[...] As stated above, XDE-729 methyl gave rise to relatively high levels of unextracted residue in microbially active soils. Generally, the pyridine ring-labelled material tended to give higher levels of unextracted residues, with 62.5 82.5% AR at 104 DAT; the phenyl ring-labelled material gave 59.5 64.4% AR as unextracted at 104 DAT. However, mineralisation was moderate with 1.8 17.3% AR as CO2 at 104 DAT with the phenyl ring-labelled material and 3.3 21.0% AR at 104 days with the pyridine ring-labelled material. Mineralisation would suggest that the molecule is undergoing significant degradation, as would the presence of polar and "other" material. In particular, the RefSol 03-G soil which met the Uniform Principles unextracted residue/mineralisation criteria, showed up to 4.4% polar material and up to 7.2% of "other" comprising a number of unidentified components, none of which exceeded 5% AR. Again, this suggests that significant degradation is occurring to the a.s. and its primary metabolites in microbially active soils rather than unchanged or relatively unchanged substance being incorporated into soil as unextracted residue. In the sterile soils, much lower levels of mineralisation and formation of unextracted residues were seen at equivalent sample times, suggesting that microbial activity is responsible for degradation of the active substance and metabolites and incorporation of the radiolabelled residue into unextracted residues. Results of the sterile incubations also suggest that there was a slowing of the degradation of XDE-729 methyl, although it was still relatively rapid (non-sterile soil DT50 values in the range of 1 2 days and DT90 values in the range 4 16 days; sterile soil DT50 in the range 7-12 days and DT90 values in the range 22-75 days. This suggests that microbial activity is involved in degradation of XDE-729 methyl, but abiotic processes are also likely to be involved. The magnitude of degradation rates seen in the hydrolysis study suggests that simple hydrolysis may not be the dominant abiotic process, but that there may be some form of catalysed process occurring to maintain the relatively rapid degradation of the a.s. in the absence of an active microbial population. In addition, the sterile incubations demonstrate that degradation of X11393729 is clearly microbially mediated, with an accumulation of residues of this metabolite at high levels at the end of the study in sterile incubations, as opposed to rapid formation followed by relatively fast decline under non-sterile conditions. This would further support the theory that the formation of unextracted residues following application of XDE-729 methyl is due to microbial degradation processes. Three metabolites were positively identified. The primary metabolite, X11393729, is the demethylated carboxylic acid metabolite and can be thought of as the acid formed by hydrolysis of the ester bond; the methyl group is lost from the pyridine ring. High levels were formed relatively quickly, maximum levels being 38.2 72.7 % AR at 3 - 7 DAT. The subsequent study in sterile samples of the same soils demonstrated slower transformation of XDE-729 methyl to the acid suggesting that although an abiotic process was capable of forming the acid, microbial degradation is still likely to be significant in the formation of the acid. The sterile incubations also demonstrated that microbial degradation is also likely to be responsible for degradation of X11393729 as its concentrations had not apparently peaked during the 62 day sterile incubation in all four soils, whereas concentrations had markedly declined by this point in the microbially active incubations. The secondary metabolite in terms of concentration was X11449757 which reached 2.7 17.4 % AR at 3 - 14 DAT. Generally the peak of formation of X11449757 was one sample time after the peak of X11393729 formation suggesting relatively rapid formation of X11449757 from X11393729. X11449757 appears to be formed from X11393729 by loss of the methyl group associated with the phenyl ring, forming a hydroxyl group. A further metabolite, X11406790, was also identified, but the maximum amount seen was 1.4% AR at 3 DAT. It is considered by the RMS that this metabolite does not need any further consideration in environmental exposure assessment for soil or groundwater. However, both X11393729 and X11449757 must be included in environmental exposure assessment for soil and groundwater. X11406790 appears to be formed from XDE-729 methyl by loss of the methyl group associated with the phenyl ring, forming a hydroxyl group.