From: Robina Suwol
Date: 14 Mar 2006
Remote Name: 188.8.131.52
THE PERCHLORATE SURPRISE
The 2005 ES&T environmental science paper of the year finds that perchlorate is everywhere.
By Alan Newman
"The Origin of Naturally Occurring Perchlorate: The Role of Atmospheric Processes" by Purnendu K. Dasgupta, P. Kalyani
Martinelango, W. Andrew Jackson, Todd A. Anderson, Kang Tian, Richard W. Tock, and Srinath Rajagopalan, Texas Tech University, 2005, 39 (6), 1569-1575.
It began with a phone call in 2003 from the Texas Commission on Environmental Quality. The commission was investigating a case of
perchlorate contamination in West Texas groundwater: Could Texas Tech University (TTU) help out? W. Andrew Jackson, an associate professor in the department of civil and environmental engineering, fielded the call and said yes.
But the staff soon ran into a problem with the samples that they were collecting. The U.S. EPA's method for measuring perchlorate in
drinking water was not sensitive enough for some of the high-salinity Texas groundwater samples. Kang Tian, a staff scientist with TTU's Institute of Environmental and Human Health, who had been charged with the analysis, turned to his Ph.D. mentor, Purnendu K. "Sandy" Dasgupta in the department of chemistry and biochemistry. With the help of Todd A. Anderson, an associate professor at the institute, the two developed a better method for perchlorate analysis which delivered the results they needed.
Meanwhile, TTU researchers were discovering that the perchlorate contamination was spread over almost 60,000 square miles. Where was it all coming from? This is an arid region with no munitions plants producing perchlorate-containing explosives. Jackson considered the possibility of perchlorate-laced fertilizer, but even the most generous calculations couldn't account for the contamination levels through an entire aquifer. "From that work, we realized that we couldn't come up with a reasonable anthropogenic source of perchlorate," recalls Jackson. However, the area had been irrigated since the 1940s; could the perchlorate have had a natural source?
The discussions included Richard W. Tock, currently an emeritus professor. Tock, whom Dasgupta describes as an "indomitable spirit", decided to conduct the ultimate quick-and-dirty experiment. Filling a 5-gallon plastic bucket with seawater, he hiked over to TTU's Center for Pulsed Power and Power Electronics and zapped the sample with a 10-gigajoule bolt of lightning. "There was a sound like a cannon going off, and the water jumped," laughs Jackson. "It is questionable whether anything happened [other] than a big bang, but it encouraged us to look at [the effect of lightning on common chlorine compounds] in depth." The researchers began more controlled experiments with spark plugs used as a safer and quieter source of lightning.
With data coming in that supported the idea of naturally occurring perchorate, which is the basis of the award-winning ES&T article,
the researchers began to consider the implications. "Perchlorate is an iodide transport inhibitor," points out Dasgupta. "Does perchlorate at environmentally meaningful exposure levels inhibit iodide transport?" In two additional papers in ES&T, Dasgupta and his colleagues have shown that perchlorate is in Texas cow's milk and, more dramatically, in human breast milk.
Dasgupta thinks that the perchlorate findings could point to a serious health issue. The World Health Organization "wants to put the U.S. on a list of borderline iodine-deficient countries. One study from Boston Medical Center found that 15% of pregnant women were acutely iodine- deficient," he points out. As a result, some of the scientific focus should be on iodine nutrition, says Dasgupta. "Perchlorate is just making it worse for some people."
Anderson agrees that a new health focus is needed. "Do people get their exposure through drinking water or food? Should perchlorate in food be factored into the equation to a greater extent before setting the exposure limits?" he asks. It all suggests that regulators need to take a second look at perchlorate.
Meanwhile, the search for naturally occurring perchlorate in the environment continues. "We find perchlorate in pretty much
everything," says P. Kalyani Martinelango, who is finishing up her Ph.D. under Dasgupta. The TTU researchers have, with the help of now- Ph.D. Srinath Rajagopalan, measured perchlorate at parts-per-trillion levels in precipitation, in the ocean, and at locations as diverse as Greenland, Hawaii, and Alaska.
Other areas of study are opening up. "There are hundreds of papers on atmospheric chlorine chemistry that never looked for perchlorate, probably because they couldn't look for it at low enough levels," points out Jackson. Moreover, the TTU researchers are finding that arid regions are storehouses of perchlorate and probably bromate. "These unsaturated zones have been understudied, and with urbanization and land-use changes and possibly climate change, the effect on groundwater is going to be more important," adds Jackson. "These overlooked species are going to gain importance in the future for long-term cycling and water quality."
With so many new avenues of research, it is not surprising that Dasgupta advocates that more environmental studies of perchlorate are needed. Citing arsenic in groundwater, he warns, "Being natural doesn't make it good."