Organophosphates degradation products

While the separation of alkylphosphonates and alkylphosphonic acids by CE is rather straightforward, sensitive detection remains a challenging task. Since these analytes do not contain a chromophore or a fluorophore, and are not easily derivatized, standard optical detection techniques such as absorbance or fluorescence cannot be employed. Representative methods for the determination of organophosphate degradation products are summarized below and grouped by the mode of detection employed. Experimental conditions for some of these methods are summarized in Table 3. 

Diisopropyl methylphosphonate is an organophosphate compound that was first produced in the United States as a by-product of the manufacture of the nerve gas isopropyl methylphosphonofluoridate (GB, or Sarin) (ATSDR 1996 EPA 1989 Robson 1977, 1981). It is not a nerve gas and is not a metabolite or degradation product (Roberts et al. 1995). Diisopropyl methylphosphonate constitutes approximately 2-3% of the crude GB product, but it is neither a metabolite nor a degradation product of GB (EPA 1989 Rosenblatt et al. 1975b). Diisopropyl methylphosphonate is not normally produced except for its use in research. One method of producing diisopropyl methylphosphonate is to combine triisopropyl phosphite and methyl iodide. The mixture is then boiled, refluxed, and distilled, yielding diisopropyl methylphosphonate and isopropyl iodide (Ford-Moore and Perry 1951). Diisopropyl methylphosphonate may also be prepared from sodium isopropyl methylphosphonate by a reaction at 270° C, but a portion of the resulting diisopropyl methylphosphonate is converted to trimethylphosphine oxide at this temperature (EPA 1989). 

Gas chromatography (GC) with either flame photometric or mass spectrometric detection is commonly used for determination of organophosphate pesticide. In some cases, GC may be used for separation of organic phosphorus species if they or their degradation products are derivatized, e.g., inositol... 

Organophosphate flame retardants and plasticisers Perfluorinated compounds Pharmaceuticals and personal care products Polar pesticides and their degradation/transformation products Surfactants and their metabolites... 

Havens and Rase reported the immobilization of an enzyme to degrade a specific organophosphate. The organophosphate was an agricultural grade material (parathion). The enzyme was harvested from recombinant Pseudomonas diminuta and immobilized by emulsifying a solution with a prepolymer. The product of the reaction was reported to have excellent stability and the method was proposed for cleanup of small spills of parathion. 

Mills and Hoffmann (1992) investigated ultrasonic degradation of parathion. Parathion (0,0-diethyl O-p-nitrophenyl triphosphate) is a major pesticide used in large quantities worldwide. Organophosphate esters such as parathion have been used as alternatives to DDT and other chlorinated hydrocarbon pesticides however, the organophosphate esters are not rapidly degraded in natural waters. At 20°C and pH 7.4, parathion has a hydrolytic half-life of 108 days and its toxic metabolite, paraoxon, has a similar half-life of 144 days. Ultrasonic irradiation of 25 mL of parathion-saturated, deionized water solution was conducted in a water-jacketed, stainless-steel cell with a Branson 200 sonifier operating at 20 kHz and 75 W/cm2. The temperature of the sonicated solution was kept constant at 30°C. All sonolytic reactions were carried out in air-saturated solution. The concentration of the parathion hydrolysis product p-nitrophenol (PNP) was determined in alkaline solution with a Shimadzu MPS-2000 UV /visible spectrophotometer. 

Effect of HS on the electrochemical reduction of p-nitrophenol (PNP) was studied by Simoes et al. (2006). PNP is the main hydrolysis product of methylpara-thion (MP), one of the most commonly used organophosphate insecticides in the world. The study was conducted using electroanalytical and UV-vis techniques, to understand how the HS can influence PNP degradation in the environment. Electroanalytical results showed that the HS experience the reduction of the nitro group of PNP by electrocatalysis (Figure 16.27a). 

Degradation of agrochemicals, solvents, degreasers, flame retardants, and chemical intermediates used in the production of high volume chemicals [113] detoxification of chlorophenols [61] Transformation of pesticides including phenylcarbamates (e.g., CIPC, IPQ and organophosphates (e.g., malathion, paraoxon, parathion) [53]... 

Conventional control of termites is heavily reliant upon prophylactic application of liquid insecticides to form a soil barrier around and beneath a structure to termite entry. These barriers, designed to repel or kill termites, degrade over time and must be reapplied every 5-10 years. A barrier termiticide application requires significant quantities of active ingredient, 5-10 kg, carried in 300 to 600 liters of water. Conventional products used as soil termiticides include organophosphates such as chlorpyrifos and isofenphos. 

Organophosphate resistance in M. persicae is due to the production of large amounts of carboxylesterase E4 that degrade as well as sequester these insecticides (12). This is believed to be the only biochemical resistance mechanism in this species in many countries, including the UK., continental Europe, Japan, and Australia (25.). E4 additionally confers low levels of resistance to carbamates and to (IS)-trans-permethrin (12). This esterase has been characterized extensively by toxicological, biochemical, immunological and molecular studies (2, 22, 22f 22, 22) ... 

---