What is the problem?
Very toxic gases can be used. Processes are generally well regulated, but even short-term low exposures may cause (usually mild) symptoms, and considerable concern.
Decisions have been made to gradually reduce methyl bromide production and use. (Recommended alternatives include metam sodium, dazomet, and chloropicrin. Sulfuryl fluoride has also been used in the United States).
Handling of imported goods that are fumigated offshore has concerned port authorities and private consumers since methyl bromide can react with sulphur-containing materials (e.g. wool, furs, feathers and leather where sulphur is added during tanning) to produce volatile malodorous sulphur compounds.
Transport and stacking of fumigated containers may be hazardous.
Soil injection techniques (e.g. in fruit farming) are reputed to be safe, but studies suggest that levels under tarpaulins can take longer than 48 hours (the recommended minimum waiting period) to fall below 5 ppm.
Magtoxin (magnesium phosphide) and similar (e.g. Al, Zn) phosphides react with water and (more readily) acids to form phosphine, a toxic gas with a garlic, fish-like odour. Used as a fumigant in preservation of stored grain (e.g. in grain elevators, marine vessels), often involving confined environments. In contact with moisture in grains, phosphine is generated along with metal (e.g. Al, Mg, and Zn) hydroxides.
Phosphine has an auto-ignition temperature of about 40ºC, and when dry may occasionally ignite at room temperature, due to impurities. Aluminium and magnesium phosphide containers may flash on opening. (Many formulations contain ammonium carbamate or similar, which liberates ammonia and carbon dioxide, reducing the explosive hazard substantially.)
Methyl bromide
Mild methyl bromide effects include nausea, vomiting, headache, dizziness, slurred speech, unsteadiness (which can persist for some days) and also various neurological effects.
Often chloropicrin is added as a warning agent as it is intensely irritating.
There is a hazard from fumigated containers, particularly immediately upon opening. Such brief relatively low exposures may cause mild to moderately acute symptoms only but more severe (respiratory or neurological) effects are possible with high acute and/or regular long-term exposures.
Levels can be assessed with automatic halogen ‘leak detectors’. These are non-specific, as they measure most (other) halogen gases as well. ‘Grab’ sampling (e.g. with Drager, Gastech tubes) is possible.
Results should be compared with the WES-TWA (5 ppm).
There is limited correlation between blood (inorganic) bromine levels and symptoms, and no BEI, but blood and/or urine levels are being investigated as monitoring tools.
Air monitoring.
Do not rely on odour as a warning.
Control measures
- appropriate signage for fumigated areas
- precautionary monitoring if air levels unknown but potentially significant
- wear adequate respiratory protective equipment, especially when opening or entering containers
- ensure containers are sealed as well as possible check for leaks if suspected
- suitable protective clothing (methyl bromide can permeate many materials)
- education on phosphine explosion risk; especially if mixed with water or in confined spaces
- be aware of the symptoms of poisoning.
