Formulation, pesticide carbamates

Meier, E.R, M.C. Warner, W.H. Dennis, W.F. Randall, and T.A. Miller. 1976. Chemical Degradation of Military Standard Formulations of Organophosphate and Carbamate Pesticides. I. Chemical Hydrolysis of Diazinon. U.S. Army Med. Bioengin. Res. Dev. Lab., Fort Detrick, Frederick, MD. Tech. Rep. 7611. 32 pp. 

Fig. 28.2. Reproduced from Figs. 1 and 2 of Ref. [49]. Currents generated by electrodes 17 h after exposure to pesticides, (a) Electrodes exposed to an or-gano-phosphate, malathion and a commercial formulation of it, Maldison. Maldison diluted to the recommended dose (RD) contains 6.1 mM malathion. (b) Electrodes exposed to a carbamate, methomyl and a commercial formulation of it, Lannate. Lannate diluted to the RD contains 2.2. mM methomyl. A is a multiple of the RD or 6.1 mM malathion or 2.2 mM methomyl.

In order to minimize waste as well as to direct selectivity, a number of approaches toward dissipation-control are being examined. For example, both volatilization and photodecomposition often can be regulated to a desired degree by incorporation of a non-volatile resin additive into the pesticide formulation (35). The technique appears promising for insecticides, and there is no reason to believe it should not work for herbicides also. Another approach is inhibition of microbial break-down for example, N-methylcarbamate inhibitors of hydrolytic enzymes, such as PCMC ( -chlorophenyl N-methylcarbamate), applied together with a herbicide such as chloropropham [isopropyl N-(3-chlorophenyl)carbamate] which is inactivated by soil microbes, more than doubled the effectiveness (36,37). 

Another method to classify pesticides is related to their main chemical structural elements or their mode of action. Examples are organochlo-rines, organophosphates, carbamates, pyrethroids, and so on (Table 11.2). In commercial products, the active ingredients are formulated (mixed) with other compounds, such as solvents, surfactants, stabilizers, and so on, that make the pesticides ready for use on farms and for private pest control. The formulations for crop protection are usually concentrates that are diluted with water before being applied on a field. 

With an excessive, single exposure, the result will be either a systemic pesticide poisoning or a topical lesion frequently observed on the skin or in the eyes. Since most acute intoxications are from the carbamate and organoposphate insecticides, the systemic manifestations are cholinergic and are due to the inhibition of acetyl cholinesterase and the resultant accumulation of the neurotransmitter acetylcholine, at the synapse. Topical effects, in contrast, either are the result of the irritant properties of the chemicals in the formulation or have an allergenic basis for their occurrence (3). However, topical effects are not necessarily exclusively the result of exposure to the active ingredient in the formulation but may result from a reaction to one or more inerts as well. 

A rather unusual case of pesticide exposure repoted to the New Zealand Poisons Information Centre concerned a helicopter pilot who was involved in the aerial application of a carbamate insecticide onto crops. Foolishly, he mixed the dry powder formulation under the still rotating blades of his helicopter, which caused the powder to disperse into... 

In addition to those listed above, many other classes of compounds are also used in several pesticide formulations dithiocar-bamates, chlorophenols, nitrophenols, and various phthalimides. While the former three classes of substances—organochlorine pesticides, organophosphates, and carbamates— are among the best known pesticides (e.g., insecticides, rodenticides), triazines, chlorophenoxy acids, and bipyridyls are used in making herbicides. There are also many pesticides that do not fall under any specific class of structures. These are discussed separately. 

Household pesticides Numerous formulations some contain hydrocarbon solvents, others are water-based. Pesticides used may include pyrethrins, organophosphates, or carbamates, but generally low potency and in concentrations less than 1.5%. The risk of pesticide poisoning is very low unless intenhonal massive exposure. Symptoms after exposure mainly due to inhalation of the hydrocarbon solvent. 

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