August 21, 1997

Methyl Bromide Poisoning: An acute toxin

Methyl bromide is a colorless, odorless gas, classified by the U.S. Environmental Protection Agency as a Category I acute toxin -- a designation reserved for the most deadly substances. Human exposure to small amounts can produce nausea, headaches and other flu-like symptoms. In larger amounts, methyl bromide has been linked to birth defects and nerve damage in laboratory animals. Methyl bromide is also a powerful destroyer of the earth's ozone layer, and under the U.S. Clean Air Act is scheduled to be banned nationally in 2001.

As a soil and harvested crop fumigant, methyl bromide is used in California on strawberries, grapes, flowers and other crops. In 1995, nearly 17.6 million pounds were applied statewide. Although the great majority is used in agriculture, 3.4 percent of the 1995 total was used to fumigate homes and businesses for termites or powder-post beetles. More than 86 percent of the structures fumigated with methyl bromide were in Los Angeles, Orange and Riverside counties (Table 1).

Table 1. Methyl Bromide applied in structural fumigations in California in 1995. (All counties with 1,000 pounds or more.)

County Methyl
Bromide (lbs.)
Home Fumigation capacity*
Los Angeles 389,346 6,489
Orange 114,320 1,905
Riverside 13,990 233
Sacramento 9,504 158
San Bernardino 9,060 151
San Joaquin 7,792 130
Sonoma 7,696 128
San Mateo 5,231 87
Marin 5,148 86
Monterey 4,645 77
Alameda 4,610 77
Santa Cruz 3,196 53
Stanislaus 3,083 51
San Diego 2,294 38
Contra Costa 2,075 35
San Luis Obispo 1,739 29
Napa 1,458 24
Fresno 1,210 20
Mendocino 1,145 19
Placer 1,101 18
Solano 1,094 18
STATEWIDE 598,656 9,978

Source: Californians for Pesticide Reform/Environmental Working Group, from California Department of Pesticide Regulation, Pesticide Use Reporting System.

*Estimate based on 2,500 sq. ft. house fumigated with 3 lbs. per 1,000 cu. ft. of methyl bromide as described in DPR HS-1717.

Houses to be fumigated are enclosed with a tent before the gas is pumped in and for at least 24 hours afterward. The amount applied varies from 1.5 pounds to 3 pounds per 1,000 cubic feet of enclosed volume (DPR 1996). The state's Pesticide Use Reporting database does not disclose the number of fumigated structures. Based on the maximum application rate for a 2,500 sq. ft. house, enough methyl bromide was used in California in 1995 for 9,978 home fumigations.