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PERCHLORATE
- TOXIC POLLUTANT
By J. Raloff
Perchlorate
is hardly a household name. Yet its notoriety is climbing as the
presence of this toxic, thyroid-hormone-disrupting salt leads to
the closure of drinking-water wells in the western United
States.
Until now,
waterborne perchlorate (ClO4-) has been
linked almost exclusively to aerospace activities, since the
compound is a major ingredient in rocket fuels. An Environmental
Protection Agency study now reports evidence of a far more
prosaic and potentially widespread source: garden-variety
fertilizers.
Other
researchers within EPA and in the fertilizer industry, however,
are challenging the new data. More embarrassing, the authors of
the new study—scientists at EPA’s National Exposure Research
Laboratory in Athens, Ga.—told Science News that
they will have to retract some of their positive findings.
Says Steve
C. McCutcheon, who heads the Athens EPA team, "We
definitely made a few mistakes" in the first analysis.
However, he argues, "we do have irrefutable evidence"
of perchlorate in all fertilizers tested.
Chilean
nitrate—historically a common ingredient in some
fertilizers—has been a known natural source of perchlorate for
more than a century. The chemical has even turned up in at least
one deposit of potash, a common fertilizer ingredient. Finally,
the aerospace industry, which is responsible for cleaning up
some of the worst perchlorate water problems so far detected,
has recently reported data from two studies finding perchlorate
in fertilizer, McCutcheon notes.
Against
this backdrop, the Athens scientists stepped in to analyze nine
fertilizers, most of them intended for lawns and gardens, using
three independent techniques. They also assayed eight fertilizer
ingredients using one or two of the techniques. In the
just-published Oct. 1 Environmental Science & Technology
(ES&T), the researchers report finding perchlorate in every
sample tested.
This
universal contamination should have been the first clue that
something might be wrong, argues chemist Edward T. Urbansky of
EPA’s lab in Cincinnati. He notes that some of the ingredients
tested, such as urea, have no mineral sources—and therefore
should contain no perchlorate.
Having
reviewed its disputed results, the Athens team will soon ask
ES&T to "correct" the data for five of the eight
fertilizer ingredients, acknowledging that it can no longer
detect perchlorate in them. However, McCutcheon emphasizes,
these retractions will not affect the results for the
fertilizers, which were more fully analyzed.
At EPA’s
National Center for Environmental Assessment in Research
Triangle Park, N.C., "We have real concerns [about the
Athens data] that are quantitative and qualitative," notes
Annie M. Jarabek. The techniques used to measure perchlorate are
still evolving and not yet unambiguous, says Jarabek, who is
heading EPA’s toxicological risk assessment on the compound.
Moreover, she wonders why the Athens team assayed fertilizers
that are used by homeowners instead of the brands that farmers
use.
Since
learning of the Athens data earlier this year, Urbansky has
analyzed some 45 fertilizers with what he says is a far more
sensitive technique than has previously been used to perchlorate.
So far, he finds "no detectable perchlorate" in
anything except a few pure sodium nitrates. Presumably, he says,
they contain the infamous Chilean nitrate.
These data
lead him to suspect "that the Athens group is almost
completely wrong" about fertilizer as a major source of
perchlorate. McCutcheon instead argues that perchlorate
concentrations are inconsistent in the fertilizers—his lab now
witnesses variations—and may trace to seasonal changes in
sources of raw materials.
Last
month, EPA added perchlorate to its list of contaminants that
water utilities must monitor. As the compound’s toxicity is
better understood, Jarabek says, it might come under federal
regulation, perhaps as early as 2003.
References
and sources for this article
From Science
News, Vol. 156, No. 16, October 16, 1999, p. 245. Copyright
© 1999, Science Service
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