Carbamate-thiocarbamate pesticides

Carbamate pesticides are used as (1) insecticides, (2) fungicides and (3) herbicides. Insecticides are generally derived from carbamic acid fungicides, from thiocarbamic acid. The herbicide carbamates are a more complex class of compounds. Tables 21 and 22 list some commercial carbamate pesticides in approximate order of decreasing toxicity. It should be noted that the relative classification of highly and moderately toxic is no measure of the relative carcino-, muta- or teratogenicities of these carbamates, since it is based solely on acute LD q data (Morgan, ref. 20). 

Carbamates and thiocarbamates are an important family of pesticides, finding applications both as insecticides and herbicides. 

The N-alkylcarbamates and thiocarbam-ates can react with nitrite under mildly acid conditions to form N-nitroso compounds. Nitrite is found in sods, in human saliva, and in cured meats. N-nitrosodimethylamine is formed by soil microorganisms from thiram. Other N-nitroso compounds could similarly be formed from other carbamate pesticides. However, the extent of the reaction of carbamates and nitrite in humans is not known. The N-nitrosodialkylamines formed from dialkylthiocarbamate pesticides and... 

Carbamate compounds are usually subdivided into at least three main groups with respect to their structure and general use (see Figure 1) insecticides, herbicides, and thio- or dithiocarbamates. A variety of R groups may be substituted in the molecule producing, as is the case for insecticides, a variety of alkyl or aryl esters of carbamic acid. Although technically characterized as carbamate pesticides, thio- and di-thiocarbamate fungicides are not included in this... 

LLE is a widely used technique among the official US-EPA methods for the preconcentration of pesticides in liquid samples. Nonpolar solvents for the LLE of pesticides include w-hexane, benzene, and ethyl acetate. Water-miscible solvents for this purpose include dichloromethane, methanol, acetonitrile, acetone, and water, which have been employed for the extraction of residues from high-moisture commodities. Mixed solvents have often been used to finely adjust the solvent strength. Thus, various carbamate pesticides were extracted from aqueous environmental samples with chloroform and determined by HPLC with a mean recovery of 71 Also, a method based on the extraction by sonication of solid samples placed in small columns with a low volume of ethyl acetate was developed for the extraction of thiocarbamates and other herbicides from soil with recoveries between 89 and 109%. ... 

The dithiocarbamates include zinc dibutyldi-thiocarbamate (ZDBC), zinc diethyldithiocarbamate (ZDEC) and zinc dimethyldithiocarbamate (ZDMC). In the rubber industry, the carbamates are principally used in gloves, condoms and elastic bands. Due to their chemical similarity with thiurams, the potential for cross-reactivity between these groups exists (Con-de-Salazar 1990a Knudsen and Menne 1996). The greatest use of carbamates is not in rubber but in pesticides and fungicides (Table 8). 

Carbamates are nonpersistent pesticides that exhibit low toxicity for warm-blooded animals and human beings. Depending on the structure (see Fig. 3), quite different pesticidal activity is obtained. V-methyl- (IX) and V,A-dimethyl-carbamates (X) possess insecticidal activity, while V-aryl-carba-mates (XI) show herbicidal activity (66). Introducing a sulfur atom or atoms into the carbamate molecule instead of oxygen atom(s) yields thiocarbamate (XII) herbicides and dithiocarbamate (XIII)... 

Organophosphates, thiocarbamates, carbamates, carbamoyloximes, dithiocarbamates, and ureas were included among 100 pesticides and metabolites detected on TLC plates by their cholinesterase inhibiting properties. After developing the plates in ether, xylene, di-n-butyl ether, n-butyl acetate or methyl-isobutyl ketone, the plates were exposed to bromine vapor. The compounds were oxidized to their oxo derivatives, which exhibited more effective cholinesterase inhibitory activity. Bovine liver suspension served as enzyme source and the substrates 2-naphthyl acetate and Fast Blue B salt as the chromogenic agents (163a). 

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