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A perchlorate is a
chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
containing the perchlorate
ion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conve ...
, . The majority of perchlorates are commercially produced salts. They are mainly used as oxidizers for pyrotechnic devices and to control
static electricity Static electricity is an imbalance of electric charges within or on the surface of a material or between materials. The charge remains until it is able to move away by means of an electric current or electrical discharge. Static electricity is na ...
in
food packaging Food packaging is a packaging system specifically designed for food and represents one of the most important aspects among the processes involved in the food industry, as it provides protection from chemical, biological and physical alteratio ...
. Perchlorate contamination in food,
water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
, and other parts of the environment has been studied in the U.S. because of harmful effects on human health. Perchlorate ions are somewhat toxic to the thyroid gland. Most perchlorates are colorless solids that are
soluble In chemistry, solubility is the ability of a substance, the solute, to form a solution with another substance, the solvent. Insolubility is the opposite property, the inability of the solute to form such a solution. The extent of the solubi ...
in water. Four perchlorates are of primary commercial interest: ammonium perchlorate ,
perchloric acid Perchloric acid is a mineral acid with the formula H Cl O4. Usually found as an aqueous solution, this colorless compound is a stronger acid than sulfuric acid, nitric acid and hydrochloric acid. It is a powerful oxidizer when hot, but aqueous s ...
, potassium perchlorate and
sodium perchlorate Sodium perchlorate is the inorganic compound with the chemical formula Na ClO4. It is a white crystalline, hygroscopic solid that is highly soluble in water and in alcohol. It is usually encountered as the monohydrate. The compound is noteworth ...
. Perchlorate is the anion resulting from the dissociation of perchloric acid and its salts upon their dissolution in water. Many perchlorate salts are soluble in non-aqueous solutions.


Production

Perchlorate salts are produced industrially by the
oxidation Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a d ...
of aqueous solutions of
sodium chlorate Sodium chlorate is an inorganic compound with the chemical formula Na ClO3. It is a white crystalline powder that is readily soluble in water. It is hygroscopic. It decomposes above 300 °C to release oxygen and leaves sodium chloride. Sever ...
by electrolysis. This method is used to prepare
sodium perchlorate Sodium perchlorate is the inorganic compound with the chemical formula Na ClO4. It is a white crystalline, hygroscopic solid that is highly soluble in water and in alcohol. It is usually encountered as the monohydrate. The compound is noteworth ...
. The main application is for rocket fuel.Helmut Vogt, Jan Balej, John E. Bennett, Peter Wintzer, Saeed Akbar Sheikh, Patrizio Gallone "Chlorine Oxides and Chlorine Oxygen Acids" in ''Ullmann's Encyclopedia of Industrial Chemistry'' 2002, Wiley-VCH. The reaction of perchloric acid with bases, such as
ammonium hydroxide Ammonia solution, also known as ammonia water, ammonium hydroxide, ammoniacal liquor, ammonia liquor, aqua ammonia, aqueous ammonia, or (inaccurately) ammonia, is a solution of ammonia in water. It can be denoted by the symbols NH3(aq). Although ...
, give salts. The highly valued ammonium perchlorate can be produced electrochemically. Curiously, perchlorate can be produced by lightning discharges in the presence of chloride. Perchlorate has been detected in rain and snow samples from
Florida Florida is a state located in the Southeastern region of the United States. Florida is bordered to the west by the Gulf of Mexico, to the northwest by Alabama, to the north by Georgia, to the east by the Bahamas and Atlantic Ocean, and to ...
and
Lubbock, Texas Lubbock ( ) is the 10th-most populous city in the U.S. state of Texas and the seat of government of Lubbock County. With a population of 260,993 in 2021, the city is also the 85th-most populous in the United States. The city is in the northw ...
. It is also present in
Martian soil Martian soil is the fine regolith (a blanket of unconsolidated, loose, heterogeneous superficial deposits covering solid rock) found on the surface of Mars. Its properties can differ significantly from those of terrestrial soil, including its to ...
.


Uses

*The dominant use of perchlorates is as oxidizers in propellants for rockets, fireworks and highway flares. Of particular value is
ammonium perchlorate composite propellant Ammonium perchlorate composite propellant (APCP) is a solid-propellant rocket fuel. It differs from many traditional solid rocket propellants such as black powder or zinc-sulfur, not only in chemical composition and overall performance but a ...
as a component of solid rocket fuel. In a related but smaller application, perchlorates are used extensively within the pyrotechnics industry and in certain munitions and for the manufacture of matches. *Perchlorate is used to control
static electricity Static electricity is an imbalance of electric charges within or on the surface of a material or between materials. The charge remains until it is able to move away by means of an electric current or electrical discharge. Static electricity is na ...
in food packaging. Sprayed onto containers it stops statically charged food from clinging to plastic or paper/cardboard surface. *Niche uses include
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. Applications Inorga ...
, which decomposes exothermically to produce oxygen, useful in oxygen "candles" on spacecraft, submarines, and in other situations where a reliable backup oxygen supply is needed. *Potassium perchlorate has, in the past, been used therapeutically to help manage Graves' disease. It impedes production of the thyroid hormones that contain iodine.


Chemical properties

The perchlorate ion is the least reactive of the generalized
chlorates The chlorate anion has the formula ClO3-. 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 ...
. Perchlorate contains
chlorine Chlorine is a chemical element with the Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate betwee ...
in its highest oxidation number. A table of reduction potentials of the four
chlorates The chlorate anion has the formula ClO3-. 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 ...
shows that, contrary to expectation, perchlorate is the weakest oxidant among the four in water. These data show that the perchlorate and chlorate are stronger oxidizers in acidic conditions than in basic conditions. Gas phase measurements of heats of reaction (which allow computation of Δ''H''f°) of various chlorine oxides do follow the expected trend wherein exhibits the largest endothermic value of Δ''H''f° (238.1 kJ/mol) while exhibits the lowest endothermic value of Δ''H''f° (80.3 kJ/mol). The chlorine in the perchlorate anion is a
closed shell In atomic physics and quantum chemistry, the electron configuration is the distribution of electrons of an atom or molecule (or other physical structure) in atomic or molecular orbitals. For example, the electron configuration of the neon atom ...
atom and is well protected by the four oxygens. Most perchlorate compounds, especially salts of
electropositive Electronegativity, symbolized as , is the tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond. An atom's electronegativity is affected by both its atomic number and the d ...
metals such as
sodium perchlorate Sodium perchlorate is the inorganic compound with the chemical formula Na ClO4. It is a white crystalline, hygroscopic solid that is highly soluble in water and in alcohol. It is usually encountered as the monohydrate. The compound is noteworth ...
or potassium perchlorate, do not oxidize organic compounds until the mixture is heated. This property is useful in many applications, such as
flare A flare, also sometimes called a fusée, fusee, or bengala in some Latin-speaking countries, is a type of pyrotechnic that produces a bright light or intense heat without an explosion. Flares are used for distress signaling, illumination, ...
s, where ignition is required to initiate a reaction. Ammonium perchlorate is stable when pure but can form potentially explosive mixtures with reactive metals or organic compounds. The
PEPCON disaster On May 4, 1988, a fire followed by several explosions occurred at the Pacific Engineering and Production Company of Nevada (PEPCON) chemical plant in Henderson, Nevada. The disaster caused two fatalities, 372 injuries, and an estimated $100 mill ...
destroyed a production plant for ammonium perchlorate when a fire caused the ammonium perchlorate stored on site to react with the aluminum that the storage tanks were constructed with and explode. In solution, Ru(II) can reduce to , while V(II), V(III), Mo(III), Cr(II) and Ti(III) can reduce to .


Biology

Over 40 phylogenetically and metabolically diverse microorganisms capable of growth via perchlorate reduction have been isolated since 1996. Most originate from the Pseudomonadota but others include the
Bacillota The Bacillota (synonym Firmicutes) are a phylum of bacteria, most of which have gram-positive cell wall structure. The renaming of phyla such as Firmicutes in 2021 remains controversial among microbiologists, many of whom continue to use the earl ...
, '' Moorella perchloratireducens'' and ''Sporomusa'' sp., and the
archaeon Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebact ...
''
Archaeoglobus fulgidus ''Archaeoglobus'' is a genus of the phylum Euryarchaeota. ''Archaeoglobus'' can be found in high-temperature oil fields where they may contribute to oil field souring. Metabolism ''Archaeoglobus'' grow anaerobically at extremely high temperat ...
''. With the exception of ''A. fulgidus'', all known microbes that grow via perchlorate reduction utilize the enzymes
perchlorate reductase Perchlorate reductase is an enzyme that catalyzes the chemical reactions: :ClO4− + 2 AH2 \rightleftharpoons ClO2− + 2 A + 2 H2O and :ClO3− + AH2 \rightleftharpoons ClO2− + A + H2O Thus, the substrates of this enzyme are a reduced el ...
and
chlorite dismutase Chlorite dismutase, also known as Chlorite O2-lyase (), is an enzyme that catalyzes the chemical reaction : ClO → Cl− + O2 Reactions that generate oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It ...
, which collectively take perchlorate to innocuous chloride. In the process, free
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
() is generated.


Natural abundance


Terrestrial abundance

Naturally occurring perchlorate at its most abundant can be found commingled with deposits of sodium nitrate in the
Atacama Desert The Atacama Desert ( es, Desierto de Atacama) is a desert plateau in South America covering a 1,600 km (990 mi) strip of land on the Pacific coast, west of the Andes Mountains. The Atacama Desert is the driest nonpolar desert in th ...
of northern Chile. These deposits have been heavily mined as sources for nitrate-based fertilizers. Chilean nitrate is in fact estimated to be the source of around of perchlorate imported to the U.S. (1909–1997). Results from surveys of ground water, ice, and relatively unperturbed deserts have been used to estimate a "global inventory" of natural perchlorate presently on Earth.


On Mars

Perchlorate was detected in martian soil at the level of ~0.6% by weight. It is conjectured to exist as a mixture of 48% , 32% and 20% . isputed – discussThese salts, formed from perchlorates, act as
antifreeze An antifreeze is an additive which lowers the freezing point of a water-based liquid. An antifreeze mixture is used to achieve freezing-point depression for cold environments. Common antifreezes also increase the boiling point of the liquid, all ...
and substantially lower the
freezing point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depend ...
of water. Based on the temperature and pressure conditions on present-day Mars at the ''
Phoenix Phoenix most often refers to: * Phoenix (mythology), a legendary bird from ancient Greek folklore * Phoenix, Arizona, a city in the United States Phoenix may also refer to: Mythology Greek mythological figures * Phoenix (son of Amyntor), a ...
'' lander site, conditions would allow a perchlorate salt solution to be stable 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 is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...
and launch propellants consisting of ammonium perchlorate or
ammonium nitrate Ammonium nitrate is a chemical compound with the chemical formula . It is a white crystalline salt consisting of ions of ammonium and nitrate. It is highly soluble in water and hygroscopic as a solid, although it does not form hydrates. It is ...
. Sensors on board ''Phoenix'' found no traces of
ammonium nitrate Ammonium nitrate is a chemical compound with the chemical formula . It is a white crystalline salt consisting of ions of ammonium and nitrate. It is highly soluble in water and hygroscopic as a solid, although it does not form hydrates. It is ...
, and thus the nitrate in the quantities present in all three soil samples is indigenous to the Martian soil. Instead, the ''Viking'' found traces of ammonium perchlorate on the planet's surface in 1977. Perchlorate is widespread in Martian soils at concentrations between 0.5 and 1%. At such concentrations, perchlorate could be an important source of oxygen, but it could also become a critical chemical hazard to astronauts. In 2006, a mechanism was proposed for the formation of perchlorates that is particularly relevant to the discovery of perchlorate at the ''Phoenix'' lander site. It was shown that soils with high concentrations of
chloride The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride salts ...
converted to perchlorate in the presence of titanium dioxide and sunlight/ultraviolet light. The conversion was reproduced in the lab using chloride-rich soils from
Death Valley Death Valley is a desert valley in Eastern California, in the northern Mojave Desert, bordering the Great Basin Desert. During summer, it is the Highest temperature recorded on Earth, hottest place on Earth. Death Valley's Badwater Basin is the ...
. Other experiments have demonstrated that the formation of perchlorate is associated with wide band gap semiconducting oxides. In 2014, it was shown that perchlorate and chlorate can be produced from chloride minerals under Martian conditions via UV using only NaCl and silicate. Further findings of perchlorate and chlorate in the Martian meteorite EETA79001 and by the Mars ''Curiosity'' rover in 2012-2013 support the notion that perchlorates are globally distributed throughout the Martian surface. With concentrations approaching 0.5% and exceeding toxic levels on Martian soil, Martian perchlorates would present a serious challenge to
human settlement In geography, statistics and archaeology, a settlement, locality or populated place is a community in which people live. The complexity of a settlement can range from a minuscule number of dwellings grouped together to the largest of ci ...
, as well as microorganisms. On the other hand, the perchlorate would provide a convenient source of
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
for the settlements. On September 28, 2015, NASA announced that analyses of spectral data from the Compact Reconnaissance Imaging Spectrometer for Mars instrument (CRISM) on board the Mars Reconnaissance Orbiter from four different locations where recurring slope lineae (RSL) are present found evidence for hydrated salts. The hydrated salts most consistent with the spectral absorption features are magnesium perchlorate, magnesium chlorate and sodium perchlorate. The findings strongly support the hypothesis that RSL form as a result of contemporary water activity on Mars.


Contamination in environment

Perchlorates are of concern because of uncertainties about toxicity and health effects at low levels in drinking water, impact on ecosystems, and indirect exposure pathways for humans due to accumulation in vegetables. They are water-soluble, exceedingly mobile in aqueous systems, and can persist for many decades under typical groundwater and surface water conditions. They originate from disinfectants, bleaching agents, herbicides, and mostly from rocket propellants. It is a byproduct of the production of rocket fuel and fireworks. Removal and recovery methods of these compounds from explosives and rocket propellants include high-pressure water washout, which generates aqueous ammonium perchlorate.


In U.S. drinking water

Low levels of perchlorate have been detected in both drinking water and
groundwater Groundwater is the water present beneath Earth's surface in rock and soil pore spaces and in the fractures of rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit of rock or an unconsolidate ...
in 26 states in the U.S., according to the Environmental Protection Agency (EPA). The chemical has been detected at levels as high as 5 µg/L at
Joint Base Cape Cod The Joint Base Cape Cod is a state-designated joint base created by the Commonwealth of Massachusetts and the United States War Department in 1935. Governor James Curley signed the state bill to allocate and purchase land for a military facilit ...
(formerly Massachusetts Military Reservation), well over the
Massachusetts Massachusetts (Massachusett language, Massachusett: ''Muhsachuweesut assachusett writing systems, məhswatʃəwiːsət'' English: , ), officially the Commonwealth of Massachusetts, is the most populous U.S. state, state in the New England ...
state regulation of 2 µg/L. Fireworks are also a source of perchlorate in lakes. At the Olin Flare Facility,
Morgan Hill, California Morgan Hill is a city in Santa Clara County, California, at the southern tip of Silicon Valley, in the San Francisco Bay Area. Morgan Hill is an affluent residential community, the seat of several high-tech companies, and a dining, entertainme ...
perchlorate contamination beneath the former flare manufacturing plant 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 The Santa Clara Valley Water District (also known as Valley Water) provides stream stewardship, wholesale water supply and flood protection for Santa Clara County, California, in the southern San Francisco Bay Area. The district encompasses all of ...
had confirmed a groundwater plume currently extending over nine miles through residential and agricultural communities. The California Regional Water Quality Control Board and the
Santa Clara Valley Water District The Santa Clara Valley Water District (also known as Valley Water) provides stream stewardship, wholesale water supply and flood protection for Santa Clara County, California, in the southern San Francisco Bay Area. The district encompasses all of ...
have engaged in a major outreach effort, a
water well test A well test is conducted to evaluate the amount of water that can be pumped from a particular water well. More specifically, a well test will allow prediction of the maximum rate at which water can be pumped from a well, and the distance that the ...
ing program has been underway for about 1,200 residential, municipal, and agricultural wells. Large ion exchange treatment units are operating in three public water supply systems which include seven municipal wells with perchlorate detection. The
potentially responsible parties Superfund is a United States federal environmental remediation program established by the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA). The program is administered by the Environmental Protection Agen ...
, Olin Corporation and Standard Fuse Incorporated, have been supplying bottled water to nearly 800 households with private wells, and the Regional Water Quality Control Board has been overseeing cleanup efforts. The source of perchlorate in California was mainly attributed to two manufacturers in the southeast portion of the Las Vegas Valley in Nevada, where perchlorate has been produced for industrial use. This led to perchlorate release into
Lake Mead Lake Mead is a reservoir formed by the Hoover Dam on the Colorado River in the Southwestern United States. It is located in the states of Nevada and Arizona, east of Las Vegas. It is the largest reservoir in the US in terms of water capacity. L ...
in Nevada and the
Colorado River The Colorado River ( es, Río Colorado) is one of the principal rivers (along with the Rio Grande) in the Southwestern United States and northern Mexico. The river drains an expansive, arid drainage basin, watershed that encompasses parts of ...
which affected regions of Nevada, California and
Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...
, where water from this reservoir is used for consumption, irrigation and recreation for approximately half the population of these states.
Lake Mead Lake Mead is a reservoir formed by the Hoover Dam on the Colorado River in the Southwestern United States. It is located in the states of Nevada and Arizona, east of Las Vegas. It is the largest reservoir in the US in terms of water capacity. L ...
has been attributed as the source of 90% of the perchlorate in Southern Nevada's drinking water. Based on sampling, perchlorate has been affecting 20 million people, with highest detection in
Texas Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...
, southern California,
New Jersey New Jersey is a state in the Mid-Atlantic and Northeastern regions of the United States. It is bordered on the north and east by the state of New York; on the east, southeast, and south by the Atlantic Ocean; on the west by the Delaware ...
, and Massachusetts, but intensive sampling of the
Great Plains The Great Plains (french: Grandes Plaines), sometimes simply "the Plains", is a broad expanse of flatland in North America. It is located west of the Mississippi River and east of the Rocky Mountains, much of it covered in prairie, steppe, an ...
and other middle state regions may lead to revised estimates with additional affected regions. An action level of 18 μg/L has been adopted by several affected states.


In food

In 2004, the chemical was found in cow's milk in California at an average level of 1.3
parts per billion In science and engineering, the parts-per notation is a set of pseudo-units to describe small values of miscellaneous dimensionless quantities, e.g. mole fraction or mass fraction. Since these fractions are quantity-per-quantity measures, they ...
(ppb, or µg/L), which may have entered the cows through feeding on crops exposed to water containing perchlorates.
Associated Press The Associated Press (AP) is an American non-profit news agency headquartered in New York City. Founded in 1846, it operates as a cooperative, unincorporated association. It produces news reports that are distributed to its members, U.S. newspa ...
.
Toxic chemical found in California milk
. ''
NBC News NBC News is the news division of the American broadcast television network NBC. The division operates under NBCUniversal Television and Streaming, a division of NBCUniversal, which is, in turn, a subsidiary of Comcast. The news division's var ...
''. June 22, 2004.
A 2005 study suggested human breast milk had an average of 10.5 µg/L of perchlorate.


In minerals and other natural occurrences

In some places, there is no clear source of perchlorate, and it may be naturally occurring. Natural perchlorate on Earth was first identified in terrestrial nitrate deposits of the
Atacama Desert The Atacama Desert ( es, Desierto de Atacama) is a desert plateau in South America covering a 1,600 km (990 mi) strip of land on the Pacific coast, west of the Andes Mountains. The Atacama Desert is the driest nonpolar desert in th ...
in Chile as early as the 1880s and for a long time considered a unique perchlorate source. The perchlorate released from historic use of Chilean nitrate based fertilizer which the U.S.imported by the hundreds of tons in the early 19th century can still be found in some groundwater sources of the United States. Recent improvements in analytical sensitivity using ion chromatography based techniques have revealed a more widespread presence of natural perchlorate, particularly in subsoils of Southwest USA, salt evaporites in California and Nevada, Pleistocene groundwater in New Mexico, and even present in extremely remote places such as
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...
. The data from these studies and others indicate that natural perchlorate is globally deposited on Earth with the subsequent accumulation and transport governed by the local hydrologic conditions. Despite its importance to environmental contamination, the specific source and processes involved in natural perchlorate production remain poorly understood. Laboratory experiments in conjunction with isotopic studies have implied that perchlorate may be produced on earth by oxidation of chlorine species through pathways involving ozone or its photochemical products. Other studies have suggested that perchlorate can also be created by lightning activated oxidation of chloride aerosols (e.g., chloride in sea salt sprays), and ultraviolet or thermal oxidation of chlorine (e.g., bleach solutions used in swimming pools) in water.


From fertilizers

Although perchlorate as an environmental contaminant is usually associated with the storage, manufacture, and testing of solid rocket motors, contamination of perchlorate has been focused in the use of fertilizer and its perchlorate release into ground water. Fertilizer leaves perchlorate anions to leak into the ground water and threaten the water supplies of many regions in the US. One of the main sources of perchlorate contamination from fertilizer use was found to come from the fertilizer derived from Chilean
caliche Caliche () is a sedimentary rock, a hardened natural cement of calcium carbonate that binds other materials—such as gravel, sand, clay, and silt. It occurs worldwide, in aridisol and mollisol soil orders—generally in arid or semiarid regions ...
(calcium carbonate), because Chile has rich source of naturally occurring perchlorate anion. Perchlorate in the solid fertilizer ranged from 0.7 to 2.0 mg g−1, variation of less than a factor of 3 and it is estimated that sodium nitrate fertilizers derived from Chilean caliche contain approximately 0.5–2 mg g−1 of perchlorate anion. The direct ecological effect of perchlorate is not well known; its impact can be influenced by factors including rainfall and irrigation, dilution, natural attenuation, soil adsorption, and bioavailability. Quantification of perchlorate concentrations in fertilizer components via ion chromatography revealed that in horticultural fertilizer components contained perchlorate ranging between 0.1 and 0.46%. Perchlorate concentration was the highest in Chilean nitrate, ranging from 3.3 to 3.98%.


Cleanup

There have been many attempts to eliminate perchlorate contamination. Current remediation technologies for perchlorate have downsides of high costs and difficulty in operation. Thus, there have been interests in developing systems that would offer economic and green alternatives.


Treatment ex situ and in situ

Several technologies can remove perchlorate, via treatments
ex situ Svalbard GLOBAL SEED BANK, an ''ex situ'' conservation. ''Ex situ'' conservation literally means, "off-site conservation". It is the process of protecting an endangered species, variety or breed, of plant or animal outside its natural habitat; ...
(away from the location) and
in situ ''In situ'' (; often not italicized in English) is a Latin phrase that translates literally to "on site" or "in position." It can mean "locally", "on site", "on the premises", or "in place" to describe where an event takes place and is used in ...
(at the location). Ex situ treatments include ion exchange using perchlorate-selective or nitrite-specific resins,
bioremediation Bioremediation broadly refers to any process wherein a biological system (typically bacteria, microalgae, fungi, and plants), living or dead, is employed for removing environmental pollutants from air, water, soil, flue gasses, industrial effluent ...
using packed-bed or fluidized-bed
bioreactor A bioreactor refers to any manufactured device or system that supports a biologically active environment. In one case, a bioreactor is a vessel in which a chemical process is carried out which involves organisms or biochemically active substances ...
s, and membrane technologies via
electrodialysis Electrodialysis (ED) is used to transport salt ions from one solution through ion-exchange membranes to another solution under the influence of an applied electric potential difference. This is done in a configuration called an electrodialysis ...
and
reverse osmosis Reverse osmosis (RO) is a water purification process that uses a partially permeable membrane to separate ions, unwanted molecules and larger particles from drinking water. In reverse osmosis, an applied pressure is used to overcome osmotic pre ...
. In ex situ treatment via ion exchange, contaminants are attracted and adhere to the ion exchange resin because such resins and ions of contaminants have opposite charge. As the ion of the contaminant adheres to the resin, another charged ion is expelled into the water being treated, in which then ion is exchanged for the contaminant. Ion exchange technology has advantages of being well-suitable for perchlorate treatment and high volume throughput but has a downside that it does not treat
chlorinated solvents An organochloride, organochlorine compound, chlorocarbon, or chlorinated hydrocarbon is an organic compound containing at least one covalently bonded atom of chlorine. The chloroalkane class ( alkanes with one or more hydrogens substituted by chlo ...
. In addition, ex situ technology of liquid phase carbon adsorption is employed, where granular activated carbon (GAC) is used to eliminate low levels of perchlorate and pretreatment may be required in arranging GAC for perchlorate elimination. In situ treatments, such as bioremediation via perchlorate-selective microbes and permeable reactive barrier, are also being used to treat perchlorate. In situ bioremediation has advantages of minimal above-ground
infrastructure Infrastructure is the set of facilities and systems that serve a country, city, or other area, and encompasses the services and facilities necessary for its economy, households and firms to function. Infrastructure is composed of public and priv ...
and its ability to treat chlorinated solvents, perchlorate, nitrate, and
RDX RDX (abbreviation of "Research Department eXplosive") or hexogen, among other names, is an organic compound with the formula (O2N2CH2)3. It is a white solid without smell or taste, widely used as an explosive. Chemically, it is classified as a ...
simultaneously. However, it has a downside that it may negatively affect secondary water quality. In situ technology of
phytoremediation Phytoremediation technologies use living plants to clean up soil, air and water contaminated with hazardous contaminants. It is defined as "the use of green plants and the associated microorganisms, along with proper soil amendments and agronom ...
could also be utilized, even though perchlorate phytoremediation mechanism is not fully founded yet. Bioremediation using perchlorate-reducing bacteria, which reduce perchlorate ions to harmless chloride, has also been proposed.


Health effects


Thyroid inhibition

Perchlorate is a potent competitive inhibitor of the thyroid
sodium-iodide symporter The sodium/iodide cotransporter, also known as the sodium/iodide symporter (NIS), is a protein that in humans is encoded by the ''SLC5A5'' gene. It is a transmembrane glycoprotein with a molecular weight of 87 k Da and 13 transmembrane domains, w ...
. Thus, it has been used to treat
hyperthyroidism Hyperthyroidism is the condition that occurs due to excessive production of thyroid hormones by the thyroid gland. Thyrotoxicosis is the condition that occurs due to excessive thyroid hormone of any cause and therefore includes hyperthyroidis ...
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 large amounts perchlorate interferes with
iodine Iodine is a chemical element with the symbol I and atomic number 53. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at , and boils to a vi ...
uptake into the
thyroid The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans it is in the neck and consists of two connected lobes. The lower two thirds of the lobes are connected by a thin band of tissue called the thyroid isthmus. The thy ...
gland. In adults, the thyroid gland helps regulate the
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
by releasing hormones, while in children, the thyroid helps in proper development. The
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, in its 2005 report, ''Health Implications of Perchlorate Ingestion'', emphasized that this effect, also known as Iodide Uptake Inhibition (IUI) is not an adverse health effect. However, in January 2008, California's Department of Toxic Substances Control stated that perchlorate is becoming a serious threat to human health and water resources. In 2010, the EPA's Office of the Inspector General determined that the agency's own perchlorate reference dose of 24.5 parts per billion protects against all human biological effects from exposure. This finding was due to a significant shift in policy at the EPA in basing its risk assessment on non-adverse effects such as IUI instead of adverse effects. The Office of the Inspector General also found that because the EPA's perchlorate reference dose is conservative and protective of human health further reducing perchlorate exposure below the reference dose does not effectively lower risk. Perchlorate affects only thyroid hormone. Because it is neither stored nor
metabolized Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
, effects of perchlorate on the thyroid gland are reversible, though effects on brain development from lack of thyroid hormone in
fetus A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal deve ...
es,
newborn An infant or baby is the very young offspring of human beings. ''Infant'' (from the Latin word ''infans'', meaning 'unable to speak' or 'speechless') is a formal or specialised synonym for the common term ''baby''. The terms may also be used to ...
s, and children are not. Toxic effects of perchlorate have been studied in a survey of industrial plant workers who had been exposed to perchlorate, compared to a control group of other industrial plant workers who had no known exposure to perchlorate. After undergoing multiple tests, workers exposed to perchlorate were found to have a significant systolic blood pressure rise compared to the workers who were not exposed to perchlorate, as well as a significant decreased thyroid function compared to the control workers. 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 The thyroid, or thyroid gland, is an endocrine gland in vertebrates. In humans it is in the neck and consists of two connected lobes. The lower two thirds of the lobes are connected by a thin band of tissue called the thyroid isthmus. The thy ...
gland's ability to absorb iodine from the
blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the c ...
stream ("iodide uptake inhibition", thus perchlorate is a known
goitrogen Goitrogens are substances that disrupt the production of thyroid hormones. This triggers the pituitary to release thyroid-stimulating hormone (TSH), which then promotes the growth of thyroid tissue, eventually leading to goiter. Goitrogenic dru ...
). The EPA converted this dose into a
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. The EPA defines an oral reference dose (abbreviated RfD) as: es ...
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 and consumes of drinking water per day over a lifetime. In 2006, a study reported a statistical association between environmental levels of perchlorate and changes in thyroid hormones of women with low iodine. The study authors were careful to point out that hormone levels in all the study subjects remained within normal ranges. The authors also indicated that they did not originally normalize their findings for creatinine, which would have essentially accounted for fluctuations in the concentrations of one-time urine samples like those used in this study. When the Blount research was re-analyzed with the creatinine adjustment made, the study population limited to women of reproductive age, and results not shown in the original analysis, any remaining association between the results and perchlorate intake disappeared. Soon after the revised Blount Study was released, Robert Utiger, a doctor with the Harvard Institute of Medicine, testified before the US Congress and stated: "I continue to believe that that reference dose, 0.007 milligrams per kilo (24.5 ppb), which includes a factor of 10 to protect those who might be more vulnerable, is quite adequate." At a 2013 presentation of a previously unpublished study, it was suggested that environmental exposure to perchlorate in pregnant women with hypothyroidism may be associated with significant risk of low IQ in their children."Perchlorate Levels in Pregnancy Linked to Low Childhood IQ"
by Nancy A. Melville, October 22, 2013


Lung toxicity

Some studies suggest that perchlorate has pulmonary toxic effects as well. Studies have been performed on rabbits where perchlorate has been injected into the trachea. The lung tissue was removed and analyzed, and it was found that perchlorate injected lung tissue showed several adverse effects when compared to the control group that had been intratracheally injected with saline. Adverse effects included inflammatory infiltrates, alveolar collapse, subpleural thickening, and lymphocyte proliferation.


Aplastic anemia

In the early 1960s, potassium perchlorate used to treat Graves disease was implicated in the development of aplastic anemia—a condition where the bone marrow fails to produce new
blood cell A blood cell, also called a hematopoietic cell, hemocyte, or hematocyte, is a cell produced through hematopoiesis and found mainly in the blood. Major types of blood cells include red blood cells (erythrocytes), white blood cells (leukocytes) ...
s in sufficient quantity—in thirteen patients, seven of whom died. Retrieved on April 3, 2009 through
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.
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.


Regulation in the U.S.


Water

In 1998, perchlorate was included in the EPA Contaminant Candidate List, primarily due to its detection in California drinking water. In 2003, a
federal district court The United States district courts are the trial courts of the U.S. federal judiciary. There is one district court for each federal judicial district, which each cover one U.S. state or, in some cases, a portion of a state. Each district cou ...
in California found that the
Comprehensive Environmental Response, Compensation and Liability Act Superfund is a United States federal environmental remediation program established by the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA). The program is administered by the Environmental Protection Agency ...
applied, because perchlorate is ignitable, and therefore was a "characteristic" hazardous waste. In 2003, California's legislature enacted AB 826, the Perchlorate Contamination Prevention Act of 2003, requiring California's
Department of Toxic Substances Control The California Department of Toxic Substances Control (or DTSC) is an agency of the government of the state of California. The mission of the DTSC is to protect public health and the environment from toxic harm. DTSC is part of the California En ...
(DTSC) to adopt regulations specifying best management practices for perchlorate and perchlorate-containing substances. On December 31, 2005, the "Perchlorate Best Management Practices" were adopted and became operative on July 1, 2006. In early 2006, EPA issued a "Cleanup Guidance" and recommended a
Drinking Water Equivalent Level The Safe Drinking Water Act (SDWA) is the principal federal law in the United States intended to ensure safe drinking water for the public. Pursuant to the act, the Environmental Protection Agency (EPA) is required to set standards for drinking w ...
(DWEL) for perchlorate of 24.5 µg/L. Both DWEL and Cleanup Guidance were based on a 2005 review of the existing research by the
National Academy of Sciences The National Academy of Sciences (NAS) is a United States nonprofit, non-governmental organization. NAS is part of the National Academies of Sciences, Engineering, and Medicine, along with the National Academy of Engineering (NAE) and the Nati ...
(NAS). Lacking a federal drinking water standard, several states subsequently published their own standards for perchlorate including Massachusetts in 2006 and California in 2007. Other states, including Arizona, Maryland, Nevada, New Mexico, New York, and Texas have established non-enforceable, advisory levels for perchlorate. In 2008 EPA issued an interim drinking water health advisory for perchlorate and with it a guidance and analysis concerning the impacts on the environment and drinking water. California also issued guidance regarding perchlorate use. Both the
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and some environmental groups voiced questions about the NAS report, but no credible science has emerged to challenge the NAS findings. In February 2008, the U.S.
Food and Drug Administration The United States Food and Drug Administration (FDA or US FDA) is a List of United States federal agencies, federal agency of the United States Department of Health and Human Services, Department of Health and Human Services. The FDA is respon ...
(FDA) reported that U.S. toddlers on average are being exposed to more than half of EPA's safe dose from food alone. In March 2009, a
Centers for Disease Control The Centers for Disease Control and Prevention (CDC) is the national public health agency of the United States. It is a United States federal agency, under the Department of Health and Human Services, and is headquartered in Atlanta, Georgi ...
study found 15 brands of infant formula contaminated with perchlorate. Combined with existing perchlorate drinking water contamination, infants could be at risk for perchlorate exposure above the levels considered safe by EPA. On February 11, 2011, EPA determined that perchlorate meets the
Safe Drinking Water Act The Safe Drinking Water Act (SDWA) is the principal federal law in the United States intended to ensure safe drinking water for the public. Pursuant to the act, the Environmental Protection Agency (EPA) is required to set standards for drinking w ...
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 system Public water system is a regulatory term used in the United States and Canada, referring to certain utilities and organizations providing drinking water. United States The US Safe Drinking Water Act and derivative legislation define "public water ...
s with a frequency and at levels that it presents a public health concern. Since then EPA has continued to determine what level of contamination is appropriate. EPA prepared extensive responses to submitted public comments. In 2016 the
Natural Resources Defense Council The Natural Resources Defense Council (NRDC) is a United States-based 501(c)(3) non-profit international environmental advocacy group, with its headquarters in New York City and offices in Washington D.C., San Francisco, Los Angeles, Chicago, Bo ...
(NRDC) filed a lawsuit to accelerate EPA's regulation of perchlorate. In 2019 EPA proposed a Maximum Contaminant Level of 0.056 mg/L for public water systems. On June 18, 2020 EPA announced that it was withdrawing its 2019 proposal and its 2011 regulatory determination, stating that it had taken "proactive steps" with state and local governments to address perchlorate contamination. In September 2020 NRDC filed suit against EPA for its failure to regulate perchlorate, and stated that 26 million people may be affected by perchlorate in their drinking water. On March 31, 2022, the EPA announced that a review confirmed its 2020 decision.


Other

FDA approved perchlorate use in food packaging in 2005.


References


External links


NAS Report: The Health Effects of Perchlorate Ingestion

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


* ttp://www.yourlawyer.com/practice/news.htm?story_id=5959&topic=Perchlorate State Threatening To Sue Military Over Water Pollution
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, 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
{{Thyroid hormone receptor modulators * Pyrotechnic oxidizers Non-coordinating anions Oxidizing agents Endocrine disruptors