Wellington, Nov 5 NZPA - Proposals by environmental risk advisers to allow port companies, log exporters and other users to continue venting poisonous methyl bromide to the atmosphere for another 10 years have been criticised by the Green Party.

"They seem to think we can continue to use the atmosphere as an open sewer," said Green Party health spokeswoman Sue Kedgley, who has campaigned for Wellington's port to stop using the gas until it can re-capture it after use to fumigate logs.

Methyl bromide is an ozone-depleting gas used primarily for the quarantine and pre-shipment treatment of timber, logs and other produce, both for export and import, to kill a wide range of pests.

New Zealand announced in 1995 that imports of the gas would be stopped in 2010.

But staff working for the Environmental Risk Management Authority (Erma) have recommended the fumigant should continue to be used for another decade.

The advisers said immediately banning the chemical would hurt the economy, with no benefits: the Government has warned that a unilateral phase-out of methyl bromide for quarantine and pre-shipment purposes "would not be in the economic best interests of the country".

Continuing to use it for another decade would have no more adverse effects than blocking import and manufacture in five years' time, they said.

"Specific local community concerns about the use of methyl bromide in particular regions can be mitigated," the Erma staff suggested.

The proposed new controls, included:

* a new safety threshold for short-term exposure, in addition to the existing one for long-term exposure;

* downwind "buffer zones" when the gas is vented to the atmosphere; and;

* air quality monitoring for all types of fumigations.

But Ms Kedgley said making sure there was no one within 50m when the heavy gas was vented did not protect communities downwind, while a safety threshold was questionable when there was no safe level for the toxin.

Authorities in Nelson had already imposed much more stringent conditions than Erma staff were proposing, after group of widows whose husbands worked at Port Nelson and died of motor neurone disease blamed the gas for causing the illness.

The Government has endorsed reducing use of methyl bromide for biosecurity purposes where "technically and economically feasible".

The 1994 Montreal Protocol called the phase-out of methyl bromide the single most important action that could be taken to protect the ozone layer.

Though use of the gas for fumigating soil has been stopped, increasing exports of logs and timber mean 170 tonnes was used in 2007.

Export logs alone used 68 percent, and that $600 million industry is expanding rapidly -- this year's exports to China are set to be double those in 2007.

Now Erma is calling for public submissions on methyl bromide, before it released a final decision in the middle of next year.

Erma said there was no single alternative to methyl bromide but research into alternatives and large-scale recapture of the gas is ongoing.

Twenty eight possible alternatives have been identified.

One eyed for the Chinese log market is phosphine, but scientists have questioned whether it is effective against fungi.

Instead, they suggested New Zealand use sulfuryl fluroide (SO2F2) -- but researchers overseas have recently shown that is a greenhouse gas nearly 5000 times more effective than carbon dioxide at warming the atmosphere.