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Paracelsus' poison

Methyl Bromide and Strawberries .. Shock .. Horror .. Oh, Wait a Minute.

There was an article on the ABC site this morning which gave us this alarming headline “Pesticide banned worldwide still used to grow 70pc of Australian strawberries”. Shocking!

Except, well, there were a few teeny tiny but important details missing. Like the fact that the rest of the world is still using the “banned” pesticide too.

Methyl Bromide (the substance involved) has been withdrawn worldwide under the Montreal protocol as it is a potent greenhouse gas (not because of toxicity, as many people have assumed from the headlines). However, world wide, there are exemptions for the use of methyl bromide as a fumigant for quarantine and production purposes (QPS) and some special (critical use) exemptions, it’s not just us. In 2005 Australia, stopped the use of methyl bromide for all but the exempt QPS uses, and for a few uses for which there was no suitable alternative to methyl bromide.

Just like the rest of the world.

In 2012 around 12,000 metric tonnes of methyl bromide were used around the world for various QPS and critical exemption purposes, Australia’s agricultural use was 32 tonnes at this time (Japan’s was 216 metric tonnes and the US 923 metric tonnes for comparison). Critical use exemptions, the ones that allow the strawberry farmers to fumigate their soil, must be applied for each year.

Like everyone else in the world, Australia developed plans to phase out the remaining methyl bromide use. Since 2005, when methyl bromide use in general was phased out, Australia has been replacing methyl bromide in the critical use exemption and (to a more limited extent) QPS categories with alternatives, dropping from 112 metric tonnes in 2005 to 32 metric tonnes in 2015.

Methyl bromide is an important pesticide fumigant, and is used to kill pathogens and pests in imported produce and some produce for export. Finding alternatives is not straight forward, for example, phosphine, one of the alternative fumigants, is highly flammable, so new handing procedures are needed to combat the risk of fire.

While reducing the amount of methyl bromide entering the atmosphere is important, the significant risk to the Australian biota and agricultural production from invasive pests and pathogens has to be weighted against the fact that human produced brominated compounds represent less than 0.03% of the total halogens released into the atmosphere, and that unlike CFC’s, which last in the atmosphere for decades, methyl bromide’s half life in the atmosphere is less than a year.

Given the relatively small impact of methyl bromide, and the continuing reduction of methyl bromide (see here for a comparison of the progress and the contribution of the US vs the rest of the world), Shock! Horror! headlines about Australia’s use for strawberries are unwarranted.

In the strawberry growing industry, methyl bromide is used to destroy pathogens and pests in the soil the strawberry runners are planted in. In Queensland and Tasmania, methyl bromide has been replaced. However, for the soils in the Victorian strawberry growing areas, the alternative fumigants aren’t as effective.

Other fumigants are being researched, but it takes time to find something that is reasonably safe, reasonably cheap and effective. One of the potential replacements, methyl iodide, has been withdrawn from the market, so the hunt is still on for a viable replacement. It may be that we have to grow our strawberries under soil-less conditions to stop disease and pest losses.

So, like all other countries, Australia has phased out methyl bromide, except for quarantine and other critical uses for which there is no effective alternative (again, just like other countries). Since 2005 we have systematically reduced the amount of methyl bromide for these uses, and are undertaking research to reduce the amount even further.

Oh, and in case you are worried that methyl bromide contaminates the strawberries, methyl bromide breaks down in the soil, and the strawberries that grow much later do not come into contact with it. There is no toxicity issue here at all.

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