Dichlorvos vaporizer

The fabric samples for exposure to dichlorvos were placed in a wooden, glass-topped museum case along with one No-Pest Strip in such a manner that the strip would not touch the samples. The time of duration to the dichlorvos vapor was four weeks, after which the fabric samples were removed from the museum case for testing. 

Exposure to dichlorvos vapor can result in exposure through not only the respiratory route but also the dermal and oral routes (e.g., through contamination of feed). 

Animals exposed to dichlorvos vapor were found to absorb at least 50% of the total material by the respiratory route. Dichlorvos can also be absorbed through the oral and dermal routes. Following oral exposure, dichlorvos is rapidly detoxified in the liver. Metabolites include 0,0 -dimethyl phosphate, monomethyl phosphate, 0-methyl-0-2,2-dichlorovinyl phosphate (desmethyl dichlorvos), and inorganic phosphate. Detoxification processes for dichlorvos are also found in plasma. 

Source Data from Sumitomo Chemical Co., Ltd. Reference Vapor pressure of other chemicals at 25°C Glycerin 10 mPa Dichlorvos 2,100 mPa... 

Pyrethroids generally have low vapor pressures. Although empenthrin (20) volatilizes at room temperature without external energy and is 31 times more volatile than allethrin, its vapor pressure is only 1/88 that of dichlorvos, a volatile organophosphorus compound. As profluthrin (40) is 13 times more volatile than allethrin and volatilizes gradually for 6 months to 1 year at room temperature, it is suitable as an insecticide for the protection of clothes. The vapor pressure of profluthrin is 10 mPa/25°C, almost the same as that of glycerin. 

Reported vapor pressures and Henry s law constants of dichlorvos at various ... 

FIGURE 18.1.1.28.1 Logarithm of vapor pressure versus reciprocal temperature for dichlorvos. 

T ichlorvos (DDVP, dichlorovinyldimethyl phosphate) was first syn-thesized in the late 1940s, but active investigation of its insecticidal properties was not initiated until 1954. Investigations at that time revealed that low concentrations of the vapor of dichlorvos were toxic to adult mosquitoes and flies and that there appeared to be a relatively wide margin of safety between the insecticidal dose and the concentration required to affect man. 

Research by personnel of the U.S. Public Health Service, particularly by George W. Pearce, resulted in the development of a solid formulation of 25% dichlorvos in montan wax, which when open to the air, released the vapor of dichlorvos continuously, in small quantities, over a prolonged period of time. This development led to a search for other, more stable formulations and eventually to the development of a formulation of 20% dichlorvos in a resin. This formulation, known as Vapona Resin Vaporizer, is referred to hereafter as the Vaporizer. 

The use of Vapona Resin Vaporizers in the home poses the possibility of an adverse effect upon persons subjected day-in and day-out to the inhalation of the vapor of dichlorvos. In order to determine the extent of this hazard, the following investigation was undertaken. 

Table IV. Concentration of Dichlorvos in Air of Homes in which Vapona Resin Vaporizers Were Installed...

Discussion. Control of insects by the continuous vaporization of di-chlorvos within enclosed spaces in which persons are housed intermittently or continuously constitutes a potential threat of the absorption of significant quantities of the material dispersed as vapor in the air. Despite extensive toxicological investigation of dichlorvos, which has included observations of human beings (4,5,6,8,12,15), no work had been done to evaluate the hazard of Vapona Resin Vaporizers under actual conditions of use. The observations described in this report were designed to reveal the significance, if any, of such hazards. 

Inhibition of the cholinesterase activity of the blood is the most sensitive means now available, with the possible exception of the inhibition of the esterase activity of the liver, for detecting the absorption of an organic phosphorus compound that is known to be capable of inducing this effect. The values indicative of cholinesterase activity are shown in Tables III and V. All subjects were exposed to the recommended dosage (one Vaporizer per 1000 cubic feet) except subjects 15 and 16, who were exposed to resin strips that contained no dichlorvos. 

The OP compounds are difficult to generalize with respect to their physical properties. They have moderate-to-considerable water solubility. Some organophosphate insecticides are water soluble, e.g., oxydemeton-methyl, azodrin, phosdrin, trichlorfon, and phosph-amidon. They also have moderate-to-considerable vapor pressures, generally in the range 10"3-10-5 mm Hg. Some organophosphate insecticides such as naled and dichlorvos are very volatile. This combination of physical and chemical properties makes the entire class of insecticides biodegradable and nonpersistent. 

As for contact insecticides, dichlorvos and nicotine were found to enter the insects through the cuticle despite their high vapor pressures (dichlorvos, 0.012 mm Hg [at 20°C] and nicotine, 0.0425 mm Hg [at 25°C]) (Gallery, 1967). Matsumura (1959) studied the uptake of malathion by American cockroaches from a glass surface and found that the highest amount was picked up by the legs, whereas the trachea played a very minor role in the total pickup procedure. The vapor pressure of malathion is 4 x 10-5 mm Hg at 30°C. 

Because of its high vapor pressure, dichlorvos is useful in the control of insects in closed spaces (e.g., warehouses, greenhouses, animal shelters, homes, and restaurants). It is available in oil solutions, emu-Isifiable concentrates, aerosols, and baits. Therapeutically, dichlorvos is used as a broad-spectrum anthelmintic (for destroying or expelling intestinal worms). It is also used as a feed through larvicide to control botfly larvae in the manure. It is primarily used for insect control. Dichlorvos is also a breakdown product of the organophosphorus pesticide trichlorfon (metrifonate). 

Chemical and Physical Properties Trichlorfon is an organophosphate compound, which has an empirical formula of C4HgCl304P and a molecular weight of 257.44. It is a racemic mixture of two isomers. Trichlorfon is a pale clear, white or yellow crystalline powder, melting point 75-84°C, boiling point 100°C, vapor pressure 7.8mmHg at 20°C, and is stable at normal temperatures and pressure. At higher temperatures and pH less than 5.5, trichlorfon decomposes to form dichlorvos (0,0-dimethyl-0-(2,2-dichlorovinyl) phosphate, DDVP). It is readily soluble in chloroform and methylene chloride, and less soluble in water, benzene, and diethyl ether. 

Most OPPs are slightly water-soluble, have a high and a low vapor pressure. Some are very miscible with water (trichlorfon, vamidothion, mevinphos, monocrotophos, omethoate, oxydeme-ton-methyl, phosphamidon). Most, with the exception of dichlorvos, are of comparatively low volatility, and are all degraded by hydrolysis, yielding water-soluble products. Parathion, for example, is freely soluble in alcohol, esters, ethers, ketones, and aromatic hydrocarbons, but is almost insoluble in water (20 ppm), petroleum ether, kerosene, and spray oils. 

DIchlorvos (DDVP, 2,2-dlchlorovlnyl dimethyl phosphate [CAS 62- 73-7]) An organophosphate-type cholinesterase inhibitor (see p 291), Extremely well absorbed through skin. Evidence of carcinogenicity In test animals (lARC 2B). 0.1 mg/m S, SEN 100 mg/m Colorless to amber liquid with a slight chemical odor. Vapor pressure is 0.032 mm Hg at 32°C (90 F). 

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