BOX 2-1

Fumigants

Fumigants are a loosely defined group of pesticide active ingredients and formulations that act through partial or sole distribution of the chemical and delivery to the target in the vapor form (Ware, 1983). Fumigants include chemicals applied to the soil before harvest to control nematodes, insects, and undesirable microorganisms (soil fumigants). They also include chemicals used after harvest to control pests in harvested commodities before storage or transport to markets and chemicals used to rid infested buildings of termites, cockroaches, and other pests. Fumigation is a specialized use that has recently attracted unusual interest because of the visibility of some fumigation operations and the past contribution of fumigants to human health and environmental problems.

Several fumigants have been withdrawn or banned, and several current fumigants are undergoing reevaluation or phaseout. Dibromochloropropane (DBCP), a soil nematicide, was widely used because it could be used after planting on numerous fruit and vegetable crops susceptible to nematode root infestation. In 1977, it was withdrawn after it was found to cause sterility in male workers exposed during manufacture. Coming from areas of manufacture, formulation, and use, it was also a contaminant in groundwater. Its registrations, except for use on pineapples in Hawaii that was deemed essential for production, were canceled by EPA in 1979. Ethylene dibromide (EDB) enjoyed widespread use as a preharvest soil fumigant to control nematodes, eggs, and soil insects. EDB was a widely distributed groundwater contaminant, partly because of its water solubility, method of use (injection into soil followed by irrigation to improve penetration), high rate of use, and stability. In one summary, wells in six states were reported to be contaminated with EDB; this resulted in contamination of 520 wells (of 5,133 tested) above the health advisory level for drinking water. Health concern resulted from positive carcinogenic testing in experimental animals. The use of EDB was cancelled by EPA in the early 1980s.

Methyl bromide is a highly effective preplant fumigant with wide use on high-value crops—such as citrus, other fruit, and nut orchard crops; grapes; and strawberries—and in nurseries. After the cancellation of EDB and DBCP, it became the fumigant of choice because of its effectiveness against a wide spectrum of pests, including arthropods, nematodes, fungi, bacteria, and weeds (Noling, 1997). Methyl bromide is an effective postharvest fumigant for stored nuts and other commodities, and its use is required in some cases to circumvent quarantine of produce that might, through shipping, transport pests into uninfested areas. It is also used to fumigate structures; this use has resulted in a few fatal accidents when reentry regulations were not followed after treatment with the chemical. Methyl bromide is a gas at ambient conditions and leaves no organic residue in the treated soil or commodity, because it breaks down to bromide and eventually carbon dioxide. But methyl bromide is stable in the atmosphere, creating a potential for exposure among workers and downwind residents and for diffusion to the stratosphere, where its interaction with high-energy ultraviolet radiation sets off a series of reac-



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