An aerobic route of degradation study in three European soils with both [14C-oxathiine]- carboxin and [14C-UL-phenyl]-carboxin has confirmed the formation of carboxin sulfoxide as the major soil metabolite (up to 78.2% AR) which is converted in part into carboxin sulfone (up to 17.0% AR). Two additional metabolites, oxathiine amide sulfoxide (P/V-54) and oxathiine amide sulfone (P/V-55), were formed with maximum concentrations of 27.4 and 14.5% AR respectively. In addition, a transient ring-opened metabolite coded M6 (see Figure B.8.9) and a metabolite coded M9 (hydrated carboxin sulfoxide) reached maximum levels of 10.1% and 9.9% AR, respectively. None of the remaining radioactive fractions exceeded 5% AR. In a rate study in a fourth European soil, a metabolite coded PH-3 was formed at up to 8.3% AR (phenyl label) after 3 d and exceeded 5% AR at sample points up to 61 d and therefore requires further consideration according to the Guidance Document on the assessment of relevance of metabolites in groundwater (Sanco/221/2000 – rev.10). In the fourth European soil a further metabolite OX-4 reached a maximum of 7.8% AR (oxathiine label) after 28 days and decreased to 6.7% AR at the end of the study. Complete mineralisation to CO2 was significant in both labelled forms of carboxin. In the oxathiine-labelled form, CO2 evolution was 27.4-53.5% AR after 120 days (4 European soils) at 20ºC. In the phenyl-labelled form, CO2 evolution was 21.3-44.3% AR after 120 days (or 60 days if the experiment was of shorter duration) (4 European soils). Unextracted residues reached 11.8-27.6% AR in the oxathiine-labelled form (4 European soils) at 20ºC and 24.9-46.6% AR in the phenyl-labelled form (4 European soils) after 120 days (or 60 days if the experiment was of shorter duration). Based on the available data, the aerobic route of degradation of carboxin in soils proposed by the Notifier is shown in Figure B.8.9. The rate of aerobic degradation of carboxin (two radiolabelled forms) was investigated in four European soils and one US soil (sandy loam – clay loam, pH 5.88-7.6, OC% 1.0-2.7) at 20-25ºC in the dark. The primary metabolite was carboxin sulfoxide and degradation rates for this compound were determined from the studies on the parent. The degradation rate of carboxin sulfone was determined in a separate study in three of the same European soils as used for the studies on carboxin. The degradation rates for the other metabolites (P/V-54, P/V-55, M9, M6, PH-3) were also determined from the studies on the parent compound in three of the European soils.