Analysis of the dissipation kinetics of thiophanate-methyl and its metabolite carbendazim in apple leaves using a modified QuEChERS-UPLC-MS/MS method.

As one of the main fungicides for the apple leaf disease control, thiophanate-methyl (TM) mainly exerts its fungicidal activity in the form of its metabolite carbendazim (MBC), whose dissipation kinetics is very distinct from that of its parent but has been paid little attention. The aim of this work was to investigate the dissipation kinetics of TM and its active metabolite MBC in apple leaves using a modified QuEChERS-UPLC-MS/MS method. The results showed that TM and MBC could be quickly extracted by this modified QuEChERS procedure with recoveries of 81.7-96.5%. The method linearity was in the range of 0.01-50.0 mg kg-1 with the quantification limit of 0.01 mg kg-1 . Then this method was applied to the analysis of fungicide dissipation kinetics in apple leaves. The results showed that the dissipation kinetics of TM for the test in 3 months can be described by a first-order kinetics model with a DT50 (dissipation half-life) range of 5.23-6.03 days and the kinetics for MBC can be described by a first-order absorption-dissipation model with the Tmax (time needed to reach peak concentration) range of 4.78-7.09 days. These models can scientifically describe the behavior of TM and MBC in apple leaves, which provides necessary data for scientific application.

Residue dissipation and risk assessment of tebuconazole, thiophanate-methyl and its metabolite in table grape by liquid chromatography-tandem mass spectrometry.

An efficient method was developed and validated for simultaneous determination of tebuconazole, thiophanate-methyl and its metabolite carbendazim in grape and soil using QuEChERS procedure and liquid chromatography-tandem mass spectrometry. The average recoveries of the method were 83.2%-105.4%, the limit of detection (LOD) ranged from 2.1 × 10-5 to 8.7 × 10-4 mg L-1, and the limit of quantitation (LOQ) was 0.1 mg kg-1. The field results showed that tebuconazole and thiophanate-methyl in soil and grape were rapidly dissipated with half-lives less than 24.7 days. The terminal residues of all analytes in grape were lower than the maximum residue limit (MRL) set by China (2 mg kg-1 for tebuconazole; 3 mg kg-1 for both thiophanate-methyl and carbendazim). Risk assessment showed that tebuconazole, thiophanate-methyl and its metabolite would be unlikely to cause health problems. However, carbendazim, the higher active metabolites of thiophanate-methyl, should receive more concerns.

[Ethyl benzimidazole carbamate: teratogenic effect and presence in the milk of cows after administration of thiophanate]. / Benzimidazole carbamate d'éthyle: effet tératogène et présence dans le lait de vache après administration de thiophanate.

After oral administration of 40 mg/kg of thiophanate to dairy cows, the active metabolite, ethyl-1H-benzimidazol-2-yl carbamate (EBC) reached a maximal concentration of 0.44 microgram/ml during the first milking and was eliminated by the mammary gland after 60 h. BCE is teratogenic in rats at doses of over 6.8 mg/kg while thiophanate at doses of up to 148 mg/kg is not. These results indicate that thiophanate treatment for dairy cattle may be questionable.

[Pharmacokinetics and anti-Dicrocoelium activity of thiophanate and its major metabolite in ruminants]. / Pharmacocinétique et activité dicrocoelicide du thiophanate et de son métabolite majeur chez les ruminants.

After a single oral dosage of 40 mg thiophanate/kg in cattle, sheep and goats, the parent compound and its main metabolite: ethyl benzimidazol-1H-yl-2-carbamate (EBC) are evidenced in plasma by HPLC analysis for 60 to 72 hours. The rate of metabolic change of thiophanate into EBC is 34% in sheep, 52% in goats and 57% in cattle. At this dosage, thiophanate seems to be effective against Dicrocoelium in sheep. On the contrary, EBC is uneffective at 15 mg/kg while it seems undetectable in plasma at any time.