Pesticides methomyl

Chang et al. [72] studied the adsorption of a more hazardous pesticide, methomyl, that is used worldwide in the cultivation of... 

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-... 

Insecticide methomyl is a very toxic pesticide and is highly soluble in water (57.9 g/1). It has a low sorption affinity to soil and can cause groundwater and surface water contamination in agricultural areas. Solubilities of methomyl in different solvents are in methanol 1000 g/1, in aceton 730 g/1, in ethanol 420 g/1, in isopropanol 220 g/1, in toluene 30 g/1. 

Figure 13.15 Chromatograms obtained by on-line ti ace enrichment of 50 ml of Ebro river water with and without the addition of different volumes of 10% Na2S03 solution for every 100 ml of sample (a) blank with the addition of 1000 p.1 of sulfite (b) spiked with 4 p.g 1 of the analytes and 1000 p.1 of sulfite (c) spiked with 4 p.g 1 of the analytes and 500 p.1 of sulfite (d) spiked with 4 p.g 1 of the analytes without sulfite. Peak identification is as follows 1, oxamyl 2, methomyl 3, phenol 4, 4-niti ophenol 5, 2,4-dinitrophenol 6, 2-chlorophenol 7, bentazone 8, simazine 9, MCPA 10, atrazine. Reprinted from Journal of Chromatography, A 803, N. Masque et ai, New chemically modified polymeric resin for solid-phase extraction of pesticides and phenolic compounds from water , pp. 147-155, copyright 1998, with permission from Elsevier Science.

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. ... 

Figure 3.20 Pesticide in rat blood serum on vinyl alcohol polymer column. Conditions column, Asahipak GS320 (vinyl alcohol copolymer gel), 50 cm x 7.6 mm i.d. eluent, 0.05 M phosphate buffer containing 0.2 M sodium chloride pH 7.2 in 20% aqueous methanol flow rate, 1.0 ml min-1 detection, UV 254 nm. Peaks 1, blood serum protein and 2, methomyl.

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. 

Materials. Aldicarb standards were obtained from the United States Environmental Protection Agency (USEPA), Quality Assurance Section and from Union Carbide Corporation. Crystalline samples of carbofuran and 3-hydroxycarbofuran were supplied by the Agricultural Chemical Group of FMC Corporation. Reference standards of methomyl (99% pure) and oxamyl (99% pure) were obtained from USEPA. HPLC grade methanol was purchased from Burdick and Jackson, Inc. Methylene chloride used for bulk extractions of the carbamate pesticides in solution was recovered, distilled and reused. Analytical reagent grade chemicals and solvents were used in all experiments. Doubly distilled deionized water was used for solution rate studies. Deionized distilled water (DDW) was used for dilutions in reactive ion exchange experim ts., , ... 

Analytical Procedures. The extraction procedure used for solution studies was based on the method supplied by Union Carbide Corporation ( ), and was reported In previous work ( ). Samples were analyzed using a Microtek GC with a Tracer NP detector as described by Lemley and Zhong ( ). Conditions used for the various pesticides analyzed and the retention times obtained are detailed In Table I. In all cases a 4 foot x 4 mm I.D. glass column packed with 1.5% SP-2250/1.95% SP-2401 on 100/120 mesh Supelcoport was used. A glass Injector was used for the analysis of carbofuran and 3-hydroxycarbofuran. Procedures were varied slightly for analysis of methomyl. The first three Inches of the column were packed with 1.5% OV-17 on 100/120 mesh Supelcoport, and a glass Injector was used without glass wool at the end. 

A third important carbamate is aldicarb or Temik , an insecticide and nematocide for potato and vegetable crops. This chemical has been foimd in water wells in 11 states above the 1 ppm EPA safety threshold, barring use in some locales in 1982. According to Union Carbide, one manufacturer, humans can safely ingest 500 ppb. But it is one of the most acutely toxic pesticides registered by the EPA. A fourth carbamate insecticide is methomyl. 

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.

Oxamyl methomyl -Phoxan, 2,4,5 trichlorophenoxy acidic acid 2.4DB, NCPB Removal of pesticides from water on graphitised carbon block 0.003- 0.07pg L1 [140]... 

Endosulfan is used as an insecticide and as a contact poison. It is used primarily on food crops, cereals, tea, coffee, fruits, and vegetables. It is also used as a wood preservative. It is compatible with many other pesticides and may be found in formulations with dimethoate, malathion, methomyl, monocrotofos, pirimicarb, triazophos, fenoprop, parathion, petroleum oils, and oxine copper. It is not compatible with alkaline materials.14... 

In rabbits, application of methomyl resulted in mild eye irritation. Pain, short-sightedness, blurred distance vision, tearing, and other eye disturbances may occur within a few minutes of eye contact with methomyl. Prolonged or repeated exposure to methomyl may cause symptoms similar to the pesticide s acute effects. Repeated exposure to small amounts of methomyl may cause an unsuspected inhibition of cholinesterase, resulting in flu-like symptoms, such as weakness, lack of appetite, and muscle aches. Cholinesterase inhibition may persist for 2 to 6 weeks. This condition is reversible if exposure is discontinued. Since cholinesterase is increasingly inhibited with each exposure, severe cholinesterase inhibition symptoms may be produced in a person who has... 

Similarly, on-column methylation has been applied to carbamate pesticides containing an active N-H group. Wien and Tanaka (41) showed that N-aryl carbamates are methylated on-column with tri-methylanilinium hydroxide-methanol to give the intact N-methyl and N-aryl derivatives. On the other hand N-methyl, 0-aryl carbamates such as carbaryl or carbofuran yielded only the methyl ethers of their respective phenols. This work has now been extended to sulfur-containing carbamates such as methomyl, methio-carb, aldicarb, etc. (42-43). Here the oxime hydrolysis products of these carbamates are chromatographed as the 0-methyl oximes. 

Another area of concern is the residual life of a pesticide once it is brought back to the hive. Microencapsulated methyl parathion was at one time believed to represent a special hazard because of its controlled release feature. Thus methyl parathion from MMP was reported to persist in stored pollen for up to 17 months.( ) Unfortunately, little is known about the persistence of insecticides in honey bee combs etnd the subsequent effects of their residues on the honey bees. Carbaryl has been shown to persist for at least eight months in colonies ( ) euid permethrln for at least seven months.O) Recently, USDA researchers at the University of Wisconsin studied samples from two bee kills that apparently Involved methomyl and MMP applied to sweet com. Samples were collected to determine, among others, whether methomyl persisted in combs. Analysis demonstrated that eight months after the insecticide application, residues of 0.03 ppm of methyl parathion and 0.03 ppm of methomyl ( 5) remained, even though the latter is considered to be a short-residual pesticide. 

Strathmann T. J. and Stone A. T. (2002a) Reduction of the pesticides oxamyl and methomyl by Fe effect of pH and inorganic ligands. Environ. Sci. Technol. 36(4),... 

Caibamate pesticides are used as insecticide, acaricide, and herbicide. Various subclasses can be distinguished. Aryl V-methyl carbamates (1), such as caibaiyl, carbofuran, propoxur, and oxime V-methyl carbamates(2), such as aldicaib, methomyl, oxamyl, have most widely been studied. LC-MS is the method-of-choice for carbamates, since their thermal lability prohibits GC analysis. 

This range of compounds consists of the many chemicals that are used to control pests worldwide. Target species include insect, animal, or plant species. Examples of the hundred or so pesticides that have been studied to determine their removal during drinking water treatment processes include -5-triazines (atrazine, simazine, cyanazine, propazine), lindane, DDT, 2, 4-D, atachlor, metolachlor, asulam, hymexazol, methomyl, imidacloprid, carbaryl, linuron, thiobencarb, and diquat. 

The U.S.A., through the National Pesticide Survey, " which was organized by the Environmental Protection Agency (US-EPA), established a fist of compounds based on the amount used (>7000 Tons), water solubility (>30 mg/1), and hydrolysis half-life (>25 weeks). The list includes some carbamate pesticides (e.g., aldicarb, propoxur, carbaryl, carbofuran, methiocarb, methomyl, oxamyl, cycloate, butylate, propham, and swep) and various derivatives (e.g., aldicarb sulphone, aldicarb sulphoxide, and 3-hidroxycarbofiiran). In Europe, a list of priority pollutants including pesticides was established in order to protect the environment from the adverse ecological impact of these compounds. ... 

The pesticide-treated vs. pesticide-free tobaccos used in this phase of the NCI study were those grown in Prince Edward Island, Canada. The commercial pesticides used on the tobacco included Chlorpyriphos , Trichlorfon , Diphenamide , Methomyl , DDT, Carbaryl , maleic hydraz-ide, and CIO alcohol. The pesticide-treated tobacco properties were described in 1980 by Tso et al. (3973, 3977) ... 

Pesticide Sample. The pesticide mixture consists of aldicarb (5.6 mg/ml), methomyl (5.3 mg/ml), captan (5.0 mg/ml), and phenmedipham (5.1 mg/ml) prepared in dichloromethane. Samples were provided courtesy of Lee Scientific. This sample was separated using an SB-Methyl-100 10 meter 100 micron I.D. column with a 0.5 micron film (Lee Scientific). The chromatograph was programmed from an initial density of 0.180 g/ml to 0.360 g/ml at 0.010 g/ml/min after a 6.0 minute initial hold. The program rate was then immediately increased to 0.040 g/ml/min to a final density of 0.600 g/ml and held for 10 minutes. The oven temperature was maintained at lOO C throughout the experiment. The sample was delivered to the column using a 200 nL injection loop and a 22 1 split ratio. 

Certain carbamates, such as, aldicarb and methomyl are classified by the U.S. EPA under Restricted Use Pesticides (RUP) because of their high acute toxicity to humans. Such RUP may only be purchased and used by certified applicators. Also, several carbamates are designated by the U.S. EPA as class P acutely toxic hazardous wastes. These compounds listed below in Table 45.1 are regulated under the category of discarded commercial chemical products, off-specification species, container residues and spills thereof. 

A significant peak broadening during the on-line extraction of pesticides with a hypercrosslinked polystyrene sorbent (SDB-1, J.T. Baker), followed by their HPLC separation and quantification on a C-18 analytical column was reported [248]. The problem was solved by replacing the siHca-based separating medium with PGC. This on-line combination provided trace determination of most polar pesticides such as clopyralid, methomyl, DIA, and picloram with detection limits at the low 0.1 Xg/L level for lOOmL drinking water samples. The study shows that the hypercrosslinked sorbent retains the pesticides much better than the PLRP-S resin. 

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