Degradation of BAS 650 F in soil starts directly after contact with microbial active soil by oxidation processes at the octyl side chain of the molecule. Some steps (M650F01 -> M650F03 and M650F02 - > M650F04) represent typical ß-oxidation reactions as known from fatty acid metabolisation. The successive shortening of the side-chain leads finally to metabolite M650F04 representing the respective pyrimidine-carboxylic acid with a still intact ring system. M650F01, M650F02, M650F03 and M650F04 are major metabolites in soil formed in maximum rates of 26.3-53.9 %AR, <5-13 %AR, 39.7-57 %AR and 25.2-55.7 %AR respectively in different soils. Formation of up to 42% AR of 14CO2 after 360 days incubation during the aerobic soil metabolism study indicate that the heterocyclic ring system can be opened and completely degraded after long term incubation. In soil degradation studies that last for 120 days the amount 14CO2 was clearly less, reaching maximum of about 6% of AR. This is comparable to the results in the soil degradation route study where the obvious increase in 14CO2 occurs later in the study.
Furthermore, the heterocycle as a whole (or parts of it) can be tightly incorporated into the heterogeneous structure of the humic substance matrix as indicated by the increasing fraction of bound residues. Fractionation of the NER showed that about 60% of NER towards the end of the incubation phase (equivalent to 2.3 - 17.9% TAR) remained unextractable with NaOH (humin fraction). Only a small portion of radioactivity (0.5 - 2.4% TAR) was associated with the humic acid fraction, whereas the fulvic acid fraction contained 2.6 - 12.7% TAR. Only low amounts of radioactivity could be partitioned from the fulvic acid fraction into ethyl acetate (0.2 - 2.2% TAR). HPLC analysis showed that these low amounts of radioactivity mainly consisted of BAS 650 F in early samples (day 1 - 6) and M650F04 in later samples (> 6 days). Some minor degradation products (M650F31, M650F33) showing different stages of oxidation (hydroxylation, keton-formation) at the octyl side-chain could also be observed, mostly in aerobic soil. The exact location of hydroxyl or keto-groups could not be determined with LC/MS-MS methods, however, the occurrence of those intermediates fits into the overall postulated route of degradation.