Chlorine cycle

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Biogeochemical chlorine cycle: chlorine is cycled through the atmosphere, mantle, crust, pedosphere, cryosphere, and oceans as chloride and organic chlorine. Arrows are labeled in fluxes of chlorine in Tg (teragram) per year. Estimates are also made of natural chlorine contents in Earth's reservoirs and the form they are stored in. The mantle constitutes the largest reservoir of chlorine at 22 x 10 teragrams. Chlorine is cycled through the pedosphere via biotic and abiotic processes that lead to this reservoir acting as a sink. Chlorine biogeochemical cycle.png
Biogeochemical chlorine cycle: chlorine is cycled through the atmosphere, mantle, crust, pedosphere, cryosphere, and oceans as chloride and organic chlorine. Arrows are labeled in fluxes of chlorine in Tg (teragram) per year. Estimates are also made of natural chlorine contents in Earth's reservoirs and the form they are stored in. The mantle constitutes the largest reservoir of chlorine at 22 x 10 teragrams. Chlorine is cycled through the pedosphere via biotic and abiotic processes that lead to this reservoir acting as a sink.

The chlorine cycle (Cl) is the biogeochemical cycling of chlorine through the atmosphere, hydrosphere, biosphere, and lithosphere. Chlorine is most commonly found as inorganic chloride ions, or a number of chlorinated organic forms. [1] [2] Over 5,000 biologically produced chlorinated organics have been identified. [3]

Contents

The cycling of chlorine into the atmosphere and creation of chlorine compounds by anthropogenic sources has major impacts on climate change and depletion of the ozone layer. Chlorine plays essential roles in many biological processes, including numerous roles in the human body. [6] It also acts as an essential co-factor in enzymes involved in plant photosynthesis. [3]

Troposphere

Chlorine plays a large role in atmospheric cycling and climate, including, but not limited to chlorofluorocarbons (CFCs). [7] The major flux of chlorine into the troposphere comes from sea salt aerosol spray. Both organic and inorganic chlorine is transferred into the troposphere from the oceans. [2] Biomass combustion is another source of both organic and inorganic forms of chlorine to the troposphere from the terrestrial reservoir. [2] Typically, organic chlorine forms are highly un-reactive and will be transferred to the stratosphere from the troposphere. The major flux of chlorine from the troposphere is via surface deposition into water systems.

Hydrosphere

Oceans are the largest source of chlorine in the Earth's hydrosphere. [2] In the hydrosphere, chlorine exists primarily as chloride due to the high solubility of the Cl− ion. [3] The majority of chlorine fluxes are within the hydrosphere due to chloride ions' solubility and reactivity within water systems. [2] The cryosphere is able to retain some chlorine deposited by rainfall and snow, but the majority is eluted into oceans.

Lithosphere

The largest reservoir of chlorine resides in the lithosphere, where 2.2×1022 kg of global chlorine is found in Earth's mantle. [2] Volcanic eruptions will sporadically release high levels of chlorine as HCl into the troposphere, but the majority of the terrestrial chlorine flux comes from seawater sources mixing with the mantle. [2]

Organically bound chlorine is as abundant as chloride ions in terrestrial soil systems, or the pedosphere. [1] Discovery of multiple Cl-mediating genes in microorganisms and plants indicate that numerous biotic processes use chloride and produce organic chlorinated compounds, as well as many abiotic processes. [1] [3] [4] [5] These chlorinated compounds can then be volatilized or leached out of soils, which makes the overall soil environment a global sink of chlorine. [1] Multiple anaerobic prokaryotes have been found to contain genes and show activity for chlorinated organic volatilization [8]

Biological processes

Chlorine's ability to completely dissociate in water is also why it is an essential electrolyte in many biological processes. [6] Chlorine, along with phosphorus, is the sixth most common element in organic matter. [1] Cells utilize chloride to balance pH and maintain turgor pressure at equilibrium. The high electrical conductivity of Cl− ions are essential for neuron signalling in the brain and regulate many other essential functions in biology [9]

Anthropogenic chlorinated compounds

The depleting effects of chlorofluorocarbons (CFCs) on ozone over Antarctica has been studied extensively since the 1980s. [7] The low reactivity of CFCs allow it to reach the upper stratosphere, where it interacts with UV-C radiation and forms highly reactive chloride ions that interact with methane. [7] These highly reactive chlorine ions will also interact with volatile organic compounds to form other ozone depleting acids. [10]

Chlorine-36 is the radioactive isotope produced in many nuclear facilities as byproduct waste. [3] Its half-life of 3.01×105 years, mobility in the pedosphere, and ability to be taken up by organisms has made it an isotope of high concern among researchers. [3] The high solubility and low reactiveness of 36Cl− is also has made it a useful application for research of biogeochemical cycling of chlorine, as most research uses it as an isotope tracer [1] [3] [4] [5] [7]

Related Research Articles

<span class="mw-page-title-main">Bromine</span> Chemical element with atomic number 35 (Br)

Bromine is a chemical element; it has symbol Br and atomic number 35. It is a volatile red-brown liquid at room temperature that evaporates readily to form a similarly coloured vapour. Its properties are intermediate between those of chlorine and iodine. Isolated independently by two chemists, Carl Jacob Löwig and Antoine Jérôme Balard, its name was derived from Ancient Greek βρῶμος (bromos) 'stench', referring to its sharp and pungent smell.

<span class="mw-page-title-main">Chlorine</span> Chemical element with atomic number 17 (Cl)

Chlorine is a chemical element; it has 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 between them. Chlorine is a yellow-green gas at room temperature. It is an extremely reactive element and a strong oxidising agent: among the elements, it has the highest electron affinity and the third-highest electronegativity on the revised Pauling scale, behind only oxygen and fluorine.

<span class="mw-page-title-main">Ozone depletion</span> Atmospheric phenomenon

Ozone depletion consists of two related events observed since the late 1970s: a steady lowering of about four percent in the total amount of ozone in Earth's atmosphere, and a much larger springtime decrease in stratospheric ozone around Earth's polar regions. The latter phenomenon is referred to as the ozone hole. There are also springtime polar tropospheric ozone depletion events in addition to these stratospheric events.

<span class="mw-page-title-main">Chlorofluorocarbon</span> Class of organic compounds

Chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) are fully or partly halogenated hydrocarbons that contain carbon (C), hydrogen (H), chlorine (Cl), and fluorine (F), produced as volatile derivatives of methane, ethane, and propane.

The term chloride refers to a compound or molecule that contains either a chlorine ion, which is a negatively charged chlorine atom, or a non-charged chlorine atom covalently bonded to the rest of the molecule by a single bond. Many inorganic chlorides are salts. Many organic compounds are chlorides. The pronunciation of the word "chloride" is.

<span class="mw-page-title-main">Haloalkane</span> Group of chemical compounds derived from alkanes containing one or more halogens

The haloalkanes are alkanes containing one or more halogen substituents. They are a subset of the general class of halocarbons, although the distinction is not often made. Haloalkanes are widely used commercially. They are used as flame retardants, fire extinguishants, refrigerants, propellants, solvents, and pharmaceuticals. Subsequent to the widespread use in commerce, many halocarbons have also been shown to be serious pollutants and toxins. For example, the chlorofluorocarbons have been shown to lead to ozone depletion. Methyl bromide is a controversial fumigant. Only haloalkanes that contain chlorine, bromine, and iodine are a threat to the ozone layer, but fluorinated volatile haloalkanes in theory may have activity as greenhouse gases. Methyl iodide, a naturally occurring substance, however, does not have ozone-depleting properties and the United States Environmental Protection Agency has designated the compound a non-ozone layer depleter. For more information, see Halomethane. Haloalkane or alkyl halides are the compounds which have the general formula "RX" where R is an alkyl or substituted alkyl group and X is a halogen.

A period 3 element is one of the chemical elements in the third row of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behavior of the elements as their atomic number increases: a new row is begun when chemical behavior begins to repeat, meaning that elements with similar behavior fall into the same vertical columns. The third period contains eight elements: sodium, magnesium, aluminium, silicon, phosphorus, sulfur, chlorine and argon. The first two, sodium and magnesium, are members of the s-block of the periodic table, while the others are members of the p-block. All of the period 3 elements occur in nature and have at least one stable isotope.

Chloromethane, also called methyl chloride, Refrigerant-40, R-40 or HCC 40, is an organic compound with the chemical formula CH3Cl. One of the haloalkanes, it is a colorless, sweet-smelling, flammable gas. Methyl chloride is a crucial reagent in industrial chemistry, although it is rarely present in consumer products, and was formerly utilized as a refrigerant. Most chloromethane is biogenic.

In chemistry, halogenation is a chemical reaction which introduces one or more halogens into a chemical compound. Halide-containing compounds are pervasive, making this type of transformation important, e.g. in the production of polymers, drugs. This kind of conversion is in fact so common that a comprehensive overview is challenging. This article mainly deals with halogenation using elemental halogens. Halides are also commonly introduced using salts of the halides and halogen acids. Many specialized reagents exist for and introducing halogens into diverse substrates, e.g. thionyl chloride.

<span class="mw-page-title-main">Hypochlorite</span> An anion

In chemistry, hypochlorite, or chloroxide is an anion with the chemical formula ClO−. It combines with a number of cations to form hypochlorite salts. Common examples include sodium hypochlorite and calcium hypochlorite. The Cl-O distance in ClO− is 1.69 Å.

In organochlorine chemistry, reductive dechlorination describes any chemical reaction which cleaves the covalent bond between carbon and chlorine via reductants, to release chloride ions. Many modalities have been implemented, depending on the application. Reductive dechlorination is often applied to remediation of chlorinated pesticides or dry cleaning solvents. It is also used occasionally in the synthesis of organic compounds, e.g. as pharmaceuticals.

Halocarbon compounds are chemical compounds in which one or more carbon atoms are linked by covalent bonds with one or more halogen atoms resulting in the formation of organofluorine compounds, organochlorine compounds, organobromine compounds, and organoiodine compounds. Chlorine halocarbons are the most common and are called organochlorides.

The pedosphere is the outermost layer of the Earth that is composed of soil and subject to soil formation processes. It exists at the interface of the lithosphere, atmosphere, hydrosphere and biosphere. The pedosphere is the skin of the Earth and only develops when there is a dynamic interaction between the atmosphere, biosphere, lithosphere and the hydrosphere. The pedosphere is the foundation of terrestrial life on Earth.

In chemistry, trihalomethanes (THMs) are chemical compounds in which three of the four hydrogen atoms of methane are replaced by halogen atoms. Trihalomethanes with all the same halogen atoms are called haloforms. Many trihalomethanes find uses in industry as solvents or refrigerants. Some THMs are also environmental pollutants, and few are considered carcinogenic.

Trichlorofluoromethane, also called freon-11, CFC-11, or R-11, is a chlorofluorocarbon (CFC). It is a colorless, faintly ethereal, and sweetish-smelling liquid that boils around room temperature. CFC-11 is a Class 1 ozone-depleting substance which damages Earth's protective stratospheric ozone layer. Also R-11 is not flammable at ambient temperature and pressure but it can become very combustible if heated and ignited by a strong ignition source.

1,1,2-Trichloro-1,2,2-trifluoroethane, also called trichlorotrifluoroethane or CFC-113, is a chlorofluorocarbon. It has the formula Cl2FC−CClF2. This colorless, volatile liquid is a versatile solvent.

<span class="mw-page-title-main">Arsenic cycle</span>

The arsenic (As) cycle is the biogeochemical cycle of natural and anthropogenic exchanges of arsenic terms through the atmosphere, lithosphere, pedosphere, hydrosphere, and biosphere. Although arsenic is naturally abundant in the Earth's crust, long-term exposure and high concentrations of arsenic can be detrimental to human health.

<span class="mw-page-title-main">Potassium cycle</span>

The potassium (K) cycle is the biogeochemical cycle that describes the movement of potassium throughout the Earth's lithosphere, biosphere, atmosphere, and hydrosphere.

<span class="mw-page-title-main">Fluorine cycle</span> Biogeochemical cycle

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<span class="mw-page-title-main">Bromine cycle</span> Biogeochemical cycle of bromine

The bromine cycle is a biogeochemical cycle of bromine through the atmosphere, biosphere, and hydrosphere.

References

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  3. 1 2 3 4 5 6 7 8 9 10 Svensson, Teresia; Kylin, Henrik; Montelius, Malin; Sandén, Per; Bastviken, David (2021). "Chlorine cycling and the fate of Cl in terrestrial environments". Environmental Science and Pollution Research. 28 (7): 7691–7709. doi:10.1007/s11356-020-12144-6. ISSN   0944-1344. PMC   7854439 . PMID   33400105.
  4. 1 2 3 4 Atashgahi, Siavash; Liebensteiner, Martin G.; Janssen, Dick B.; Smidt, Hauke; Stams, Alfons J. M.; Sipkema, Detmer (2018). "Microbial Synthesis and Transformation of Inorganic and Organic Chlorine Compounds". Frontiers in Microbiology. 9: 3079. doi: 10.3389/fmicb.2018.03079 . ISSN   1664-302X. PMC   6299022 . PMID   30619161.
  5. 1 2 3 4 Vodyanitskii, Yu. N.; Makarov, M. I. (2017). "Organochlorine compounds and the biogeochemical cycle of chlorine in soils: A review". Eurasian Soil Science. 50 (9): 1025–1032. Bibcode:2017EurSS..50.1025V. doi:10.1134/S1064229317090113. ISSN   1064-2293. S2CID   134940144.
  6. 1 2 Berend, Kenrick; van Hulsteijn, Leonard Hendrik; Gans, Rijk O.B. (2012). "Chloride: The queen of electrolytes?". European Journal of Internal Medicine. 23 (3): 203–211. doi:10.1016/j.ejim.2011.11.013. PMID   22385875.
  7. 1 2 3 4 Kim, Ki-Hyun; Shon, Zang-Ho; Nguyen, Hang Thi; Jeon, Eui-Chan (2011). "A review of major chlorofluorocarbons and their halocarbon alternatives in the air". Atmospheric Environment. 45 (7): 1369–1382. Bibcode:2011AtmEn..45.1369K. doi:10.1016/j.atmosenv.2010.12.029.
  8. ↑ Aulenta, Federico; Pera, Antonio; Rossetti, Simona; Petrangeli Papini, Marco; Majone, Mauro (2007). "Relevance of side reactions in anaerobic reductive dechlorination microcosms amended with different electron donors". Water Research. 41 (1): 27–38. doi:10.1016/j.watres.2006.09.019. PMID   17107702.
  9. ↑ Vardi (2010). "GABA, Glycine and Cation-Chloride Cotransporters in Retinal Function and Development". Chapter 19 - GABA, Glycine and Cation-Chloride Cotransporters in Retinal Function and Development. Academic Press. pp. 383–412. doi:10.1016/B978-0-12-374373-2.00019-4. ISBN   9780123743732.
  10. ↑ Faxon, C. B.; Allen, D. T. (2013). "Chlorine chemistry in urban atmospheres: a review". Environmental Chemistry. 10 (3): 221–233. doi: 10.1071/EN13026 . ISSN   1449-8979.
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