Perchlorate

From Academic Kids

Perchlorates are the salts of perchloric acid (HClO4). They occur both naturally and through manufacturing. They are commonly found in rocket fuel and explosives, often those used by the military. Ammonium perchlorate is a major ingredient of rocket fuel. They have also been used in airbags, fireworks, and Chilean fertilizers. Both potassium perchlorate (KClO4) and ammonium perchlorate (NH4ClO4) are used extensively within the pyrotechnics industry. Lithium perchlorate, which decomposes exothermically to give oxygen, is used in oxygen "candles" on spacecraft, submarines and in other esoteric situations where a reliable backup or supplimentary oxygen supply is needed. Most perchlorate salts are soluble in water, giving strongly oxidizing solutions.

Contents

Scientific definition

The perchlorate ion is ClO4-.

A perchlorate (compound) is a compound containing this group, with chlorine in oxidation state +7.

Perchlorate pollution

Perchlorates are a neurotoxin. They have been found to affect the thyroid gland in particular. When perchlorates enter the body, they block iodine uptake to the thyroid gland, which is needed to create thyroid hormones used by the body for metabolism as well as for growth and development in children. This can result in tumor growth on the thyroid gland. The chemical is particularly dangerous to women of childbearing age and developing fetuses, since it is known to cause mental retardation in unborn children as well as infants. Children up to 12 years old and people with hypothyroidism are also at serious risk. It is also believed that there may be a connection between perchlorates and the increase in learning disabilities over the past few decades.

Perchlorates have been found in both drinking water and groundwater in 35 states in the US according to the Environmental Protection Agency. In California, perchlorates were found in the water supply above the state's 2 microgram per liter (µg/L) (parts per billion, weight over volume (ppb w/v)) allowable level. In 2004, the chemical was also found in cow's milk in the area with an average level of 1.3 µg/L, which may have entered the cows through feeding on crops that had exposure to water containing perchlorates.Template:Ref These crops, which have been contaminated through soil and fertilizers containing perchlorates, included ones to be eaten by humans. In Massachusetts, perchlorates were found in groundwater in the area of Massachusetts Military Reservation on Cape Cod and other Department of Defense facilities. According to the Impact Area Groundwater Study Program [1] (http://www.groundwaterprogram.org/), the chemical has been detected as high as 5 µg/L in Massachusetts, well over the state regulation of 1 µg/L. As of 2004, towns that have been contaminated in Massachusetts include Bourne, Westford, Hadley, and Methuen.

As of 2004, the EPA has not yet made a nationwide regulation on the allowable level of perchlorates in water. They have suggested the level to be 1 µg/L, but this has been opposed by the Pentagon. The Pentagon has claimed that up to 200 µg/L should be allowed. The Pentagon has also asked the United States Congress to allow them to be exempted from environmental laws that cover the cleanup of explosive residues which cause perchlorate contamination.

On January 10, 2005, the National Academy of Sciences released a report prepared by the National Research Council that found, contrary to the EPA's preliminary findings, 20 ppb was safe for consumption by adults. The findings have met with controversy as the Natural Resources Defense Council released a series of documents obtained under FOIA that indicate a possible bias on the part of the committee designated to research the issue. Another organization, Environment California, released its own report, emphasizing the harmful effects of perchlorates on "expecting mothers, their developing fetuses and their infant children". It is too early to determine what, if any, regulatory impact the NAS study will have.

The NAS recommended that drinking water standards for babies be set at 4 micrograms per liter, for infants are more susceptible to the effects of perchlorate. This followed a study that suggested that human breast milk had an average of 10.5 µg/L of perchlorate.Template:Ref

Types of perchlorates

See Category:Perchlorates for a bigger list.

References

External links

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