Under aerobic conditions degradation of dimethachlor proceeds via three different routes. The relative importance of the routes depends on the microbial activity and the physico-chemical properties of the soils, and on the incubation conditions such as temperature and soil humidity. On route “A” the methoxy-ethyl side chain is degraded to produce CGA 39026 followed by dealkylation under formation of CGA 16942. Subsequent dechlorination can result in the postulated CGA 37734. The oxidative degradation steps of the methoxy-ethyl side chain in CGA 39026, leading to CGA 103699 are in common with the degradation of CGA 39981 via route “B”. Laboratory soil degradation studies indicate that route “A” is quantitatively less pronounced than the other aerobic paths. Degradation route “B” involves the dechlorination and subsequent hydroxylation of the acetyl side chain yielding CGA 39981, which is oxidised to CGA 103699 and then dealkylated to CGA 37734, or oxidised to a major acid metabolite, CGA 50266. Degradation of the metabolite CGA 103699 (from routes “A” and “B”) occurs by successive oxidation leading to the bi-acid CGA 102935, which is supposed either to de-alkylate or to deacetylate or to enter the non-extractable fraction. Formation of the oxalamic acid CGA 50266 via route “B” as oxidation product of CGA 39981 is prominent in all soils. Degradation of the metabolite CGA 50266 leads to high amounts of non-extractable residues and CO2. A further oxidation product of CGA 39981 is SYN 530561 oxidised at the methyl-side chain to a carboxyl acid that is subsequently metabolised to form non-extractable residues and CO2. The secondary amine CGA 37734 is subject to further oxidation or becomes fixed to the soil matrix. Its degradation to the primary amine (substituted aniline) has never been observed; instead, relatively high amounts of bound residues and CO2 are formed which represent the ultimate metabolisation steps in soil. A glutathione pathway (route “C”) is postulated as a very important degradation process, which leads to the formation of sulphur containing metabolites. This glutathione path seems to be a very efficient mode of detoxification and is strongly pronounced in microbially active soils. Presumably via conjugation to glutathione and subsequent cleavage reactions the chlorine of the parent molecule is replaced by sulphur thus leading to the sulfonic acid derivative CGA 354742, which besides CGA 50266 is the most prominent soil metabolite of dimethachlor. The glutathione pathway was also observed in plant and in animal metabolism studies where intermediate metabolites of this pathway have been identified. CGA 354742 can be further oxidised at the isopropyl moiety to form the bi-acid CGA 373464, which can be further hydrolysed to CGA 103699 and/or oxidised to form the bi-acid CGA 102935. Microbially mediated dealkylation/desulfonation/hydrolysis of CGA 373464 via CGA 369873 can also result ultimately in CGA 37734, bound residues and CO2. A second glutathion path via SYN 528702 leads either via CGA 103699 to route “B” or via dealkylation to CGA 37734. Under anaerobic conditions the degradation process stops at the stage of CGA 42443 as the main degradation product, formed of dimethachlor by simple reductive dechlorination. When CGA 42443 is exposed to aerobic conditions, it is readily degraded by oxidation to form CGA 50266 via CGA 39981 as shown above with route “B”. Under sterile conditions no significant degradation of dimethachlor occurs. Abiotic processes, such as photolysis or hydrolysis on soil surfaces do not significantly contribute to the soil degradation of dimethachlor. The formation of bound residues is the major dissipation pathway. Up to about 50 to 60 % of the applied radioactivity are bound to soil within a period of 2-4 months. As shown by organic matter fractionation the majority of the residues are either bound to the insoluble humin fraction or can also be found in the fulvic acid fraction. Bound residues can also represent an important pool for 14CO2 release as indicated by the decrease in both bound and extractable residues towards the end of the study period and the simultaneous increase in 14CO2 at equivalent amounts. Lower amounts of the applied radioactivity were bound to sterile soils where the degradation rate was significantly lowered. However, dimethachlor was found to be degraded even under these conditions. Under laboratory conditions, mineralisation rates between 10 and 42 % of the applied radioactivity were observed during study periods of up to approximately 3 to 6 months. The extent of mineralisation in the field is not known due to the fundamental problems of sampling volatiles under these conditions, although it can be assumed at least to be equivalent or even higher in view of a higher bioactivity of field soils in general.