by Jean B. Ristaino
Methyl bromide is a widely used fumigant in U.S. agriculture and is one of the five most used pesticides in the U.S. Between 25 and 27,000 metric tons of methyl bromide are applied annually. More than 75% of the use of methyl bromide is for preplant fumigation of soil (Figure 1). In addition, methyl bromide is used for post-harvest treatment of nonperishables (13%) and perishables (8.6%) and for quarantine purposes (<1%). The compound also occurs as an intermediate in chemical manufacturing and is used as a medical sterilant. Methyl bromide is an effective herbicide, nematicide, insecticide, and fungicide and has been used commercially in the U.S. for soil fumigation and quarantine purposes for most of the 20th century.
Figure 1. Commercial fumigation of agricultural soils with methyl bromide.
Considerable evidence has accumulated that methyl bromide is a potent ozone depletor and the compound is scheduled to be phased out in the U.S. by 2001 under the Clean Air Act (Figure 2). The use of methyl bromide was a critical factor in dramatic changes in crop production systems in California, Florida, North Carolina, and elsewhere. Crop rotations were once standard methods of pest management before widespread use of soil fumigation and plastic mulching. Production of crops such as strawberries and fresh market tomatoes have become highly dependent on methyl bromide use leading to reductions in crop rotations and reductions in diversification in production practices. The economic viability of specific crops in Florida, California, North Carolina, and other states could be impacted by the loss of use of this compound if no alternatives are available. Figure 2. History of the Antarctic ozone hole from 1970 to 1993.
Figure 2. History of the Antarctic ozone hole from 1970 to 1993.