Carbaryl water-soil system

Studies were initiated at Iowa State University in 1977 to determine if pesticides would be contained and degraded when deposited in water/soil systems. Although the addition of known amounts of the selected pesticides was controlled, the physical environment was not temperature, humidity, wind speed, etc. were normal for the climate of Central Iowa. Four herbicides and two insecticides were chosen on the basis of three factors. Firstly, they represented six different families of pesticides. The four herbicides, alachlor, atrazine, trifluralin, and 2,4-D ester, represent the acetanilides, triazines, dinitroanilines, and phenoxy acid herbicides, respectively. The two insecticides, carbaryl and para-thion, represent the carbamate and organophosphorus insecticides, respectively. Secondly, the pesticides were chosen on the basis of current and projected use in Iowa Q) and the Midwest. Thirdly, the chosen pesticides were ones for which analytical methodology was available. 

Phenylcarbamates, or carbanilates, generally exhibit low water solubilities, and thus they are almost immobile in soil systems. Chlorpropham and Propham are readily volatilized from soil systems, but Terbutol and Carbaryl (Fig. 10, Table 3) are not. Ester- and amide-hydrolysis, N-dealkylation and hydroxylation are among the chemical reactions that carbamates undergo. The N-methylcar-bamate insecticides (Fig. 10, Table 3) commonly used in soils are Carbaryl, Methiocarb,Aldicarb,and Carbofuran [74,173]. 

Phenylcarbamates and Carbanilates. The phenylcarbamate pesticides are much more water soluble than the substituted anilines (Table VIII), but despite the higher solubilities they are also immobile in soil systems. All are herbicides except for carbaryl which is an insecticide. Chlorpropham and terbutol resisted leaching, and propham leached only slightly 137, 143, 144, 343, 344, 345, 346), In herbicide mobility studies in soils, Harris (151) ranked chlorpropham with the substituted anilines as having low movement. 

Depending on the characteristics of the electron donor, optical techniques and amperometry can be used. The use of the three enzymes, in homogeneous phase, has been applied in combination with pervaporation as sample pretreatment, for the determination of dichlorvos in soil and water samples [382]. Acceptable recoveries for dichlorvos (90-110%) in natural waters and spiked soil samples were reported. The whole procedure offers a sample frequency of 2 h [382]. Microgravimetric measurements of this multi-enzymatic system have also been reported using benzidines (3,3 - diamino-benzidine) as substrate of peroxidase, which is oxidized to an insoluble product [383]. Similarly to the previous example using this technique, the limits of detection achieved for carbaryl and dichlorvos are not as good as those obtained amperometrically. 

Carbaryl has been widely used as an insecticide on lawns or gardens. It has a low toxicity to mammals. Carbofuran has a high water solubility and acts as a plant systemic insecticide. As such, it is taken up by the roots and leaves of plants so that insects are poisoned by the plant material on which they feed. Pirimicarb has been widely used in agrieulture as a systemie aphicide. Unlike many earbamates, it is rather persistent, with a strong tendeney to bind to soil. 

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