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EPA Proposes Weak "Safety Reference" Levels for Perchlorate Contamination of Food & Water

From: Environmental News Service <> 2/21/05

EPA Sets Reference Dose for Perchlorate

WASHINGTON, DC, February 21, 2005 (ENS) -
The U.S. Environmental Protection
Agency (EPA) has established an official reference dose of 0.0007 mg/kg/day
of perchlorate. This level is consistent with the recommended reference dose
included in the January 2005 issued by the National Academy of Sciences

A reference dose is a scientific estimate of a daily exposure level that is
not expected to cause adverse health effects in humans.

Perchlorate, the explosive component of solid rocket fuel, can affect the
thyroid gland's ability to make essential hormones. For fetuses, infants and
children, disruptions in thyroid hormone levels can cause lowered IQ, mental
retardation, loss of hearing and speech, and motor skill deficits.
Perchlorate contaminates at least 350 drinking water sources in 22 states,
and has been found in many important foods including milk, lettuce and other
leafy green vegetables.

Perchlorate also has been used in missile and rocket propellants, munitions
and fireworks, flares, automobile airbags and pharmaceuticals. It may also
occur naturally and has been found in some fertilizer.

The EPA's reference dose, which assumes total intake from both water and
food sources, is "appropriate and protective for all populations, including
the most sensitive subgroups," the agency says.

Perchlorate exposure has the potential of blocking iodide uptake to the
thyroid gland. The National Academy of Sciences identified the non-adverse
effect of the inhibition of iodine uptake as the key biochemical event that
precedes the occurrence of all potential adverse effects of perchlorate

The EPA says its reference dose is conservative and health protective
because it is designed to prevent the occurrence of any biochemical changes
that could lead to adverse health effects.

The selected reference dose contains a 10-fold uncertainty factor to
protect the most sensitive population, the fetuses of pregnant women who
might have hypothyroidism or iodide deficiency.

This uncertainty factor also covers variability among other human life
stages, gender and individual sensitivities, protecting not only adults, but
also other sensitive subpopulations such as premature neonates, infants and
developing children.

EPA's reference dose for perchlorate will be posted on the agency's online
IRIS database, which contains risk information on possible human health
effects from exposure to chemical substances in the environment.

EPA's new reference dose translates to a Drinking Water Equivalent Level
(DWEL) of 24.5 ppb.

A Drinking Water Equivalent Level (DWEL), which assumes that all of a
contaminant comes from drinking water, is the concentration of a contaminant
in drinking water that will have no adverse effect with a margin of safety.

Because there is a margin of safety built into the reference dose and the
DWEL, exposures above the DWEL are not necessarily considered unsafe, the
agency said.

But Renee Sharp, senior analyst for the Environmental Working Group, a
research and advocacy organization, points out that this is a hypothetical
translation assuming a 154 pound adult male drinking two liters of water per
day and getting perchlorate from no other source.

Currently there are no enforceable perchlorate safety standards at the
state or federal level. However, Massachusetts has proposed a standard of
one part per billion (ppb) in drinking water, and California is considering
a drinking water standard of six ppb.

EPA's Superfund cleanup program plans to issue guidance based on the new
reference dose.

The perchlorate summary is available on the IRIS web site at: and at:

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