tions that lead to depletion of stratospheric ozone (Methyl Bromide Global Coalition, 1992).
Because of its ozone-depleting potential, methyl bromide is scheduled for phaseout in the United States by the year 2001 as a consequence of rules in the 1990 Clean Air Act Amendments and Montreal Protocol agreements (Honagonahalli and Seiber, 1997). In 1993, nearly 15 million pounds of methyl bromide were used in California (California Environmental Protection Agency, 1994), partly because of the unusually high application rate—up to 500 lb/acre in some preplant uses.
There is some anxiety regarding the availability or suitability of alternatives to methyl bromide if the scheduled phaseout occurs. Current registered alternatives are 1,3-D (1,3-dichloropropane, Telone II) and metam sodium, which generates the active fumigant methylisothiocyanate when the parent chemical breaks down in soil or water. Telone was placed in the reregistration and special-processes review by EPA in 1986; this requires EPA to conduct a risk–benefit analysis leading to a regulatory decision (Roby and Melichar, 1996). Telone was also suspended by the California Department of Pesticide Regulation (DPR) in 1990 after air monitoring showed residues above the state's acceptable air concentration limit around fumigated fields in California's San Joaquin Valley. The suspension was lifted in 1994 on the basis of changes in application practice and additional monitoring studies conducted by the registrant and further review by DPR.
MITC received adverse publicity after a 1991 spill of metam sodium in the Sacramento River that caused widespread intoxication of fish and other aquatic organisms and loss of vegetation. But metam sodium registration continues, and the product is finding expanding markets as the regulatory status of methyl bromide and Telone remains in some question. Another alternative is chloropicrin, which is often used as an odorant or residual pesticide in combination with methyl bromide and other mainstream fumigants. Other fumigants include phosphine, which is released from aluminum and other phosphide salts for control of rodents and other vertebrate pests, and sulfuryl fluoride (Vikane). Nonfumigant pesticides, such as carbofuran and methomyl, can be substituted for fumigants in some soil pest-control situations. Nonsynthetic alternatives to fumigants are also receiving increasing attention. These include solar heating and natural nematicide chemicals present in some plants in the case of soil fumigation and controlled atmospheres and heating in the case of postharvest and building-space fumigation.
The fumigant situation is a highly visible, somewhat controversial dilemma that faces conventional pesticides on many fronts. Long-standing, well-accepted chemicals can come under increasing scrutiny as a result of some adverse characteristic (chronic toxicity in experimental animals, groundwater contamination, stratospheric ozone depletion) or changes in federal or state regulations. Registrants conduct additional studies to preserve registration of their products. Agriculturists worry about whether loss of productivity will result if particular pesticides are no longer available. Some in the public sector call for swift action in removing or restricting offending chemicals. And researchers go back to the drawing board to devise new solutions to pest problems.