrations in the environment is available. The need for further work and for a risk assessment on these metabolites, especially for M18, may need to be discussed during the peer review. Prosulfuron is poorly mineralised (up to 21.5 %) and bound residues are formed in significant amounts (up to 57 % (phenyl; within one year) or 34.3 % (triazine; within 120 days).