Actinides in the environment

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The actinide series is a group of chemical elements with atomic numbers ranging from 89 to 102, [note 1] including notable elements such as uranium and plutonium. The nuclides (or isotopes) thorium-232, uranium-235, and uranium-238 occur primordially, while trace quantities of actinium, protactinium, neptunium, and plutonium exist as a result of radioactive decay and (in the case of neptunium and plutonium) neutron capture of uranium. [note 2] These elements are far more radioactive than the naturally occurring thorium and uranium, and thus have much shorter half-lives. Elements with atomic numbers greater than 94 do not exist naturally on Earth, and must be produced in a nuclear reactor. [2] However, certain isotopes of elements up to californium (atomic number 98) still have practical applications which take advantage of their radioactive properties. [3] [4]

Contents

While all actinides are radioactive, actinides and actinide compounds comprise a significant portion of the Earth's crust. [5] There is enough thorium and uranium to be commercially mined, with thorium having a concentration in the Earth's crust about four times that of uranium. [6] The global production of uranium in 2021 was over six million tons, with Australia having been the leading supplier. [7] Thorium is extracted as a byproduct of titanium, zirconium, tin, and rare earths from monazite, from which thorium is often a waste product. Despite its greater abundance in the Earth's crust, the low demand for thorium in comparison to other metals extracted alongside thorium has led to a global surplus. [8]

The primary hazard associated with actinides is their radioactivity, though they may also cause heavy metal poisoning if absorbed into the bloodstream. [9] Generally, ingested insoluble actinide compounds, such as uranium dioxide and mixed oxide (MOX) fuel, will pass through the digestive tract with little effect since they have long half-lives, and cannot dissolve and be absorbed into the bloodstream. [10] Inhaled actinide compounds, however, will be more damaging as they remain in the lungs and irradiate lung tissue.

Actinium

Actinium can be found naturally in traces in uranium ore as 227Ac, an α and β emitter with half-life 21.773 years. Uranium ore contains about 0.2 mg of actinium per ton of uranium. It is more commonly made in milligram amounts by neutron irradiation of 226Ra in a nuclear reactor. Natural actinium almost exclusively consists of one isotope, 227Ac, with only minute traces of other shorter-lived isotopes (225Ac and 228Ac) occurring in other decay chains. [11]

Thorium

Monazite, a rare-earth-and-thorium-phosphate mineral, is the primary source of the world's thorium MonaziteUSGOV.jpg
Monazite, a rare-earth-and-thorium-phosphate mineral, is the primary source of the world's thorium

In India, a large amount of thorium ore can be found in the form of monazite in placer deposits of the Western and Eastern coastal dune sands, particularly in the Tamil Nadu coastal areas. The residents of this area are exposed to a naturally occurring radiation dose ten times higher than the worldwide average. [12]

Occurrence

Thorium is found at low levels in most rocks and soils, where it is about three times more abundant than uranium and about as abundant as lead. On average, soil commonly contains around 6 parts per million (ppm) thorium. [13] Thorium occurs in several minerals; the most common is the rare earth-thorium-phosphate mineral monazite, which contains up to 12% thorium oxide. Several countries have substantial deposits. 232Th decays very slowly (its half-life is about three times the age of the Earth). Other isotopes of thorium occur in the thorium and uranium decay chains. These are shorter-lived and hence much more radioactive than 232Th, though on a mass basis they are negligible.

Effects in humans

Thorium has been linked to liver cancer. In the past, thoria (thorium dioxide) was used as a contrast agent for medical X-ray radiography but its use has been discontinued. It was sold under the name Thorotrast.

Protactinium

Protactinium-231 occurs naturally in uranium ores such as pitchblende, to the extent of 3 ppm in some ores. Protactinium is naturally present in soil, rock, surface water, groundwater, plants and animals in very low concentrations (on the order of 1 ppt[ Unclear whether this means parts per thousand or parts per trillion ] or 0.1 picocuries per gram (pCi/g).

Uranium

Uranium is a natural metal which is widely found. It is present in almost all soils and it is more plentiful than antimony, beryllium, cadmium, gold, mercury, silver, or tungsten, and is about as abundant as arsenic or molybdenum. Significant concentrations of uranium occur in some substances such as phosphate rock deposits, and minerals such as lignite, and monazite sands in uranium-rich ores (it is recovered commercially from these sources).

Seawater contains about 3.3 parts per billion of uranium by weight [14] as uranium (VI) forms soluble carbonate complexes. Extraction of uranium from seawater has been considered as a means of obtaining the element. Because of the very low specific activity of uranium the chemical effects of it upon living things can often outweigh the effects of its radioactivity. Additional uranium has been added to the environment in some locations, from the nuclear fuel cycle and the use of depleted uranium in munitions.

Neptunium

Like plutonium, neptunium has a high affinity for soil. [15] However, it is relatively mobile over the long term, and diffusion of neptunium-237 in groundwater is a major issue in designing a deep geological repository for permanent storage of spent nuclear fuel. 237Np has a half-life of 2.144 million years and is therefore a long-term problem; but its half-life is still much shorter than those of uranium-238, uranium-235, or uranium-236, and 237Np therefore has higher specific activity than those nuclides. It is used only to make plutonium-238 when bombarded with neutrons in a lab.

Plutonium

Sources

Plutonium in the environment has several sources. These include:

Environmental chemistry

Plutonium, like other actinides, readily forms a plutonium dioxide (plutonyl) core (PuO2). In the environment, this plutonyl core readily complexes with carbonate as well as other oxygen moieties (OH−, NO2−, NO3−, and SO42−) to form charged complexes which can be readily mobile with low affinities to soil.

PuO2 formed from neutralizing highly acidic nitric acid solutions tends to form polymeric PuO2 which is resistant to complexation. Plutonium also readily shifts valences between the +3, +4, +5 and +6 states. It is common for some fraction of plutonium in solution to exist in all of these states in equilibrium.

Plutonium is known to bind to soil particles very strongly; see above[ where? ] for an X-ray spectroscopic study of plutonium in soil and concrete. While caesium has very different chemistry from the actinides, it is well known that both caesium and many actinides bind strongly to the minerals in soil. It has been possible to use 134Cs-labeled soil to study the migration of Pu and Cs is soils. It has been shown that colloidal transport processes control the migration of Cs (and will control the migration of Pu) in the soil at the Waste Isolation Pilot Plant. [16]

Americium

Americium often enters landfills from discarded smoke detectors. The rules for the disposal of smoke detectors are very relaxed in most municipalities. For instance, in the UK it is permissible to dispose of a smoke detector containing americium by placing it in the dustbin with normal household rubbish, but each dustbin worth of rubbish is limited[ clarification needed ][ by law? ] to only containing one smoke detector. The manufacture of products containing americium (such as smoke detectors) as well as nuclear reactors and explosions may also release the americium into the environment. [17]

Picture illustrating David "Radioactive Boyscout" Hahn. David Hahn.jpg
Picture illustrating David "Radioactive Boyscout" Hahn.

In 1999, a truck transporting 900 smoke detectors in France was reported to have caught fire; it is claimed that this led to a release of americium into the environment. [18] In the U.S., the "Radioactive Boy Scout" David Hahn was able to buy thousands of smoke detectors at remainder prices and concentrate the americium from them.

There have been cases of humans being exposed to americium. The worst case was that of Harold McCluskey, who was exposed to an extremely high dose of americium-241 after an accident involving a glove box. He was subsequently treated with chelation therapy. It is likely that the medical care which he was given saved his life; despite similar biodistribution and toxicity to plutonium, the two radioactive elements have different solution-state chemistries. [19] Americium is stable in the +3 oxidation state, while the +4 oxidation state of plutonium can form in the human body. [20]

The most common isotope americium-241 decays (half-life 432 years) to neptunium-237 which has a much longer half-life, so in the long term, the issues discussed above for neptunium apply. [21]

Americium released into the environment tends to remain in soil and water at relatively shallow depths and may be taken up by animals and plants during growth; shellfish such as shrimp take up americium-241 in their shells, and parts of grain plants can become contaminated by exposure. [22] In a 2021 paper, J.D. Chaplin et al. reported advances in the diffusive gradients in thin films technique, which have provided a method to measure labile bioavailable americium in soils, as well as in freshwater and seawater. [23]

Curium

Atmospheric curium compounds are poorly soluble in common solvents and mostly adhere to soil particles. Soil analysis revealed about 4,000 times higher concentration of curium in the sandy soil particles than in water present in the soil pores. An even higher ratio of about 18,000 was measured in loam soils. [24]

Californium

Californium is fairly insoluble in water, but it adheres well to ordinary soil, and concentrations of it in the soil can be 500 times higher than in the water surrounding the soil particles. [25]

Notes

  1. ↑ Lawrencium, element 103, is sometimes included in the actinide series despite being a part of the 6d transition series.
  2. ↑ It is suspected, though unconfirmed, that the long-lived isotope 244Pu may exist primordially. [1]

See also

Related Research Articles

<span class="mw-page-title-main">Americium</span> Chemical element with atomic number 95 (Am)

Americium is a synthetic chemical element; it has symbol Am and atomic number 95. It is radioactive and a transuranic member of the actinide series in the periodic table, located under the lanthanide element europium and was thus named after the Americas by analogy.

The actinide or actinoid series encompasses at least the 14 metallic chemical elements in the 5f series, with atomic numbers from 89 to 102, actinium through nobelium. The actinide series derives its name from the first element in the series, actinium. The informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide.

<span class="mw-page-title-main">Curium</span> Chemical element with atomic number 96 (Cm)

Curium is a synthetic chemical element; it has symbol Cm and atomic number 96. This transuranic actinide element was named after eminent scientists Marie and Pierre Curie, both known for their research on radioactivity. Curium was first intentionally made by the team of Glenn T. Seaborg, Ralph A. James, and Albert Ghiorso in 1944, using the cyclotron at Berkeley. They bombarded the newly discovered element plutonium with alpha particles. This was then sent to the Metallurgical Laboratory at University of Chicago where a tiny sample of curium was eventually separated and identified. The discovery was kept secret until after the end of World War II. The news was released to the public in November 1947. Most curium is produced by bombarding uranium or plutonium with neutrons in nuclear reactors – one tonne of spent nuclear fuel contains ~20 grams of curium.

<span class="mw-page-title-main">Neptunium</span> Chemical element with atomic number 93 (Np)

Neptunium is a chemical element; it has symbol Np and atomic number 93. A radioactive actinide metal, neptunium is the first transuranic element. It is named after Neptune, the planet beyond Uranus in the Solar System, which uranium is named after. A neptunium atom has 93 protons and 93 electrons, of which seven are valence electrons. Neptunium metal is silvery and tarnishes when exposed to air. The element occurs in three allotropic forms and it normally exhibits five oxidation states, ranging from +3 to +7. Like all actinides, it is radioactive, poisonous, pyrophoric, and capable of accumulating in bones, which makes the handling of neptunium dangerous.

<span class="mw-page-title-main">Protactinium</span> Chemical element with atomic number 91 (Pa)

Protactinium is a chemical element; it has symbol Pa and atomic number 91. It is a dense, radioactive, silvery-gray actinide metal which readily reacts with oxygen, water vapor, and inorganic acids. It forms various chemical compounds, in which protactinium is usually present in the oxidation state +5, but it can also assume +4 and even +3 or +2 states. Concentrations of protactinium in the Earth's crust are typically a few parts per trillion, but may reach up to a few parts per million in some uraninite ore deposits. Because of its scarcity, high radioactivity, and high toxicity, there are currently no uses for protactinium outside scientific research, and for this purpose, protactinium is mostly extracted from spent nuclear fuel.

<span class="mw-page-title-main">Thorium</span> Chemical element with atomic number 90 (Th)

Thorium is a chemical element. It has the symbol Th and atomic number 90. Thorium is a weakly radioactive light silver metal which tarnishes olive gray when it is exposed to air, forming thorium dioxide; it is moderately soft and malleable and has a high melting point. Thorium is an electropositive actinide whose chemistry is dominated by the +4 oxidation state; it is quite reactive and can ignite in air when finely divided.

The transuranium elements are the chemical elements with atomic numbers greater than 92, which is the atomic number of uranium. All of them are radioactively unstable and decay into other elements. With the exception of neptunium and plutonium which have been found in trace amounts in nature, none occur naturally on Earth and they are synthetic.

<span class="mw-page-title-main">Nuclear fuel cycle</span> Process of manufacturing and consuming nuclear fuel

The nuclear fuel cycle, also called nuclear fuel chain, is the progression of nuclear fuel through a series of differing stages. It consists of steps in the front end, which are the preparation of the fuel, steps in the service period in which the fuel is used during reactor operation, and steps in the back end, which are necessary to safely manage, contain, and either reprocess or dispose of spent nuclear fuel. If spent fuel is not reprocessed, the fuel cycle is referred to as an open fuel cycle ; if the spent fuel is reprocessed, it is referred to as a closed fuel cycle.

<span class="mw-page-title-main">Decay chain</span> Series of radioactive decays

In nuclear science, the decay chain refers to a series of radioactive decays of different radioactive decay products as a sequential series of transformations. It is also known as a "radioactive cascade". The typical radioisotope does not decay directly to a stable state, but rather it decays to another radioisotope. Thus there is usually a series of decays until the atom has become a stable isotope, meaning that the nucleus of the atom has reached a stable state.

A period 7 element is one of the chemical elements in the seventh 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 seventh period contains 32 elements, tied for the most with period 6, beginning with francium and ending with oganesson, the heaviest element currently discovered. As a rule, period 7 elements fill their 7s shells first, then their 5f, 6d, and 7p shells in that order, but there are exceptions, such as uranium.

Mixed oxide fuel, commonly referred to as MOX fuel, is nuclear fuel that contains more than one oxide of fissile material, usually consisting of plutonium blended with natural uranium, reprocessed uranium, or depleted uranium. MOX fuel is an alternative to the low-enriched uranium fuel used in the light-water reactors that predominate nuclear power generation.

Neptunium (93Np) is usually considered an artificial element, although trace quantities are found in nature, so a standard atomic weight cannot be given. Like all trace or artificial elements, it has no stable isotopes. The first isotope to be synthesized and identified was 239Np in 1940, produced by bombarding 238
U
 with neutrons to produce 239
U
, which then underwent beta decay to 239
Np
.

<span class="mw-page-title-main">Minor actinide</span> Category of elements in spent nuclear fuel

A minor actinide is an actinide, other than uranium or plutonium, found in spent nuclear fuel. The minor actinides include neptunium, americium, curium, berkelium, californium, einsteinium, and fermium. The most important isotopes of these elements in spent nuclear fuel are neptunium-237, americium-241, americium-243, curium-242 through -248, and californium-249 through -252.

Major actinides is a term used in the nuclear power industry that refers to the isotopes of plutonium uranium and thorium present in nuclear fuel, as opposed to the minor actinides neptunium, americium, curium, berkelium, and californium, including other isotopes of uranium and plutonium and other actinides.

<span class="mw-page-title-main">Weapons-grade nuclear material</span> Nuclear material pure enough to be used for nuclear weapons

Weapons-grade nuclear material is any fissionable nuclear material that is pure enough to make a nuclear weapon and has properties that make it particularly suitable for nuclear weapons use. Plutonium and uranium in grades normally used in nuclear weapons are the most common examples.

Plutonium-241 is an isotope of plutonium formed when plutonium-240 captures a neutron. Like some other plutonium isotopes, 241Pu is fissile, with a neutron absorption cross section about one-third greater than that of 239Pu, and a similar probability of fissioning on neutron absorption, around 73%. In the non-fission case, neutron capture produces plutonium-242. In general, isotopes with an odd number of neutrons are both more likely to absorb a neutron and more likely to undergo fission on neutron absorption than isotopes with an even number of neutrons.

Long-lived fission products (LLFPs) are radioactive materials with a long half-life produced by nuclear fission of uranium and plutonium. Because of their persistent radiotoxicity, it is necessary to isolate them from humans and the biosphere and to confine them in nuclear waste repositories for geological periods of time. The focus of this article is radioisotopes (radionuclides) generated by fission reactors.

<span class="mw-page-title-main">Nuclear transmutation</span> Conversion of an atom from one element to another

Nuclear transmutation is the conversion of one chemical element or an isotope into another chemical element. Nuclear transmutation occurs in any process where the number of protons or neutrons in the nucleus of an atom is changed.

<span class="mw-page-title-main">Actinide chemistry</span> Branch of nuclear chemistry

Actinide chemistry is one of the main branches of nuclear chemistry that investigates the processes and molecular systems of the actinides. The actinides derive their name from the group 3 element actinium. The informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide. All but one of the actinides are f-block elements, corresponding to the filling of the 5f electron shell; lawrencium, a d-block element, is also generally considered an actinide. In comparison with the lanthanides, also mostly f-block elements, the actinides show much more variable valence. The actinide series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.

Robert Guillaumont is a French chemist and honorary professor at the University of Paris-Saclay in Orsay (1967-1998), Member of the French Academy of Sciences and the French Academy of Technologies

References

  1. ↑ Wu, Yang; Dai, Xiongxin; Xing, Shan; Luo, Maoyi; Christl, Marcus; Synal, Hans-Arno; Hou, Shaochun (2022). "Direct search for primordial 244Pu in Bayan Obo bastnaesite". Chinese Chemical Letters. 33 (7): 3522–3526. doi:10.1016/j.cclet.2022.03.036 . Retrieved 29 January 2024.
  2. ↑ Seaborg, Glenn T.; Segrè, Emilio (June 1947). "The Trans-Uranium Elements". Nature. 159 (4052): 863–865. Bibcode:1947Natur.159..863S. doi:10.1038/159863a0. PMID   20252546.
  3. ↑ "Americium in Ionization Smoke Detectors". www.epa.gov. Environmental Protection Agency. 27 November 2018.
  4. ↑ Ellis, Jason K. (2 December 2020). "ORNL's californium-252 will play pivotal role in new reactor startups | ORNL". www.ornl.gov. Oak Ridge National Laboratory.
  5. ↑ Herring, J. Stephen (2012). Encyclopedia of sustainability science and technology. New York: Springer. p. 11202. ISBN   978-0-387-89469-0.
  6. ↑ Herring, p. 11203
  7. ↑ "Uranium Mining Overview - World Nuclear Association". world-nuclear.org. World Nuclear Association.
  8. ↑ Herring, pp. 11204-11205
  9. ↑ Briner, Wayne (25 January 2010). "The Toxicity of Depleted Uranium". International Journal of Environmental Research and Public Health. 7 (1): 303–313. doi: 10.3390/ijerph7010303 . PMC   2819790 . PMID   20195447.
  10. ↑ Keith, S; Faroon, O; Roney, N; Scinicariello, F; Wilbur, S; Ingerman, L; Llados, F; Plewak, D; Wohlers, D; Diamond, G (February 2013). "Public Health Statement for Uranium". Toxicological Profile for Uranium. Agency for Toxic Substances and Disease Registry (US). PMID   24049861.{{cite book}}: |journal= ignored (help)
  11. ↑ Peppard, D. F.; Mason, G. W.; Gray, P. R.; Mech, J. F. (1952). "Occurrence of the (4n + 1) series in nature" (PDF). Journal of the American Chemical Society. 74 (23): 6081–6084. doi:10.1021/ja01143a074.
  12. ↑ "Compendium Of Policy And Statutory Provisions Relating To Exploitation Of Beach Sand Minerals". Government Of India. Archived from the original on 2008-12-04. Retrieved 2008-12-19.
  13. ↑ THORIUM Agency for Toxic Substances and Disease Registry. July 1999.
  14. ↑ "Uranium: the essentials". WebElements. Retrieved 2008-12-19.
  15. ↑ "Neptunium" (PDF). Argonne National Laboratory, EVS. August 2005. Archived from the original (PDF) on 2008-12-19. Retrieved 2008-12-19.
  16. ↑ Whicker, R.D.; S.A. Ibrahim (2006). "Vertical migration of 134Cs bearing soil particles in arid soils: implications for plutonium redistribution". Journal of Environmental Radioactivity. 88 (2): 171–188. doi:10.1016/j.jenvrad.2006.01.010. PMID   16564117.
  17. ↑ Bunzl, K.; Kracke, W. (1994). "Fate of fall-out plutonium and americium in the environment: selected examples". Journal of Alloys and Compounds. 213–214. Elsevier B.V.: 212–218. doi:10.1016/0925-8388(94)90906-7.
  18. ↑ "Radiological Agent: Americium-241". CBWInfo.com. Archived from the original on 2009-01-08. Retrieved 2008-12-19.
  19. ↑ Taylor, David M. (July 1989). "The biodistribution and toxicity of plutonium, americium and neptunium". Science of the Total Environment. 83 (3): 217–225. Bibcode:1989ScTEn..83..217T. doi:10.1016/0048-9697(89)90094-6. PMID   2781271.
  20. ↑ PubChem. "Americium". pubchem.ncbi.nlm.nih.gov. Retrieved 2019-12-13.
  21. ↑ Stoll 2017-10-10T22:55:00Z, Carol (10 October 2017). "Facts About Neptunium". livescience.com. Retrieved 2019-12-13.{{cite web}}: CS1 maint: numeric names: authors list (link)
  22. ↑ "Public Health Statement for Americium". CDC - ATSDR. Retrieved 11 September 2016.
  23. ↑ Chaplin J, Warwick P, Cundy A, Bochud F, Froidevaux P (25 August 2021). "Novel DGT Configurations for the Assessment of Bioavailable Plutonium, Americium, and Uranium in Marine and Freshwater Environments". Analytical Chemistry. 93 (35): 11937–11945. doi: 10.1021/acs.analchem.1c01342 . PMID   34432435. S2CID   237307309.
  24. ↑ Human Health Fact Sheet on Curium Archived 2006-02-18 at the Wayback Machine , Los Alamos National Laboratory
  25. ↑ "Human Health Fact Sheet: Californium" (PDF). Argonne National Laboratory. August 2005. Archived from the original (PDF) on July 21, 2011.

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