The following reactions are believed to be involved in chlorsulfuron (DPX-W4189) degradation in acidic and alkaline soils: - Bridge cleavage of chlorsulfuron to form IN-A4097; - O-Demethylation of triazine methoxy group to form IN-M6957; - Hydrolysis of IN-M6957 and subsequent triazine ring opening to form an intermediate, which through subsequent metabolism forms IN-JJ998; - Bridge cleavage IN-M6957 to form IN-A4097 and IN-B5528; - Metabolism of IN-JJ998 to form IN-A4097; - O-Demethylation of IN-A4098 to form IN-B5528 and deamination of IN-B5528 to form IN-F5475; - Indirect photolysis of chlorsulfuron to form IN-V7160; - Ring cleavage of IN-A4097 and IN-F5475 leading to CO2 and bound residues; - Under strongly anaerobic and acidic conditions, bridge cleavage to form IN-D5293. A major pathway proposed for the degradation of chlorsulfuron in aerobic soils is cleavage of the sulfonylurea bridge through aqueous hydrolysis. The rapid formation of IN-A4097 and IN-A4098 demonstrates that this is the first functioning degradation pathway. Sulfonylurea bridge cleavage through aqueous hydrolysis is an abiotic pathway, as is demonstrated in the occurrence of chlorsulfuron degradation and the formation of significant amount of IN-A4097 and IN-4098 in sterile acidic aqueous solutions. IN-A4098 can subsquently be O-demethylated to form IN-B5528 which can be deaminated to form IN-F5475. It is thought that IN-F5475 is in equilibrium with the ring-opened hydrated form ant this ultimately is the form that is mineralised to CO2 and provides the ring fragments that are incorporated into the soil organic matter. Another important degradation pathways initially involves O-demethylation of the triazine ring of chlorsulfuron to IN-M6957, which is thought to be abiotic since it is also found in the (sterile) aqueous hydrolysis study. IN-M6957 rapidly forms an unstable intermediate that degrades to form the guanidine IN-JJ998. IN-JJ998 can subsequently be metabolised through microbial action to form IN-A4097. The rapid conversion to IN-JJ998 is perhaps why IN-M6957 reaches a maximum of 5% in soil and is not considered a major degradation product. This conversion is thought to be microbially mediated. The level of formation of this degradation product is indirectly controlled by the effect of soil acidity on the rate of aqueous hydrolysis, since bridge-intact IN-M6957 is the precursor. This pathway is therefore more important in alkaline soils where bridge-intact chlorsulfuron and IN-M6957 are more likely to be observed due to the slower rate of bridge cleavage through aqueous hydrolysis. The sulfonylurea bridge of IN-M6957 can also cleave to form IN-A4097 and IN-B5528. Since the soil pH can affect the rate of chlorsulfuron degradation through its effect on the rate of aqueous hydrolysis it can thus change the relative importance of this versus microbial degradation. However, the degradation products in acidic and alkaline soils are not different, only the relative maximum levels of formation of these products is different. For example, the sulfonylurea bridge cleavage products IN-A4097 and IN-A4098 are generally found in greater amounts in lab and field studies conducted in acidic soils than in those conducted in alkaline soils. Indirect photolysis is thought to be responsible for the formation of IN-V7160 because it is found in aerobic soils treated with light (soil photolysis study) or in field soils and not in laboratory studies conducted in the dark. It is theorised that this forms due to free radicals generated through light energy and that this degradation product can degrade by microbial action to IN-A4098. Carbon dioxide evolution from [14C]chlorsulfuron is measurable for both labels (phenyl and triazine) demonstrating that mineralisation of both rings does occur, which eventually leads to complete dissipation of molecular fragments of the active substance from the environment. Major soil metabolites (found at >10%) in soils therefore include IN-A4097, IN-A4098 and IN-JJ998.