PERCHLORATE EFFECTS ON RAT THYROID
According to a recent EPA report ( the pdf
file "Perchlorate Environmental Contamination," found at http://www.epa.gov/ncea/perch.htm
), perchlorate affects rat thyroids in the following manner:
.01 mg/kg (350 ppb standard adult dose) induces a 10-20% decline in
iodide uptake by the thyroid (page 170 / 5.64). This is roughly
the dose found in Rancho Cordova's drinking water.
.1 mg/kg (3500 ppb standard adult dose) induces hypertrophy of thyroid
follicular cells and lumen shrinkage in rat pups (page 134 / 5.28).
Exposure levels in drinking water may have reached this level during
the period of greatest perchlorate dumping (1950's-1960's). This
was judged to be the lowest adverse effect from which an uncertainty
factor of 100 was applied to determine the reference dose of .0009 mg/kg.
1 mg/kg (35,000 ppb standard adult dose) induces a 10% drop in T3 and
T4 hormone levels, with only the T3 being statistically significant.
T3 levels drop by 60% at the 3 mg/kg level (p.140 / 5.32).
10 mg/kg (350,000 ppb standard adult dose) induces a significant increase
in TSH (p.143 / 5.35), thickening of the corpus callosum in the brain
(p.132 / 5.62), and adverse bone marrow effects secondary to endocrine
disruption (p. 107 / 5.61).
A key concern is irrigated food crops, with an estimate that produce
from the lower Colorado River could contain a dose equivalent to 1.6
mg/kg, or roughly the 50,000 ppb standard adult drinking water dose
(page 7.9). Note that the adult standard is a 70 kilogram individual
drinking 2 liters of water a day, and that it would take a unusually
high consumption of Colorado River fruits and vegetables to approximate
the .1 mg/kg level of adverse effect on rat pups. For those who
are concerned, these are the food crops irrigated by the lower Colorado:
most of the nation's winter lettuce, and a significant portion of the
nation's avocados, lemons, and cantaloupes. Grapefruit, watermelon,
broccoli, and onion production are also locally important for the west
coast market.
Larry Ladd
Community Representative
Aerojet Health Assessment Site Team
Rancho Cordova, California
