Gas link possible in Nelson nerve-disease deaths

Toxicology professor Ian Shaw says early findings of research at Canterbury University support a possible link. Photo / Supplied

Scientists are investigating a possible link between a rare degenerative nerve disease and a toxic gas blamed for the deaths of four Nelson port workers.

Methyl bromide is under review by the Environmental Risk Management Authority after concerns were raised about the safety of port workers and nearby residents, as well as its depleting effect on the ozone layer.

A group of widows claims exposure to methyl bromide might be linked to the deaths of their husbands, all of whom died of motor neurone disease from 2002-04 after working at Nelson Port. A public health study five years ago found no evidence of that.

Now, toxicology professor Ian Shaw says early findings of research at Canterbury University support a possible link, although the work is a long way from proving a connection.

In what Dr Shaw described as a "crucial step", the first stage of the experiment mixed methyl bromide with a protective chemical found in human cells, called glutathione, and found that the two reacted.

The next stage - injecting human cells with methyl bromide - should be completed within the next six weeks. By then submissions will have closed (on February 26) on the Erma review.

"If our hypothesis is right, when you expose a cell to methyl bromide the levels of glutathione will go down," said Dr Shaw.

That would mean the cell was not protected against chemical attack if it got another dose of the gas, he said.

"The methyl bromide can start to react with the cell DNA or proteins in the cell that are really important.

"If it was a nerve cell, for example, it could stop that nerve cell functioning." That could trigger motor neurone disease, he said.

The Ministry of Agriculture and Forestry wants to keep using methyl bromide to kill insects and other pests in goods travelling in and out of the country. Use of the gas to fumigate export logs is increasing and some countries, such as India, require it.

The Council of Trade Unions, representing 39 unions including the port workers', says fumigators are finding better and safer options and there is no need to keep using the gas. It wants it banned because of uncertainty about the level of toxicity and the possible link to motor neurone disease.

The disease destroys nerve cells between the brain and muscles, wasting and paralysing muscles and killing most sufferers within two to five years of diagnosis.

Of 16 Nelson people diagnosed with motor neurone in the decade to 2005, Nelson Medical Officer of Health Ed Kiddle found six had worked in the port area and at least three were likely to have been exposed to the gas.

Dr Shaw believes Dr Kiddle should have looked further into the rate of port deaths. The rate among port workers was many hundreds of times higher than normal, he said.

Methyl Bromide is used at several ports, including Tauranga, and to a lesser extent, Auckland.

Its use for anything other than quarantine and pre-shipment fumigation is banned under the Montreal Protocol because of its ozone-destroying potential.

Erma says it will decide whether to ban it between mid-year to late this year after the application, public submissions and other information has been considered.

A preliminary staff report recommends keeping it in use.