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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. 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

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  1. Health Implications of Perchlorate Ingestion Summary of a National Research Council Review of other studies SCAG WPTF Presentation of February 10, 2005

  2. 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”

  3. 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-

  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

  5. 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.)

  6. 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.”

  7. 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

  8. 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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