Consumer Watchdog: Arsenic in the air

Safe pollution levels are breached by burning timber treated with arsenic, a study shows. Photo / Greater Wellington Regional Council

Burning treated wood in fireplaces is causing nationwide pollution

New Zealanders looking for a cheap way to warm their homes are being warned not to use treated timber offcuts in their fireplaces.

Research by Perry Davy, of GNS Science, and others has shown that people burning treated timber are pumping arsenic into the air at a higher rate than had been suspected.

Much of the country's timber is treated with copper, chromium and arsenic (CCA), although it does not have to be labelled as such when sold.

New Zealand has the highest per-capita use of CCA timber in the world. Its use is restricted in many other countries, including Australia.

Davy's research found several acute episodes of atmospheric arsenic that were from domestic fire emissions.

He said it was hard to tell how many households were responsible but it was more than previously thought.

The problem was nationwide and widespread, he said. "There is some elevated risk to the population in breathing in contaminated material," he said. "Arsenic probably has carcinogenic potential."

Burning CCA seemed "opportunistic" because peak arsenic concentrations did not always coincide with when domestic fires were contributing the largest amounts overall into the atmosphere, his study said.

"CCA-treated timber is only used as and when it is available, for example, off-cuts from building activities. It would be too expensive to use treated timber as a primary fuel source. However, sufficient quantities must have been burned for arsenic to be picked up by our monitoring."

Burning treated wood is illegal but Davy said it could be hard for people to recognise whether wood had been treated. Burning off-cuts from construction or old decking timber was cheaper than buying wood supplied for fires.

Most timber lost its staining after a year or so, and some had never had it. "Some of it has no staining to show that it is treated but most housing construction timber is treated with arsenic."

Davy's study found average concentrations of arsenic at urban locations in New Zealand could exceed the national ambient air-quality guideline by up to two times. His research used a sample of particles in the air pollution, which were analysed to determine the source.

To prove Ministry for the Environment guidelines were being breached, a study had to monitor the pollution levels all year using a batch-processing method.

Tamsin Mitchell, of the Greater Wellington Regional Council, has done just that and is set to publish a report on arsenic levels shortly.

Daniel Gudsell, from Abodo, a company that treats wood with non-arsenic preservative, said treated wood was difficult to dispose of.

"Companies leave treated wood waste on the roadside for people to use as firewood because it's expensive to dump." He said it would be hard to stop it happening as long as arsenic-treated wood was widely used.

"We're arguing that rather than saying, 'Don't burn treated wood', we should take the arsenic out so if they do burn it, it won't raise the arsenic level in the atmosphere."