Experiments were performed in order to better define the degradation mechanisms and kinetics for aldicarb and its two metabolites, aldicarb sulfoxide and aldicarb sulfone. The mechanisms studied were oxidation in surface soil and saturated zone soil samples, degradation in saturated zone soil samples and distilled water hydrolysis. The studies showed that soil is an important mechanistic factor, probably because surface catalysis occurs. Temperature and pH are important factors in determining degradation rates. The experiments seem to indicate that microbial oxidation is an important degradation mechanism in the surface soil, but the breakdown of aldicarb residues to noncarbamates is largely the result of chemical hydrolysis. The reduction of aldicarb sulfoxide to aldicarb was observed in the presence of limestone but only after an incubation period of two to six months. No reduction of aldicarb sulfone to aldicarb sulfoxide was observed in these experiments. The complexity of degradation is such that laboratory studies can augment but not replace well‐designed experiments conducted under actual field conditions.
TEMIK ALDICARB PESTICIDE thion standard represents 97.770 of the total shoot radioactivity. The remaining two unidentified bands (Rf's 0.05 and 0.31) represent 0.7 and 1.6% of the total shoot radioactivity.Injection of a sample of the major tlc band into the gas chromatograph described earlier produced a single peak having the same .retention time (3 min) as that of a Guthion standard injected under the same conditions. Further chromatographic analyses involving the use of a gc/ms produced a mass spectrum of unit resolution similar to that reported by Damico (1966) for Guthion. Final proof of structure was apparent after comparing the infrared spectrum of the major labeled tlc band to the infrared spectrum of [14C]Guthion standard (Figure 8). Guthion, therefore, may be classified as a systemic since it is readily absorbed through roots and foliage of the plants and is translocated intact without harm throughout the plant system, thus rendering untreated areas insecticidal.
Unsaturated zone studies to measure the movement and degradation of aldicarb and aldoxycarb residues were conducted in 1983 at seven locations: Maricopa, Arizona; Harrellsville, North Carolina; Blackstone, Virginia; Blissfield, Michigan; Bluecast, Indiana; Pasco, Washington; and Fort Pierce, Florida. The Blissfield and Bluecast studies also included monitoring of tiledrain water and the Fort Pierce test included shallow ground water analyses. These research studies indicate that aldicarb or aldoxycarb residues will not enter drinking water supplies under agricultural conditions similar to those encountered in these seven field studies. Most, if not all, of the residues will degrade in the unsaturated zone at a rate corresponding to half-lives of between 0.5 and 2.0 months. The field studies also demonstrate that aldicarb and aldoxycarb residues degrade at about the same rate.
The potential for TEMIK®; aldicarb pesticide to appear in potable water is estimated by applying a numerical indexing system. The index recognizes four basic categories of factors that affect the potential of chemical residues to occur in potable water. Values are assigned to the factors based on published data, designed laboratory tests and estimates based on knowledge about the use of the pesticide. An area with a high index number is expected to have a higher potential for aldicarb residue to appear in potable water than an area with a lower number. The index does not give quantitative values for aldicarb residue concentrations but indicates the sensitivity of an area to significant intrusion into water supplies. The system has been calibrated by adjusting scoring to reflect results of on‐site monitoring from different climatic and geographical areas. The reliability of the index is believed to be comparable in accuracy to simulation modeling and has the advantage of greater adaptability to a wide variety of areas.
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