Source: Massachusetts Department of Environment Protection
Ammonium perchlorate (NH4ClO4) is an inorganic chemical widely used as an oxidizer in solid propellants for rockets, missiles and fireworks. Perchlorate is thus found in surface and ground waters around military operations, defense contracting or manufacturing facilities. Perchlorate is highly mobile in water and can persist for many decades under typical ground and surface water conditions.
Human exposure to perchlorate can occur through the ingestion of perchlorate-contaminated water. Infants can be exposed to perchlorate through breast milk, as breast tissue appears to concentrate perchlorate. Skin absorption of perchlorate as a result of skin contact during showering and bathing is expected to be low, because perchlorate is completely ionized in water. It also doesn’t volatilize, so it will not be in the air and will not be inhaled during showering.
Perchlorate disrupts normal function of the thyroid gland. It interferes with iodide transport into the thyroid gland, decreasing the availability of iodide needed for the synthesis of thyroid hormones, which are essential for metabolism and normal growth and development. The impacts of disrupting thyroid hormone synthesis are greatest on pregnant women and their developing fetuses, infants, children, and individuals who have low levels of thyroid hormones.
Adverse health effects associated with perchlorate exposure are expected to be similar to those caused by iodine deficiency in humans. In areas of inadequate iodine intake, thyroid hormone synthesis and secretion decline, and the effects manifested in such iodine-deficient individuals, depending on the severity of the iodine deficiency, include: impairment in physical development, behavior, movement, speech, hearing, vision, and intelligence. Other effects of iodine deficiency also include signs and symptoms of hypothyroidism, enlargement of the thyroid gland, and possibly thyroid tumors. Impaired brain development and lower IQ were observed in children born even to mildly or moderately iodine deficient mothers. Recent studies on people and animal models indicate that perchlorate does interfere with thyroid function and may lead to similar effects.
In the absence of a federal drinking water standard, the Massachusetts Department of Environmental Protection (MA DEP) has developed a draft toxicity value and is working towards the development of standards for perchlorate, including a drinking water standard or Massachusetts Maximum Contaminant Level (MMCL) and cleanup standards for hazardous waste sites under the Massachusetts Contingency Plan (MCP, MGL Chapter 21E). The starting point for standard setting is a reference dose (RfD) or a toxicity value, for perchlorate. At this time, MA DEP has a recommended draft reference dose for perchlorate of 3 X 10-5 mg/kg-day, which was used to issue interim drinking water advice of 1 part per billion for the Bourne Water District, which if exceeded, triggers a requirement that sensitive subgroups be notified to not drink the water. The sensitive subgroups are pregnant women, infants, children up to the age of 12 and individuals with untreated hypothyroidism (individuals being treated for hypothyroidism should discuss their potential sensitivity to perchlorate with their doctor). Pending finalization of MA DEP’s RfD and related standards, this interim advice to Bourne will be used by MA DEP to guide decisions for other water supplies where perchlorate may be detected.
MA DEP’s draft RfD value was peer reviewed by an independent panel of scientists, who concurred that it was scientifically appropriate. It will be issued with MA DEP’s proposed revisions to the MGL Chapter 21E regulations and will undergo additional public review. After addressing additional comments received during the regulatory comment period, MA DEP will adopt a final reference dose and will proceed with standard setting for cleaning up waste sites. MA DEP will consider the results of current testing by water suppliers to determine if a MCL is needed, and if so, the levels measured along with information on the costs of testing and treatment will be factored into MA DEP’s decision. The National Academy of Science is reviewing the scientific information on perchlorate and MA DEP is following this work.