I don't know the science well enough to know whether the "out of thin
air" hypothesis of perchlorate formation is true, but it is plausible.
The important thing is to recognize that the presence of natural
perchlorate in some areas does nothing to lessen the importance of
remediating anthropogenic perchlorate elsewhere. Other toxic substances
- particularly metals - are present and bioavailable in many areas, yet
we still require clean up of industrial and other releases.
Furthermore, the typical source concentrations of perchlorate found at
facilities that have produced, tested, and disposed of solid rocket fuel
are much higher.
If it can be shown that large numbers of people have ingested natural
perchlorate for long periods of time, with no health effects, then these
natural perchlorate deposits might lead to weaker regulations, but
that's a big IF.
And the widespread presence of perchlorate in the environment, as a
source of food contamination, may actually lead to more protective
drinking water standards because it must be assumed that water supplies
only a fraction of a typical person's dose.
Lenny
Lenny Siegel wrote:
Widespread Presence of Naturally Occurring Perchlorate in High Plains of
Texas and New Mexico
Srinath Rajagopalan, Todd A. Anderson, Lynne Fahlquist, Ken A.
Rainwater, Moira Ridley, and W. Andrew Jackson*
Environmental Science & Technology
Accepted March 10, 2006
Abstract:
Perchlorate (ClO4-) occurrence in groundwater has previously been linked
to industrial releases and the historic use of Chilean nitrate
fertilizers. However, recently a number of occurrences have been
identified for which there is no obvious anthropogenic source.
Groundwater from an area of 155 000 km2 in 56 counties in northwest
Texas and eastern New Mexico is impacted by the presence of ClO4-.
Concentrations were generally low (<4 ppb), although some areas are
impacted by concentrations up to 200 ppb. ClO4- distribution is not
related to well type (public water system, domestic, agricultural, or
water-table monitoring) or aquifer (Ogallala, Edward Trinity High
Plains, Edwards Trinity Plateau, Seymour, or Cenozoic). Results from
vertically nested wells strongly indicate a surface source. The source
of ClO4- appears to most likely be atmospheric deposition. Evidence
supporting this hypothesis primarily relates to the presence of ClO4- in
tritium-free older water, the lack of relation between land use and
concentration distribution, the inability of potential anthropogenic
sources to account for the estimated mass of ClO4-, and the positive
relationship between conserved anions (e.g., IO3-, Cl-, SO4-2) and
ClO4-. The ClO4- distribution appears to be mainly related to
evaporative concentration and unsaturated transport. This process has
led to higher ClO4- and other ion concentrations in groundwater where
the water table is relatively shallow, and in areas with lower saturated
thickness. Irrigation may have accelerated this process in some areas by
increasing the transport of accumulated salts and by increasing the
number of evaporative cycles. Results from this study highlight the
potential for ClO4- to impact groundwater in arid and semi-arid areas
through long-term atmospheric deposition.
For the original abstract or to download the entire article (NON-ES&T
SUBSCRIBERS MUST PAY A FEE), go to
http://dx.doi.org/10.1021/es052155i
--
Lenny Siegel
Director, Center for Public Environmental Oversight
c/o PSC, 278-A Hope St., Mountain View, CA 94041
Voice: 650/961-8918 or 650/969-1545
Fax: 650/961-8918
<lsiegel@cpeo.org>
http://www.cpeo.org
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