Health Implications of Perchlorate Ingestion (2005) / Chapter Skim
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1 Introduction
1 Introduction
Pages 19-34
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From page 19... ...
to assess the adverse health effects of perchlorate ingestion from clinical, toxicologic, medical, and public-health perspectives. They also asked the NRC to evaluate the scientific literature, including human and animal data, and to assess the key studies underlying EPA's 2002 draft risk assessment, Perchlorate Environmental Contamination: Toxicological Reviewand Risk Characterization, with respect to quality, reliability, and relevance for drawing conclusions about the health implications of exposure to low concentrations of perchlorate in drinking water.
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. The peer review concluded that the scientific database was insufficient to conduct a "credible quantitative risk analysis." As a result, an independent peer-review panel met in May 1997 and developed a testing strategy to address data gaps and reduce uncertainties regarding possible health effects of low-concentration perchlorate ingestion.
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. EPA issued a revised draft risk assessment in 2002 that incorporated revisions suggested by the peer review and new data generated as of fall 2001.
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Before the 1940s, annual global production of perchlorate was estimated to be 1,800 tons. In the middle 1940s, annual perchlorate production increased dramatically to 18,000 tons because of demand by the military and aerospace industry.
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Data on California indicate that perchlorate ranges from less than 4 to 67 ppb, with 6.7 ppb as the median concentration of values above the minimum reporting level. The data do not represent perchlorate concentrations in all water sources.
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from 1-2 inant :1 in in perchlorate States Rico = mu mu Data TABLE Contam Location United Puerto California ppb1 Median Maxim Maxim a b c d Abbreviations: Source:
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Thus, the contamination of public water supplies and food sources has raised substantial concerns about the effects of low-level perchlorate ingestion and forced the debate over a drinking-water standard into the public spotlight. SENSITIVE POPULATIONS Transfer of iodide from blood into the thyroid gland is essential for the synthesis of the thyroid hormones: thyroxine (T4)
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Thus, fetuses and preterm newborns constitute the most sensitive populations although infants and developing children are also considered sensitive populations. People who have compromised thyroid function resulting from conditions that reduce thyroid hormone production and people who are iodide-deficient also constitute potentially sensitive populations.
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28 2002a. EPA Source: ure.
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COMMITTEE'S CHARGE AND APPROACH TO CHARGE The members of the NRC committee were selected for their expertise in pediatrics; endocrinology; pediatric endocrinology; thyroid endocrinology, physiology, and carcinogenesis; immunology; veterinary pathology; animaltoxicology;neurotoxicology;developmentaltoxicology;physiologically basedpharmacokineticmodeling;epidemiology;biostatistics;andrisk assessment. The committee was asked to accomplish the following tasks: · Evaluate the current state of the science regarding potential adverse effects of disruption of thyroid function in humans and laboratory animals at various stages of life.
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If deficiencies in EPA's analysis are found, such as lack of consideration of a key study, provide suggestions as to how EPA might modify its assessment. Provide a range of values consistent with scientificevidence for percentage iodide uptake that would protect persons at various life stages and with varied thyroid status.2 On the basis of the scientific evidence, provide information that can be used to inform the selection of uncertainty factors used in the approximation of a safe lifetime perchlorate exposure for humans, especially sensitive populations.
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evidence establishes a causal relationship. Using that hierarchy where appropriate, the committee was able to reach conclusions regarding the potential adverse effects of perchlorate exposure.
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Chapter 5 reviews the committee's critique of EPA's 2002 draft risk assessment, Perchlorate Environmental Contamination: Toxicological Review and Risk Characterization. Research that could reduce uncertainty regarding health effects of perchlorate exposure is presented in Chapter 6.
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2004c. Revisions to the Unregu lated Contaminant Monitoring Rule Fact Sheet.
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1985. Request for CDC Assistance Regarding Potential Health Effects of Perchlorate Contamination at the San Gabriel Valley Superfund Sites.
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