Pine-beetle-ravaged forests could pollute drinking water

Posted: Oct 30, 2012

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Battling the beetle

Trees killed by the mountain pine beetle epidemic in Colorado could lead to the contamination of the drinking water supply by a known carcinogen, a study has found.

Levels of cancer-causing trihalomethanes (THM) in water treatment facilities have increased on average by 2 parts per billion per year in areas of the state struck by mountain pine beetles, reaching an average of 70 ppb by 2011, according to a study published yesterday in Nature Climate Change.

In some facilities, concentrations were as high as 111 ppb. U.S. EPA limits THM concentrations in drinking water to 80 ppb.

"It's a bit of a concern that levels at treatment facilities are getting awfully close or surpassing EPA standards," said Kristin Mikkelson, lead author of the study and a researcher in hydrological engineering at the Colorado School of Mines. The scientists relied on water quality data from the state Department of Public Health and Environment, as well as nine water treatment facilities.

As trees die off, they decompose and release carbon into waterways and soil. This carbon reacts with chlorine disinfectants in water treatment plants to form water disinfection byproducts, some of which include THM.

Five facilities in Dillon, Winter Park, Kremmling, Steamboat Springs and Granby -- serving areas with forests affected by the beetles -- were used in the experimental group. Four other facilities in Colorado were used in the control group.

A legacy from an epidemic

Comparing data from before 2008 and after, the researchers found that levels of total THM increased by nearly one-third. Although the pine beetle outbreak began in 2004 and 2005 in Colorado, it takes three to five years for the pine needles to drop on the forest floor and begin degrading.

Levels of THM tend to be highest in late summer, after the season in which more trees die from pine beetle infestations.

"We don't know if this is going to occur over the longer term or if it will occur in other places," Mikkelson said, or whether it will have human health implications in the long term.

Last year, the pine beetle epidemic killed about 3.8 million acres of trees across the Western states, according to the Forest Service, a drop from a peak of nearly 9 million acres in 2009. The Forest Service expects the epidemic to continue to shrink as the declining number of pine trees leaves beetles without food. Rising temperatures due to climate change have been identified as a factor in exploding pine beetle populations.

A spokesman from the Colorado Department of Public Health and Environment did not comment directly on the findings of the study but said the department had not changed its water monitoring program to look for an increase in organic carbon or water disinfection byproducts like THM.

"Chlorination of organic matter in the water does create [disinfection byproducts]" said Mark Salley, communications director for the department. "However, much of the organic matter can [or] is filtered out by public water systems before the chlorination step."

Mikkelson will expand her research to investigate how rising levels of organic carbon react with metals in soil.

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