1. Is Methyl Bromide dangerous?
As a fumigant, Methyl Bromide (MeBr/CH3Br) is typically used in concentrations of 48g/m3, which is about 13,000 parts per million (ppm). At this concentration, MeBr is acutely toxic to a wide range of insect pests, plants, animals and people.
However, like most chemicals, it is safe to use if instructions are followed properly. When used as a fumigant, following the fumigation period, the concentration in a container or chamber is diluted with fresh air through venting (either fan forced or by natural dispersion).
Concentrations must be at or below 5ppm before it is considered safe. The vented gas rapidly mixes and dilutes with air in the atmosphere.
The 5ppm concentration is the Australian occupational exposure guideline which is considered to cause no adverse health effects for exposures of eight hours per day, five days per week (that is, 40-hours weekly exposure).
As people respond differently to exposure concentrations, there is a conservative element of safety built into exposure guidelines so sensitive individuals are protected. It is estimated the 5ppm exposure guideline may be as much as 30 times below a ‘no observable effect level’.1
The New Zealand Government has prepared a document comparing MeBr toxicity and carbon monoxide (CO) emitted from car exhausts. The exposure dangers were considered similar. People do not run their car engines in a closed garage as it is too dangerous. However CO emitted by cars on roads does not pose the same danger. MeBr presents a similar risk.
The NZ document also addressed the issue of suspected links between MeBr and motor neuron disease, which had been reported previously. The health investigation reported no links.
2. Who is responsible for MeBr control and use in Australia?
In Australia there are different levels of control across Commonwealth, state and local governments.
At the Commonwealth level, various agencies manage MeBr. The Australian Pesticides and Veterinary Medicines Authority (APVMA) is responsible for registering safe and efficient use of agricultural and veterinary products (up to the point of sale) and then responsibility is transferred to the states.
The Department of Environment is responsible for monitoring and reporting critical use exemptions, and quarantine and pre-shipment MeBr use to members of the Montreal Protocol.
The Department of Agriculture ( the department) regulates MeBr quarantine fumigations and requires that licensed fumigators undertake MeBr fumigation training and competency assessment to become accredited under a compliance agreement (Onshore or Perishable Goods MeBr Fumigation Scheme). The locations where fumigations are performed must be quarantine approved premises (QAP), and the premises are assessed for fumigation suitability before approval.
One aspect of the assessment is the proximity of the QAP and fumigation area to other enterprises or dwellings and the inclusion of fumigation exclusion zones (as required under the AFAS Methyl Bromide Fumigation Standard). Fumigators are subject to regular audits by departmental officers.
At the state level, responsibility may fall under primary industry and energy, agriculture or health portfolios. It is regulated by the licensing of pesticide operators/fumigators and the controlled sale of MeBr. Other state agencies such as work safe, transport and environment departments may have involvement in MeBr.
Local councils are responsible for actual land use zoning (for example, industrial, commercial, residential) so use of MeBr as a fumigant must also be considered under land use requirements.
3. How widely is MeBr used?
MeBr use is controlled under the Montreal Protocol because it is an ozone depleting substance. The high impact, long-lived ozone depleting substances such as chlorofluorocarbons, hydrochlorofluorocarbons and halons are already controlled. Australia has critical use exemptions for MeBr as a soil fumigant/steriliser. We use about 30 tonnes per annum on soils, primarily for strawberry runners. Quarantine and pre-shipment (QPS) use of MeBr (for pest control) is not controlled under the Montreal Protocol. About 690 tonnes of methyl bromide is used in Australia per annum (p.a.) for import, export or interstate QPS fumigations.
Worldwide production and consumption of MeBr has reduced significantly during the past few decades to about 11,268 tonnes p.a. for QPS use and 6,937 tonnes p.a. for critical use exemptions2. In contrast, sources produced by marine and terrestrial plants and marine animals such as sponges, filter feeders, invertebrate moss animals, sea whips, fans, slugs and snails3, are estimated to produce between 1,000,000 and 2,000,000 tonnes p.a.
4. Where is MeBr used?
Imported items must be fumigated close to where they enter Australia to ensure potential pests and diseases do not become established. Consequently, most import fumigations occur at seaport facilities (cargo terminals) or in nearby container treatment facilities.
Export fumigations can occur on farms, or central grain/harvest facilities, in silos or under tarpaulins.
In some instances, a small quantity of MeBr is used to condition soil for susceptible plants to improve survival against soil borne diseases.
The majority of MeBr is used as a quarantine treatment for traded commodities (imports, exports and interstate) including:
- perishable fruits
- fresh flowers, bulbs, nursery stock, seeds for sowing
- personal effects (clothes, artefacts, hides, skins, furs)
- timber items (logs, furniture, building materials, pallets, other manufactured wooden articles)
- grains and cereals
- dried foods
- hay, straw and cotton;
- plant equipment and machinery.
5. How is MeBr used?
An example of MeBr use is in the fumigation of large quantities of timber imports. Timber is covered by a tarpaulin to contain the MeBr, the ‘tent’ is filled with MeBr and left for a prescribed5 period of time to fumigate any pests that may be contained within the timber shipment. After a period, the MeBr is then extracted from the tarpaulin tent and can be reused.
6. Are there any alternatives?
For some commodities there are alternatives for QPS treatments; however, these depend on the commodity being treated. Some commodities are damaged or tainted by MeBr.
In Australia other quarantine treatments include:
- Ethylene oxide (requires a vacuum chamber to control potential explosions)
- heat treatment
- gamma irradiation
- cold storage
- Phosphine (which is flammable and can create pest resistance).
Australia, along with other countries, has been undertaking research into alternatives that can be used in place of MeBr. If the research supports the use of these alternatives, they will be used as a biosecurity treatment in the future.
1 US-EPA 2005
2 TEAP May 2012 Progress Report
3 G.W. Gribble Chemical Society Reviews 1999, 5