Methyl parathion detection limit

The detection limits for 2,6-dinitroaniline herbicides are between 20 and 200 ng substance per chromatogram zone (Table 1). Similar results are also obtained with methyl and ethyl parathion (pink-colored zones). 

After drying in a stream of cold air coumaphos (hRj 30-35) appeared as an intense red chromatogram zone on a colorless background, while parathion methyl (hRj 40-45), fenitrothion (h/ f 45-50) and parathion ethyl (hRf 60-65) yielded yellow zones as they did with sodium hydroxide alone (. v.). The detection limit for coumaphos was 10 ng per chromatogram zone. 

Chromosome aberrations were detected in lymphocytes of individuals acutely intoxicated by methyl parathion by the inhalation route (Van Bao et al. 1974). Blood samples were taken 3-6 days after exposure and again at 30 and 380 days. A temporary but significant (p<0.05) increase was noted in the frequency of stable chromosomal aberrations in the exposed individuals. The study limitations include small sample size, absence of a control group, lack of quantification of exposure levels, and a possible concomitant exposure to other substances via the dermal route. 

There is limited information available regarding the distribution of methyl parathion after dermal exposure in humans. Two subjects, dermally exposed to methyl parathion, had 2.74 and 1.23 mg on their hands. Twenty-four hours after exposure, the serum levels were 0.027 and 0.032 mg/L, respectively (Ware et al. 1973). Twelve hours after cotton fields were sprayed, five men entered the treated fields for 5 hours. An average of 1.7 mg methyl parathion was detected on their hands. Serum concentrations averaged 0.156 mg/L in these subjects after 3 hours of exposure. Levels decreased to 0.1 and 0.002 mg/L at 2 and 24 hours postexposure, respectively (Ware et al. 1975). Although 0.5 mg methyl parathion was detected on the hands of four subjects, none was found in the serum (Ware et al. 1974). No information on the tissue distribution of methyl parathion in humans was found. 

The available evidence suggests that excretion of methyl parathion metabolites in humans and animals following acute oral exposure is essentially the same and occurs rapidly. Excretion occurs primarily via the urine. Methyl parathion can also be excreted in breast milk, although it has been detected only in a limited number of samples from women of central Asia, for which exposure data were not available (Lederman 1996) (see also Section 3.4.2.2). A study in rats also reported excretion of methyl parathion in the milk (Golubchikov 1991 Goncharuk et al. 1990). 

Data from a single study in dogs suggest that hepatic first-pass metabolism may limit systemic availability of the parent compound following oral exposure (Braeckman et al. 1983). Placental transfer of methyl parathion was demonstrated in pregnant rats 1-3 days before parturition. Thirty minutes after administration, both methyl parathion and methyl paraoxon were found in fetal brain, liver, and muscle methyl parathion, but not methyl paraoxon, was detected in placenta and maternal liver (Ackermann and Engst 1970). Methyl parathion binds reversibly to serum albumin, but is readily distributed to the tissues (Braeckman et al. 1980, 1983). 

In a study to determine the concentrations of pesticides in air collected during times of peak pesticide use in California, air samples were collected at applications sites and at locations adjacent to the application sites (Baker et al. 1996). Of the samples collected adjacent to the application sites, 50% had levels of methyl parathion greater than the detectable limit of 0.2 ng/m, while 21% had levels of methyl paraoxon... 

Groundwater has also been surveyed for methyl parathion. In a study of well water in selected California communities, methyl parathion was not detected (detection limit of 5 ppb) in the 54 wells sampled (Maddy et al. 1982), even though the insecticide had been used in the areas studied for over 15 years. An analysis of 358 wells in Wisconsin produced the same negative results (Krill and Sonzogni 1986). In a sampling of California well water for pesticide residues, no methyl parathion was detected in any of the well water samples (California EPA 1995). In a study to determine the residue levels of pesticides in shallow groundwater of the United States, water samples from 1,012 wells and 22 springs were analyzed. Methyl parathion was not detected in any of the water samples (Kolpin et al. 1998). In a study of water from near-surface aquifers in the Midwest, methyl parathion was not detected in any of the water samples from 94 wells that were analyzed for pesticide levels (Kolpin et al. 1995). 

Methyl parathion has been reported in groundwater in Idaho at a median level of 0.01 ppb with contamination due to a point source (EPA 1988c). A study of tap water in Ontario showed no detectable methyl parathion at a detection limit of 1 ng/L (Le Bel et al. 1979). 

Citrus fruits from markets in Spain were analyzed for residues of methyl parathion along with other organophosphorus insecticides (Torres et al. 1997). Of the 171 orange samples analyzed, 14 had levels of methyl parathion <0.2 ppm, while 5 had levels >0.2 ppm. Levels ranged from the 0.1 ppm limit of detection to 3.8 ppm depending on the type of orange. Of the 15 grapefruit samples analyzed, 1 was found to contain methyl parathion at a level of 0.3 ppm. 

The purpose of this chapter is to describe the analytical methods that are available for detecting, measuring, and/or monitoring methyl parathion, its metabolites, and other biomarkers of exposure and effect to methyl parathion. The intent is not to provide an exhaustive list of analytical methods. Rather, the intention is to identify well-established methods that are used as the standard methods of analysis. Many of the analytical methods used for environmental samples are the methods approved by federal agencies and organizations such as EPA and the National Institute for Occupational Safety and Health (NIOSH). Other methods presented in this chapter are those that are approved by groups such as the Association of Official Analytical Chemists (AOAC) and the American Public Health Association (APHA). Additionally, analytical methods are included that modify previously used methods to obtain lower detection limits and/or to improve accuracy and precision. 

Methyl parathion was determined in dog and human serum using a benzene extraction procedure followed by GC/FID detection (Braeckman et al. 1980, 1983 DePotter et al. 1978). An alkali flame FID (nitrogen-phosphorus) detector increased the specificity of FID for the organophosphorus pesticides. The detection limit was in the low ppb (pg/L). In a comparison of rat blood and brain tissue samples analyzed by both GC/FPD and GC/FID, Gabica et al. (1971) found that GC/FPD provided better specificity. The minimum detectable level for both techniques was 3.0 ppb, but GC/FPD was more selective. The EPA-recommended method for analysis of low levels (<0.1 ppm) of methyl parathion in tissue, blood, and urine is GC/FPD for phosphorus (EPA 1980d). Methyl parathion is not thermally stable above 120 °C (Keith and Walters 1985). 

Analysis of methyl parathion in sediments, soils, foods, and plant and animal tissues poses problems with extraction from the sample matrix, cleanup of samples, and selective detection. Sediments and soils have been analyzed primarily by GC/ECD or GC/FPD. Food, plant, and animal tissues have been analyzed primarily by GC/thermionic detector or GC/FPD, the recommended methods of the Association of Official Analytical Chemists (AOAC). Various extraction and cleanup methods (AOAC 1984 Belisle and Swineford 1988 Capriel et al. 1986 Kadoum 1968) and separation and detection techniques (Alak and Vo-Dinh 1987 Betowski and Jones 1988 Clark et al. 1985 Gillespie and Walters 1986 Koen and Huber 1970 Stan 1989 Stan and Mrowetz 1983 Udaya and Nanda 1981) have been used in an attempt to simplify sample preparation and improve sensitivity, reliability, and selectivity. A detection limit in the low-ppb range and recoveries of 100% were achieved in soil and plant and animal tissue by Kadoum (1968). GC/ECD analysis following extraction, cleanup, and partitioning with a hexane-acetonitrile system was used. 

Using established extraction and cleanup methods, followed by GC/FPD and GC/thermionic detection, Carey et al. (1979) obtained detection limits in the ppb range and recoveries of 80-110% in soil and 70-100% in plant tissue. Good sensitivity and recovery were maintained in a simplified extraction procedure of sediments followed by GC/FPD analysis (Belisle and Swineford 1988). Bound methyl parathion residues that were not extracted with the usual methods were extracted using supercritical methanol by Capriel et al. (1986). They were able to remove 38% of the methyl parathion residues bound to soil, but 34% remained unextractable, and 28% could not be accounted for. 

O ring. At 20 min inhibition time the detection limits for malathion, parathion methyl and paraoxon were 3, 0.5 and 5pg I respectively. Although these bienzymatic systems look simple, it is difficult to provide optimal conditions for both enzymes. In general the optimum pH, temperature and buffer molarity for different enzymes are different. The experimental conditions are at the levels below the optimum capacity of both enzymes [14], This disadvantage can be minimized by use of a single enzyme system, which is readily inhibited by the pesticide. 

MWNTs favored the detection of insecticide from 1.5 to 80 nM with a detection limit of InM at an inhibition of 10% (Fig. 2.7). Bucur et al. [58] employed two kinds of AChE, wild type Drosophila melanogaster and a mutant E69W, for the pesticide detection using flow injection analysis. Mutant AChE showed lower detection limit (1 X 10-7 M) than the wild type (1 X 10 6 M) for omethoate. An amperometric FIA biosensor was reported by immobilizing OPH on aminopropyl control pore glass beads [27], The amperometric response of the biosensor was linear up to 120 and 140 pM for paraoxon and methyl-parathion, respectively, with a detection limit of 20 nM (for both the pesticides). Neufeld et al. [59] reported a sensitive, rapid, small, and inexpensive amperometric microflow injection electrochemical biosensor for the identification and quantification of dimethyl 2,2 -dichlorovinyl phosphate (DDVP) on the spot. The electrochemical cell was made up of a screen-printed electrode covered with an enzymatic membrane and combined with a flow cell and computer-controlled potentiostat. Potassium hexacyanoferrate (III) was used as mediator to generate very sharp, rapid, and reproducible electric signals. Other reports on pesticide biosensors could be found in review [17],... 

From the slope of the plot of current vs. (current/concentration of ATCh), the Km app for AChE was determined to be 0.66 mM. This biosensor also showed good precision and operational stability for the measurement of ATCh. The relative inhibition of AChE activity was calculated as a function of paraoxon concentration.. The linearity was observed up to 6.9 nM (slope, 14.36%/nM correlation coefficient, 0.9859) to 6.9 nM and the limit of detection of 0.5 nM (0.145 ppb). Moreover, the detection limit for methyl parathion using the present sensor could be expected to be 1.65 nM. Real sample analysis results were in good agreement (90%), which demonstrates the validity of this MWCNTs-SPE modified biosensor to a practical problem. 

Water samples (800 ml) were filtered through the membranes and were extracted by methanol after addition of sodium sulphate. Dimethoate, parathion, and parathion-methyl were tested. The method enabled the determination of these compormds with a detection limit of 0.05 /rg/1 and recoveries ranging from 66 to 94%. 

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