Ozone-friendly pesticide is a potent warming gas

Scientists have discovered that an ozone-friendly replacement for the fumigant methyl bromide is a stronger than expected greenhouse gas. Although current releases represent a tiny proportion of total greenhouse emissions, they are set to rise.

A fumigant touted as a benign replacement for ozone-depleting methyl bromide has been found to be a potent greenhouse gas. New research shows sulphuryl fluoride has a longer atmospheric lifetime than expected and a higher global warming potential (GWP).1 Sulphuryl fluoride, or Profume, is made by Dow Agrosciences for post-harvest fumigation of grain, flour mills and storage facilities. Dow also markets the gas under the name Vikane for treating termite-infested wood.

The company received a US Environmental Protection Agency (EPA) award for stratospheric ozone protection for developing the product and other "economic and effective alternatives to methyl bromide".

Methyl bromide is being phased out under the Montreal Protocol. Developed countries have agreed to end its use by 2005 except for certain critical applications. The US is the biggest user and received exemptions totalling 2,763 tonnes for 2010 (ENDS Report 407, pp 55-56 ).

As pressure mounts to phase out the ozone-depleter, use of sulphuryl fluoride is likely to rise. Mads Sulbaek Anderson and colleagues at the University of California at Irvine worked with Ford Motor Company researchers to study how long the chemical lasts in the atmosphere. They estimate about 3,000 tonnes are produced per year worldwide, all of which is released to the air during use.

Laboratory experiments showed sulphuryl fluoride would not be destroyed quickly by substances such as ozone, chlorine or hydroxyl radicals, which remove many pollutants from the atmosphere. Instead, they say its most likely fate is biological degradation or breakdown in the ocean.

Previous research suggested the gas had an atmospheric lifetime of five years, but Dr Anderson’s findings point towards 30-40 years. That would mean a GWP 4,000 times greater than that of carbon dioxide.

This makes sulphuryl fluoride a more potent greenhouse gas than the refrigerant HFC 134a, which has a GWP 1,430 times that of CO2 , but less than sulphur hexafluoride which has a potential of 22,800 times.

The researchers’ data suggest sulphuryl fluoride, which is not regulated under the Kyoto Protocol, could contribute up to 12 million tonnes of CO2 equivalent per year. Dow is quick to point out this figure represents only a few hundredths of a percent of global CO2 emissions.

The controversy surrounding sulphuryl fluoride has parallels with recent discussions over nitrogen trifluoride, another EPA award-winning chemical whose broader effects on the environment appear to have been overlooked (ENDS Report 406, p 18 ).

Sulphuryl fluoride has received approval as a wood preservative under the EU biocidal products Directive. Dow is required to work towards monitoring atmospheric levels of the compound.

The gas is also in the final stages of the approval process under the EU’s plant protection products Directive. Member states can grant provisional authorisations in the interim. In the UK, trained operators are allowed to use sulphuryl fluoride to fumigate empty flour mills and grain stores.

A Dow spokesman could not provide UK usage data but said only one UK company, Igrox, is trained to use the gas. Igrox advertises Profume for the control of pests such as the confused flour beetle, rust red flour beetle and Mediterranean flour moth.

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