Methiocarb

Crystalline or powder solid mp 120°C (248°F) almost insoluble in water, 27 mg/L at 20°C (68°F) readily dissolves in methylene chloride, chloroform, toluene and isopropanol. 

LD50 oral (rat) 15-20 mg/kg LD50 oral (guinea pig) 40 mg/kg LD50 skin (rat) 350 mg/kg LD50 skin (wild bird) 100 mg/kg 

Synonyms 4-methylthio-3,5-dimethylphe-nyl-A-methylcarbamate 4-methylmer-capto-3,5-xylyl-A-methylcarbamate 4-(methylthio)- 3,5 -xylenol methylcarba- 

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X5lenol is an important starting material for insecticides, xylenol—formaldehyde resins, disinfectants, wood preservatives, and for synthesis of a-tocopherol (vitamin E) (258) and i7/-a-tocopherol acetate (USP 34-50/kg, October 1994). The Bayer insecticide Methiocarb is manufactured by reaction of 3,5-x5lenol with methylsulfenyl chloride to yield 4-methylmercapto-3,5-xylenol, followed by reaction with methyl isocyanate (257). Disinfectants and preservatives are produced by chlorination to 4-chloro- and 2,4-dich1oro-3,5-dimethylpheno1 (251). 

PROVADA , methiocarb, 113 PRO VERA , conjugated estrogen, 113 Provhon Fine Chemicals N.V, 144 Provhon Group N.V, 144 Pmssic acid, 113 Pseudocumene, 113 PTTimahTbk, 177 PTZ , phenothiazine, 113... 

APCI can help to reduce matrix effects when analyzing for carbamate insecticides. Eor example, when analyzing for methiocarb in citrus products, the apparent recoveries were in the region of 50% with ESI. However, on changing to APCI, the apparent recoveries were increased to 110%. This is an example where APCI can be an alternative API method if matrix effects are a problem with ESI. It is important to note that the analyte must show sufficient sensitivity to both API techniques. 

Half-lives of two pesticides were estimated using the assumption that the decay was a first-order process. Half-lives were 28 8.5 days and 12 3.4 days for thiophanate-methyl and methiocarb, respectively. Crop volume was not a significant determinant of exposure using a grid count method. This was probably due to a large variation in the results with this method. 

Three pesticides having large variation in recommended dose rate were selected for this study. All were considered chemically stable and non-volatile. Model pesticides that were selected were thiophanate-methyl (CAS 23564-05-08 tradename Topsin M 500 g a.i./L), methiocarb (CAS 2032-65-... 

For extraction of thiophanate-methyl, methanol (250 mL per glove) was added to the gloves, and, for extraction of methiocarb, 250 mL 60/40 (v/v%) methanol/water (per glove) was added to the gloves and adjusted to pH 4.5 with acetic acid. Gloves were then ultrasonicated for 10 min and extracted for 30 min by shaking at 200 strokes per min. 

Note HV = high-volume application LV = Low-volume application Tpm = thiophanate-methyl Meth = methiocarb Aba = abamectin. 

Figure 1 Increase of average DFR of methiocarb (o), thiophanate-methyl (+), and abamectin ( ) due to application with either high-volume or low-volume techniques.

The DFR values were followed over a period of 4 weeks from the high-volume application. The decrease of DFR in the two zones was monitored in six greenhouses (three times after application of thiophanate-methyl and three times after application of methiocarb). Figure 2 shows typical log-transformed decays of DFR (average of two samples for each zone) for methiocarb and thiophanate-methyl. Assuming a first-order decay, half-lives were calculated using Equations (3) and (4) and were found to be 29 8.5 days and 11 3.4 days for thiophanate-methyl and methiocarb, respectively. 

Table 3 Range, Median, GM, and GSD of Assessed Total Dermal and Respiratory Exposure to Thiophanate-Methyl and Methiocarb...

Lrom the regression analyses it is clear that significant relationships were observed between respiratory exposure to thiophanate-methyl and methiocarb (adjusted to the number of flowers harvested) and dislodgeable foliar residues during re-entry. 

Data on the DFR of chlorothalonil on carnation crops in previous studies indicated an increase in DFR of 10 to 20% with solvent extraction (unpublished data). However, in all of the current experiments, no differences were observed between dislodgeable foliar residue and solvent-extracted foliar residue for the pesticides methiocarb and thiophanate-methyl. 

Half-life estimates of approximately 28 days for thiophanate-methyl indicate a very slow decay compared to methiocarb with an estimate of half-life of about 11 days. The application of a model based on a first-order decay process resulted in fairly high R2 and significant fit. The results suggest that both pesticides are relatively stable compared to other compounds under similar environmental conditions (Brouwer et al., 1994). With respect to the objectives of the study and the proposed model, it can be stated that the results confirm the assumption of a linear relationship between application rate (for both application techniques) and the increase of dislodgeable foliar residue. This relationship holds for modeling purposes. The contribution of the crop density or total crop surface area to the process of interception cannot be quantified with the results of the present study. Because the interception factor ranges from about 0.35 to 0.9 (Willis and McDowell, 1987), the... 

Soekhoe, U. and Kerstens, H.J. (1995) Determination ofPropoxur, Methiocarb, and Tinopal on Gloves, Filters, and Leaves by High Performance Liquid Chromatography, Report DATV/BT/076, TNO Nutrition and Food Research Institute, Department of Occupational Toxicology, Rijswijk, The Netherlands (in Dutch). 

Coumaphos Methiocarb Potentiometric AChE Methiocarb 8 X 10 7 M Coumaphos 5 X 10 8 M ... 

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