Radioactive contamination

Radioactive contamination, also called radiological contamination, is the deposition of, or presence of radioactive substances on surfaces or within solids, liquids or gases (including the human body), where their presence is unintended or undesirable (from the International Atomic Energy Agency (IAEA) definition).

Such contamination presents a hazard because of the radioactive decay of the contaminants, which produces such harmful effects as ionizing radiation (namely alpha, beta, and gamma rays) and free neutrons. The degree of hazard is determined by the concentration of the contaminants, the energy of the radiation being emitted, the type of radiation, and the proximity of the contamination to organs of the body. It is important to be clear that the contamination gives rise to the radiation hazard, and the terms "radiation" and "contamination" are not interchangeable.

The sources of radioactive pollution can be classified into two groups: natural and man-made. Following an atmospheric nuclear weapon discharge or a nuclear reactor containment breach, the air, soil, people, plants, and animals in the vicinity will become contaminated by nuclear fuel and fission products.

 

Chernobyl disaster

The Chernobyl disaster was a nuclear accident that occurred on Saturday 26 April 1986, at the No. 4 reactor in the Chernobyl Nuclear Power Plant, near the city of Pripyat in the north of the Ukrainian SSR in the Soviet Union. It is considered the worst

nuclear disaster in history both in terms of cost and casualties, and is one of only two nuclear energy accidents rated at seven—the maximum severity—on the International Nuclear Event Scale, the other being the 2011 Fukushima Daiichi nuclear disaster in Japan. The initial emergency response, together with later decontamination of the environment, ultimately involved more than 500,000 personnel and cost an estimated 18 billion Soviet rubles—roughly US$68 billion in 2019, adjusted for inflation.

Although it is difficult to compare releases and spread of radioactive material between the Chernobyl accident and a deliberate air burst nuclear detonation, it has still been estimated that about four hundred times more radioactive material was released from Chernobyl than by the atomic bombing of Hiroshima and Nagasaki together. At Chernobyl approximately 100,000 square kilometers (39,000 sq mi) of land was significantly contaminated with fallout, with the worst hit regions being in Belarus, Ukraine and Russia. Lower levels of contamination were detected over all of Europe except for the Iberian Peninsula.

Contamination from the Chernobyl accident was scattered irregularly depending on weather conditions, much of it deposited on mountainous regions such as the Alps, the Welsh mountains and the Scottish Highlands, where adiabatic cooling caused radioactive rainfall. The resulting patches of contamination were often highly localized, and localized water-flows contributed to large variations in radioactivity over small areas. Sweden and Norway also received heavy fallout when the contaminated air collided with a cold front, bringing rain. There was also groundwater contamination.

Prior to the completion of the New Safe Confinement building at the reactor No. 4, rainwater acted as a neutron moderator triggering increased fission in the remaining materials risking criticality. Gadolinium nitrate solution was used to quench neutrons to slow the fission.

Even after the completion of the building, fission reactions may be increasing and scientists are working to understand the cause and risks. As of May 2021, while neutron radiation had slowed across most of the destroyed fuel, a sealed off room in the basement had actually recorded a doubling in neutron radiation. This indicated increasing levels of fission as water levels dropped, which was the opposite of what was expected, and was a typical compared to other fuel containing areas. Levels are increasingly slowly, so scientists are expected to have several years to solve the problem. However, if the trend continues it could create a self-sustaining reaction, which would likely spread more radioactive dust and debris through the New Safe Confinement, making future cleanup even more difficult. Potential solutions include using a robot to drill into the fuel and insert boron carbide control rods.

 

Fukushima Daiichi nuclear disaster

The Fukushima Daiichi nuclear disaster was a 2011 nuclear accident at the Fukushima Daiichi Nuclear Power Plant in Ōkuma, Fukushima Prefecture, Japan. The event was caused by the 2011 Tōhoku earthquake and tsunami.

It was the most severe nuclear accident since the Chernobyl disaster in 1986. It was classified as Level 7 on the International Nuclear Event Scale (INES), after initially being classified as Level 5, joining Chernobyl as the only other accident to receive such classification.

The accident was triggered by the Tōhoku earthquake and tsunami on Friday, 11 March 2011. On detecting the earthquake, the active reactors automatically shut down their normal power-generating fission reactions. Because of these shutdowns and other electrical grid supply problems, the reactors electricity supply failed, and their emergency diesel generators automatically started. Critically, these were required to provide electrical power to the pumps that circulated coolant through the reactors cores. This continued circulation was vital to remove residual decay heat, which continues to be produced after fission has ceased. However, the earthquake had also generated a tsunami 14 meters (46 ft) high that arrived shortly afterwards and swept over the plant's seawall and then flooded the lower parts of reactors 1–4. This flooding caused the failure of the emergency generators and loss of power to the circulating pumps. The resultant loss of reactor core cooling led to three nuclear meltdowns, three hydrogen explosions, and the release of radioactive contamination in Units 1, 2 and 3 between 12 and 15 March 2011. The spent fuel pool of previously shut down Reactor 4 increased in temperature on 15 March due to decay heat from newly added spent fuel rods, but did not boil down sufficiently to expose the fuel.

In the days after the accident, radiation released to the atmosphere forced the government to declare an ever-larger evacuation zone around the plant, culminating in an evacuation zone with a 20 km radius. All told, some 154,000 residents evacuated from the communities surrounding the plant due to the rising off-site levels of ambient ionizing radiation caused by airborne radioactive contamination from the damaged reactors.

Large amounts of water contaminated with radioactive isotopes were

released into the Pacific Ocean during and after the disaster. Michio Aoyama, a professor of radioisotope geoscience at the Institute of Environmental Radioactivity, has estimated that 18,000 terabecquerel (TBq) of radioactive caesium-137 were released into the Pacific during the accident, and in 2013, 30 gigabecquerel (GBq) of caesium 137 were still flowing into the ocean every day. The plant's operator has since built new walls along the coast and has created a 1.5 km long "ice wall" of frozen earth to stop the flow of contaminated water.

In June 2011, TEPCO stated the amount of contaminated water in the complex had increased due to substantial rainfall. On 13 February 2014, TEPCO reported 37 kBq (1.0 microcurie) of caesium-134 and 93 kBq (2.5 microcuries) of caesium-137 were detected per liter of groundwater sampled from a monitoring well. Dust particles gathered 4 km from the reactors in 2017 included microscopic nodules of melted core samples encased in cesium. After decades of exponential decline in ocean cesium from weapons testing fallout, radioactive isotopes of cesium in the Sea of Japan increased after the accident from 1.5 mBq/L to about 2.5 mBq/L and are still rising as of 2018, while those just off the eastern coast of Japan are declining.

Since the 2011 Fukushima Daiichi nuclear disaster, the nuclear plant has accumulated 1.25 million tonnes of waste water, stored in 1,061 tanks on the land of the nuclear plant, as of March 2021. It will run out of land for water tanks by 2022. It has been suggested the government could have solved the problem by allocating more land surrounding the power plant for water tanks, since the surrounding area had been designated as unsuitable for humans. Regardless, the government was reluctant to act. Mainichi Shimbun criticized the government for showing "no sincerity" in "unilaterally push[ing] through with the logic that there will no longer be enough storage space.

On 13 April 2021, the Cabinet of Prime Minister Suga unanimously approved that TEPCO dump the stored water to the Pacific Ocean over a course of 30 years. The Cabinet asserted the dumped water will be treated and diluted to drinkable standard. The idea of dumping had been floated by Japanese experts and officials as early as June 2016.

 

Caesium-137

Caesium-137 (¹³⁷₅₅Cs), or radiocaesium, is a radioactive isotope of caesium that is formed as one of the more common fission products by the nuclear fission of uranium-235 and

other fissionable isotopes in nuclear reactors and nuclear weapons. Trace quantities also originate from natural fission of uranium-238. It is among the most problematic of the short-to-medium-lifetime fission products. When suddenly released at high temperature, as in the case of the Chernobyl nuclear accident and with atomic bombs explosions, because of the relatively low boiling point (671 °C, 1240 F) of the element, ¹³⁷Cs is easily volatilized in the atmosphere and transported in the air on very long distances. After the radioactive fallout, it is deposited onto the soil and easily moves and spreads in the environment because of the high water solubility of caesium's most common chemical compounds, which are salts. ¹³⁷Cs was discovered by Glenn T. Seaborg and Margaret Melhase.

Decay

Caesium-137 has a half-life of about 30.17 years. About 94.6% decays by beta emission to a metastable nuclear isomer of barium: barium-137m (^137mBa, Ba-137m). The remainder directly populates the ground state of barium-137, which is stable. Metastable barium has a half-life of about 153 seconds, and is responsible for all of the gamma ray emissions in samples of caesium-137. ^137mBa decays to the ground state by emission of photons having energy 0.6617 MeV. A total of 85.1% of ¹³⁷Cs decays lead to gamma ray emission in this way. One gram of caesium-137 has an activity of 3.215 terabecquerel (TBq).

Health risk of radioactive caesium

Caesium-137 reacts with water, producing a water-soluble compound (caesium hydroxide). The biological behaviour of caesium is similar to that of potassium and rubidium. After entering the body, caesium gets more or less uniformly distributed throughout the body, with the highest concentrations in soft tissue. The biological half-life of caesium is about 70 days.

Important researches have shown a remarkable concentration of ¹³⁷Cs in the exocrine cells of the pancreas, which are those most affected by cancer. In 2003, in autopsies performed on 6 children dead in the polluted area near Chernobyl where they also reported a higher incidence of pancreatic tumors, Bandazhevsky found a concentration of ¹³⁷Cs 40-45 times higher than in their liver, thus demonstrating that pancreatic tissue is a strong accumulator and secretor in the intestine of radioactive cesium.

Radioactive caesium in the environment

Caesium-137, along with other radioactive isotopes caesium-134, iodine-131, xenon-133, and strontium-90, were released into the environment during nearly all nuclear weapon tests and some nuclear accidents, most notably the Chernobyl disaster and the Fukushima Daiichi disaster.

 

Chernobyl disaster

As of today and for the next few hundred years or so, caesium-137 and strontium-90 continue to be the principal source of radiation in the zone of alienation around the Chernobyl nuclear power plant, and pose the greatest risk to health, owing to their approximately 30 year half-life and biological uptake. The mean contamination of caesium-137 in Germany following the Chernobyl disaster was 2000 to 4000 Bq/m². This corresponds to a contamination of 1 mg/km² of caesium-137, totaling about 500 grams deposited over all of Germany. In Scandinavia, some reindeer and sheep exceeded the Norwegian legal limit (3000 Bq/kg) 26 years after Chernobyl. As of 2016, the Chernobyl caesium-137 has decayed by half, but could have been locally concentrated by much larger factors.

 

Fukushima Daiichi disaster

In April 2011, elevated levels of caesium-137 were also being found in the environment after the Fukushima Daiichi nuclear disasters in Japan. In July 2011, meat from 11 cows shipped to Tokyo from Fukushima

Prefecture was found to have 1,530 to 3,200 becquerels per kilogram of ¹³⁷Cs, considerably exceeding the Japanese legal limit of 500 becquerels per kilogram at that time. In March 2013, a fish caught near the plant had a record 740,000 becquerels per kilogram of radioactive caesium, above the 100 becquerels per kilogram government limit. A 2013 paper in Scientific Reports found that for a forest site 50 km from the stricken plant, ¹³⁷Cs concentrations were high in leaf litter, fungi and detritivores, but low in herbivores. By the end of 2014, "Fukushima-derived radiocaesium had spread into the whole western North Pacific Ocean", transported by the North Pacific current from Japan to the Gulf of Alaska. It has been measured in the surface layer down to 200 meters and south of the current area down to 400 meters.

Caesium-137 is reported to be the major health concern in Fukushima. A number of techniques are being considered that will be able to strip out 80% to 95% of the caesium from contaminated soil and other materials efficiently and without destroying the organic material in the soil. These include hydrothermal blasting. The caesium precipitated with ferric ferrocyanide (Prussian blue) would be the only waste requiring special burial sites. The aim is to get annual exposure from the contaminated environment down to 1 mSv above background. The most contaminated area where radiation doses are greater than 50 mSv/year must remain off limits, but some areas that are currently less than 5 mSv/year may be decontaminated, allowing 22,000 residents to return.

Effects of climate change

The effects of climate change span the physical environment, ecosystems and human societies. It also includes the economic and social changes which stem from living in a warmer world. Human-caused climate change is one of the threats to sustainability.

Many physical impacts of climate change are already visible, including extreme weather events, glacier retreat, changes in the timing of seasonal events (e.g., earlier flowering of plants), sea level rise, and declines in Arctic sea ice extent. The ocean has taken up between 20 and 30% of human-induced atmospheric carbon dioxide since the 1980s, leading to ocean acidification. The ocean is also warming and since 1970 has absorbed more than 90% of the excess heat in the climate system.

Climate change has already impacted ecosystems and humans. In combination with climate variability, it makes food insecurity worse in many places and puts pressure on fresh water supply. This, in combination with extreme weather events, leads to negative effects on human health. Climate change has also contributed to desertification and land degradation in many regions of the world. This has implications for livelihoods as many people are dependent on land for food, feed, fibre, timber and energy. Rising temperatures, changing precipitation patterns and the increase in extreme events threaten development because of negative effects on economic growth in developing countries. Climate change already contributes to migration in different parts of the world.

The future impact of climate change depends on the extent to which nations implement prevention efforts, reduce greenhouse gas emissions, and adapt to unavoidable climate change effects. Much of the policy debate concerning climate change mitigation has been framed by projections for the twenty-first century. The focus on a limited time window obscures some of the problems associated with climate change. Policy decisions made in the next few decades will have profound impacts on the global climate, ecosystems and human societies, not just for this century, but for the next millennia, as near-term climate change policies significantly affect long-term climate change impacts.

Stringent mitigation policies might be able to limit global warming (in 2100) to around 2 °C or below, relative to pre-industrial levels. Without mitigation, increased energy demand and the extensive use of fossil fuels may lead to global warming of around 4 °C. With higher magnitudes of global warming, societies and ecosystems will likely encounter limits to how much they can adapt.

Observed and future warming

Global warming refers to the long-term rise in the average temperature of the Earth's climate system. It is a major aspect of climate change, and has been demonstrated by the instrumental

 temperature record which shows global warming of around 1 °C since the pre-industrial period, although the bulk of this (0.9 °C) has occurred since 1970. A wide variety of temperature proxies together prove that the 20th century was the hottest recorded in the last 2,000 years. Compared to climate variability in the past, current warming is also more globally coherent, affecting 98% of the planet. The impact on the environment, ecosystems, the animal kingdom, society and humanity depends on how much more the Earth warms.

The Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report concluded, "It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century." This has been brought about primarily through the burning of fossil fuels which has led to a significant increase in the concentration of GHGs in the atmosphere.

Physical impacts

A broad range of evidence shows that the climate system has warmed. Evidence of global warming is shown in the graphs (below right) from the US National Oceanic and Atmospheric Administration (NOAA).

Some of the graphs show a positive trend, e.g., increasing temperature over land and the ocean, and sea level rise. Other graphs show a negative trend, such as decreased snow cover in the Northern Hemisphere, and declining Arctic sea ice, both of which are indicative of global warming. Evidence of warming is also apparent in living (biological) systems such as changes in distribution of flora and fauna towards the poles.

Human-induced warming could lead to large-scale, abrupt and/or irreversible changes in physical systems. An example of this is the melting of ice sheets, which contributes to sea level rise and will continue for thousands of years. The probability of warming having unforeseen consequences increases with the rate, magnitude, and duration of climate change.

Wildlife and nature

Recent warming has strongly affected natural biological systems. Species worldwide are moving poleward to
colder areas. On land, species move to higher elevations, whereas marine species find colder water at greater depths. Of the drivers with the biggest global impact on nature, climate change ranks third over the five decades before 2020, with only change in land use and sea use, and direct exploitation of organisms having a greater impact.

The impacts of climate change in nature and nature's contributions to humans are projected to become more pronounced in the next few decades. Examples of climatic disruptions include fire, drought, pest infestation, invasion of species, storms, and coral bleaching events. The stresses caused by climate change, added to other stresses on ecological systems (e.g. land conversion, land degradation, harvesting, and pollution), threaten substantial damage to or complete loss of some unique ecosystems, and extinction of some critically endangered species. Key interactions between species within ecosystems are often disrupted because species from one location do not move to colder habitats at the same rate, giving rise to rapid changes in the functioning of the ecosystem.

Regional effects

Regional effects of global warming vary in nature. Some are the result of a generalised global change, such as
rising temperature, resulting in local effects, such as melting ice. In other cases, a change may be related to a change in a particular ocean current or weather system. In such cases, the regional effect may be disproportionate and will not necessarily follow the global trend.

There are three major ways in which global warming will make changes to regional climate: melting or forming ice, changing the hydrological cycle (of evaporation and precipitation) and changing currents in the oceans and air flows in the atmosphere. The coast can also be considered a region, and will suffer severe impacts from sea level rise.

The Arctic, Africa, small islands, Asian megadeltas and the Middle East are regions that are likely to be especially affected by climate change. Low-latitude, less-developed regions are at most risk of experiencing negative impacts due to climate change. Developed countries are also vulnerable to climate change. For example, developed countries will be negatively affected by increases in the severity and frequency of some extreme weather events, such as heat waves.

Projections of climate changes at the regional scale do not hold as high a level of scientific confidence as projections made at the global scale. It is, however, expected that future warming will follow a similar geographical pattern to that seen already, with the greatest warming over land and high northern latitudes, and least over the Southern Ocean and parts of the North Atlantic Ocean. Land areas warm faster than ocean, and this feature is even stronger for extreme temperatures. For hot extremes, regions with the most warming include Central and Southern Europe and Western and Central Asia.

On humans

The effects of climate change, in combination with the sustained increases in greenhouse gas emissions, have led scientists to characterize it as a climate emergency. Some climate researchers and activists have called it an existential threat to civilization. Some areas may become too hot for humans to live in while people in some areas may experience displacement triggered by flooding and other climate change related disasters.

The vulnerability and exposure of humans to climate change varies from one economic sector to another and will have different impacts in different countries. Wealthy industrialised countries, which have emitted the most CO₂, have more resources and so are the least vulnerable to global warming. Economic sectors that are likely to be affected include agriculture, human health, fisheries, forestry, energy, insurance, financial services, tourism, and recreation. The quality and quantity of freshwater will likely be affected almost everywhere. Some people may be particularly at risk from climate change, such as the poor, young children and the elderly. According to the World Health Organization, between 2030 and 2050, "climate change is expected to cause about 250,000 additional deaths per year." As global temperatures increase, so does the number of heat stress, heatstroke, and cardiovascular and kidney disease deaths and illnesses. When air pollution worsens, so does respiratory health, particularly for the 300 million people worldwide living with asthma; there is more airborne pollen and mold to torment hay fever and allergy sufferers.

Abrupt or irreversible changes

Self-reinforcing feedbacks amplify and accelerate climate change. 

The climate system exhibits threshold behaviour or tipping points when these feedbacks lead parts of the Earth system into a new state, such as the runaway loss of ice sheets or the destruction of too many forests. Tipping points are studied using data from Earth's distant past and by physical modelling. There is already moderate risk of global tipping points at 1 °C above pre-industrial temperatures, and that risk becomes high at 2.5 °C.

Tipping points are "perhaps the most ‘dangerous’ aspect of future climate changes", leading to irreversible impacts on society. Many tipping points are interlinked, so that triggering one may lead to a cascade of effects. A 2018 study states that 45% of environmental problems, including those caused by climate change are interconnected and make the risk of a domino effect bigger.

Irreversible change

Warming commitment to CO
2 concentrations.

If emissions of CO
2 were to be abruptly stopped and no negative emission technologies deployed, the Earth's climate would not start moving back to its pre-industrial state. Instead, temperatures would stay elevated at the same level for several centuries. After about a thousand years, 20% to 30% of human-emitted CO
2 will remain in the atmosphere, not taken up by the ocean or the land, committing the climate to warming long after emissions have stopped. Pathways that keep global warming under 1.5 °C often rely on large-scale removal of CO
2, which feasibility is uncertain and has clear risks.

Irreversible impacts

There are a number of examples of climate change impacts that may be irreversible, at least over the timescale of many human generations. These include the large-scale singularities such as the melting of the Greenland and West Antarctic ice sheets, and changes to the AMOC. In biological systems, the extinction of species would be an irreversible impact. In social systems, unique cultures may be lost due to climate change. For example, humans living on atoll islands face risks due to sea level rise, sea surface warming, and increased frequency and intensity of extreme weather events.

Global catastrophic risk

A global catastrophic risk is a hypothetical future event which could damage human well-being on a global scale, even endangering or destroying modern civilization. An event that could cause human extinction or permanently and drastically curtail humanity's potential is known as an existential risk.

Potential global catastrophic risks include anthropogenic risks, caused by humans (technology, governance, climate change), and non-anthropogenic or external risks. Examples of technology risks are hostile artificial
intelligence and destructive biotechnology or nanotechnology. Insufficient or malign global governance creates risks in the social and political domain, such as a global war, including 
nuclear holocaust, bioterrorism using genetically modified organisms, cyberterrorism destroying critical infrastructure like the electrical grid; or the failure to manage a natural pandemic.
Problems and risks in the domain of earth system governance include global warming, environmental degradation, including extinction of species, famine as a result of non-equitable resource distribution, human overpopulation, crop failures and non-sustainable agriculture.

Examples of non-anthropogenic risks are an asteroid impact event, a supervolcanic eruption, a lethal gamma-ray burst, a geomagnetic storm destroying electronic equipment, natural long-term climate change, hostile extraterrestrial life, or the predictable Sun transforming into a red giant star engulfing the Earth.