Effects of the Chernobyl disaster


The 1986 Chernobyl disaster triggered the release of substantial amounts of radioactive contamination into the atmosphere in the form of both particulate and gaseous radioisotopes. it is the most significant unintentional release of radioactivity into the environment.
The work of the Scientific Committee on Problems of the Environment, suggests that the Chernobyl incident cannot be directly compared to atmospheric tests of nuclear weapons through a single number, with one being simply times larger than the other. This is partly due to the fact that the isotopes released at Chernobyl tended to be longer-lived than those released by the detonation of atomic bombs.
The economic damage caused by the disaster is estimated at $235 billion.

Radiation effects on humans

According to a 2009 United Nations Scientific Committee on the Effects of Atomic Radiation, the Chernobyl accident had by 2005 caused 61,200 man-Sv of radiation exposure to recovery workers and evacuees, 125,000 man-Sv to the populace of Ukraine, Belarus, and Russia, and a dose to most of the more distant European countries amounting to 115,000 man-Sv. The same report estimated a further 25% more exposure would be received from residual radiosotopes after 2005. The total global collective dose from Chernobyl was earlier estimated by UNSCEAR in 1988 to be "600,000 man Sv, equivalent on average to 21 additional days of world exposure to natural background radiation."

Dose to the general public within 30 km of the plant

The inhalation dose for the public during the time of the accident and their evacuation from the area in what is now the 30 km evacuation zone around the plant has been estimated to be between 3 and 150 mSv.
Thyroid doses for adults around the Chernobyl area were estimated to be between 20 and 1000 mSv, while for one-year-old infants, these estimates were higher, at 20 to 6000 mSv. For those who left at an early stage after the accident, the internal dose due to inhalation was 8 to 13 times higher than the external dose due to gamma/beta emitters. For those who remained until later, the inhalation dose was 50 to 70% higher than the dose due to external exposure. The majority of the dose was due to iodine-131 and tellurium and rubidium isotopes.
The ingestion doses in this same group of people have also been estimated using the cesium activity per unit of area, isotope ratios, an average day of evacuation, intake rate of milk and green vegetables, and what is known about the transfer of radioactivity via plants and animals to humans. For adults, the dose has been estimated to be between 3 and 180 mSv, while for one-year-old infants, a dose of between 20 and 1300 mSv has been estimated. Again, the majority of the dose was thought to be mostly due to iodine-131.

Childhood exposure

Ukraine, Belarus and parts of Russia received substantial amounts of radiation exposure after the Chernobyl disaster in 1986, but prior to the disaster the number of children affected by thyroid cancer was relatively low globally. Every year about, "0.1–2.2 individuals per million of all aged under 15 years old world wide" were affected by thyroid cancer. Research has shown after the Chernobyl disaster the level of thyroid cancer, particularly in children near the radiation exposure, has abnormally increased. Although iodine-131 has a relatively short half-life compared to other radioactive isotopes, iodine-131 made its way through the food chain through a milk-to-consumer pathway. 95% of iodine-131 was ingested through milk shortly after the disaster. Communities were unaware of the contamination deposited in soil and the transforming capabilities of radiation into other food sources. Through the consumption of milk, children received abnormal amounts of radiation exposure.
The high absorption rate discovered in children has also shown to be inversely proportional to age.
There is a high rate of thyroid cancer among children less than 15 years old who were exposed to the radiation after the disaster and an increasing level of dosage as age decreases. This inverse proportion could be explained by the way in which children absorb iodine-131. Children have smaller thyroid glands compared to adults and have a different dosage response after the ingestion of iodine-131. A cohort study conducted in 2013 discovered a similar trend between age and dosage response. The cohort was composed of 12,000 participants, all of which were exposed to the radiation in Belarus and reported to be under the age of 18 at the time of the exposure.

Future study

Studying the populations that were exposed to radiation after the Chernobyl accident has provided important data linking exposure to radiation and the future development of cancer.
Cases of pediatric thyroid cancer, likely caused by absorption of Iodine-131 into the thyroid gland, increased in Ukraine and Belarus 3 to 4 years after the accident. Children were most at risk, and cases did not seem to increase in adults. The greatest increase was seen in children who were the youngest at the time of exposure, and most of the pediatric thyroid cases were reported in Gomel, Belarus, where the population was exposed to the highest levels of contamination. The majority of the cases that appeared in the exposed population were papillary thyroid cancer.
Before the accident, the rate of thyroid cancer in children in Belarus was less than 1 per million. By 1995, nine years after the disaster, the number of cases of pediatric thyroid cancer in Gomel Oblast rose to 100 per million per year. Even as adults those who were exposed to the radiation as children may still be at risk of developing thyroid cancer decades after the exposure. It is important to study the at risk population throughout their lives, and observe if different patterns arise in tumors that develop with longer latency.
A group of experts who are part of the Agenda for Research on Chernobyl Health have proposed a series of potential studies that would examine the continued effects from the Chernobyl accident, and provide more information on the full extent of related health consequences. Results from lifelong observation of the exposed population could provide more information on risks as well as future pagainst radiation exposure.

Short-term health effects and immediate results

The explosion at the power station and subsequent fires inside the remains of the reactor resulted in the development and dispersal of a radioactive cloud which drifted not only over Russia, Belarus, and Ukraine, but also over most of Europe and as far as Canada. In fact, the initial evidence in other countries that a major release of radioactive material had occurred came not from Soviet sources, but from Sweden, where on 28 April workers at the Forsmark Nuclear Power Plant were found to have radioactive particles on their clothing.
It was Sweden's search for the source of radioactivity that led to the first hint of a serious nuclear problem in the Western Soviet Union.
Contamination from the Chernobyl disaster was not evenly spread across the surrounding countryside but scattered irregularly depending on weather conditions. Reports from Soviet and Western scientists indicate that Belarus received about 60% of the contamination that fell on the former Soviet Union. A large area in Russia south of Bryansk was also contaminated, as were parts of northwestern Ukraine.
203 people were hospitalized immediately, of whom 31 died. Most of these were fire and rescue workers trying to bring the disaster under control, who were not fully aware of how dangerous the radiation exposure was. 135,000 people were evacuated from the area, including 50,000 from the nearby town of Pripyat, Ukraine. Health officials have predicted that over the next 70 years there will be a 28% increase in cancer rates in much of the population which was exposed to the 5–12 EBq of radioactive contamination released from the reactor.
Soviet scientists reported that the Chernobyl Unit 4 reactor contained about 180–190 metric tons of uranium dioxide fuel and fission products. Estimates of the amount of this material that escaped range from 5 to 30%. Because of the intense heat of the fire, and with no containment building to stop it, part of the ejected fuel was vaporized or particularized and lofted high into the atmosphere, where it spread.

Workers and "liquidators"

The workers involved in the recovery and clean up after the disaster, called "liquidators", received high doses of radiation. In most cases, these workers were not equipped with individual dosimeters to measure the amount of radiation received, so experts could only estimate their doses. Even where dosimeters were used, dosimetric procedures varied - some workers are thought to have been given more accurate estimated doses than others. According to Soviet estimates, between 300,000 and 600,000 people were involved in the cleanup of the 30 km evacuation zone around the reactor, but many of them entered the zone two years after the disaster.
Estimates of the number of "liquidators" vary; the World Health Organization, for example, puts the figure at about 600,000; Russia lists as liquidators some people who did not work in contaminated areas. In the first year after the disaster, the number of cleanup workers in the zone was estimated to be 2,000. These workers received an estimated average dose of 165 millisieverts.
A sevenfold increase in DNA mutations has been identified in children of liquidators conceived after the accident, when compared to their siblings that were conceived before. However, this effect has diminished sharply over time.

Evacuation

Military authorities started evacuating people from the area around Chernobyl only on the second day after the disaster. By May 1986, about a month later, all those living within a radius of the plant had been relocated. This area is often referred to as the zone of alienation. However, significant radiation affected the environment over a much wider scale than this 30 km radius encloses.
According to reports from Soviet scientists, 28,000 square kilometers were contaminated by caesium-137 to levels greater than 185 kBq per square meter. Roughly 830,000 people lived in this area. About 10,500 km 2 were contaminated by caesium-137 to levels greater than 555 kBq/m2. Of this total, roughly 7,000 km2 lie in Belarus, 2,000 km2 in the Russian Federation and 1,500 km2 in Ukraine. About 250,000 people lived in this area. These reported data were corroborated by the International Chernobyl Project.

Civilians

Some children in the contaminated areas were exposed to high thyroid doses of up to 50 gray, mostly due to an intake of radioactive iodine-131 from contaminated milk produced locally. Several studies have found that the incidence of thyroid cancer among children in Belarus, Ukraine, and Russia has risen sharply since the Chernobyl disaster. The International Atomic Energy Agency notes "1800 documented cases of thyroid cancer in children who were between 0 and 14 years of age when the disaster occurred, which is far higher than normal", although this source fails to note the expected rate. The childhood thyroid cancers that have appeared are of a large and aggressive type but, if detected early, can be treated. Treatment entails surgery followed by iodine-131 therapy for any metastases. To date, such treatment appears to have been successful in the vast majority of cases.
Late in 1995, the World Health Organization linked nearly 700 cases of thyroid cancer among children and adolescents to the Chernobyl disaster, and among these, some 10 deaths are attributed to radiation. However, the rapid increase in thyroid cancers detected suggests some of this increase may be an artifact of the screening process. Typical latency time of radiation-induced thyroid cancer is about 10 years, but the increase in childhood thyroid cancers in some regions was observed as early as 1987.

Plant and animal health

A large swath of pine forest killed by acute radiation was named the Red Forest. The dead pines were bulldozed and buried. Livestock were removed during the human evacuations. Elsewhere in Europe, levels of radioactivity were examined in various natural foodstocks. In both Sweden and Finland, fish in deep freshwater lakes were banned for resale and landowners were advised not to consume certain types. Information regarding physical deformities in the plant and animal populations in the areas affected by radioactive fallout require sampling and capture, along with DNA testing, of individuals to determine if abnormalities are the result of natural mutation, radiation poisoning, or exposure to other contaminants in the environment.
Animals living in contaminated areas in and around Chernobyl have suffered from a variety of side effects caused by radiation. Oxidative stress and low levels of antioxidants have had severe consequences on the development of the nervous system, including reduced brain size and impaired cognitive abilities. It has been found that birds living in areas with high levels of radiation have statistically significantly smaller brains, which has shown to be a deficit to viability in the wild. Barn swallows that live in or around Chernobyl have displayed an increased rate of physical abnormalities compared to swallows from uncontaminated areas. Abnormalities included partially albinistic plumage, deformed toes, tumors, deformed tail feathers, deformed beaks, and deformed air sacks. Birds with these abnormalities have a reduced viability in the wild and a decrease in fitness. Moeller et al. claimed in 2007 that these effects were likely due to radiation exposure and elevated teratogenic effects of radioactive isotopes in the environment although these conclusions have been challenged. Various birds in the area appear to have adapted to lower levels of radiation by producing more antioxidants, such as glutathione, to help mitigate the oxidative stress.
Invertebrate populations significantly decreased. As of 2009, most radioactivity around Chernobyl was located in the top layer of soil, where many invertebrates live or lay their eggs. The reduced abundance of invertebrates could have negative implications for the entire ecosystem surrounding Chernobyl.
Radionuclides migrate through either soil diffusion or transportation within the soil solution. The effects of ionizing radiation on plants and trees in particular depends on numerous factors, including climatic conditions, the mechanism of radiation deposition, and the soil type. In turn, radiated vegetation affects organisms further up the food chain. In general, the upper-level trophic organisms received less contamination, due to their ability to be more mobile and feed from multiple areas.
The amount of radioactive nuclides found to have been deposited into surrounding lakes has increased the normal baseline radioactive amounts by 100 percent. Most of the radionuclides in surrounding water areas were found in the sediments at the bottom of the lakes. There has been a high incidence of chromosomal changes in plant and animal aquatic organisms, and this generally has correlated with the contamination and resulting genetic instability. Most of the lakes and rivers surrounding the Chernobyl exclusion zone are still highly contaminated with radionuclides as the natural decontamination processes of nuclides with longer half-lives can take many years.
One of the main mechanisms by which radionuclides were passed to humans was through the ingestion of milk from contaminated cows. Most of the rough grazing that the cows took part in contained plant species such as coarse grasses, sedges, rushes, and plants such as heather. These plant species grow in soils that are high in organic matter, low in pH, and are often very well hydrated, thus making the storage and intake of these radionuclides much more feasible and efficient. In the early stages following the Chernobyl accident, high levels of radionuclides were found in the milk and were a direct result of contaminated feeding. Within two months of banning most of the milk that was being produced in the affected areas, officials had phased out the majority of the contaminated feed that was available to the cows and much of the contamination was isolated. In humans, ingestion of milk containing abnormally high levels of iodine radionuclides was the precursor for thyroid disease, especially in children and in the immunocompromised.
Some plants and animals were able to adapt to the increased radiation levels present in and around Chernobyl. Arabidopsis, a plant native to Chernobyl, was able to resist high concentrations of ionizing radiation and resist forming mutations. This species of plant has been able to develop mechanisms to tolerate chronic radiation that would otherwise be harmful or lethal to other species.
Studies suggest the 30 km "exclusion zone" surrounding the Chernobyl disaster has become a wildlife sanctuary. Animals have reclaimed the land including species such as the Przewalski’s horse, Eurasian lynx, wild boar, grey wolf, elk, red deer, moose, brown bear, turtle, voles, mice, shrews, European badger, Eurasian beaver, raccoon dog, red fox, roe deer, European bison, black stork, golden eagle, white-tailed eagle and eagle owl whose populations are all thriving. When the disaster first occurred, the health and reproductive ability of many animals and plants were negatively affected for the first six months. However, 30 years later, animals and plants have reclaimed the abandoned zone to make it their habitat. Even the site of the explosion was flourishing with wildlife in 2012 as birds nested in the wrecked nuclear plant, and plants and mushrooms lived in and on the site. A 2015 study found similar numbers of mammals in the zone compared to nearby similar nature reserves and the wildlife population was probably higher than it had been before the accident.
Due to the bioaccumulation of caesium-137, some mushrooms as well as wild animals which eat them, e.g. wild boars hunted in Germany and deer in Austria, may have levels which are not considered safe for human consumption. Mandatory radioactivity testing of sheep in parts of the UK that graze on lands with contaminated peat was lifted in 2012.
In 2016, 187 local Ukrainians had returned and were living permanently in the zone.

Human pregnancy

Despite spurious studies from Germany and Turkey, the only robust evidence of negative pregnancy outcomes that transpired after the accident was the increase in elective abortions, these "indirect effects", in Greece, Denmark, Italy etc., have been attributed to "anxieties created" by the media.
Researchers at the time knew that very high doses of radiation increase the rate of physiological pregnancy and fetal abnormalities, but select researchers who were familiar with both the prior human exposure data and animal testing knew that, unlike the dominant linear no-threshold model of radiation and cancer rate increases, the "Malformation of organs appears to be a deterministic effect with a threshold dose" below which no rate increase is observed. Frank Castronovo of the Harvard Medical School discussed this teratology issue in 1999, publishing a detailed review of dose reconstructions and the available pregnancy data following the Chernobyl accident, which included data from Kiev's two largest obstetrics hospitals. Castronovo concludes that "the lay press with newspaper reporters playing up anecdotal stories of children with birth defects" and dubious studies that flawed by "selection bias", are the two primary factors causing the persistent belief that Chernobyl increased the background rate of birth defects. However, the vast amount of pregnancy data simply does not support this perception because, since no pregnant individuals took part in the most radioactive liquidator operations, no pregnant individuals were exposed to the threshold dose.
Despite Mr. Castronovo's statements Karl Sperling, Heidemarie Neitzel and Hagen Scherb reported that the prevalence of Down syndrome in West Berlin, Germany, peaked 9 months following the main fallout. From 1980 to 1986 the birth prevalence of Down syndrome was quite stable. In 1987, 46 cases were diagnosed and most of the increase resulted from a cluster of 12 children born in January 1987. The prevalence of Down Syndrome in 1988 was 1.77, and in 1989, it reached pre-Chernobyl values. The authors noted that the cluster of children would have been conceived when radioactive clouds containing radionucleotides with short half-lives, like iodine, would have been covering the region and also that the isolated geographical position of West Berlin prior to reunification, the free genetic counseling, and complete coverage of the population through one central cytogenetic laboratory supported completeness of case ascertainment; in addition, constant culture preparation and analysis protocols ensure a high quality of data.

Long-term health effects

Science and politics: the problem of epidemiological studies

The issue of long-term effects of the Chernobyl disaster on civilians is very controversial. The number of people whose lives were affected by the disaster is sizable. Over 300,000 people were resettled because of the disaster; millions lived and continue to live in the contaminated area. On the other hand, most of those affected received relatively low doses of radiation; there is little evidence of increased mortality, cancers or birth defects among them; and when such evidence is present, existence of a causal link to radioactive contamination is uncertain.
An increased incidence of thyroid cancer among children in areas of Belarus, Ukraine and Russia affected by the Chernobyl disaster has been firmly established as a result of screening programs and, in the case of Belarus, an established cancer registry. The findings of most epidemiological studies must be considered interim, say experts, as analysis of the health effects of the disaster is an ongoing process. Multilevel modelling indicates that long-term psychological distress among Belarusians affected by the Chernobyl disaster is better predicted by stress-moderating psychosocial factors present in one's daily life than by level of residential radiation contamination.
Epidemiological studies have been hampered in Ukraine, Russian Federation and Belarus by a lack of funds, an infrastructure with little or no experience in chronic disease epidemiology, poor communication facilities and an immediate public health problem with many dimensions. Emphasis has been placed on screening rather than on well-designed epidemiological studies. International efforts to organize epidemiological studies have been slowed by some of the same factors, especially the lack of a suitable scientific infrastructure.
Furthermore, the political nature of nuclear energy may have affected scientific studies. In Belarus, Yury Bandazhevsky, a scientist who questioned the official estimates of Chernobyl's consequences and the relevancy of the official maximum limit of 1,000 Bq/kg, was imprisoned from 2001 to 2005. Bandazhevsky and some human rights groups allege his imprisonment was a reprisal for his publication of reports critical of the official research being conducted into the Chernobyl incident.
The activities undertaken by Belarus and Ukraine in response to the disaster — remediation of the environment, evacuation and resettlement, development of uncontaminated food sources and food distribution channels, and public health measures — have overburdened the governments of those countries. International agencies and foreign governments have provided extensive logistic and humanitarian assistance. In addition, the work of the European Commission and World Health Organization in strengthening the epidemiological research infrastructure in Russia, Ukraine and Belarus is laying the basis for major advances in these countries' ability to carry out epidemiological studies of all kinds.

Caesium radioisotopes

Immediately after the disaster, the main health concern involved radioactive iodine, with a half-life of eight days. Today, there is concern about contamination of the soil with strontium-90 and caesium-137, which have half-lives of about 30 years. The highest levels of caesium-137 are found in the surface layers of the soil where they are absorbed by plants, insects and mushrooms, entering the local food supply. Some scientists fear that radioactivity will affect the local population for the next several generations. Note that caesium is not mobile in most soils because it binds to the clay minerals.
Tests showed that caesium-137 levels in trees of the area were continuing to rise. It is unknown if this is still the case. There is some evidence that contamination is migrating into underground aquifers and closed bodies of water such as lakes and ponds. The main source of elimination is predicted to be natural decay of caesium-137 to stable barium-137, since runoff by rain and groundwater has been demonstrated to be negligible.

Thyroid cancer

An increased incidence of thyroid cancer was observed for about 4 years after the accident and slowed in 2005. The large increase in incidence of thyroid cancer happened amongst individuals who were adolescents and young children living during the time of the accident, and residing in the most contaminated areas of Belarus, the Russian Federation and Ukraine. High levels of radioactive iodine were released in the environment from the Chernobyl reactor after the accident, and accumulated in pastures which were eaten by cows. The milk was later consumed by children who already had an iodine deficient diet, therefore causing more of the radioactive iodine to be accumulated. Radioactive iodine has a short half-life, 8.02 days, if the contaminated milk would have been avoided or stopped, it is likely that most of the rise in radiation-induced thyroid cancer wouldn’t have happened.
Within the highly contaminated areas – Belarus, the Russian Federation and Ukraine, there were around 5000 cases of thyroid cancer that have been diagnosed since the accident. These cases were found in individuals who were aged 18 and younger during the time of the accident.
Supported by the Russian Federation and Ukraine, The European Commission, the National Cancer Institute of the US, and the Sasakawa Memorial Health Foundation, The Chernobyl Tissue Bank was created in 1998, 6 years after published research showed a rise in childhood thyroid cancer. The project is the first international co-operation that collects biological samples from patients exposed to radioiodine during childhood. It started collecting a variety of biological samples from patients on 1 October 1998 and since July 2001 has been a source for ethically available tissue samples - specifically extracted nucleic acids and tissue sections - for 21 research projects in Japan, Europe and the USA. The CTB serves as a model for tissue banking for cancer research in the molecular age.

34 years after the incident

Twenty-five years after the incident, restriction orders had remained in place in the production, transportation and consumption of food contaminated by Chernobyl fallout. In the UK, only in 2012 the mandatory radioactivity testing of sheep in contaminated parts of the UK that graze on lands was lifted. They covered 369 farms on 750 km2 and 200,000 sheep. In parts of Sweden and Finland, restrictions are in place on stock animals, including reindeer, in natural and near-natural environments. "In certain regions of Germany, Austria, Italy, Sweden, Finland, Lithuania and Poland, wild game, wild mushrooms, berries and carnivorous fish from lakes reach levels of several thousand Bq per kg of caesium-137", while "in Germany, caesium-137 levels in wild boar muscle reached 40,000 Bq/kg. The average level is 6,800 Bq/kg, more than ten times the EU limit of 600 Bq/kg", according to the TORCH 2006 report. The European Commission has stated that "The restrictions on certain foodstuffs from certain Member States must therefore continue to be maintained for many years to come".
As of 2009, sheep farmed in some areas of the UK are still subject to inspection which may lead to them being prohibited from entering the human food chain because of contamination arising from the accident:
Some of this radioactivity, predominantly radiocaesium-137, was deposited on certain upland areas of the UK, where sheep-farming is the primary land-use. Due to the particular chemical and physical properties of the peaty soil types present in these upland areas, the radiocaesium is still able to pass easily from soil to grass and hence accumulate in sheep. A maximum limit of 1,000 becquerels per kilogramme of radiocaesium is applied to sheep meat affected by the accident to protect consumers. This limit was introduced in the UK in 1986, based on advice from the European Commission's Article 31 group of experts. Under power provided under the Food and Environment Protection Act 1985, Emergency Orders have been used since 1986 to impose restrictions on the movement and sale of sheep exceeding the limit in certain parts of Cumbria, North Wales, Scotland and Northern Ireland... When the Emergency Orders were introduced in 1986, the Restricted Areas were large, covering almost 9,000 farms, and over 4 million sheep. Since 1986, the areas covered by restrictions have dramatically decreased and now cover 369 farms, or part farms, and around 200,000 sheep. This represents a reduction of over 95% since 1986, with only limited areas of Cumbria, South Western Scotland and North Wales, covered by restrictions.

369 farms and 190,000 sheep are still affected, a reduction of 95% since 1986, when 9,700 farms and 4,225,000 sheep were under restriction across the United Kingdom.
Restrictions were finally lifted in 2012.
In Norway, the Sami people were affected by contaminated food.
Data from a long-term monitoring program from 1998 to 2015 shows a significant decrease in internal radiation exposure of the inhabitants of small villages in Belarus 80 km north of Gomel. Resettlement may even be possible in parts of the prohibited areas provided that people comply with appropriate dietary rules.

Effect on the natural world

According to reports from Soviet scientists at the First International Conference on the Biological and Radiological Aspects of the Chernobyl Accident, fallout levels in the 10 km zone around the plant were as high as 4.81 GBq/m2. The so-called "Red Forest" is the swath of pine trees, located immediately behind the reactor complex within the 10 km zone, which were killed off by heavy radioactive fallout. The forest is so named because in the days following the disaster the trees appeared to have a deep red hue as they died because of extremely heavy radioactive fallout. In the post-disaster cleanup operations, a majority of the 10 km2 forest was bulldozed and buried. The site of the Red Forest remains one of the most contaminated areas in the world.
In recent years there have been many reports suggesting the zone may be a fertile habitat for wildlife. For example, in the 1996 BBC Horizon documentary 'Inside Chernobyl's Sarcophagus', birds are seen flying in and out of large holes in the structure itself. Other casual observations suggest biodiversity around the massive radioactivity release has increased due to the removal of human influence. Storks, wolves, beavers, and eagles have been reported in the area.
Barn swallows sampled between 1991 and 2006 both in the Chernobyl exclusion zone had more physical abnormalities than control sparrows sampled elsewhere in Europe. Abnormal barn swallows mated with lower frequency, causing the percentage of abnormal swallows to decrease over time. This demonstrated the selective pressure against the abnormalities was faster than the effects of radiation that created the abnormalities. "This was a big surprise to us," Dr. Mousseau said. "We had no idea of the impact."
It is unknown whether fallout contamination will have any long-term adverse effect on the flora and fauna of the region, as plants and animals have significantly different and varying radiologic tolerance compared with humans. Some birds are reported with stunted tail feathers. There are reports of mutations in plants in the area. The Chernobyl area has not received very much biological study, although studies that have been done suggest that apparently healthy populations may be sink instead of source populations; in other words, that the apparently healthy populations are not contributing to the survival of species.
Using robots, researchers have retrieved samples of highly melanized black fungus from the walls of the reactor core itself. It has been shown that certain species of fungus, such as Cryptococcus neoformans and Cladosporium, can actually thrive in a radioactive environment, growing better than non-melanized variants, implying that they use melanin to harness the energy of ionizing radiation from the reactor.

Studies on wildlife in the Exclusion Zone

The Exclusion Zone around the Chernobyl nuclear power station is reportedly a haven for wildlife. As humans were evacuated from the area 25 years ago, existing animal populations multiplied and rare species not seen for centuries have returned or have been reintroduced, for example Eurasian lynx, wild boar, Eurasian wolf, Eurasian brown bear, European bison, Przewalski's horse, and Eurasian eagle owls. Birds even nest inside the cracked concrete sarcophagus shielding the shattered remains of Reactor 4. In 2007 the Ukrainian government designated the Exclusion Zone as a wildlife sanctuary, and at 488.7 km2 it is one of the largest wildlife sanctuaries in Europe.
According to a 2005 U.N. report, wildlife has returned despite radiation levels that are presently 10 to 100 times higher than normal background radiation. Although radiation levels were significantly higher soon after the accident, they have fallen because of radioactive decay.
Møller and Tim Mousseau have published the results of the largest census of animal life in the Chernobyl Exclusion Zone. It said, contrary to the Chernobyl Forum's 2005 report, that the biodiversity of insects, birds and mammals is declining. Møller and Mousseau have been criticized strongly by Sergey Gaschak, a Ukrainian biologist who did field work for the pair beginning in 2003. He regards their conclusions to be the result of a biased and unscientific anti-nuclear political agenda, unsupported by the data he collected for them. "I know Chernobyl Zone," he says. "I worked here many years. I can’t believe their results."
Some researchers have said that by halting the destruction of habitat, the Chernobyl disaster helped wildlife flourish. Biologist Robert J. Baker of Texas Tech University was one of the first to report that Chernobyl had become a wildlife haven and that many rodents he has studied at Chernobyl since the early 1990s have shown remarkable tolerance for elevated radiation levels.
Møller et al. suggested that the reproductive success and annual survival rates of barn swallows are much lower in the Exclusion Zone; 28% of barn swallows inhabiting Chernobyl return each year, while at a control area at Kanev, 250 km to the southeast, the return rate is around 40%. A later study by Møller et al. furthermore claimed an elevated frequency of eleven categories of subtle physical abnormalities in barn swallows, such as bent tail feathers, deformed air sacs, deformed beaks, and isolated albinistic feathers.
Smith et al. have disputed Møller's findings and instead proposed that a lack of human influence in the Exclusion Zone locally reduced the swallows' insect prey and that radiation levels across the vast majority of the exclusion zone are now too low to have an observable negative effect. But the criticisms raised were responded to in Møller et al.. It is possible that barn swallows are particularly vulnerable to elevated levels of ionizing radiation because they are migratory; they arrive in the exclusion area exhausted and with depleted reserves of radio-protective antioxidants after their journey.
Several research groups have suggested that plants in the area have adapted to cope with the high radiation levels, for example by increasing the activity of DNA cellular repair machinery and by hypermethylation. Given the uncertainties, further research is needed to assess the long-term health effects of elevated ionizing radiation from Chernobyl on flora and fauna.
In 2015, long-term empirical data showed no evidence of a negative influence of radiation on mammal abundance.

Chernobyl Forum report and criticisms

In September 2005, a comprehensive report was published by the Chernobyl Forum, comprising a number of agencies including the International Atomic Energy Agency, the World Health Organization, United Nations bodies and the Governments of Belarus, the Russian Federation and Ukraine. This report titled: "Chernobyl's legacy: Health, Environmental and Socio-Economic Impacts", authored by about 100 recognized experts from many countries, put the total predicted number of deaths due to the disaster around 4,000. This predicted death toll includes the 47 workers who died of acute radiation syndrome as a direct result of radiation from the disaster, nine children who died from thyroid cancer and an estimated 4000 people who could die from cancer as a result of exposure to radiation. This number was subsequently updated to 9000 excess cancer deaths.
An IAEA press officer admitted that the 4000 figure was given prominence in the report "...to counter the much higher estimates which had previously been seen.... "It was a bold action to put out a new figure that was much less than conventional wisdom.""
The report also stated that, apart from a 30 kilometre area around the site and a few restricted lakes and forests, radiation levels had returned to acceptable levels. For full coverage see the IAEA Focus Page.
The methodology of the Chernobyl Forum report, supported by Elisabeth Cardis of the International Agency for Research on Cancer, has been disputed by some advocacy organizations opposed to nuclear energy, such as Greenpeace and the International Physicians for Prevention of Nuclear Warfare, as well as some individuals such as Dr. Michel Fernex, retired medical doctor from the WHO and campaigner Dr. Christopher Busby. The main criticism has been with regard to the restriction of the Forum's study to Belarus, Ukraine and Russia. Furthermore, it only studied the case of 200,000 people involved in the cleanup, and the 400,000 most directly affected by the released radioactivity. German Green Party Member of the European Parliament Rebecca Harms, commissioned a report on Chernobyl in 2006. The 2006 TORCH report claimed that:
In terms of their surface areas, Belarus and Austria were most affected by higher levels of contamination. Other countries were seriously affected; for example, more than 5% of Ukraine, Finland and Sweden were contaminated to high levels. More than 80% of Moldova, the European part of Turkey, Slovenia, Switzerland, Austria and the Slovak Republic were contaminated to lower levels. And 44% of Germany and 34% of the UK were similarly affected.

While the IAEA/WHO and UNSCEAR considered areas with exposure greater than 40,000 Bq/m2, the TORCH report also included areas contaminated with more than 4,000 Bq/m2 of Cs-137.
The TORCH 2006 report "estimated that more than half the iodine-131 from Chernobyl was deposited outside the former Soviet Union. Possible increases in thyroid cancer have been reported in the Czech Republic and the UK, but more research is needed to evaluate thyroid cancer incidences in Western Europe". It predicted about 30,000 to 60,000 excess cancer deaths, 7 to 15 Times greater than the figure of 4,000 in the IAEA press release; warned that predictions of excess cancer deaths strongly depend on the risk factor used; and predicted excess cases of thyroid cancer range between 18,000 and 66,000 in Belarus alone depending on the risk projection model. However, elevated incidence thyroid cancer is still seen among Ukrainians who were exposed to radioactivity due to Chernobyl accident during their childhood, but who were diagnosed the malignancy as adults.
Another study claims possible heightened mortality in Sweden.
Greenpeace quoted a 1998 WHO study, which counted 212 dead from only 72,000 liquidators. The environmental NGO estimated a total death toll of 93,000 but cite in their report that "The most recently published figures indicate that in Belarus, Russia and the Ukraine alone the disaster could have resulted in an estimated 200,000 additional deaths in the period between 1990 and 2004." In its report, Greenpeace suggested there will be 270,000 cases of cancer alone attributable to Chernobyl fallout, and that 93,000 of these will probably be fatal compare with the IAEA 2005 report which claimed that "99% of thyroid cancers wouldn't be lethal".
According to the Union Chernobyl, the main organization of liquidators, 10% of the 600,000 liquidators are now dead, and 165,000 disabled.
According to an April 2006 report by the International Physicians for Prevention of Nuclear Warfare, entitled "Health Effects of Chernobyl - 20 years after the reactor catastrophe", more than 10,000 people are today affected by thyroid cancer and 50,000 cases are expected. In Europe, the IPPNW claims that 10,000 deformities have been observed in newborns because of Chernobyl's radioactive discharge, with 5,000 deaths among newborn children. They also state that several hundreds of thousands of the people who worked on the site after the disaster are now sick because of radiation, and tens of thousands are dead.
Revisiting the issue for the 25th anniversary of the Chernobyl disaster, the Union of Concerned Scientists described the Forum's estimate of four thousand as pertaining only to "a much smaller subgroup of people who experienced the greatest exposure to released radiation". Their estimates for the broader population are 50,000 excess cancer cases resulting in 25,000 excess cancer deaths.

Human health effects Studies

The majority of premature deaths caused by Chernobyl are expected to be the result of cancers and other diseases induced by radiation in the decades after the event. This will be the result of a large population exposed to relatively low doses of radiation increasing the risk of cancer across that population. Interpretations of the current health state of exposed populations vary. Therefore, estimates of the ultimate human impact of the disaster have relied on numerical models of the effects of radiation on health. Furthermore, the effects of low-level radiation on human health are not well understood, and so the models used, notably the linear no threshold model, are open to question.
Given these factors, studies of Chernobyl's health effects have come up with different conclusions and are sometimes the subject of scientific and political controversy. The following section presents some of the major studies on this topic.

Official studies

Chernobyl Forum report

In September 2005, a draft summary report by the Chernobyl Forum, comprising a number of UN agencies including the International Atomic Energy Agency, the World Health Organization, the United Nations Development Programme, other UN bodies and the Governments of Belarus, the Russian Federation and Ukraine, set the number of deaths due to the accident at about 50, and added that a "total of up to 4000 people could eventually die of radiation exposure from the Chernobyl nuclear power plant accident".
The full version of the WHO health effects report adopted by the UN, published in April 2006, included an added 5000 eventually possible fatalities from significantly contaminated areas in Belarus, Russia and Ukraine and predicted that, in total, an upper limit of 9000 might eventually die from cancer among the 6.9 million most-exposed Soviet citizens. Some newspapers and antinuclear organizations claimed the paper was minimizing the consequences of the accident.

2008 UNSCEAR report

The United Nations Scientific Committee on the Effects of Atomic Radiation produced a detailed report on the effects of Chernobyl for the General Assembly of the UN in 2011. This report concluded that 134 staff and emergency workers suffered acute radiation syndrome and of those 28 died of radiation exposure within three months. Many of the survivors suffered skin conditions and radiation induced cataracts, and 19 had since died, but from conditions not necessarily associated with radiation exposure. Of the several hundred thousand liquidators, apart from some emerging indications of increased leukaemia, there was no other evidence of health effects.
In the general public in the affected areas, the only effect with 'persuasive evidence' was a substantial fraction of the 6,000 cases of thyroid cancer in adolescents of whom by 2005 15 cases had proved fatal. There was no evidence of increased rates of solid cancers or leukaemia among the general population. However, there was a widespread psychological worry about the effects of radiation.
The total deaths reliably attributable by UNSCEAR to the radiation produced by the accident therefore was 62.
The report concluded that 'the vast majority of the population need not live in fear of serious health consequences from the Chernobyl accident'.

Unofficial studies

TORCH report

In 2006 German Green Party Member of the European Parliament Rebecca Harms commissioned two UK scientists for an alternate report in response to the UN report. The report included areas not covered by the Chernobyl forum report, and also lower radiation doses. It predicted about 30,000 to 60,000 excess cancer deaths and warned that predictions of excess cancer deaths strongly depend on the risk factor used, and urged more research stating that large uncertainties made it difficult to properly assess the full scale of the disaster.

Greenpeace

claimed contradictions in the Chernobyl Forum reports, quoting a 1998 WHO study referenced in the 2005 report, which projected 212 dead from 72,000 liquidators. In its report, Greenpeace suggested there will be 270,000 cases of cancer attributable to Chernobyl fallout, and that 93,000 of these will probably be fatal, but state in their report that "The most recently published figures indicate that in Belarus, Russia and Ukraine alone the accident could have resulted in an estimated 200,000 additional deaths in the period between 1990 and 2004." Blake Lee-Harwood, campaigns director at Greenpeace, believes that cancer was likely to be the cause of less than half of the final fatalities and that "intestinal problems, heart and circulation problems, respiratory problems, endocrine problems, and particularly effects on the immune system," will also cause fatalities. However, concern has been expressed about the methods used in compiling the Greenpeace report. It is not peer reviewed nor does it rely on peer review science as the Chernobyl Forum report did.

April 2006 IPPNW report

According to an April 2006 report by the German affiliate of the International Physicians for Prevention of Nuclear Warfare, entitled "Health Effects of Chernobyl", more than 10,000 people are today affected by thyroid cancer and 50,000 cases are expected. The report projected tens of thousands dead among the liquidators. In Europe, it alleges that 10,000 deformities have been observed in newborns because of Chernobyl's radioactive discharge, with 5000 deaths among newborn children. They also claimed that several hundreds of thousands of the people who worked on the site after the accident are now sick because of radiation, and tens of thousands are dead.

Yablokov/Nesterenko publication

is an English translation of the 2007 Russian publication Chernobyl by Alexey Yablokov, Vassily Nesterenko and Alexey Nesterenko. It was published online in 2009 by the New York Academy of Sciences in their Annals of the New York Academy of Sciences. The New York Academy of Sciences included a disclaimer to inform readers it did not commission, endorse or peer review the work.
"In no sense did Annals of the New York Academy of Sciences or the New York Academy of Sciences commission this work; nor by its publication does the Academy validate the claims made in the original Slavic language publications cited in the translated papers. Importantly, the translated volume has not been formally peer‐reviewed by the New York Academy of Sciences or by anyone else."
The report presents an analysis of scientific literature and concludes that medical records between 1986, the year of the accident, and 2004 reflect 985,000 deaths as a result of the radioactivity released. The authors suggest that most of the deaths were in Russia, Belarus and Ukraine, but others were spread through the many other countries the radiation from Chernobyl struck. The literature analysis draws on over 1,000 published titles and over 5,000 internet and printed publications discussing the consequences of the Chernobyl disaster. The authors contend that those publications and papers were written by leading Eastern European authorities and have largely been downplayed or ignored by the IAEA and UNSCEAR. Author Alexy V. Yablokov was also one of the general editors on the Greenpeace commissioned report also criticizing the Chernobyl Forum findings published one year prior to the Russian-language version of this report.
A critical review by Dr. Monty Charles in the journal Radiation Protection Dosimetry states that Consequences is a direct extension of the 2005 Greenpeace report, updated with data of unknown quality. The New York Academy of Sciences also published a severely critical review by M. I. Balonov from the Institute of Radiation Hygiene which stated that "The value of is not zero, but negative, as its bias is obvious only to specialists, while inexperienced readers may well be put into deep error." Several other critical responses have also been published.

Higher than statistically normal appearances of defects

The American Academy of Pediatrics published a study state that the overall rate of neural tube defects in the Rivne region of the Ukraine is one of the highest in Europe. The rate in Polissia is 27.0 per 10,000. The study suggested that rates of microcephaly and microphthalmia may also be higher than normal.

Other studies and claims

Since March 2001, 400 lawsuits have been filed in France against "X" by the , including 200 in April 2006. These persons are affected by thyroid cancer or goitres, and have filed lawsuits alleging that the French government, at the time led by Prime Minister Jacques Chirac, had not adequately informed the population of the risks linked to the Chernobyl radioactive fallout. The complaint contrasts the health protection measures put in place in nearby countries with the relatively high contamination suffered by the east of France and Corsica. Although the 2006 study by the French Institute of Radioprotection and Nuclear Safety said that no clear link could be found between Chernobyl and the increase of thyroid cancers in France, it also stated that papillary thyroid cancer had tripled in the following years.

International response

After the Chernobyl Disaster, many countries were reluctant to expand their own nuclear programs. Some countries, such as Italy and Switzerland tried to ban nuclear power all together. Others, such as the Dutch and Finland postponed the addition of nuclear power plants. The disaster reaffirmed policy made by Austria and Sweden to terminate use of all nuclear energy. Germany set up regulatory organizations and new policy including the Federal Ministry of Environment and Reactor Safety and a new act for precaution protection against nuclear radiation.
Policy levers were not only implemented on a national level, but on an international level as well. In June 1986, the European Community implemented new standards for cesium. They attempted to do the same for iodine, but could not reach an agreement. Additionally several international programs were formed, including the World Association of Nuclear Operators. This association essentially linked 130 operators in 30 different countries. Nuclear engineers would visit nuclear plants worldwide to learn and work towards better safety precautions.
The International Atomic Energy Agency, established in 1957, created the Nuclear Safety Assistance Coordination Centre, which serves as an example of the international, multilateral cooperation resulting from the disaster. They created the Convention on Early Notification of a Nuclear Accident and Convention on Assistance in the Case of a Nuclear Accident or Radiological Emergency. Nations called for a more comprehensive set of obligatory regulations for nuclear power plants from safe management of installation to safe management of radioactive waste. They also created the Joint Convention of Safety of Spent Fuel Management in which obliged nations to create proper policy to control nuclear power plant management.