Thiocarbamate pesticides

AL Howard, C Braue, LT Taylor. Feasibility of thiocarbamate pesticide analysis in apples by supercritical fluid extraction and high-performance liquid chromatography. J Chromatogr Sci 31 323-329, 1993. 

Dithiocarbamate pesticides syn, thiocarbamate pesticides, salts and complexes including and based on dithiocarbamic acid, a seed disinfectant, like the deer poison zinc dimethyldithiocarbamatecyclohexy-lamine complex, metam-sodium, nabam, and maneb. 

The carcinogenic activity of chemical substances is important as well. They are present in pesticides of different classes OCPs (DDT, aldrine, heptachlor, methoxychlor), thiocarbamates (thiram, zineb, ziram), carbamides (monuron) [3], etc. Even if the official description of a given pesticide does not denote its carcinogenic (mutagenic, teratogenic, embryotoxic, etc.) activity, this merely means that this particular pesticide was not studied sufficiently. 

Pesticides Triazines, phenylureas, OPs, chloroacetanilides, thiocarbamates River water Online SPE... 

Analysis of pesticides in water was performed by fully automated online solid-phase extraction-liquid chromatography-tandem mass spectrometry (SPE-LC-MS/ MS) [25, 31]. These pesticides (a total of 22 belonging to the classes of triazines, OP, chloroacetanilides, phenylureas, thiocarbamates, acid herbicides, and anilides) were selected on the basis of previously published studies [20, 25], information gathered from the water authorities, and known use in rice crops. 

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... 

There are limited commercial uses of carbonyl sulfide. It is produced only in small quantities and used for small-scale experimental purposes and as a nonisolated, site-limited intermediate in the synthesis of organic sulfur compounds, thiocarbamate herbicides, and alkyl carbonates. Pesticide manufacturers... 

Modification of the Toxicity of Pesticides with Formulation Additives. Potentially the use of additives to modulate the toxicity of pesticides could lead to a considerable increase in their safety to non-target species, man included. This concept has been well explored and exploited in adding safeners to certain herbicides such as the thiocarbamates. These compounds stimulate defensive metabolic reactions in the crop species but not in weeds This principle has also been applied to vertebrates, but only to a very limited degree. Under some circumstances the thiocarbamate rice herbicide, molinate, may show toxicity to carp in nearby ponds. Based on a knowledge of the safeners that are active in plants, a compound was discovered that, when applied with molinate, acted as an antidote/safener for the carp (20). Little effort, either theoretical or empirical, seems to have gone into developing other such examples. 

Immunochemical methods are rapidly gaining acceptance as analytical techniques for pesticide residue analysis. Unlike most quantitative methods for measuring pesticides, they are simple, rapid, precise, cost effective, and adaptable to laboratory or field situations. The technique centers around the development of an antibody for the pesticide or environmental contaminant of interest. The work hinges on the synthesis of a hapten which contains the functional groups necessary for recognition by the antibody. Once this aspect is complete, immunochemical detection methods may take many forms. The enzyme-linked immunosorbent assay (ELISA) is one form that has been found useful in residue applications. This technique will be illustrated by examples from this laboratory, particularly molinate, a thiocarbamate herbicide used in rice culture. Immunoassay development will be traced from hapten synthesis to validation and field testing of the final assay. 

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%. ... 

Among the pesticides, intermediate or strong volatility is characteristic for certain thiocarbamates, acetamides, benzonitriles and esters. For example, EPTC (s-ethyldipropyl thiocarbamate) has a vapour tension of... 

The metabohsm of compounds predominantly results in more polar compounds than the precursor molecules, so for the follow-up of pesticides in the environment in the late 1980s and early 1990s FAB and CF-FAB-MS at this stage of MS development met the need. CF-FAB-MS was appHed by Reiser et al. [171] to unknown sulfonylurea herbicide metabohtes using packed capillary columns. New and unusual heterocychc ring-opened metabohtes and hydrolysis products were identified and metaboHc pathways proposed. The metabohsm of cycloate, a thiocarbamate herbicide, was inveshgated [177]. 

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). 

The formation of S-alkyl thiocarbamates was studied from fundamental and applied viewpoints. These compounds represent an important synthetic target due to their pesticide properties. The conventional method implies the alkylation of sodium thiocarbamates by alkyl chlorides (Eq. 58). This lengthy reaction requires heating but the thermally unstable products suffer partial... 

After the cleanup step, the solution obtained has to be evaporated. Recently a device for the flash evaporation of sample extracts was developed for the evaporation of toxin-containing extracts (45). One has to be careful when using it in the analysis of volatile pesticide (thiocarbamates), because during the evaporation a large loss of residues may sometimes occur, resulting in low recovery. Snyder columns (Kontes) are the best glassware for the evaporation of these volatile pesticides. 

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)... 

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