OAK RIDGE, Tenn., Oct. 20, 2004 — An award-winning system developed at Oak Ridge National Laboratory to clean up perchlorate pollution is now also helping scientists determine whether the contamination is natural or man-made.
This latter application could be instrumental in tracking environmental perchlorate, finding its source and resolving resulting liability issues, said ORNL scientist Baohua Gu, who headed development of the treatment system.
Perchlorate, or ClO4-, disrupts the thyroid gland that regulates metabolism in adults and physical development in children and is increasingly being found in soil and water. It is used to make solid rocket propellant and explosives but also occurs naturally, as in nitrate soils from Chile used to make fertilizers, making the source sometimes difficult to trace.
Conventional treatments use tiny resin beads to trap the perchlorate, but the spent resin becomes contaminated, and disposal is costly or impractical.
The ORNL system removes and breaks down perchlorate into harmless chloride and water and recharges the resin so it can be reused many times. The process costs up to 80 percent less than conventional methods and is one of R&D Magazine's top 100 inventions for 2004.
But Gu and ORNL colleagues Jusuke Horita and Gilbert Brown along with others from Louisiana State University, University of Illinois, and USGS have found another benefit: the process of removing perchlorate also purifies it, allowing the scientists to isolate trace quantities and examine the compound more closely than ever before.
Using isotopic analysis, they compared naturally-occurring perchlorate from Chile's Atacama Desert to synthetic or manufactured samples and found the natural type had a much higher value of the oxygen-17 isotope (an oxygen atom with 8 protons and 9 neutrons in the nucleus) but a lower chlorine-37 value (a chlorine atom with 17 protons and 20 neutrons in the nucleus).
A report on the study appears in the current edition of Environmental Science and Technology, which is published by the American Chemical Society.
"Isotopic comparison of natural and non-naturally occurring perchlorate has not been feasible because of the difficulties in extracting and analyzing trace quantities of perchlorate from soil or groundwater that contain large quantities of impurities like nitrates and other salt deposits," Gu said. "Our findings show that the ORNL treatment system provides a tool for the identification and forensics of perchlorate contamination in the environment."
ORNL has licensed the resin technology to the Purolite company and the regeneration and recovery technology to Calgon Carbon Corporation. The system also is being tested at two contaminated sites in California. Gu will present findings from those tests at meetings this month with municipal water utilities and environmental remediation groups in California.
The Environmental Protection Agency proposed one part per billion in 2002 as the legal limit for perchlorate in drinking water, but that standard is under debate, Gu said.
"The presence of natural or atmospheric perchlorate in the environment obviously has far-reaching ramifications, ranging from public health issues to huge liabilities that could be imposed by agricultural and environmental cleanup needs," Gu said. "It recently has been found in lettuce and milk, which begs the questions: How is it getting there and migrating through the environment? Where is the liability?
"Our technology could have a huge impact on how those questions are answered."
ORNL is managed by UT-Battelle for the Department of Energy.
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