Reviews of Environmental Contamination and Toxicology

Aldicarb (2-methyl-2[methylthio]propionaldehyde 0-[methyl carbamoyl]-oxime; TEMIK^®, Rhone-Poilenc’s registered trademark) effectively controls a wide variety of insects, mites, and nematodes and is used worldwide on more than 40 economically important crops. Aldicarb is a potent acetylcholinesterase inhibitor and is commercially available only in granular formulations containing 5% to 10% active ingredient. As formulated, the potential hazard of aldicarb to human health and to the environment is sinificantly reduced.

Since the 1984 tragedy in Bhopal, India, methyl isocyanate (MIC) has been studied extensively to provide data on its toxicity following short-term exposures to MIC vapor. The purpose of this article is to review the toxicologic studies on MIC which were conducted in laboratories under controlled and objective conditions. Human exposure data are, on occasion, discussed, but only for the purpose of comparing results of selected laboratory animal studies with clinical findings. In addition, results of unpublished MIC studies performed in the 1960s at Mellon Institute are presented to expand the toxicity data files and provide a better understanding of MIC’s mechanism of action. As will become evident, the relatively simple molecule of MIC has a complex mode of toxic action. Furthermore, there is no universal agreement on how MIC reacts with biological systems or, following in vivo exposure, which organ systems are affected and for what length of time.

Aldicarb, [2-methyl-2-(methylthio)propionaldehyde O-(methylcarbamoy1)-oxime], the active ingredient in TEMIK^® insecticide/nematicide, was discovered in 1962 (Weiden et al. 1965) and is currently registered in over 60 countries for a large number of crops. It is applied to the soil for nematode control and for insect or mite control as a result of its efficient translocation (systemic activity) by the plant. Toxic metabolites, primarily a result of soil microbial action, are the sulfoxide, [2-methyl-2-(methylsulfinyl)propionaldehyde O-(methylcarbamoyl)oxime], and the sulfone, [2-methyl-2-(methylsulfonyl)-propionaldehyde O-(methylcarbamoyl)oxime]. Aldicarb, aldicarb sulfoxide, and aldicarb sulfone are all white crystalline materials at room temperature with water solubilities of 6, 330, and 8 mg/mL, respectively (Hornsby et al. 1983).