health implications of perchlorate ingestion
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Health Implications of Perchlorate Ingestion. Summary of a National Research Council Review of other studies SCAG WPTF Presentation of February 10, 2005. Problem Definition. Perchlorate used for rocket fuel, fireworks, and flares Perchlorate ( ClO 4 - ) ion moves readily with water

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health implications of perchlorate ingestion

Health Implications of Perchlorate Ingestion

Summary of a National Research Council Review of other studies

SCAG WPTF Presentation of February 10, 2005

problem definition
Problem Definition
  • Perchlorate used for rocket fuel, fireworks, and flares
  • Perchlorate (ClO4-) ion moves readily with water
  • 11 million people served water containing ClO4- at  4 μg/L (PPB)
  • 2002 EPA Risk Assessment suggested effect at 1 PPB
  • EPA offensive puts DOD and NASA on Defensive
  • Test, storage, production facilities across the US
  • National Research Council (NRC) asked to mediate & “Access health effects from perchlorate ingestion”
human physiology of clo4
Human Physiology of ClO4-
  • ClO4- competes (ineffectively) with Iodine ion or Iodide (I-) in thyroid uptake (transport)
  • Iodine need for normal hormonal activity, but is an element and cannot be manufactured by our bodies
  • Lack of iodine cause goiters, poor homeostasis, and neural defects in adults and developing offspring
  • Sources include iodized salt, sea salt, some sea foods
  • Typical US diet is about 5-10x excess
  • Fortunately (unless radioactive), body conserves I-
medicinal uses of clo 4
Medicinal Uses of ClO4-
  • 50s/60s potassium perchlorate treatment of Hyperthyroidism (overactive thyroid)
  • Healthy people rapidly excrete KClO4- in urine
  • High dose, long term ClO4- depletes Iodine
  • Ecological (non-clinical) exposure
    • Does not cause hypothyroidism (underactive thyroid)
    • Does not alter thyroid function in healthy pregnancies/births
    • Results unclear on Attention Deficit Hyperactivity Disorder
    • Workplace exposure, probably no impact, but small N
    • Sample size too small to analyze for thyroid cancers
    • Insufficient data on sensitive subpopulations
epa rodent assessment
EPA Rodent Assessment
  • Subjective/inconsistent response
    • brain structure size
    • greater pup activity
    • thyroid cysts
  • Used to develop a No Adverse Effect Level
  • May confuse a high does toxic from low dose chronic
  • (High does may cause excessive cellular replacement resulting in replication mutations.)
nrc analysis
NRC Analysis
  • NRC believes body compensates (homeostasis) by first adjusting hormone (TSH) output, then enlarging the thyroid, then adverse outcome of hypothyroidism
  • Change in TSH is natural response to dose variabilitya pre-adverse effect response
  • Inhibition of iodide uptake is a more reliable and valid measure, it has been unequivocally demonstrated in humans exposed to perchlorate, and it is the key event that precedes all thyroid-mediated effects of perchlorate exposure.”
dose assessment
Dose Assessment
  • 2002 EPA Risk Assessment
    • 0.03 ug/kg-day
    • as water ingestion about 1 PPB
  • NRC study with 10 fold safety
    • 0.7 ug/kg-day
    • about 20 PPB as water
nrc conclusions
NRC Conclusions
  • Higher (than EPA) dose should be safe
  • Iodine depletion is a slow process, probably greater than most common sensitive exposure period
  • More studies, using quantitative end points, on pregnant primates and rodents should occur
  • More occupational exposure assessments
  • Concerned/sensitive individuals can take an additional (but unnecessary) step of monitoring body TSH or I levels, increase iodine intake, and/or use bottled water
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