Methyl bromide: A fumigant gas that is an effective pesticide. Methyl bromide has been used to treat the soil, grain bins, and many agricultural products. Because it contains bromine, it depletes stratospheric ozone when released to the atmosphere. Among agricultural workers who apply pesticides, the risk of prostate cancer have been found to rise with increasing frequency of use of methyl bromide and with longer lifetime exposure to this pesticide. Risks were two to four times higher than among men who were not exposed to methyl bromide. Based on animal studies, the US National Institute for Occupational Safety and Health (NIOSH) lists methyl bromide as a potential occupational carcinogen. Under a treaty known as the Montreal Protocol, methyl bromide was to be banned for most uses by the end of 2004.