Fumigant

One of the most effective fumigants is methyl bromide. It essentially sterilizes soil when applied under a ground covering, because it kills insects, nematodes, and weed seed but also is used to fumigate warehouses. Overexposure to this compound causes respiratory distress, cardiac arrest, and central nervous effects. The inhalation LC50 is 0.06 mg/L (15 min) of air (rat) and 7900 ppm (1.5 h) (human). Methyl bromide has been classified as an ozone depleter under the Clean Air Act and is due to be phased out of use by 2005. 

Chloropicrin (trichloronitromethane) is another soil/space fumigant that has been used for many years. It has an inhalation LC50 of 150 ppm (15 min). Thus it is highly toxic by inhalation, can injure the heart, and cause severe eye damage. 

This section has covered only a few of the pesticides available today on the United States and world markets. An understanding of the basic chemical processes affected by pesticides has led to the discovery and production of new families of chemicals. Today s modem pesticide is generally safe to use if the directions on the label are followed. Advances in instrumentation and an understanding of how adverse health effects are produced have resulted in the production of many environmentally friendly but effective pesticides. 

Methyl bromide, CH3Br (boiling point 4.5°C)—Methyl bromide is a gaseous fumigant used both in the soil and on commodities. In the soil, it is used for preplant soil fumigation with chloropicrin to control nematodes, insects, and fungi. Its use was banned in 2005, except for critical use exemptions, because it is an ozone depleter. Methyl bromide has an oral LD50 in rats of 100 mg/kg. 

Ethylene dichloride, CH2C1CH2C1 (bp 84°C)—Ethylene dichloride is primarily used as a commodity fumigant. Its oral LD50 in rats is 670-890 mg/kg. 

Chloropicrin, CC13N02 (bp 112°C)—Chloropicrin is a tear gas used as both a soil and a commodity fumigant. Chloropicrin has a strong odor and irritant effect, so it is often added as a warning agent to fumigants. Its oral LD50 in rats is 250 mg/kg. 

Phosphine, PH3 (bp 87.4°C)—Phosphine is a stored-grain fumigant. It is generated by the reaction of aluminum phosphide (AIP) with water vapor in the surrounding air. Its inhalation LC50 (4 hr) in rats is 11 ppm. 

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BrCHi CHjBr. A colourless liquid with a sweet odour, m.p. 10°C, b.p. 132°C. Manufactured by passing ethene through bromine or bromine and water at about 20 C. Chemical properties similar to those of 1,2-dichloroethane when heated with alkali hydroxides, vinyl bromide is formed. Used extensively in petrols to combine with the lead formed by the decomposition of lead tetraethyl, as a fumigant for stored products and as a nematocide. 

HCOOCHjCHj. Colourless liquid with the odour of peach-kernels b.p. 54 C, Prepared by boiling ethanol and methanoic acid in the presence of a little sulphuric acid the product is diluted with water and the insoluble ester separated and distilled. Used as a fumigant and larvicide for dried fruits, tobacco and foodstuffs. It is also used in the synthesis of aldehydes. 

Most of the trichloroethylene produced is used for metal degreasing. Other important uses are in the scouring of wool and as an extractive solvent, e.g. for olive and soya bean oils. Minor uses are as a heat transfer medium, anaesthetic, insecticide and fumigant, paint remover and fire extinguisher. 

Bromine is used in the manufacture of many important organic compounds including 1,2-dibromoethane (ethylene dibromide), added to petrol to prevent lead deposition which occurs by decomposition of the anti-knock —lead tetraethyl bromomethane (methyl bromide), a fumigating agent, and several compounds used to reduce flammability of polyester plastics and epoxide resins. Silver(I) bromide is used extensively in the photographic industry... 

It is used to make sulfite paper and other papers, to fumigate fumigant, and to bleach dried fruits. The element is a good insulator. 

Bromine is used in making fumigants, flameproofing agents, water purification compounds, dyes, medicinals, sanitizers, inorganic bromides for photography, etc. Organic bromides are also important. 

Until It was banned in the United States in 1984 1 2 di bromoethane (ethylene dibromide orEDB)waspro duced on a large scale for use as a pesticide and soil fumigant... 

Soil conditioning Soil disinfectant Soil flushing Soil fumigants Soiling of fabrics Soil modification Soil pesticides Soil remediation Soils... 

Fig. 8. Characteristic plume patterns where (--) represents dry-adiabatic lapse rate and (—), air (a) fanning (b) fumigation (c) lofting and (d) looping.

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