Pesticide Aldicarb sulfoxide

In this study, the preliminary findings showed that the HPLC/fluorescence data were in agreement for all 12 carbamates with HPLC/ESI-MS/MS for most of the nine fruits and vegetables at the 1.0 ng g fortification level. The recoveries were generally within 70-120% however, at the 1.0 ng g level in each commodity, HPLC/ESI-MS (single-stage MS) had difficulty with interferences for three out of the 12 carbamate pesticides (aldicarb sulfoxide, aldicarb sulfone, and 3-hydroxycarbofuran), which made quantification impossible for these three compounds. 

Oxime carbamates are generally applied either directly to the tilled soil or sprayed on crops. One of the advantages of oxime carbamates is their short persistence on plants. They are readily degraded into their metabolites shortly after application. However, some of these metabolites have insecticidal properties even more potent than those of the parent compound. For example, the oxidative product of aldicarb is aldicarb sulfoxide, which is observed to be 10-20 times more active as a cholinesterase inhibitor than aldicarb. Other oxime carbamates (e.g., methomyl) have degradates which show no insecticidal activity, have low to negligible ecotoxicity and mammalian toxicity relative to the parent, and are normally nondetectable in crops. Therefore, the residue definition may include the parent oxime carbamate (e.g., methomyl) or parent and metabolites (e.g., aldicarb and its sulfoxide and sulfone metabolites). The tolerance or maximum residue limit (MRL) of pesticides on any food commodity is based on the highest residue concentration detected on mature crops at harvest or the LOQ of the method submitted for enforcement purposes if no detectable residues are found. For example, the tolerances of methomyl in US food commodities range from 0.1 to 6 mg kg for food items and up to 40 mg kg for feed items. ... 

Base hydrolysis kinetic data are reported for ppb solutions of carbofuran,3-OH carbofuran, methomyl and oxamyl. The results are compared with those reported previously for aldicarb, aldlcarb sulfoxide, and aldicarb sulfone. Second order reaction rate constants, k, have been calculated and range from 169 liter mln mole for oxamyl to 1.15 liter mln mole for aldicarb. The order for rate of base hydrolysis is as follows oxamyl >3-hydroxycarbofuran >aldicarb sulfone v- carbofuran >aldicarb sulfoxide > methomyl -v aldicarb. The activation energy for the base hydrolysis of carbofuran was measured to be 15.1 +0.1 kcal mole , and is similar to the value previously reported for aldicarb sulfone. Rapid detoxification of aldicarb, a representative oxime carbamate pesticide, by in situ hydrolysis on reactive ion exchange beds is reported. 

The oxidation of pesticide compounds usually generates products with aqueous mobilities that are either similar to or greater than that of the parent compound. The oxidation of aldicarb, for example, produces aldicarb sulfoxide and aldicarb sulfone, both of which have lower A/qc values than aldicarb (Moye and Miles, 1988). Similarly, because most phototransformations involve either the hydrolysis or oxidation of the parent compound, they yield products that are generally more polar (Mill and Mabey, 1985), and thus more water soluble than the parent compound. Reduction reactions, by contrast, may result in products that are less water soluble than their parent compound. Examples include the reduction of aldicarb sulfoxide to aldicarb (Miles and Delfino, 1985 Lightfoot et al, 1987) and the reduction of phorate sulfoxide to phorate (Coats, 1991). The reactivity of transformation products may be either higher or lower than that of their parent compounds. However, those in the former category (i.e., reactive intermediates) are, of course, much less likely to be detected in the hydrologic system than more stable products. 

The analytical solution to Equation 2 for a range of boundary conditions is a model of pesticide fate that has been used under a variety of laboratory situations to study the basic principles of soil-water-pesticide interaction. It is in fact limited to such laboratory cases, as steady state water flow is an assumption used in deriving the equation. As a modeling approach it is useful in those research studies in which careful control of water and solute fluxes can be used to study degradation and adsorption. For example, Zhong et al. (11) present a study of aldicarb in which the adsorption and degradation of aldicarb, aldicarb sulfone and aldicarb-sulfoxide were simultaneously determined from laboratory soil column effluent data. The solution to a set of equations of the form of Equation 2 was used. A number of similar studies for other chemicals could be cited that have provided useful basic information on pesticide behavior in soil (4,12,13). Yet, these equations are not useful in the field unless re-formulated to describe transient water and solute fluxes rather than steady ones. Early models of pesticide fate based upon Equation 2 (14) were constrained by such assumptions, but were... 

The following example using aldicarb illustrates how to derive an ADI. Aldicarb is a pesticide that has been detected in ground water in Florida and elsewhere. The EPA is currently in the process of establishing a drinking water criterion for aldicarb. Weil and Carpenter (19) studied the effects of aldicarb sulfoxide on rats and determined a NOEL of 0.125 mg/kg/day. This is supported by another rat study by Mirrow et al. (20), which resulted in a NOEL equal to 0.12 mg/kg/day. An ADI is estimated for aldicarb, using the NOEL from the Weil and Carpenter study and an uncertainty factor of 100 ... 

Many P450 isoz5unes catalyze heteroatom oxidations, such as sulfoxidation, of substrates (89-92). Thus, the biodegradation of the pesticide aldicarb as well as neuroleptic drugs in the liver proceed through substrate sulfoxidation by P450 isozymes (93,94). Mechanistic studies on substrate sulfoxidation by P450 enzymes and biomimetic models have been performed (95-99) and... 

The non-atmospheric pressure ionisation interfaces (non-API) PBl and TSP besides the API interfaces ESI and APCI were applied for the analysis of the N-methylcarbamate pesticides (methomyl, aldicarb, aldicarb sulfoxide, aldicarb sul-... 

Individual pesticide formulations, such as technical grade aldicarb, were successfully fractionated (aldicarb sulfoxide and sulfone and propionaldoxime) using a 30/70 methanol/water mobile phase on a C g column (A = 240 nm) when 200 pL of a 2.3 mg/mL sample was injected [200],... 

Newsome et al. [974] studied the chromatography of 11 carbamate pesticides (e.g., aldicaib, aldicarb sulfoxide and sulfone, oxamyl, cathofiiran, 3-hydroxy- and 3-ketocaiboiuran) on a Cg column. A postcolumn o-phthalaldehyde derivatization technique (A = 336 run, ex 440 nm, em) was compared with an atmospheric pressure ionization MS detector. A 20-min 12/78 -> 70/30 acetonitrile/water gradient generated good resolution and peak shapes. Detection limits forall compounds were tabulated and were 0.1 ng for fluorescence and 1 ng for APCl/MS. 

Methods have also been developed for specific classes of pesticides. N-methylcarbamates are systemic insecticides characterized by moderate polarity and relatively low thermal stability. For these reasons, LC methods are more suitable than GC methods for the analysis of environmental samples. In the case of aldicarb, metabolic pathways involve oxidative conversion to aldicarb sulfoxide and aldicarb sulfone. These fransformafion products are reportedly more toxic and persistent than the parent compound [83] and are important to monitor along with the parent compound. One of the first LC methods for the determination of carbamate pesticides and their transformation products is based on LC... 

The most toxic of the pesticides used in the USSR was the systemic insectoacaricide aldicarb (FD5o=0.93 mg/kg), which breaks down in the soil, forming the also highly toxic sulfoxide and sulfone. The herbicide propanile transforms in the soil into a dioxin-like substance [38]. 

Particle beam using El and Cl Ionization was useful for the analysis of several thermally labile pesticides such as aldicarb sulfone and fenamiphos sulfoxide, resulted in molecular ions and structurally relevant fragment ions (Figures 12 and 13). The thermospray spectra for these two pesticides are also presented for comparison. The thermospray spectra consisted of only [M+H] and [M+NH4]+ ions. 

Sulfoxidation. This is a fairly common transformation of sulfur-containing pesticides such as aldicarb (6) (eq. 8) and EPTC (19). 

The contamination of fruits and vegetables with pesticides became a problem with the increased application of pesticides because of an intensified agriculture. So the comparison of APCI and ESI-LC-MS for the determination of 10 pesticides of carbamate type (pirimicarb, carbofuran, 3-hydroxycarbofuran, aldicarb, and its metabolites, the sulfoxide and the sulfone), besides others in fruits, met the... 

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