Fumigants are applied to control rodents, nematodes, insects, weed seeds, and fungi anywhere in soil, or on structures, crops, grains, and commodities.20 Although many different chemical classes were used as fumigants, only a few remain in use today in the United States. Many fumigants, especially halogenated solvents, were abandoned because of their toxicity. In the 1987 Montreal Protocol an international agreement was adapted to phase out ozone-depleting chemicals such as methyl bromide, which was scheduled to be discontinued in 2005. Unfortunately many agricultural companies received exemptions, as satisfactory substitutes for some of its uses have not emerged.
Although fumigants exist as solids, liquids, or gases, they are most commonly used in the gaseous form or as volatile liquids, explaining why inhalation is the most common route of exposure (Table 116–1). Because of their gaseous forms, fumigants are generally heavier than air. Therefore, they will stay concentrated above the ground surface and lower floors of buildings. In addition, many do not have good warning properties. Several, such as methyl bromide and sulfuryl fluoride, are colorless and the toxic concentrations are below the odor threshold, making them particularly dangerous. While phosphides have a "rotten fish" or garliclike odor, toxic exposures are often debilitating, not allowing for escape.
Table 116–1. Physical Properties and Industrial Use of Fumigants |Favorite Table|Download (.pdf)
Table 116–1. Physical Properties and Industrial Use of Fumigants
|Chloropicrin||Dichloropropene||Ethylene Dibromidea||Metam Sodium||Methyl Bromide||Phosphine||Sulfuryl Fluoride||Methyl Iodide|
|State||Liquid||Liquid||Liquid||Powder turns yellow-green liquid||Gas||Solid→gas||Gas||Liquid|
|Odor||Intense||Garlic||Sweet/chloroform||Sulfur||None||Rotten fish, garlic||None||Pungent|
|Use||Soilb||Soil||Soil, cropb||Soil||Soil, structural, cropb||Rodenticideb||Structural||Soil|
|Historical use||Fire extinguisher||Fire extinguisher|
Methyl bromide (CH3Br) was used as an anesthetic in the early 1900s, but fatalities halted this practice. It was used as a fire retardant during World War II, a role that persisted into the 1960s in Europe. Like many other halogenated hydrocarbons, methyl bromide was also used as a refrigerant, methylating agent, chemical precursor, and as a fumigant in fruit packaging. Industrial use and its naturally occurring environmental production in oceans have led to low concentrations of methyl bromide in ambient air, water, and food.27 Diets that are high in marine products and fruits may increase environmental exposure to methyl bromide.27
Occupational and environmental exposures to ...