An international conference on protecting the ozone layer has ended with governments agreeing to a global survey of the amounts of a key chemical being used in so-called quarantine and pre-shipment.

The quantities of methyl bromide, a pesticide and ozone-damaging chemical, used by farmers for fumigating soils are well known. But the precise levels used to treat shipments of big commodity crops such as rice and maize and consignments in wooden pallets are unknown.

Experts estimate that in 2002 the quantities were around 11,000 tonnes growing to 18,000 tonnes in 2004.

But it is thought that the levels are an underestimate because not all countries are supplying full and accurate figures on the precise levels being used.

The survey is aimed at resolving these uncertainties and may be a first step towards controlling the levels of methyl bromide used in quarantine and pre- shipment.

It will be carried out by scientific and technical experts to the Montreal Protocol, the 17 year-old international agreement set up under the auspices of the United Nations Environment Program (UNEP) to protect the ozone layer from chemical attack.

The survey was among several key decisions made at the sixteenth meeting of the Parties to the Montreal Protocol which ended in the early hours of November 27, in the historic European city of Prague, Czech Republic.

Requests for so called "critical use exemptions" for farmers for methyl bromide were also considered based on recommendations by the Protocol¹s scientific and technical experts.

Under an agreement made in the middle of the 1990s, the chemical is scheduled for a full phase out in developed world agriculture next year. In 1991 consumption of methyl bromide was around 63,800 tonnes.

But some farmers, including some in Australia, Europe, and the United States, claim that the current alternatives to methyl bromide in some places and for certain crops, such as strawberries and tomatoes, are not sufficiently effective.

They have thus requested exemptions from the deadline for 2005 and 2006.

At the meeting, the Parties to the Protocol agreed to exemptions for developed world farmers totaling just over 2,600 tonnes for 2005 in addition to just over 12,150 tonnes agreed to at a special meeting in March this year.

Based on recommendations by the scientific and technical panels to the Protocol, it was agreed to grant developed world farmers a total of just over 11,400 tonnes-worth of exemptions in 2006.

A further 3,000 tonnes-worth of exemptions were also ³provisionally² approved for 2006 which will be reviewed by the scientific and technical experts over the coming months.

The experts will report back to governments as to whether these 3,000 tonnes should be formally granted or whether reliable, ozone-friendly, alternatives exist. This will be debated at a special one-day Extraordinary Meeting of the Parties scheduled for late June or early July next year.

Governments agreed that the levels of exemptions granted should take into account existing stockpiles of unused or recycled methyl bromide.

Klaus Toepfer, the executive director of UNEP, which hosts the Ozone Secretariat at its headquarters in Nairobi, Kenya, said: ³I am delighted that Governments could agree on such a range of sometimes difficult issues. I am also delighted that their decisions were based on sound science.²

³The Montreal Protocol is without doubt one of the most successful, global, environment treaties and has been strengthened by the political commitment show here in Prague. Indeed, I was pleased to note that throughout our discussions all governments stated clearly that they had every intention to phase out methyl bromide and that these critical use exemptions are temporary measures,² he added.

The meeting also made other key decisions including one to grant essential use exemptions for CFCs used in metered-dose inhalers. Under the agreements, the United States has been granted 1,900 tonnes of CFCs and Europe several hundred tonnes for use in inhalers containing the chemical salbutamol.