Arsenic leaching not serious risk, study finds

Arsenic leaching from treated vineyard posts in Marlborough is unlikely to pose a significant risk to soil and water in the future, a study has found.

Marlborough District Council last year commissioned research into leaching after concerns that millions of posts treated with copper, chrome and arsenic could affect water quality.

A study by HortResearch last year confirmed leaching of arsenic did occur but revealed most of the chemical remained close to the posts.

While some of those spots had arsenic and chromium concentrations in excess of Australian guidelines, they were very low when averaged over the entire vineyard area.

HortResearch has now completed another study looking at the risks of arsenic accumulating in soil and groundwater over successive generations.

The results were due to be presented to a council environment committee meeting today.

The study found soil arsenic concentrations would stabilise after 100 to 300 years.

In some ground water, arsenic levels would increase by 0.5 to 0.7 parts per billion compared with drinking water guidelines of 10 parts per billion.

However, in the Southern Valleys, a concentration of up to 13 parts per billion could accumulate, but only after several hundred years.

That was because ground water in the deep aquifers recycled relatively slowly, although the result was based on conservative assumptions regarding soil adsorption of leached arsenic.

Environment committee chairman Gerald Hope said the conclusion that there was unlikely to be a contamination risk in the medium to long term was encouraging.

"I think it's reassuring that there's no real risk to water supplies, especially those used for drinking water."

The issue -- which he said had resulted in some "scaremongering" when it first emerged -- did provide a signal that alternative methods for treating timber might be warranted in the future.

"There's a perception that arises whenever you have a poison that it's nasty and toxic. We need to address that, but it will be a long term project."

Meanwhile, the council did recommend that a "watching brief" be maintained and highlighted the potential for further study, especially in the Southern Valleys aquifers.

It suggested research into options to reduce the accumulation of arsenic could be useful, while using alternative posts or sealing the end of treated posts could also be encouraged.

- NZPA