2005 National Academy of Sciences Reference
Dose for Perchlorate by Weight, Drinking Water Consumption, and
Food Exposure
POTENTIAL PERCHLORATE STANDARDS (1/11/05)
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| BASED
ON REPRO/DEV. ENDPOINT |
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| Alan
Roberson, AWWA Director of Regulatory Affairs |
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| NAS
NOEL=0.007 mg/kg/day |
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UF=10 |
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| NAS
RfD=0.0007 mg/kg/day |
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| Numbers
below are in ppb |
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| 70
kg male |
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Relative Source
Contribution |
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| Water |
100% |
80% |
40% |
20% |
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| 1
l/day |
49.0 |
39.2 |
19.6 |
9.8 |
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| 1.2 |
40.8 |
32.7 |
16.3 |
8.2 |
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| 2 |
24.5 |
19.6 |
9.8 |
4.9 |
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| 2.5 |
19.6 |
15.7 |
7.8 |
3.9 |
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| 3 |
16.3 |
13.1 |
6.5 |
3.3 |
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| 50
kg pregnant female |
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Relative Source
Contribution |
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| Water |
100% |
80% |
40% |
20% |
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| 1
l/day |
35.0 |
28.0 |
14 |
7 |
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| 1.2 |
29.2 |
23.3 |
11.7 |
5.8 |
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| 2 |
17.5 |
14.0 |
7.0 |
3.5 |
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| 2.5 |
14.0 |
11.2 |
5.6 |
2.8 |
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| 3 |
11.7 |
9.3 |
4.7 |
2.3 |
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| 30
kg child approaching puberty |
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Relative Source
Contribution |
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| Water |
100% |
80% |
40% |
20% |
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| 1
l/day |
21.0 |
16.8 |
8.4 |
4.2 |
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| 1.2 |
17.5 |
14.0 |
7.0 |
3.5 |
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| 2 |
10.5 |
8.4 |
4.2 |
2.1 |
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| 2.5 |
8.4 |
6.7 |
3.4 |
1.7 |
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| 3 |
7.0 |
5.6 |
2.8 |
1.4 |
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| 7
kg bottle-fed baby |
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Relative Source
Contribution |
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| Water |
100% |
80% |
40% |
20% |
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| 0.5
l/day |
9.8 |
7.8 |
3.9 |
2.0 |
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| 1 |
4.9 |
3.9 |
2.0 |
1.0 |
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| 1.5 |
3.3 |
2.6 |
1.3 |
0.7 |
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| 3
kg bottle-fed baby |
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Relative Source
Contribution |
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| Water |
100% |
80% |
40% |
20% |
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| 0.5
l/day |
4.2 |
3.4 |
1.7 |
0.8 |
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| 1 |
2.1 |
1.7 |
0.8 |
0.4 |
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| 1.5 |
1.4 |
1.1 |
0.6 |
0.3 |
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SPECIAL NOTE: WHAT'S A SAFE DOSE?
In 2002 the US EPA submitted a proposed reference
dose of 1 part-per-billion (ppb) for perchlorate in drinking water. This
was based on perceived changes in infant rat brain structure at a dose
equivalent to 300 ppb for a 150 pound human adult or as low as 45 ppb
for a bottle-fed infant. Increased skin irritability in mice ears, suggesting
some sort of immune system effect, was found at a dose about four times
higher. While perchlorate concentrations of this magnitude are rare in
drinking water, the ability of the chemical to concentrate a thousand-fold
in irrigated alfalfa hay is of some concern because of the potential route
of human exposure via dairy cattle.
Published research from Texas Tech suggested that tadpoles exposed
to as little as 5 ppb perchlorate for long periods of time are more
likely to not properly develop fore-legs. Amphibian metamorphisis is
notoriously sensitive to thyroid hormone disruption. Regulators are
waiting for additional research to confirm or correct these surprising
results. The majority of reviewers in the 2002 external peer review
held in Sacramento seemed to think a reference dose in the 3 to 10 ppb
range was justified by the available evidence, and a minority of the
reviewers thought the standard should allow higher concentrations.
Current standards in various states
reflect this range:
- Wells outside a Cape Cod military base
are voluntarily shut down at 0.4 ppb perchlorate. Action levels in
Massachusetts, Maryland, and New Mexico are at 1 ppb, although federal
cleanup is only currently authorized in the
4-18 ppb range.
- Superfund sites in California currently
require well shutdown at 4 ppb while the state debates a public health
goal between 2 to 6 ppb; Texas also has a 4 ppb action level in residential
areas, but will tolerate 10 ppb in industrial areas.
- New York is adopting a 5 ppb standard.
- Colorado River-dependent Arizona has
a 14 ppb perchlorate standard, while similarly dependent Nevada enforces
an 18 ppb standard.
For further information, contact the scientists
conducting the government investigation of environmental perchlorate
at http://www.clu-in.org/studio/perchlorate_060402/
