Environmental Science & Technology  [Printer-friendly version]
February 2, 2006


The 2005 ES&T environmental science paper of the year finds that
perchlorate is everywhere.

[Rachel's introduction: The rocket fuel, perchlorate, has been
measured in water and in vegetables all across the country. Now it
turns out that perchlorate isn't just an industrial chemical -- it
also occurs widely in nature. So risk assessors now need to ask
themselves, what are the health effects of Teflon PLUS perchlorate
PLUS any other single chemical? The honest answer: no one knows. But
risk assessors will give an answer anyway, by pretending perchlorate
isn't there even when they know it is. This is the opposite of a
precautionary approach. Is it ethical?]

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),

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."

Copyright 2006 American Chemical Society