Methyl parathion applicators

Dermal exposure to methyl parathion is not likely to be a health concern to the general population, with the possible exception of individuals in the immediate vicinity of a field during application of the pesticide. Dermal exposure, however, is a major source of exposure for workers directly involved in the manufacture, application, and cleanup of the chemical, and for field workers. Laundry workers cleaning the clothing of such workers may also be exposed. 

Mental disturbances have been reported after organophosphate exposure. Neuropsychiatric symptoms occurred in two aerial applicators, one of whom used methyl parathion as well as other insecticides. One of these pilots had high levels of exposure to a mixture containing methyl parathion, toxaphene, and Dipterex when his clothing became saturated when the tank of his aircraft accidentally overflowed. Several months after the accident, the subject complained of anxiety, dizziness, emotional lability, and frequent and severe disagreements with family members and associates. Similar observations had been... 

LD50 values for the dermal route of exposure to methyl parathion have been established in acute studies for rats 67 mg/kg for males and females (Gaines 1960), 110 mg/kg for males, and 120 mg/kg for females (EPA 1978e). The LD50 in male mice exposed by dermal application of methyl parathion to their hind feet (rather than shaved backs) was 1,200 mg/kg (Skinner and Kilgore 1982a). The mice were muzzled to prevent oral exposure from grooming. 

Following single dermal applications of 10 mg/kg of radiolabeled methyl parathion to pregnant rats, methyl parathion was found to be widely distributed to all major tissues and organs. Concentrations were highest in plasma and kidney, maximum levels measured 2 hours postapplication. Peak levels in liver, brain, fetus, and placenta, were measured 2 to 10 hours later, at which times the highest concentration of methyl parathion was in the fetus (Abu-Quare et al. 2000). 

In a study of pregnant rats that were exposed to radiolabeled methyl parathion by single dermal application, half-life elimination rate constants for various tissues ranged from 0.04 to 0.07 hour, highest values noted in plasma, kidneys, and fetus. Of the applied radioactivity, 14% was recovered in the urine in the first hour postapplication. By the end of the 96-hour study, 91% of the applied dose had been recovered in the urine. Fecal excretion accounted for only 3% of the administered dose (Abu-Qare et al. 2000). 

Limited information regarding potential for age-related differences in susceptibility to methyl parathion in humans was reported by Dean et al. (1984). Seven children (ranging in age from 2 to 11 years) and three adults were exposed to unknown concentrations of methyl parathion sprayed illegally inside a house at a concentration of 4% (>3 times the recommended concentration for field applications). The children... 

As a result of its use as an insecticide on cotton, fruit trees, vegetables, and other crops, methyl parathion is released directly to the atmosphere during application. It is applied primarily by spraying from aircraft or ground equipment (NPIRS 1986). Aerial application of methyl parathion to agricultural fields releases the insecticide to the air. 

Methyl parathion may also be introduced into the air as a result of its volatilization from plant surfaces, and somewhat from soil, especially in the period just after application. Under simulated field conditions (20° C air velocity 1 meter/second relative air humidity 40-60%), an emulsifiable concentrate formulation of methyl parathion was applied to bare soil and bean plants. After 24 hours, the amounts of methyl parathion that had volatilized from bare soil and bean plants were 5 and 64% of the applied amount, respectively (Rudel 1997). 

Methyl parathion can be released to surface waters by storm runoff from sprayed fields atmospheric deposition following aerial application (wet deposition from rain and fog water) waste water releases from formulation, manufacturing, or processing facilities and spills. 

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... 

Atmospheric concentrations of methyl parathion following application of the pesticide to tobacco fields were studied by Jackson and Lewis (1978). They found that levels of methyl parathion decreased rapidly following application of either the emulsifiable concentrate or the microencapsulated form. Air concentrations for the emulsifiable concentrate ranged from 7,408 ng/m immediately following application to 13 ng/m 9 days later. The corresponding measurements for the microencapsulated form were 3,783 and 16 ng/m. ... 

Samples of rainfall in Iowa have been analyzed for levels of pesticides (Nations and Hallberg 1992). Samples collected in April, May, and June of the three years in the study period of 1987-1990 had the highest levels of methyl parathion, corresponding to the application to crops. Methyl parathion was found in 4 of the 318 rain samples analyzed at a maximum concentration of 2.77 pg/L. In a study of... 

In random samples of soil taken from five Alabama counties, only 3 of 46 soil samples contained methyl parathion. The concentration in these samples was <0.1 ppm (Albright et al. 1974). Aspartofthe National Soils Monitoring Program, soil and crop samples from 37 states were analyzed for methyl parathion during 1972. Methyl parathion was detected in only 1 soil sample, at a concentration of <0.1 ppm and taken from South Dakota, out of 1,246 total samples taken from the 37 states (Carey et al. 1979). In soil and sediment samples collected from a watershed area in Mississippi, methyl parathion was not detected in the soil samples. In three wetland sediment cores, however, measurable concentrations of methyl parathion were detected during application season (Cooper 1991). 

Table 8-1. Regulations and Guidelines Applicable to Methyl Parathion...

Koen JG, Huber JF. 1970. A rapid method for residue analysis by column liquid chromatography with polarographic detection Application to the determination of parathion and methyl parathion on crops. Anal Chim Acta 51 303-307. 

Methyl parathion is used primarily on cotton. It was one of the first insecticides restricted under the 1996 Food Quality Protection Act (FQPA), which developed new safety standards for human health, especially that of children. It can no longer be used on many fruits and vegetables. Malathion and parathion are the broadest spectrum organophosphate insecticides. There are many other organophosphate insecticides in use in the U.S. today. Many are produced at the 1-5 million Ib/yr level for specific applications. Three other leading organophosphates besides those mentioned already are chlorpyrifos, terbufos, and phorate. 

A reentry study 12 hr after application in Arizona cotton, exposing volunteers to methyl parathion, ethyl parathion, or monocrotophos for 5 hr produced no clinical signs of poisoning. However, cholinesterase depression averaged 147., and both ethyl-and methyl-parathion were found in the blood as well as p-nitrophenol (PNP) in the urine. These workers were not judged in jeopardy as cholinesterase depression was less than 307. and the PNP excretion was less than 4 mg following exposure (22). 

Our first objective was to determine whether microencapsulated methyl parathion Is unique In Its property to be carried back to the hive by bees. To that end a mixture of three commonly used insecticides along with MMP was applied to a plot of blooming rape. The agents were azlnphos-methyl (Guthlon), parathion, and carbaryl (Sevin). By using a mixture on a single plot the effects of variation In bee visitation were eliminated and the tendencies to be carried to the hive could be measured by the relative residue levels in the pollen samples. Five applications were made over a period of seventeen days. Pollen samples were collected from hives placed near the field after two, three, four, and five successive applications approximately two days after each application was made. The application rates were doubled for the last two applications. The data are shown In Table I. 

Although the residues found cannot be correlated with the application rates, the results nevertheless demonstrate that all insecticides used in this test were absorbed on the pollen and carried back to the hive. These observations have been confirmed using other approaches by USDA and university researchers at the University of Wisconsin, who reported that foraging bees have brought back to their hives permethrln, carbaryl, and methyl parathion emulslfiable concentrate (MPEG) when applied to shedding corn.Q)... 

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. 

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