Uranium in the environment is a global health concern, and comes from both natural and man-made sources. Mining, phosphates in agriculture, weapons manufacturing, and nuclear power are sources of uranium in the environment. [1]
In the natural environment, radioactivity of uranium is generally low, [1] but uranium is a toxic metal that can disrupt normal functioning of the kidney, brain, liver, heart, and numerous other systems. [2] Chemical toxicity can cause public health issues when uranium is present in groundwater, especially if concentrations in food and water are increased by mining activity. [1] The biological half-life (the average time it takes for the human body to eliminate half the amount in the body) for uranium is about 15 days. [3]
Uranium's radioactivity can present health and environmental issues in the case of nuclear waste produced by nuclear power plants or weapons manufacturing.
Uranium is weakly radioactive and remains so because of its long physical half-life (4.468 billion years for uranium-238). The use of depleted uranium (DU) in munitions is controversial because of questions about potential long-term health effects. [4] [5]
Uranium is a naturally occurring element found in low levels within all rock, soil, and water. This is the highest-numbered element to be found naturally in significant quantities on earth. According to the United Nations Scientific Committee on the Effects of Atomic Radiation the normal concentration of uranium in soil is 300 μg/kg to 11.7 mg/kg. [6]
It is considered to be more plentiful than antimony, beryllium, cadmium, gold, mercury, silver, or tungsten and is about as abundant as tin, arsenic or molybdenum. It is found in many minerals including uraninite (most common uranium ore), autunite, uranophane, torbernite, and coffinite. [7] 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). Coal fly ash from uranium bearing coal is particularly rich in uranium and there have been several proposals to "mine" this waste product for its uranium content. [8] [9] Due to the fact that part of the ash of a coal power plant escapes through the smokestack, the radioactive contamination released by coal power plants in regular operation is actually higher than that of nuclear power plants. [10] [11]
Seawater contains about 3.3 parts per billion of uranium by weight, approximately (3.3 µg/kg) or, 3.3 micrograms per liter of seawater. [12]
Mining is the largest source of uranium contamination in the environment. [1] Uranium milling creates radioactive waste in the form of tailings, which contain uranium, radium, and polonium. Consequently, uranium mining results in "the unavoidable radioactive contamination of the environment by solid, liquid and gaseous wastes". [13]
Seventy percent of global uranium resources are on or adjacent to traditional lands belonging to Indigenous people, and perceived environmental risks associated with uranium mining have resulted in environmental conflicts involving multiple actors wherein local campaigns become national or international debates. [14]
Some of these environmental conflicts have limited uranium exploration. Incidents at Ranger uranium mine in the Northern Territory of Australia and disputes over Indigenous land rights led to increased opposition to development of the nearby Jabiluka deposits and suspension of that project in the early 2000s. Similarly, environmental damage from Uranium mining on traditional Navajo lands in the southwestern United States resulted in restrictions on additional mining in Navajo lands in 2005. [14]
The radiation hazards of uranium mining and milling were not appreciated in the early years, resulting in workers exposed to high levels of radiation. Inhalation of radon gas caused sharp increases in lung cancers among underground uranium miners employed in the 1940s and 1950s. [15]
Military activity is a source of uranium, especially at nuclear or munitions testing sites. Depleted uranium (DU) is a byproduct of uranium enrichment that is used for defensive armor plating and armor-piercing projectiles. Uranium contamination has been found at testing sites in the UK, in Kazakhstan, and in several countries as a result of DU munitions used in the Gulf War and the Yugoslav wars. [1] During a three-week period of conflict in 2003 in Iraq, 1,000 to 2,000 tonnes of DU munitions were used. [16]
Combustion and impact of DU munitions can produce aerosols that disperse uranium metal into the air and water where it can be inhaled or ingested by humans. [17] A United Nations Environment Programme (UNEP) study has expressed concerns about groundwater contamination from these munitions. [18] Studies of DU aerosol exposure suggest that uranium particles would quickly settle out of the air, [19] and thus should not affect populations more than a few kilometres from target areas. [17]
The nuclear power industry is also a source of uranium in the environment in the form of radioactive waste or through nuclear accidents such as Three Mile Island or the Chernobyl disaster. [14] Perceived risks of contamination associated with this industry contribute to the anti-nuclear movement. [14]
In 2020, there were over 250,000 metric tons of high-level radioactive waste being stored globally in temporary containers. This waste is produced by nuclear power plants and weapons facilities, and is a serious human health and environmental issue. There are plans to permanently dispose of high-level waste in deep geological repositories, but none of these are operational. Corrosion of aging temporary containers has caused some waste to leak into the environment. [20]
Spent uranium dioxide fuel is very insoluble in water, it is likely to release uranium (and fission products) even more slowly than borosilicate glass when in contact with water. [21]
Soluble uranium salts are toxic, though less so than those of other heavy metals such as lead or mercury. The organ which is most affected is the kidney. Soluble uranium salts are readily excreted in the urine, although some accumulation in the kidneys does occur in the case of chronic exposure. The World Health Organization has established a daily "tolerated intake" of soluble uranium salts for the general public of 0.5 μg/kg body weight (or 35 μg for a 70 kg adult): exposure at this level is not thought to lead to any significant kidney damage. [22] [23]
Tiron may be used to remove uranium from the human body, in a form of chelation therapy. [24] Bicarbonate may also be used as uranium (VI) forms complexes with the carbonate ion.
Uranium mining produces toxic tailings that are radioactive and may contain other toxic elements such as radon. Dust and water leaving tailing sites may carry long-lived radioactive elements that enter water sources and the soil, increase background radiation, and eventually be ingested by humans and animals. A 2013 analysis in a medical journal found that, "The effects of all these sources of contamination on human health will be subtle and widespread, and therefore difficult to detect both clinically and epidemiologically." [25] A 2019 analysis of the global uranium industry said that the industry was shifting mining activities toward the Global South where environmental regulations are typically less stringent; and that people in impacted communities would "surely experience adverse environmental consequences" and public health issues arising from mining activities carried out by powerful multi-national corporations or mining companies based in foreign countries. [26]
In 1950, the US Public Health service began a comprehensive study of uranium miners, leading to the first publication of a statistical correlation between cancer and uranium mining, released in 1962. [27] The federal government eventually regulated the standard amount of radon in mines, setting the level at 0.3 WL on January 1, 1969. [28]
Out of 69 present and former uranium milling sites in 12 states, 24 have been abandoned, and are the responsibility of the US Department of Energy. [29] Accidental releases from uranium mills include the 1979 Church Rock uranium mill spill in New Mexico, called the largest accident of nuclear-related waste in US history, and the 1986 Sequoyah Corporation Fuels Release in Oklahoma. [30]
In 1990, Congress passed the Radiation Exposure Compensation Act (RECA), granting reparations for those affected by mining, with amendments passed in 2000 to address criticisms with the original act. [27]
The use of depleted uranium (DU) in munitions is controversial because of questions about potential long-term health effects. [4] [5] [31] Normal functioning of the kidney, brain, liver, heart, and numerous other systems can be affected by uranium exposure, because uranium is a toxic metal. [2] Some people have raised concerns about the use of DU munitions because of its mutagenicity, [32] teratogenicity in mice, [33] [34] neurotoxicity, [35] and its suspected carcinogenic potential. Additional concerns address unexploded DU munitions leeching into groundwater over time. [36]
The toxicity of DU is a point of medical controversy. Multiple studies using cultured cells and laboratory rodents suggest the possibility of leukemogenic, genetic, reproductive, and neurological effects from chronic exposure. [4] A 2005 epidemiology review concluded: "In aggregate the human epidemiological evidence is consistent with increased risk of birth defects in offspring of persons exposed to DU." [37] The World Health Organization states that no risk of reproductive, developmental, or carcinogenic effects have been reported in humans due to DU exposure. [38] [39] This report has been criticized by Dr. Keith Baverstock for not including possible long-term effects. [40]
Most scientific studies have found no link between uranium and birth defects, but some claim statistical correlations between soldiers exposed to DU, and those who were not, concerning reproductive abnormalities.
One study found epidemiological evidence for increased risk of birth defects in the offspring of persons exposed to DU. [37] Several sources have attributed an increased rate of birth defects in the children of Gulf War veterans and in Iraqis to inhalation of depleted uranium. [34] [41] A 2001 study of 15,000 Gulf War combat veterans and 15,000 control veterans found that the Gulf War veterans were 1.8 (fathers) to 2.8 (mothers) times more likely to have children with birth defects. [42] A study of Gulf War Veterans from the UK found a 50% increased risk of malformed pregnancies reported by men over non-Gulf War veterans. The study did not find correlations between Gulf war deployment and other birth defects such as stillbirth, chromosomal malformations, or congenital syndromes. The father's service in the Gulf War was associated with increased rate of miscarriage, but the mother's service was not. [43]
Uranium causes reproductive defects and other health problems in rodents, frogs and other animals. Uranium was also shown to have cytotoxic, genotoxic and carcinogenic effects in animals. [44] [45] It has been shown in rodents and frogs that water-soluble forms of uranium are teratogenic. [37] [33] [34]
Bacteria and Pseudomonadota, such as Geobacter and Burkholderia fungorum (strain Rifle), can reduce and fix uranium in soil and groundwater. [46] [47] [48] These bacteria change soluble U(VI) into the highly insoluble complex-forming U(IV) ion, hence stopping chemical leaching.
It has been suggested that it is possible to form a reactive barrier by adding something to the soil which will cause the uranium to become fixed. One method of doing this is to use a mineral (apatite) [49] while a second method is to add a food substance such as acetate to the soil. This will enable bacteria to reduce the uranium(VI) to uranium(IV), which is much less soluble. In peat-like soils, the uranium will tend to bind to the humic acids; this tends to fix the uranium in the soil. [50]
Background radiation is a measure of the level of ionizing radiation present in the environment at a particular location which is not due to deliberate introduction of radiation sources.
Radon is a chemical element; it has symbol Rn and atomic number 86. It is a radioactive noble gas and is colorless and odorless. Of the three naturally occurring radon isotopes, only radon-222 has a sufficiently long half-life for it to be released from the soil and rock, where it is generated. Radon isotopes are the immediate decay products of radium isotopes. Radon's most stable isotope, radon-222, has a half-life of only 3.8 days, making radon one of the rarest elements. Radon will be present on Earth for several billion more years, despite its half-life being a mere 3.8 days, because it is constantly being produced as a step in the decay chain of uranium-238, and that of thorium-232, each of which is an extremely abundant radioactive nuclide with a half-life of several billion years. The decay of radon produces many other short-lived nuclides, known as "radon daughters", ending at stable isotopes of lead. Radon-222 occurs in significant quantities as a step in the normal radioactive decay chain of uranium-238, also known as the uranium series, which slowly decays into a variety of radioactive nuclides and eventually decays into lead-206, which is stable. Radon-220 occurs in minute quantities as an intermediate step in the decay chain of thorium-232, also known as the thorium series, which eventually decays into lead-208, which is stable.
Uranium is a chemical element; it has symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium radioactively decays by emitting an alpha particle. The half-life of this decay varies between 159,200 and 4.5 billion years for different isotopes, making them useful for dating the age of the Earth. The most common isotopes in natural uranium are uranium-238 and uranium-235. Uranium has the highest atomic weight of the primordially occurring elements. Its density is about 70% higher than that of lead and slightly lower than that of gold or tungsten. It occurs naturally in low concentrations of a few parts per million in soil, rock and water, and is commercially extracted from uranium-bearing minerals such as uraninite.
Depleted uranium is uranium with a lower content of the fissile isotope 235
U
than natural uranium. Natural uranium contains about 0.72% 235
U
, while the DU used by the U.S. Department of Defense contains 0.3% 235
U
or less. The less radioactive and non-fissile 238
U
constitutes the main component of depleted uranium.
Radioactive contamination, also called radiological pollution, is the deposition of, or presence of radioactive substances on surfaces or within solids, liquids, or gases, where their presence is unintended or undesirable.
Soil contamination, soil pollution, or land pollution as a part of land degradation is caused by the presence of xenobiotic (human-made) chemicals or other alteration in the natural soil environment. It is typically caused by industrial activity, agricultural chemicals or improper disposal of waste. The most common chemicals involved are petroleum hydrocarbons, polynuclear aromatic hydrocarbons, solvents, pesticides, lead, and other heavy metals. Contamination is correlated with the degree of industrialization and intensity of chemical substance. The concern over soil contamination stems primarily from health risks, from direct contact with the contaminated soil, vapour from the contaminants, or from secondary contamination of water supplies within and underlying the soil. Mapping of contaminated soil sites and the resulting clean ups are time-consuming and expensive tasks, and require expertise in geology, hydrology, chemistry, computer modelling, and GIS in Environmental Contamination, as well as an appreciation of the history of industrial chemistry.
Environmental radioactivity is not limited to actinides; non-actinides such as radon and radium are of note. While all actinides are radioactive, there are a lot of actinides or actinide-relating minerals in the Earth's crust such as uranium and thorium. These minerals are helpful in many ways, such as carbon-dating, most detectors, X-rays, and more.
Radium and radon are important contributors to environmental radioactivity. Radon occurs naturally as a result of decay of radioactive elements in soil and it can accumulate in houses built on areas where such decay occurs. Radon is a major cause of cancer; it is estimated to contribute to ~2% of all cancer related deaths in Europe.
Nuclear power has various environmental impacts, both positive and negative, including the construction and operation of the plant, the nuclear fuel cycle, and the effects of nuclear accidents. Nuclear power plants do not burn fossil fuels and so do not directly emit carbon dioxide. The carbon dioxide emitted during mining, enrichment, fabrication and transport of fuel is small when compared with the carbon dioxide emitted by fossil fuels of similar energy yield, however, these plants still produce other environmentally damaging wastes. Nuclear energy and renewable energy have reduced environmental costs by decreasing CO2 emissions resulting from energy consumption.
Environmental toxicology is a multidisciplinary field of science concerned with the study of the harmful effects of various chemical, biological and physical agents on living organisms. Ecotoxicology is a subdiscipline of environmental toxicology concerned with studying the harmful effects of toxicants at the population and ecosystem levels.
Christopher Busby is a British scientist primarily studying the health effects of internal ionising radiation. Busby is a director of Green Audit Limited, a private company, and scientific advisor to the Low Level Radiation Campaign (LLRC).
Study of the environmental impact of war focuses on the modernization of warfare and its increasing effects on the environment. Scorched earth methods have been used for much of recorded history. However, the methods of modern warfare cause far greater devastation on the environment. The progression of warfare from chemical weapons to nuclear weapons has increasingly created stress on ecosystems and the environment. Specific examples of the environmental impact of war include World War I, World War II, the Vietnam War, the Rwandan Civil War, the Kosovo War and the Gulf War.
The Church Rock uranium mill spill occurred in the U.S. state of New Mexico on July 16, 1979, when United Nuclear Corporation's tailings disposal pond at its uranium mill in Church Rock breached its dam. The accident remains the largest release of radioactive material in U.S. history, having released more radioactivity than the Three Mile Island accident four months earlier.
Uranium mining and the Navajo people began in 1944 in northeastern Arizona, northwestern New Mexico, and southeastern Utah.
The uranium mining debate covers the political and environmental controversies of uranium mining for use in either nuclear power or nuclear weapons.
Nuclear labor issues exist within the international nuclear power industry and the nuclear weapons production sector worldwide, impacting upon the lives and health of laborers, itinerant workers and their families.
Bioremediation of radioactive waste or bioremediation of radionuclides is an application of bioremediation based on the use of biological agents bacteria, plants and fungi to catalyze chemical reactions that allow the decontamination of sites affected by radionuclides. These radioactive particles are by-products generated as a result of activities related to nuclear energy and constitute a pollution and a radiotoxicity problem due to its unstable nature of ionizing radiation emissions.
Uranium acid mine drainage refers to acidic water released from a uranium mining site using processes like underground mining and in-situ leaching. Underground, the ores are not as reactive due to isolation from atmospheric oxygen and water. When uranium ores are mined, the ores are crushed into a powdery substance, thus increasing surface area to easily extract uranium. The ores, along with nearby rocks, may also contain sulfides. Once exposed to the atmosphere, the powdered tailings react with atmospheric oxygen and water. After uranium extraction, sulfide minerals in uranium tailings facilitates the release of uranium radionuclides into the environment, which can undergo further radioactive decay while lowering the pH of a solution.