Arsenic threat to soil and groundwater from fences and decking

Arsenic from treated timber used in some decking, fencing and utility poles is likely to leach into the environment for decades, new research has found, posing a grave threat to ground water and soil.

Scientists from the University of Florida, University of Miami and Florida International University examined leaching from actual wooden decks as well as from simulated landfills and found that deck wood leached high levels of arsenic into rainwater run-off and into the soil. It also carried on leaching arsenic while sitting in simulated landfills.

The studies, published in the journal Environmental Science and Technology, focused on leaching from chromated copper arsenate, or CCA, treated woods. These woods had been phased out for residential use in the US in 2003 but are still used for utility poles and industrial construction timbers.

Researchers studied rainwater runoff from a CCA treated deck for one year and found that arsenic contamination was 100 times higher than runoff from an untreated deck. In addition, a layer of sand under the deck had arsenic levels 15 to 30 times higher than background levels, while water that percolated through the sand was also contaminated.

"What's important for people to realise is that arsenic is relatively mobile, so it's something we have to be concerned about - how to manage this huge stock of CCA wood that remains to be disposed of," said Tim Townsend, University of Florida associate professor of environmental engineering.

The researchers concluded that by 2000, Florida had imported 28,000 metric tons of arsenic, 4,600 of which have already leached into the environment. They predict that as much as 11,000 additional tons of arsenic will leach into the soil and water from decks and other treated structures over the next 40 years.

"These estimates provide decision-makers with information that helps them decide whether or not CCA-treated wood should go into lined or unlined landfills," Townsend added.

Floridian law doesn't currently require that construction and demolition landfills be equipped with linings to prevent leaching, a possible solution to the problem. However, with researchers estimating that between 20 and 50 tons of arsenic has already leached into construction and demolition landfills in Florida before 2000, and an expected increase of between 350 and 830 tons of the heavy metal by 2040, it may be something that state authorities should consider again.

The problem of arsenic pollution is not confined to Florida, however. This week the City of Nogales in Arizona, granted a contract to Severn Trent Services to provide arsenic removal technology to meet new EPA drinking water standards. Total arsenic in well locations at three of the city's water treatment facilities has measured between 17 and 29 parts per billion, while the new limit is 10 ppb. The arsenic removal systems will be installed during the first few months of this year.

David Hopkins



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