Aldicarb groundwater contaminant

Dailey et al. [15] also prepared and characterized y8-CyD complexes of the insecticides aldicarb and sulprofos. Groundwater contamination by aldicarb is of particular concern owing to its acute toxicity to mammals longer residual effects of sulprofos and a reduction in its phytotoxicity and operator hazards were the benefits expected from its complexation with CyDs. Formulations of the 8-CyD complex of sulprofos were tested for toxicity against the tobacco budworm on cotton [31]. Although none of the new formulations was as efficacious as the commercial formulation, the addition of additives such as Airvol 205 increased their toxicity against budworm. 

An example of an extremely toxic carbamate is aldicarb [2-methyl-2-(methylthio) propionaldehyde]. Both oral and dermal routes are the primary portals of entry, and it has an oral LD50 of 1.0 mg/kg (rat)and a dermal LD50 of 20 mg/kg (rabbit). For this reason it is recommended for application to soils on crops such as cotton, citrus, and sweet potatoes. This compound moves readily through soil profiles and has contaminated groundwater supplies. 

Aldicarb is highly water soluble and soil application of this insecticide has the potential to result in runoff or leaching of the insecticide or active metabolites and contamination of surface or groundwater. Aldicarb is acutely toxic to bees, birds, and fish. Species-specific rates of bioactivation may influence the sensitivity of a particular organism to this insecticide. 

Table II records the concentrations of aldicarb residues found in water samples from monitoring wells which had detectable residues present at some time during the sampling period. No significant residues were detected at any time in any other wells (12 more wells in Fields 1 and 2, 13 in Field 3, 16 in Fields 4 and 5, 10 in Field 6, 11 in Field 7, and 1 in each of Fields 8 and 9). Well depths in the groundwater increase in the sequence indicated by the designation A, B or C associated with the location number for any field. The wells which initially contained contaminated or uncontaminated water in any field were at similar depths in the water table thus, the pattern of residue occurrences cannot be ascribed to inappropriate well placement or depth.

In this paper, procedures for calibrating flow models and contaminant transport models are outlined and some of the difficulties frequently encountered during calibration are discussed. An example of a contaminant transport model applied to a problem involving aldicarb migration in groundwater in Wisconsin is also presented. 

Several other reports have studied aldicarb, a CM pesticide found in groundwater in several areas of the United States. Individuals exposed to drinking water contaminated with aldicarb showed an increase in the absolute number and the relative percentage of CDS (cytotoxic/suppressor) lymphocytes with a decreasing ratio of CD4" (helper T)/ CDS" " ceils... 

Chronic exposure to aldicarb-contaminated groundwater and human imtnune function. Fnvimn. Res. 41, 633-645. 

A number of carbamates have been used as insecticides and a few as herbicides. Kinetic parameters for several of these compounds are summarized in Table 8.6. Note that the base-catalyzed reaction is the more important, however, some reports indicate that for some compounds, the direct reaction with water can be significant with values of 6-7. Unfortunately, there is only limited information in this area. Note that these data also illustrate how the substituents on the N influence hydrolysis. The feb values for the dimethyl compounds are orders of magnitude lower than the methyl counterparts. Aldicarb represents a variation in that the ester component of the molecule is derived from an oxime (RCH=NOH) rather than an alcohol. It also illustrates the significance of hydrolysis in understanding its environmental behavior. Aldicarb has been very effective in controUing insect pests in potatoes, but because of its high water solubility (6000 ppm) has been detected as a contaminant in groundwater. This effect has been observed only in acid (pH 5.5) but not in basic (pH 8.0) soils. 

Water contaminated with mixtures of the pesticides aldicarb = 1.13) or atrazine = 2.61) and nitrate = -4.39) was administered to mice at concentrations simulating contaminated groundwater at levels found environmentally in midwestem United States farming communities. Though the pesticides alone are immunotoxic, nitrate is not. The mixtures of single pesticides with nitrate, however, reduced the ability to make antibodies against a foreign protein in laboratory animals [35]. No mechanistic explanation for this phenomenon was offered by the authors. 

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