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EXTOXNET PIP - METHIDATHION Page 3 o potential that the compound would accumulate in fish tissues [6]. Maximum levels of the residues of the pesticide after 1 month of exposure to very low concentrations in the water, 0.05 ug/L, were 1.0 ug/kg in the edible tissue, ug/kg in nonedible tissue, and 2.4 ug/kg in whole fish. These concentrations indicate a low bioconcentration facto of 46 for whole fish. After 2 weeks in water without methidathion, the concentration in whole fish fell by nearly 80% [2]. . Effects on other organisms: Methidathion is slightly toxic to bees [13]. Environmental Fate: . Breakdown in soil and groundwater: Methidathion is of low persistence in the soil environment; reported field half-lives are 5 to 23 days, with a representative value of about 7 days [19]. Breakdown of the compound in soil occurs through the action of soil microorganisms [83]. Under alkaline conditions, methidathion is rapidly degrade by chemical action [8]. Methidathion and its breakdown products are poorly bound by soils, and so may be mobil [19,81]. However, they have not been detected in any groundwater sources. This is probably due to the short half- life of the compound and its degradates. . Breakdown in water: No data are currently available. . Breakdown in vegetation: In plants, methidathion is rapidly metabolized [13]. Oranges sprayed with Supracide , a rate of nearly 2 pounds per acre had residues of the compound of about 0.1 ug/ml [81]. Within 2 days over 60% the compound was removed from the outside of the fruit, and within I week, less than I% of the compound remained [81]. Physical Properties: . Appearance: Methidathion is a colorless crystalline compound at room temperature [13]. . Chemical Name: S-2,3-dihydro-5-methoxy-2-oxo-1,3,4-thiadiazol-3-yhnethyl 0,0-dimethylphosphorodithioate [13] . CAS Number: 950-37-8 . Molecular Weight: 302.33 • Water Solubility: 240 mg/L @ 20 C [13] . Solubility in Other Solvents: v.s. in octanol, ethanol, xylene, acetone, and cyclohexane [13] . Melting Point: 39.5 C [13] • Vapor Pressure: 186 mPa @ 20 C [13] . Partition Coefficient: 4.7243 [8] . Adsorption Coefficient: 400 (estimated) [19] Exposure Guidelines: . ADI: 0.001 mg/kg/day [38] . MCL: Not Available . RfD: 0.001 mg/kg/day [53] . PEL: Not Available . HA: Not Available . TLV: Not Available Basic Manufacturer: --iba-Geigy Corporation P.O. Box 18300 ttp://extoxnet.orst.edu/pips/methidat.htm 7/2/20