Ammonium Nitrate Chemistry

New Zealand's Toxic Methyl Bromide Problem

Concerns are mounting in New Zealand around the continued use of methyl bromide for fumigation.  Methyl bromide is a highly effective fumigant, but it is also depletes the ozone layer and is harmful to human health.  Under the Montreal Protocol for the regulation of ozone depleting substances, use of methyl bromide is banned for all but a few exempt quarantine purposes. This ban has seen measured atmospheric levels of this substance drop from about 10 to 8 parts per trillion. In New Zealand, however, methyl bromide usage is soaring, with a 2020 deadline to eliminate methyl bromide emissions looming.

One of the biggest exemptions for methyl bromide use is in fumigating logs for export. China and India are the main destinations and both prefer methyl bromide treatment as a bio-security measure. New Zealand is a significant exporter of logs to China and India, and in recent years has grown to become one of the biggest users of methyl bromide worldwide. The NZ government have a 2020 deadline in place to recapture methyl bromide after fumigation, but the timber industry is struggling to settle on a way to do this. New Zealand news site Stuff have been running a series of investigative articles into the methyl bromide problem, highlighting the issues surrounding methyl bromide elimination, as well as the link between methyl bromide and motor neuron disease.  A motor neuron disease cluster in NZ port workers has been attributed to methyl bromide exposure and is providing new insight into the mechanism of MND.

The timber industry in Australia also uses methyl bromide to fumigate logs for export, and there is no clear strategy to bring this to an end.  There is little regulation of air toxics in Australia, with the National Environment Protection (Air Toxics) Measure only tasked with collecting data on the emission of air toxics. Moreover, only five compounds are included (formaldehyde, benzene, toluene, xylenes, and benzo(a)pyrene). Safe Work Australia recommend a 5 ppm exposure limit for methyl bromide but this is out of step with the latest research on methyl bromide toxicity. Community exposure limits have been estimated at only 0.2 ppm for acute exposure, and as low as 0.002 ppm (or 2 parts per billion) for chronic exposure.

Methyl bromide continues to prove a health threat in New Zealand, Australia, the United States, and elsewhere. It also contributes to man-made ozone layer degradation, where international action has already managed to make a significant impact. Tighter implementation of the Montreal protocol to eliminate methyl bromide emissions altogether promises further environmental benefits alongside reduced health impacts.