Perchlorate
Encyclopedia
Perchlorates are the salts derived from perchloric acid
(H
Cl
O4
). They occur both naturally and through manufacturing. They have been used as a medicine for more than 50 years to treat thyroid gland disorders. They are used extensively within the pyrotechnics industry, and ammonium perchlorate
is also a component of solid rocket fuel
. 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 supplementary oxygen supply is needed. Most perchlorate salts are soluble in water.
is . The ion has a molecular mass of 99.45 amu
.
A perchlorate (compound) is a compound containing this group, with chlorine
in oxidation state
+7.
This shows that the chlorates are stronger oxidizers in acidic conditions than basic conditions, while chlorine is unchanged.
Gas phase measurements of heats of reaction (which allow computation of ΔHf°) of various chlorine oxides do follow the expected trend wherein Cl2O7 exhibits the largest endothermic value of ΔHf° (238.1 kJ/mol) while Cl2O exhibits the lowest endothermic value of ΔHf° (80.3 kJ/mol).
The central chlorine in the perchlorate anion is a closed shell atom and is well protected by the four oxygens. Hence, perchlorate reacts sluggishly. Most perchlorate compounds, especially salts of electropositive metals such as sodium perchlorate
or potassium perchlorate
, are slow to react unless heated. This property is useful in many applications, such as flare
s, where the device should not explode, or even catch fire spontaneously.
Mixtures of perchlorates with organic compounds are more reactive. Although they do not usually catch fire or explode unless heated, there are a number of exceptions. Large amounts of improperly stored ammonium perchlorate led to the PEPCON disaster
, in which an explosion destroyed one of the two large-scale production plants for ammonium perchlorate
in the US.
, if a Roman numeral in brackets follows the word "chlorate", this indicates the oxyanion
contains chlorine in the indicated oxidation state, namely
Using this convention, "chlorate" means any chlorine oxyanion. Commonly, "chlorate" refers only to the oxyanion where chlorine is in the +5 oxidation state.
of the space shuttle
contain 350 metric tons of ammonium perchlorate
each.
since the 1950s. At very high doses (70,000–300,000 ppb
) the administration of potassium perchlorate was considered the standard of care in the United States, and remains the approved pharmacologic intervention for many countries. In the early 1960s, potassium perchlorate was implicated in the development of aplastic anemia
—a condition where the bone marrow
fails to produce new blood cell
s in sufficient quantity—in thirteen patients, seven of whom died. Subsequent investigations have indicated the connection between administration of potassium perchlorate and development of aplastic anemia to be "equivocable at best", which means that the benefit of treatment, if it is the only known treatment, outweighs the risk, and it appeared a contaminant poisoned the 13.
Involving ozone
or hydroxyl radical
s as oxidizer for sodium chloride
from the sea and are somewhat similar to the formation processes of iodates also present in the atmosphere.
As most perchlorates are readily soluble in water, an accumulation of perchlorates in the environment only occurs in arid areas with little or no rainfall. It is known since the beginning of the 20th century that the Atacama Desert
contains not only large amounts of nitrate
s but also trace amounts of perchlorates. The concentration varies but is in the mg/kg range. The dry southwest of the United States also shows accumulation of perchlorates. With the use of nitrates from the Atacama Desert, so called Chile saltpeter as fertilizer
the chlorates were also distributed into the environment. As the Chile saltpeter was mostly substituted by nitrates produced by the Haber Bosch process, which contains no perchlorates this source of perchlorates nearly vanished.
In 2006, a mechanism for the formation of perchlorates that is particularly apropos to the discovery of perchlorate at the Mars Phoenix lander site was proposed. It was shown that soils with high concentrations of natural salts could have some of their chloride converted to perchlorate in the presence of sunlight and/or ultraviolet light. The mechanism was reproduced in the lab using chloride-rich soils from Death Valley
. In 2010, perchlorate was found at the 1000 ppb levels in a vast section of Antarctica, with implications that it is formed naturally and globally on Earth and probably on Mars. Recent isotopic studies have shown that natural perchlorate is produced on Earth by the oxidation of chlorine species through pathways involving tropospheric ozone or its photochemical products.
of chloride salts or by the neutralization of perchloric acid
, which is produced by electrolysis of chlorine, with ammonia
or other base
.
The electrolysis involves the following reactions:
The industrial scale synthesis for sodium perchlorates starts from sodium chloride
. If the electrolysis is not done with the method described at chlorine
, but a mixing of the chlorine
evolved and the sodium hydroxide is allowed, the reaction mentioned above takes place. The hypochlorite
and the chlorate
are intermediates in this process.
in 26 states in the U.S., according to the Environmental Protection Agency
. In 2004, the chemical was also found in cow's milk
in California with an average level of 1.3 parts per billion ("ppb" or µg/L), which may have entered the cows through feeding on crops that had exposure to water containing perchlorates. According to the Impact Area Groundwater Study Program, the chemical has been detected as high as 5 µg/L in Massachusetts, well over the state regulation of 2 µg/L.
In some places, perchlorate is detected because of contamination from industrial sites that use or manufacture it. In other places, there is no clear source of perchlorate. In those areas it may be naturally occurring, or could be present because of the use of Chilean fertilizers, which were imported to the U.S. by the hundreds of tons in the early 19th century. One recent area of research has even suggested that perchlorate can be created when lightning strikes a body of water, and perchlorates are created as a byproduct of chlorine generators used in swimming pool chlorination systems. In 2010, perchlorate was found at the 1000ppb levels in a vast section of Antarctica, with implications that it is formed naturally and globally on Earth and, it is presumed, on Mars most likely by photochemical reactions in the atmosphere].
Fireworks are also a source of perchlorate in lakes.
criteria for regulation as a contaminant. The Agency found that perchlorate may have an adverse effect on the health of persons and is known to occur in public water systems with a frequency and at levels that it presents a public health concern. As a result of EPA's regulatory determination, it begins a process to determine what level of contamination is the appropriate level for regulation. EPA prepared, as part of its regulatory determination, extensive responses to submitted public comments. The "docket ID" for EPA's regulatory action is EPA-HQ-OW-2009-0297 and can be found on regulations.gov.
Prior to issuance of its regulatory determination, EPA issued a recommended Drinking Water Equivalent Level (DWEL) for perchlorate of 24.5 µg/L. In early 2006, EPA issued a “Cleanup Guidance” for this same amount. Both the DWEL and the Cleanup Guidance were based on a thorough review of the existing research by the National Academy of Science (NAS). This followed numerous other studies, including one that suggested human breast milk
had an average of 10.5 µg/L of perchlorate. Both the Pentagon and some environmental groups have voiced questions about the NAS report, but no credible science has emerged to challenge the NAS findings. In February 2008, U.S. Food and Drug Administration said that U.S. toddlers on average are being exposed to more than half of the U.S. EPA's safe dose from food alone. In March 2009, a Centers for Disease Control study found 15 brands of infant formula contaminated with perchlorate. Combined with existing perchlorate drinking water contamination, infants could be at risk for exposure to perchlorate above the levels considered safe by E.P.A.
The US Environmental Protection Agency has issued substantial guidance and analysis concerning the impacts of perchlorate on the environment as well as drinking water. http://www.epa.gov/safewater/contaminants/unregulated/perchlorate.html California has also issued guidance regarding perchlorate use. http://www.cdph.ca.gov/certlic/drinkingwater/Pages/Perchlorate.aspx
Several states have enacted drinking water standard for perchlorate including Massachusetts in 2006. California's legislature enacted AB 826, the Perchlorate Contamination Prevention Act of 2003, requiring California's Department of Toxic Substance Control (DTSC) to adopt regulations specifying best management practices for perchlorate and perchlorate-containing substances. The Perchlorate Best Management Practices were adopted on December 31, 2005 and became operative on July 1, 2006. http://www.dtsc.ca.gov/HazardousWaste/Perchlorate/ California issued drinking water standards in 2007. Several other states, including Arizona, Maryland, Nevada, New Mexico, New York, and Texas have established non-enforceable, advisory levels for perchlorate.
Courts have been called upon to take action with regard to perchlorate. For example, in 2003, a federal district court in California found that Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) applied because perchlorate is ignitable and therefore a “characteristic” hazardous waste. (see Castaic Lake Water Agency v. Whittaker, 272 F. Supp. 2d 1053, 1059-61 (C.D. Cal. 2003)).
One example of perchlorate related problems was found at the Olin Flare Facility, Morgan Hill, California - Perchlorate contamination beneath a former flare manufacturing plant in California was first discovered in 2000, several years after the plant had closed. The plant had used potassium perchlorate as one of the ingredients during its 40 years of operation. By late 2003, the state of California and the Santa Clara Valley Water District had confirmed a groundwater plume currently extending over nine miles through residential and agricultural communities.
The Regional Water Quality Control Board and the Santa Clara Valley Water District have engaged in a major outreach effort that has received extensive press and community response. A well testing program is underway for approximately 1,200 residential, municipal, and agricultural wells in the area. Large ion exchange treatment units are operating in three public water supply systems that include seven municipal wells where perchlorate has been detected. The potentially responsible parties, Olin Corporation and Standard Fuse Incorporated, are supplying bottled water to nearly 800 households with private wells. The Regional Water Quality Control Board is overseeing potentially responsible party (PRP) cleanup efforts.http://www.epa.gov/region09/toxic/perchlorate/per_ca.html#olin
The two production sites of PEPCON and Kerr-McGee
in Henderson, Nevada
, which were the biggest producers until the explosion of PEPCON
in 1988 and the closure of the Kerr McGee plant in 1998, leaked significant amounts of perchlorates into the Las Vegas Wash
and from there into Lake Mead
and the Colorado River
.
The disposal of unused rocket motors and ammunition has led to contamination by perchlorates of several military installations.
as well as two recently identified Firmicutes
, Moorella perchloratireducens and Sporomusa sp.
The NAS found that perchlorate affects only the thyroid gland. It is not stored in the body, it is not metabolized
, and any effects of perchlorate on the thyroid gland are fully reversible once exposure stops. There has been some concern on perchlorate's effects on fetus
es, newborns and children, but several peer-reviewed studies on children and newborns also provide reason to believe that low levels of perchlorate do not pose a threat to these populations. On October 1, 2004, the American Thyroid Association (ATA) reported that perchlorate may not be as harmful to newborns, pregnant women and other adults as previously thought.
A study involving healthy adult volunteers determined that at levels above 0.007 milligrams per kilogram per day (mg/(kg·d)), perchlorate can temporarily inhibit the thyroid
gland’s ability to absorb iodine
from the blood
stream ("iodide uptake inhibition", thus perchlorate is a known goitrogen
). The EPA converted this dose into a reference dose
of 0.0007 mg/(kg·d) by dividing this level by the standard intraspecies uncertainty factor of 10. The agency then calculated a "drinking water equivalent level" of 24.5 ppb by assuming a person weighs 70 kilograms (154 pounds) and consumes 2 liters (68 ounces) of drinking water per day over a lifetime. Thus, 25 ppb was set as the recommended drinking water standard (the DWEL). For that reason, most media reports call this the "safe" level of exposure. The NAS report also stated additional research would be helpful, but emphasized that the existing database on perchlorate was sufficient to make its reference dose recommendation and ensure it would be protective for everyone.
Recent research, however, has shown inhibition of iodide uptake in the thyroids of women at much lower levels, levels attainable from normally contaminated water and milk.
The extreme temperatures found on Mars typically lead to either crystallization or evaporation of water, making it difficult to imagine that water could be found in liquid form. The salts formed from perchlorates discovered at the Phoenix landing site act as “anti-freeze” and will substantially lower the freezing point of water. Based on the temperature and pressure conditions on present-day Mars at the Phoenix lander site, conditions would allow a perchlorate salt solution to be present in liquid form for a few hours each day during the summer.
The possibility that the perchlorate was a contaminant brought from Earth has been eliminated by several lines of evidence. The Phoenix retro-rockets used ultra pure hydrazine
and launch propellants consisted of ammonium perchlorate. Sensors on board Phoenix found no traces of ammonium, and thus the perchlorate in the quantities present in all three soil samples is indigenous to the martian soil.
Perchloric acid
Perchloric acid is the inorganic compound with the formula HClO4. Usually encountered as an aqueous solution, this colourless compound is a strong acid comparable in strength to sulfuric and nitric acids. It is a powerful oxidizer, but its aqueous solutions up to appr. 70% are remarkably inert,...
(H
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
Cl
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
O4
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
). They occur both naturally and through manufacturing. They have been used as a medicine for more than 50 years to treat thyroid gland disorders. They are used extensively within the pyrotechnics industry, and ammonium perchlorate
Ammonium perchlorate
Ammonium perchlorate is an inorganic compound with the formula NH4ClO4. It is the salt of perchloric acid and ammonia. It is a powerful oxidizer, which is why its main use is in solid propellants...
is also a component of solid rocket fuel
Ammonium Perchlorate Composite Propellant
Ammonium perchlorate composite propellant is a modern solid rocket propellant used in both manned and unmanned rocket vehicles. It differs from many traditional solid rocket propellants such as black powder or Zinc-Sulfur, not only in chemical composition and overall performance, but also by the...
. Lithium perchlorate
Lithium perchlorate
Lithium perchlorate is the inorganic compound with the formula LiClO4. This white or colourless crystalline salt is noteworthy for its high solubility in many solvents. It exists both in anhydrous form and as a trihydrate.-Uses:...
, which decomposes exothermically to give oxygen, is used in oxygen "candles"
Chemical oxygen generator
A chemical oxygen generator is a device releasing oxygen created by a chemical reaction. The oxygen source is usually an inorganic superoxide, chlorate, or perchlorate. A promising group of oxygen sources are ozonides. The generators are usually ignited mechanically, by a firing pin, and the...
on spacecraft, submarines and in other esoteric situations where a reliable backup or supplementary oxygen supply is needed. Most perchlorate salts are soluble in water.
Chemical definition
The chemical notation for the perchlorate ionIon
An ion is an atom or molecule in which the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge. The name was given by physicist Michael Faraday for the substances that allow a current to pass between electrodes in a...
is . The ion has a molecular mass of 99.45 amu
Atomic mass unit
The unified atomic mass unit or dalton is a unit that is used for indicating mass on an atomic or molecular scale. It is defined as one twelfth of the rest mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state, and has a value of...
.
A perchlorate (compound) is a compound containing this group, with chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
in oxidation state
Oxidation state
In chemistry, the oxidation state is an indicator of the degree of oxidation of an atom in a chemical compound. The formal oxidation state is the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. Oxidation states are typically represented by...
+7.
- Ammonium perchlorateAmmonium perchlorateAmmonium perchlorate is an inorganic compound with the formula NH4ClO4. It is the salt of perchloric acid and ammonia. It is a powerful oxidizer, which is why its main use is in solid propellants...
, NH4ClO4 - Caesium perchlorate, CsClO4
- Lithium perchlorateLithium perchlorateLithium perchlorate is the inorganic compound with the formula LiClO4. This white or colourless crystalline salt is noteworthy for its high solubility in many solvents. It exists both in anhydrous form and as a trihydrate.-Uses:...
, LiClO4 - Magnesium perchlorateMagnesium perchlorateMagnesium perchlorate is a powerful oxidizing agent, with the formula Mg2.Magnesium perchlorate decomposes at 250 °C. The heat of formation is -568.90 kJ mol-1....
, Mg(ClO4)2 - Perchloric acidPerchloric acidPerchloric acid is the inorganic compound with the formula HClO4. Usually encountered as an aqueous solution, this colourless compound is a strong acid comparable in strength to sulfuric and nitric acids. It is a powerful oxidizer, but its aqueous solutions up to appr. 70% are remarkably inert,...
, HClO4 - Potassium perchloratePotassium perchloratePotassium perchlorate is the inorganic salt with the chemical formula KClO4. Like other perchlorates, this salt is a strong oxidizer and potentially reacts with many organic substances...
, KClO4 - Rubidium perchlorateRubidium perchlorateRubidium perchlorate, RbClO4, is the perchlorate of rubidium. It is an oxidizing agent, as are all perchlorates.It has two allotropes. One, below 279 °C crystallizes in orthorhombic crystal system with lattice constants a = 0.927 nm, b = 0.581 nm, c = 0.753 nm...
, RbClO4 - Silver perchlorateSilver perchlorateSilver perchlorate is the chemical compound with the formula AgClO4. This white solid forms a monohydrate and is mildly deliquescent. It is a useful source of the Ag+ ion, although the presence of perchlorate presents risks.-Solubility:...
, AgClO4 - Sodium perchlorateSodium perchlorateSodium perchlorate is the inorganic compound with the chemical formula NaClO4. It is the most soluble of the common perchlorate salts. It is a white crystalline, hygroscopic solid that is highly soluble in water and in alcohol...
, NaClO4
Reactivity as an oxidant
The perchlorate ion is the least reactive oxidizer of the generalized chlorates. This appears to be a paradox, since higher oxidation numbers are expected to be progressively stronger oxidizers, and less stable. A table of reduction potentials of the four chlorates shows that, contrary to expectation, perchlorate is the weakest oxidant among the four in water.| Half-reaction | E° (V) |
|---|---|
| H+ + HOCl + e– → ½Cl2(g) + H2O |
1.63 |
| 3H+ + HOClO + 3e– → ½Cl2(g) + 2H2O |
1.64 |
| 6H+ + ClO3– + 5e– → ½Cl2(g) + 3H2O |
1.47 |
| 8H+ + ClO4– + 7e– → ½Cl2(g) + 4H2O |
1.42 |
| ½Cl2(g) + e– → Cl– |
1.36 |
| ClO– + H2O + 2e– → Cl– + 2OH– |
0.89 |
| ClO2– + 2H2O + 4e– → Cl– + 4OH– |
0.78 |
| ClO3– + 3H2O + 6e– → Cl– + 6OH– |
0.63 |
| ClO4– + 4H2O + 8e– → Cl– + 8OH– |
0.56 |
This shows that the chlorates are stronger oxidizers in acidic conditions than basic conditions, while chlorine is unchanged.
Gas phase measurements of heats of reaction (which allow computation of ΔHf°) of various chlorine oxides do follow the expected trend wherein Cl2O7 exhibits the largest endothermic value of ΔHf° (238.1 kJ/mol) while Cl2O exhibits the lowest endothermic value of ΔHf° (80.3 kJ/mol).
The central chlorine in the perchlorate anion is a closed shell atom and is well protected by the four oxygens. Hence, perchlorate reacts sluggishly. Most perchlorate compounds, especially salts of electropositive metals such as sodium perchlorate
Sodium perchlorate
Sodium perchlorate is the inorganic compound with the chemical formula NaClO4. It is the most soluble of the common perchlorate salts. It is a white crystalline, hygroscopic solid that is highly soluble in water and in alcohol...
or potassium perchlorate
Potassium perchlorate
Potassium perchlorate is the inorganic salt with the chemical formula KClO4. Like other perchlorates, this salt is a strong oxidizer and potentially reacts with many organic substances...
, are slow to react unless heated. This property is useful in many applications, such as flare
Flare (pyrotechnic)
A flare, also sometimes called a fusee, is a type of pyrotechnic that produces a brilliant light or intense heat without an explosion. Flares are used for signalling, illumination, or defensive countermeasures in civilian and military applications...
s, where the device should not explode, or even catch fire spontaneously.
Mixtures of perchlorates with organic compounds are more reactive. Although they do not usually catch fire or explode unless heated, there are a number of exceptions. Large amounts of improperly stored ammonium perchlorate led to the PEPCON disaster
PEPCON disaster
The PEPCON disaster was an industrial disaster that occurred in Henderson, Nevada on May 4, 1988 at the Pacific Engineering Production Company of Nevada plant. The chemical fire and subsequent explosions claimed two lives, injured 372 people, and caused an estimated US$100 million of damage...
, in which an explosion destroyed one of the two large-scale production plants for ammonium perchlorate
Ammonium perchlorate
Ammonium perchlorate is an inorganic compound with the formula NH4ClO4. It is the salt of perchloric acid and ammonia. It is a powerful oxidizer, which is why its main use is in solid propellants...
in the US.
Other oxyanions
Using Stock nomenclatureStock nomenclature
Stock nomenclature for inorganic compounds is a widely used system of chemical nomenclature developed by the German chemist Alfred Stock and first published in 1919...
, if a Roman numeral in brackets follows the word "chlorate", this indicates the oxyanion
Oxyanion
An oxyanion or oxoanion is a chemical compound with the generic formula AxOyz− . Oxoanions are formed by a large majority of the chemical elements. The formulae of simple oxoanions are determined by the octet rule...
contains chlorine in the indicated oxidation state, namely
| Common name | Stock name | Oxidation state | Formula |
|---|---|---|---|
| Hypochlorite Hypochlorite The hypochlorite ion, also known as chlorate anion is ClO−. A hypochlorite compound is a chemical compound containing this group, with chlorine in oxidation state +1.Hypochlorites are the salts of hypochlorous acid... |
Chlorate(I) | +1 | ClO− |
| Chlorite Chlorite The chlorite ion is ClO2−. A chlorite is a compound that contains this group,with chlorine in oxidation state +3. Chlorites are also known as salts of chlorous acid.-Oxidation states:... |
Chlorate(III) | +3 | ClO2− |
| Chlorate Chlorate The chlorate anion has the formula ClO. In this case, the chlorine atom is in the +5 oxidation state. "Chlorate" can also refer to chemical compounds containing this anion; chlorates are the salts of chloric acid. "Chlorate", when followed by a roman numeral in parentheses, e.g... |
Chlorate(V) | +5 | ClO3− |
| Perchlorate | Chlorate(VII) | +7 | ClO4− |
Using this convention, "chlorate" means any chlorine oxyanion. Commonly, "chlorate" refers only to the oxyanion where chlorine is in the +5 oxidation state.
Oxidizer
The high oxygen content and the high stability of perchlorates make them ideal oxidizers for fireworks and airbags and as key compounds in solid rocket fuel. The solid rocket boostersSpace Shuttle Solid Rocket Booster
The Space Shuttle Solid Rocket Boosters were the pair of large solid rockets used by the United States' NASA Space Shuttle during the first two minutes of powered flight. Together they provided about 83% of liftoff thrust for the Space Shuttle. They were located on either side of the rusty or...
of the space shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
contain 350 metric tons of ammonium perchlorate
Ammonium perchlorate
Ammonium perchlorate is an inorganic compound with the formula NH4ClO4. It is the salt of perchloric acid and ammonia. It is a powerful oxidizer, which is why its main use is in solid propellants...
each.
Automotive
Perchlorate is used in airbags, seat belt pre-tensioner, TPMS (tire pressure monitor system) valve sensors, batteries for keyless entry system—mentioned in Hyundai TSB 07-00-001 dated 02-07Medical applications
Perchlorate has been used as a medication to treat hyperthyroidismHyperthyroidism
Hyperthyroidism is the term for overactive tissue within the thyroid gland causing an overproduction of thyroid hormones . Hyperthyroidism is thus a cause of thyrotoxicosis, the clinical condition of increased thyroid hormones in the blood. Hyperthyroidism and thyrotoxicosis are not synonymous...
since the 1950s. At very high doses (70,000–300,000 ppb
PPB
PPB can stand for:* Party political broadcast, a type of political programming in the United Kingdom* parts-per-billion, a unit of concentration* Portland Police Bureau, a police agency for the city of Portland...
) the administration of potassium perchlorate was considered the standard of care in the United States, and remains the approved pharmacologic intervention for many countries. In the early 1960s, potassium perchlorate was implicated in the development of aplastic anemia
Aplastic anemia
Aplastic anemia is a condition where bone marrow does not produce sufficient new cells to replenish blood cells. The condition, per its name, involves both aplasia and anemia...
—a condition where the bone marrow
Bone marrow
Bone marrow is the flexible tissue found in the interior of bones. In humans, bone marrow in large bones produces new blood cells. On average, bone marrow constitutes 4% of the total body mass of humans; in adults weighing 65 kg , bone marrow accounts for approximately 2.6 kg...
fails to produce new blood cell
Blood cell
A blood cell, also called a hematocyte, is a cell normally found in blood. In mammals, these fall into three general categories:* red blood cells — Erythrocytes* white blood cells — Leukocytes* platelets — Thrombocytes...
s in sufficient quantity—in thirteen patients, seven of whom died. Subsequent investigations have indicated the connection between administration of potassium perchlorate and development of aplastic anemia to be "equivocable at best", which means that the benefit of treatment, if it is the only known treatment, outweighs the risk, and it appeared a contaminant poisoned the 13.
Natural formation of perchlorates
There are several well-documented mechanisms for natural formation of perchlorate.Involving ozone
Ozone
Ozone , or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope...
or hydroxyl radical
Hydroxyl radical
The hydroxyl radical, •OH, is the neutral form of the hydroxide ion . Hydroxyl radicals are highly reactive and consequently short-lived; however, they form an important part of radical chemistry. Most notably hydroxyl radicals are produced from the decomposition of hydroperoxides or, in...
s as oxidizer for sodium chloride
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...
from the sea and are somewhat similar to the formation processes of iodates also present in the atmosphere.
As most perchlorates are readily soluble in water, an accumulation of perchlorates in the environment only occurs in arid areas with little or no rainfall. It is known since the beginning of the 20th century that the Atacama Desert
Atacama Desert
The Atacama Desert is a plateau in South America, covering a strip of land on the Pacific coast, west of the Andes mountains. It is, according to NASA, National Geographic and many other publications, the driest desert in the world...
contains not only large amounts of nitrate
Nitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
s but also trace amounts of perchlorates. The concentration varies but is in the mg/kg range. The dry southwest of the United States also shows accumulation of perchlorates. With the use of nitrates from the Atacama Desert, so called Chile saltpeter as fertilizer
Fertilizer
Fertilizer is any organic or inorganic material of natural or synthetic origin that is added to a soil to supply one or more plant nutrients essential to the growth of plants. A recent assessment found that about 40 to 60% of crop yields are attributable to commercial fertilizer use...
the chlorates were also distributed into the environment. As the Chile saltpeter was mostly substituted by nitrates produced by the Haber Bosch process, which contains no perchlorates this source of perchlorates nearly vanished.
In 2006, a mechanism for the formation of perchlorates that is particularly apropos to the discovery of perchlorate at the Mars Phoenix lander site was proposed. It was shown that soils with high concentrations of natural salts could have some of their chloride converted to perchlorate in the presence of sunlight and/or ultraviolet light. The mechanism was reproduced in the lab using chloride-rich soils from Death Valley
Death Valley
Death Valley is a desert valley located in Eastern California. Situated within the Mojave Desert, it features the lowest, driest, and hottest locations in North America. Badwater, a basin located in Death Valley, is the specific location of the lowest elevation in North America at 282 feet below...
. In 2010, perchlorate was found at the 1000 ppb levels in a vast section of Antarctica, with implications that it is formed naturally and globally on Earth and probably on Mars. Recent isotopic studies have shown that natural perchlorate is produced on Earth by the oxidation of chlorine species through pathways involving tropospheric ozone or its photochemical products.
Industrial production
Perchlorates are produced either by electrolysisElectrolysis
In chemistry and manufacturing, electrolysis is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction...
of chloride salts or by the neutralization of perchloric acid
Perchloric acid
Perchloric acid is the inorganic compound with the formula HClO4. Usually encountered as an aqueous solution, this colourless compound is a strong acid comparable in strength to sulfuric and nitric acids. It is a powerful oxidizer, but its aqueous solutions up to appr. 70% are remarkably inert,...
, which is produced by electrolysis of chlorine, with ammonia
Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...
or other base
Base (chemistry)
For the term in genetics, see base A base in chemistry is a substance that can accept hydrogen ions or more generally, donate electron pairs. A soluble base is referred to as an alkali if it contains and releases hydroxide ions quantitatively...
.
The electrolysis involves the following reactions:
- 3 Cl2 + 6 OH− → 5 Cl− + ClO3− + 3 H2O
- ClO3− + H2O → ClO4− + 2 H+ + 2 e-
The industrial scale synthesis for sodium perchlorates starts from sodium chloride
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...
. If the electrolysis is not done with the method described at chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
, but a mixing of the chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
evolved and the sodium hydroxide is allowed, the reaction mentioned above takes place. The hypochlorite
Hypochlorite
The hypochlorite ion, also known as chlorate anion is ClO−. A hypochlorite compound is a chemical compound containing this group, with chlorine in oxidation state +1.Hypochlorites are the salts of hypochlorous acid...
and the chlorate
Chlorate
The chlorate anion has the formula ClO. In this case, the chlorine atom is in the +5 oxidation state. "Chlorate" can also refer to chemical compounds containing this anion; chlorates are the salts of chloric acid. "Chlorate", when followed by a roman numeral in parentheses, e.g...
are intermediates in this process.
Perchlorate-free product development
In response to concerns regarding perchlorate, efforts have been undertaken to produce substitutes for products using perchlorate. For example, efforts to create perchlorate-free flares include both spectrally balanced decoy and colored flare compositions that include nitrate or oxide oxidizers. Because nitrate oxidizers are less reactive than perchlorate oxidizers, high-energy fuels have used to compensate for this energy shortfall. Some of these high-energy fuels were produced using mechanical alloying technology.Environmental presence
Low levels of perchlorate have been detected in both drinking water and groundwaterGroundwater
Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...
in 26 states in the U.S., according to the Environmental Protection Agency
United States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...
. In 2004, the chemical was also found in cow's milk
Milk
Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...
in California with an average level of 1.3 parts per billion ("ppb" or µg/L), which may have entered the cows through feeding on crops that had exposure to water containing perchlorates. According to the Impact Area Groundwater Study Program, the chemical has been detected as high as 5 µg/L in Massachusetts, well over the state regulation of 2 µg/L.
In some places, perchlorate is detected because of contamination from industrial sites that use or manufacture it. In other places, there is no clear source of perchlorate. In those areas it may be naturally occurring, or could be present because of the use of Chilean fertilizers, which were imported to the U.S. by the hundreds of tons in the early 19th century. One recent area of research has even suggested that perchlorate can be created when lightning strikes a body of water, and perchlorates are created as a byproduct of chlorine generators used in swimming pool chlorination systems. In 2010, perchlorate was found at the 1000ppb levels in a vast section of Antarctica, with implications that it is formed naturally and globally on Earth and, it is presumed, on Mars most likely by photochemical reactions in the atmosphere].
Fireworks are also a source of perchlorate in lakes.
Regulatory Activity
On February 11, 2011, the U.S. Environmental Protection Agency (EPA) issued a "regulatory determination" that perchlorate meets the Safe Drinking Water ActSafe Drinking Water Act
The Safe Drinking Water Act is the principle federal law in the United States intended to ensure safe drinking water for the public. Pursuant to the act, the Environmental Protection Agency is required to set standards for drinking water quality and oversee all states, localities, and water...
criteria for regulation as a contaminant. The Agency found that perchlorate may have an adverse effect on the health of persons and is known to occur in public water systems with a frequency and at levels that it presents a public health concern. As a result of EPA's regulatory determination, it begins a process to determine what level of contamination is the appropriate level for regulation. EPA prepared, as part of its regulatory determination, extensive responses to submitted public comments. The "docket ID" for EPA's regulatory action is EPA-HQ-OW-2009-0297 and can be found on regulations.gov.
Prior to issuance of its regulatory determination, EPA issued a recommended Drinking Water Equivalent Level (DWEL) for perchlorate of 24.5 µg/L. In early 2006, EPA issued a “Cleanup Guidance” for this same amount. Both the DWEL and the Cleanup Guidance were based on a thorough review of the existing research by the National Academy of Science (NAS). This followed numerous other studies, including one that suggested human breast milk
Breast milk
Breast milk, more specifically human milk, is the milk produced by the breasts of a human female for her infant offspring...
had an average of 10.5 µg/L of perchlorate. Both the Pentagon and some environmental groups have voiced questions about the NAS report, but no credible science has emerged to challenge the NAS findings. In February 2008, U.S. Food and Drug Administration said that U.S. toddlers on average are being exposed to more than half of the U.S. EPA's safe dose from food alone. In March 2009, a Centers for Disease Control study found 15 brands of infant formula contaminated with perchlorate. Combined with existing perchlorate drinking water contamination, infants could be at risk for exposure to perchlorate above the levels considered safe by E.P.A.
The US Environmental Protection Agency has issued substantial guidance and analysis concerning the impacts of perchlorate on the environment as well as drinking water. http://www.epa.gov/safewater/contaminants/unregulated/perchlorate.html California has also issued guidance regarding perchlorate use. http://www.cdph.ca.gov/certlic/drinkingwater/Pages/Perchlorate.aspx
Several states have enacted drinking water standard for perchlorate including Massachusetts in 2006. California's legislature enacted AB 826, the Perchlorate Contamination Prevention Act of 2003, requiring California's Department of Toxic Substance Control (DTSC) to adopt regulations specifying best management practices for perchlorate and perchlorate-containing substances. The Perchlorate Best Management Practices were adopted on December 31, 2005 and became operative on July 1, 2006. http://www.dtsc.ca.gov/HazardousWaste/Perchlorate/ California issued drinking water standards in 2007. Several other states, including Arizona, Maryland, Nevada, New Mexico, New York, and Texas have established non-enforceable, advisory levels for perchlorate.
Courts have been called upon to take action with regard to perchlorate. For example, in 2003, a federal district court in California found that Comprehensive Environmental Response, Compensation and Liability Act (CERCLA) applied because perchlorate is ignitable and therefore a “characteristic” hazardous waste. (see Castaic Lake Water Agency v. Whittaker, 272 F. Supp. 2d 1053, 1059-61 (C.D. Cal. 2003)).
One example of perchlorate related problems was found at the Olin Flare Facility, Morgan Hill, California - Perchlorate contamination beneath a former flare manufacturing plant in California was first discovered in 2000, several years after the plant had closed. The plant had used potassium perchlorate as one of the ingredients during its 40 years of operation. By late 2003, the state of California and the Santa Clara Valley Water District had confirmed a groundwater plume currently extending over nine miles through residential and agricultural communities.
The Regional Water Quality Control Board and the Santa Clara Valley Water District have engaged in a major outreach effort that has received extensive press and community response. A well testing program is underway for approximately 1,200 residential, municipal, and agricultural wells in the area. Large ion exchange treatment units are operating in three public water supply systems that include seven municipal wells where perchlorate has been detected. The potentially responsible parties, Olin Corporation and Standard Fuse Incorporated, are supplying bottled water to nearly 800 households with private wells. The Regional Water Quality Control Board is overseeing potentially responsible party (PRP) cleanup efforts.http://www.epa.gov/region09/toxic/perchlorate/per_ca.html#olin
The two production sites of PEPCON and Kerr-McGee
Kerr-McGee
The Kerr-McGee Corporation, founded in 1929, was an energy company involved in the exploration and production of oil and gas. On June 23, 2006, Houston-based Anadarko Petroleum Corporation agreed to acquire Kerr-McGee in an all-cash transaction totaling $16.5 billion plus the assumption of $2.6...
in Henderson, Nevada
Henderson, Nevada
-Demographics:According to the 2000 census, there were 175,381 people, 66,331 households, and 47,095 families residing in the city. The population density was 2,200.8 people per square mile . There were 71,149 housing units at an average density of 892.8 per square mile...
, which were the biggest producers until the explosion of PEPCON
PEPCON disaster
The PEPCON disaster was an industrial disaster that occurred in Henderson, Nevada on May 4, 1988 at the Pacific Engineering Production Company of Nevada plant. The chemical fire and subsequent explosions claimed two lives, injured 372 people, and caused an estimated US$100 million of damage...
in 1988 and the closure of the Kerr McGee plant in 1998, leaked significant amounts of perchlorates into the Las Vegas Wash
Las Vegas Wash
Las Vegas Wash is a 12 mile-long channel which feeds most of Las Vegas Valley's excess water into Lake Mead. The wash is sometimes called an urban river, and it exists in its present capacity because of an urban population. The wash also works in a systemic conjunction with the pre-existing...
and from there into Lake Mead
Lake Mead
Lake Mead is the largest reservoir in the United States. It is located on the Colorado River about southeast of Las Vegas, Nevada, in the states of Nevada and Arizona. Formed by water impounded by the Hoover Dam, it extends behind the dam, holding approximately of water.-History:The lake was...
and the Colorado River
Colorado River
The Colorado River , is a river in the Southwestern United States and northwestern Mexico, approximately long, draining a part of the arid regions on the western slope of the Rocky Mountains. The watershed of the Colorado River covers in parts of seven U.S. states and two Mexican states...
.
The disposal of unused rocket motors and ammunition has led to contamination by perchlorates of several military installations.
Biological functions
Over 40 phylogenetically and metabolically diverse microorganisms capable of perchlorate reduction have been isolated since 1996, including members of the ProteobacteriaProteobacteria
The Proteobacteria are a major group of bacteria. They include a wide variety of pathogens, such as Escherichia, Salmonella, Vibrio, Helicobacter, and many other notable genera....
as well as two recently identified Firmicutes
Firmicutes
The Firmicutes are a phylum of bacteria, most of which have Gram-positive cell wall structure. A few, however, such as Megasphaera, Pectinatus, Selenomonas and Zymophilus, have a porous pseudo-outer-membrane that causes them to stain Gram-negative...
, Moorella perchloratireducens and Sporomusa sp.
Health effects
Perchlorate adversely affects human health by interfering with iodine uptake into the thyroid gland. In adults, the thyroid gland helps regulate the metabolism by releasing hormones, while in children, the thyroid helps in proper development. Perchlorate is becoming a serious threat to human health and water resources.The NAS found that perchlorate affects only the thyroid gland. It is not stored in the body, it is not metabolized
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
, and any effects of perchlorate on the thyroid gland are fully reversible once exposure stops. There has been some concern on perchlorate's effects on fetus
Fetus
A fetus is a developing mammal or other viviparous vertebrate after the embryonic stage and before birth.In humans, the fetal stage of prenatal development starts at the beginning of the 11th week in gestational age, which is the 9th week after fertilization.-Etymology and spelling variations:The...
es, newborns and children, but several peer-reviewed studies on children and newborns also provide reason to believe that low levels of perchlorate do not pose a threat to these populations. On October 1, 2004, the American Thyroid Association (ATA) reported that perchlorate may not be as harmful to newborns, pregnant women and other adults as previously thought.
A study involving healthy adult volunteers determined that at levels above 0.007 milligrams per kilogram per day (mg/(kg·d)), perchlorate can temporarily inhibit the thyroid
Thyroid
The thyroid gland or simply, the thyroid , in vertebrate anatomy, is one of the largest endocrine glands. The thyroid gland is found in the neck, below the thyroid cartilage...
gland’s ability to absorb iodine
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
from the blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
stream ("iodide uptake inhibition", thus perchlorate is a known goitrogen
Goitrogen
Goitrogens are substances that suppress the function of the thyroid gland by interfering with iodine uptake, which can, as a result, cause an enlargement of the thyroid, i.e., a goitre.-Goitrogenic drugs and chemicals:...
). The EPA converted this dose into a reference dose
Reference dose
A reference dose is the United States Environmental Protection Agency's maximum acceptable oral dose of a toxic substance. Reference doses are most commonly determined for pesticides...
of 0.0007 mg/(kg·d) by dividing this level by the standard intraspecies uncertainty factor of 10. The agency then calculated a "drinking water equivalent level" of 24.5 ppb by assuming a person weighs 70 kilograms (154 pounds) and consumes 2 liters (68 ounces) of drinking water per day over a lifetime. Thus, 25 ppb was set as the recommended drinking water standard (the DWEL). For that reason, most media reports call this the "safe" level of exposure. The NAS report also stated additional research would be helpful, but emphasized that the existing database on perchlorate was sufficient to make its reference dose recommendation and ensure it would be protective for everyone.
Recent research, however, has shown inhibition of iodide uptake in the thyroids of women at much lower levels, levels attainable from normally contaminated water and milk.
Discovery of perchlorate on Mars
In June 2008, the Wet Chemistry Laboratory (WCL) on board the 2007 Phoenix Mars Lander performed the first wet chemical analysis of martian soil. The analyses on three samples, two from the surface and one from 5 cm depth, revealed a slightly alkaline soil and low levels of salts typically found on Earth. Most unexpected though was the presence of ~ 0.6 wt % perchlorate (ClO4-), most likely as a Mg(ClO4)2 phase.The extreme temperatures found on Mars typically lead to either crystallization or evaporation of water, making it difficult to imagine that water could be found in liquid form. The salts formed from perchlorates discovered at the Phoenix landing site act as “anti-freeze” and will substantially lower the freezing point of water. Based on the temperature and pressure conditions on present-day Mars at the Phoenix lander site, conditions would allow a perchlorate salt solution to be present in liquid form for a few hours each day during the summer.
The possibility that the perchlorate was a contaminant brought from Earth has been eliminated by several lines of evidence. The Phoenix retro-rockets used ultra pure hydrazine
Hydrazine
Hydrazine is an inorganic compound with the formula N2H4. It is a colourless flammable liquid with an ammonia-like odor. Hydrazine is highly toxic and dangerously unstable unless handled in solution. Approximately 260,000 tons are manufactured annually...
and launch propellants consisted of ammonium perchlorate. Sensors on board Phoenix found no traces of ammonium, and thus the perchlorate in the quantities present in all three soil samples is indigenous to the martian soil.
External links
- NAS Report: The Health Effects of Perchlorate Ingestion
- Facts and truth about perchlorate (Sponsored by the chemical companies that produce it)
- NRDC's criticism of NAS report
- Environment California report (Executive Summary with link to full text)
- Macho Moms: Perchlorate pollutant masculinizes fish: Science News Online, Aug. 12, 2006
- New Scientist Space Blog: Phoenix discovery may be bad for Mars life
- "State Threatening To Sue Military Over Water Pollution", Associated PressAssociated PressThe Associated Press is an American news agency. The AP is a cooperative owned by its contributing newspapers, radio and television stations in the United States, which both contribute stories to the AP and use material written by its staff journalists...
, May 19, 2003. - "Health Effects Of Perchlorate From Spent Rocket", SpaceDaily.com, July 11, 2002.
- = Dept of Defense, Dept of Energy, and US Environmental Protection Agency's Strategic Environmental Research and Development Program, Elimination of Perchlorate Oxidizers from Pyrotechnic Flare Compositions, 2009