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e a XTOXNET PIP - METHIDATHION Pagel of 3 3. EXTOXNET Extension Toxicology Network Pesticide Information Profiles A Pesticide Information Project of Cooperative Extension Offices of Cornell University, Oregon State University, the University of Idaho, and the University of California at Davis and the Institute for Environmental Toxicology, Michigan State University. Major support and funding was provided by the USDA/Extension Service/National ' Agricultural Pesticide Impact Assessment Program. II, EXTOXNET primary files maintained and archived at Oregon State University Revised June 1996 :Methidathion, Trade and Other Names: Trade names for products containing methidathion include Sornonic, Somonil, Supracide; Suprathion and Ultracide. The compound may be found in formulations with many other pesticides. Regulatory Status: Methidathion is an highly toxic compound in EPA toxicity class I. Labels for products containing it must bear the Signal Word DANGER. Methidathion is a Restricted Use Pesticide (RUP), except for use in nurseries, and on safflower and sunflowers. Chemical Class: organophosphate Introduction: Methidathion is a non-systemic organophosphorous insecticide and acaricide with stomach and contact action. The compound is used to control a variety of insects and mites in many crops such as fruits, vegetables, tobacco, alfalfa, and sunflowers, and also in greenhouses and on rose cultures. It is especially useful against scale insects. It works by inhibiting certain enzyme actions in the target pests. It is available in emulsifiable concentrate, wettable powder, and ultra-low volume (ULV) liquid. Formulation: It is available in emulsifiable concentrate, wettable powder, and ultra-low volume (ULV) liquid formulations. Toxicological Effects: . Acute toxicity: Methidathion is highly toxic via the oral route, with reported acute oral LD50 values of 25 to 54 mg/kg in the rat, and 18 to 25 mg/kg in the mouse [2,13]. Other reported oral LD50 values include 25 mg/kg in guinea pigs, 80 mg/kg in rabbits, and 200 mg/kg in dogs [2]. It is highly toxic via the dermal route as well, with reported dermal LD50 values of 85 to 94 mg/kg in the rat [2]. Methidathion is only a mild skin irritant and is nonirritating to the eyes (in rabbits). Via the inhalation route, it may be slightly toxic, with a reported 4-hour inhalation LC50 of 3.6 mg/L in rats [13]. Effects due to acute methidathion exposures are similar to those caused by other organophosphate pesticides, and may include nausea, vomiting, cramps, diarrhea, salivation, headache, dizziness, muscle twitching, difficulty breathing, blurred vision, and tightness in the chest [2]. High acute exposure may cause intense breathing problems, including paralysis of the respiratory muscles. . Chronic toxicity: Beagle dogs fed small doses of the compound for 2 years experienced no compound related effects at or below the dose of 0.10 mg/kg/day [2,8]. At doses of 0.4 mg/kg/day and above, the dogs experienced enzymatic changes and liver alterations. Inhibition of red blood cell cholinesterase, an enzyme, was observed only at the highest dose tested (1.6 mg/kg/day) [2]. Rats also have a low tolerance for the