Buddhahood

From Wikipedia, the free encyclopedia

Seated Buddha, from the Seokguram, Silla.

 

In Buddhism, buddhahood (Sanskrit: buddhatva; Pali: buddhatta or buddhabhāva; Chinese: 佛果) is the condition or rank of a buddha "awakened one".

The goal of Mahayana's bodhisattva path is Samyaksambuddhahood, so that one may benefit all sentient beings by teaching them the path of cessation of dukkha. Mahayana theory contrasts this with the goal of the Theravada path, where the goal is individual arhatship.

Explanation of the term Buddha

In Theravada Buddhism, Buddha refers to one who has become awake through their own efforts and insight, without a teacher to point out the dharma (Sanskrit; Pali dhamma; "right way of living"). A samyaksambuddha re-discovered the truths and the path to awakening and teaches these to others after his awakening. A pratyekabuddha also reaches Nirvana through his own efforts, but does not teach the dharma to others. An arhat needs to follow the teaching of a Buddha to attain Nirvana, but can also preach the dharma after attaining Nirvana. In one instance the term buddha is also used in Theravada to refer to all who attain Nirvana, using the term Sāvakabuddha to designate an arhat, someone who depends on the teachings of a Buddha to attain Nirvana. In this broader sense it is equivalent to the arhat.

Buddhahood is the state of an awakened being, who having found the path of cessation of dukkha ("suffering", as created by attachment to desires and distorted perception and thinking) is in the state of "No-more-Learning".

There is a broad spectrum of opinion on the universality and method of attainment of Buddhahood, depending on Gautama Buddha's teachings that a school of Buddhism emphasizes. The level to which this manifestation requires ascetic practices varies from none at all to an absolute requirement, dependent on doctrine. Mahayana Buddhism emphasizes the bodhisattva ideal instead of the Arhat.

The Tathagatagarba and Buddha-nature doctrines of Mahayana Buddhism consider Buddhahood to be a universal and innate property of absolute wisdom. This wisdom is revealed in a person's current lifetime through Buddhist practice, without any specific relinquishment of pleasures or "earthly desires". 

Buddhists do not consider Gautama to have been the only Buddha. The Pāli Canon refers to many previous ones (see list of the named Buddhas), while the Mahayana tradition additionally has many Buddhas of celestial origin (see Amitābha or Vairocana as examples, for lists of many thousands of Buddha names (see Taishō Tripiṭaka numbers 439–448).

Nature of the Buddha

The various Buddhist schools hold some varying interpretations on the nature of Buddha (see below).

Attainments

The Buddha, in Greco-Buddhist style, first-second century, Gandhara (now Pakistan). (Standing Buddha).

 

All Buddhist traditions hold that a Buddha is fully awakened and has completely purified his mind of the three poisons of craving, aversion and ignorance. A Buddha is no longer bound by saṃsāra, and has ended the suffering which unawakened people experience in life.

Most schools of Buddhism have also held that the Buddha was omniscient. However, the early texts contain explicit repudiations of making this claim of the Buddha.

Ten characteristics of a Buddha

Some Buddhists meditate on (or contemplate) the Buddha as having ten characteristics (Ch./Jp. 十號). These characteristics are frequently mentioned in the Pāli Canon as well as Mahayana teachings, and are chanted daily in many Buddhist monasteries:

1. Thus gone, thus come (Skt: tathāgata)
2. Worthy one (Skt: arhat)
3. Perfectly self-enlightened (Skt: samyak-saṃbuddha)
4. Perfected in knowledge and conduct (Skt: vidyā-caraṇa-saṃpanna )
5. Well gone (Skt: sugata)
6. Knower of the world (Skt: lokavida)
7. Unsurpassed (Skt: anuttara)
8. Leader of persons to be tamed (Skt: puruṣa-damya-sārathi)
9. Teacher of the gods and humans (Skt: śāsta deva-manuṣyāṇaṃ)
10. The Blessed One or fortunate one (Skt: bhagavat)

The tenth epithet is sometimes listed as "The World Honored Enlightened One" (Skt. Buddha-Lokanatha) or "The Blessed Enlightened One" (Skt. Buddha-Bhagavan).

Ten Indispensable Duties of a Buddha

According to Buddhist texts, upon reaching Buddhahood each Buddha must perform ten acts during his life to complete his duty as a Buddha.

1. A Buddha must predict that another person will attain Buddhahood in the future.
2. A Buddha must inspire somebody else to strive for Buddhahood.
3. A Buddha must convert all whom he must convert (i.e. his chief disciples, etc.).
4. A Buddha must live at least three-quarters of his potential lifespan.
5. A Buddha must have clearly defined what are good deeds and what are evil deeds.
6. A Buddha must appoint two of his disciples as his chief disciples.
7. A Buddha must descend from Tavatimsa Heaven after teaching his mother.
8. A Buddha must hold an assembly at Lake Anavatapta.
9. A Buddha must bring his parents to the Dhamma.
10. A Buddha must have performed the great Miracle at Savatthi.

Buddha as a supreme human

In the Pāli Canon, Gautama Buddha is known as being a "teacher of the gods and humans", superior to both the gods and humans in the sense of having nirvana or the greatest bliss, whereas the devas, or gods, are still subject to anger, fear and sorrow.

In the Madhupindika Sutta (MN 18), Buddha is described in powerful terms as the Lord of the Dhamma (Pali: Dhammasami, skt.: Dharma Swami) and the bestower of immortality (Pali: Amatassadata). 

Similarly, in the Anuradha Sutta (SN 44.2) Buddha is described as

the Tathagata—the supreme man, the superlative man, attainer of the superlative attainment.
[Buddha is asked about what happens to the Tathagatha after death of the physical body. Buddha replies],
"And so, Anuradha—when you can't pin down the Tathagata as a truth or reality even in the present life—is it proper for you to declare, 'Friends, the Tathagata—the supreme man, the superlative man, attainer of the superlative attainment—being described, is described otherwise than with these four positions: The Tathagata exists after death, does not exist after death, both does & does not exist after death, neither exists nor does not exist after death'?

In the Vakkali Sutta (SN 22.87) Buddha identifies himself with the Dhamma:

O Vakkali, whoever sees the Dhamma, sees me [the Buddha]

Another reference from the Aggañña Sutta of the Digha Nikaya, says to his disciple Vasettha:

O Vasettha! The Word of Dhammakaya is indeed the name of the Tathagata

Shravasti Dhammika, a Theravada monk, writes:

In the centuries after his final Nibbāna it sometimes got to the stage that the legends and myths obscured the very real human being behind them and the Buddha came to be looked upon as a god. Actually, the Buddha was a human being, not a 'mere human being' as is sometimes said but a special class of human called a 'complete person' (mahāparisa). Such complete persons are born no different from others and indeed they physically remain quite ordinary.

Sangharakshita also states that "The first thing we have to understand - and this is very important - is that the Buddha is a human being. But a special kind of human being, in fact the highest kind, so far as we know."

Buddha as a human

When asked whether he was a deva or a human, he replied that he had eliminated the deep-rooted unconscious traits that would make him either one, and should instead be called a Buddha; one who had grown up in the world but had now gone beyond it, as a lotus grows from the water but blossoms above it, unsoiled.

Andrew Skilton writes that the Buddha was never historically regarded by Buddhist traditions as being merely human:

It is important to stress that, despite modern Theravada teachings to the contrary (often a sop to skeptical Western pupils), he was never seen as being merely human. For instance, he is often described as having the thirty-two major and eighty minor marks or signs of a mahāpuruṣa, "superman"; the Buddha himself denied that he was either a man or a god; and in the Mahāparinibbāna Sutta he states that he could live for an aeon were he asked to do so.

However, Thích Nhất Hạnh, a Vietnamese Buddhist monk in the Zen tradition, states that "Buddha was not a god. He was a human being like you and me, and he suffered just as we do."

Jack Maguire writes that Buddha is inspirational based on his humanness.

A fundamental part of Buddhism's appeal to billions of people over the past two and a half millennia is the fact that the central figure, commonly referred to by the title "Buddha", was not a god, or a special kind of spiritual being, or even a prophet or an emissary of one. On the contrary, he was a human being like the rest of us who quite simply woke up to full aliveness.

Basing his teachings on the Lotus Sutra, the Chinese monk Chi-hi (the founder of the Tendai Sect) developed an explanation of life "three thousand realms in a single moment", which posits a Buddha nature that can be awakened in any life, and that it is possible for a person to become "enlightened to the Law". In this view, the state of Buddhahood and the states of ordinary people are exist with and within each other.

Nichiren, the founder of Nichiren Buddhism states that the real meaning of the Lord Shakyamuni Buddha’s appearance in this world lay in his behavior as a human being. He also stated that "Shakyamuni Buddha . . . the Lotus Sutra . . . and we ordinary human beings are in no way different or separate drom each other".

Mahāsāṃghika supramundane Buddha

In the early Buddhist schools, the Mahāsāṃghika branch regarded the buddhas as being characterized primarily by their supramundane nature. The Mahāsāṃghikas advocated the transcendental and supramundane nature of the buddhas and bodhisattvas, and the fallibility of arhats. Of the 48 special theses attributed by the Samayabhedoparacanacakra to the Mahāsāṃghika Ekavyāvahārika, Lokottaravāda, and the Kukkuṭika, 20 points concern the supramundane nature of buddhas and bodhisattvas. According to the Samayabhedoparacanacakra, these four groups held that the Buddha is able to know all dharmas in a single moment of the mind. Yao Zhihua writes:

In their view, the Buddha is equipped with the following supernatural qualities: transcendence (lokottara), lack of defilements, all of his utterances preaching his teaching, expounding all his teachings in a single utterance, all of his sayings being true, his physical body being limitless, his power (prabhāva) being limitless, the length of his life being limitless, never tiring of enlightening sentient beings and awakening pure faith in them, having no sleep or dreams, no pause in answering a question, and always in meditation (samādhi).

A doctrine ascribed to the Mahāsāṃghikas is, "The power of the tathāgatas is unlimited, and the life of the buddhas is unlimited." According to Guang Xing, two main aspects of the Buddha can be seen in Mahāsāṃghika teachings: the true Buddha who is omniscient and omnipotent, and the manifested forms through which he liberates sentient beings through skillful means. For the Mahāsaṃghikas, the historical Gautama Buddha was one of these transformation bodies (Skt. nirmāṇakāya), while the essential real Buddha is equated with the Dharmakāya.

As in Mahāyāna traditions, the Mahāsāṃghikas held the doctrine of the existence of many contemporaneous buddhas throughout the ten directions. In the Mahāsāṃghika Lokānuvartana Sūtra, it is stated, "The Buddha knows all the dharmas of the countless buddhas of the ten directions." It is also stated, "All buddhas have one body, the body of the Dharma." The concept of many bodhisattvas simultaneously working toward buddhahood is also found among the Mahāsāṃghika tradition, and further evidence of this is given in the Samayabhedoparacanacakra, which describes the doctrines of the Mahāsāṃghikas.

A statue of Gautama Buddha at Tawang Monastery, India.

Depictions of the Buddha in art

Buddha statues at Shwedagon Pagoda

 

Buddhas are frequently represented in the form of statues and paintings. Commonly seen designs include:

• The Seated Buddha
• The Reclining Buddha
• The Standing Buddha
• Hotei or Budai, the obese Laughing Buddha, usually seen in China (This figure is believed to be a representation of a medieval Chinese monk who is associated with Maitreya, the future Buddha, and is therefore technically not a Buddha image.)
• the Emaciated Buddha, which shows Siddhartha Gautama during his extreme ascetic practice of starvation.

The Buddha statue shown calling for rain is a pose common in Laos.

Markings

Most depictions of Buddha contain a certain number of markings, which are considered the signs of his enlightenment. These signs vary regionally, but two are common:

• a protuberance on the top of the head (denoting superb mental acuity)
• long earlobes (denoting superb perception)

In the Pāli Canon, there is frequent mention of a list of thirty-two physical characteristics of the Buddha.

Hand-gestures

The poses and hand-gestures of these statues, known respectively as asanas and mudras, are significant to their overall meaning. The popularity of any particular mudra or asana tends to be region-specific, such as the Vajra (or Chi Ken-in) mudra, which is popular in Japan and Korea but rarely seen in India. Others are more common; for example, the Varada (Wish Granting) mudra is common among standing statues of the Buddha, particularly when coupled with the Abhaya (Fearlessness and Protection) mudra.

Radioactive contamination

From Wikipedia, the free encyclopedia

The Hanford site represents two-thirds of the United States' high-level radioactive waste by volume. Nuclear reactors line the riverbank at the Hanford Site along the Columbia River in January 1960.

 

The sources of radioactive pollution can be classified into two groups: natural and man made.

As of 2013, the Fukushima nuclear disaster site remains highly radioactive, with some 160,000 evacuees still living in temporary housing, and some land will be unfarmable for centuries. The difficult cleanup job will take 40 or more years, and cost tens of billions of dollars.

 

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 emit harmful ionising radiation such as alpha particles or beta particles, gamma rays or 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.

Contamination may affect a person, a place, an animal, or an object such as clothing. 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. A spilled vial of radioactive material like uranyl nitrate may contaminate the floor and any rags used to wipe up the spill. Cases of widespread radioactive contamination include the Bikini Atoll, the Rocky Flats Plant in Colorado, the Fukushima Daiichi nuclear disaster, the Chernobyl disaster, and the area around the Mayak facility in Russia.

Sources of contamination

Global airborne contamination Atmospheric nuclear weapon tests almost doubled the concentration of ¹⁴C in the Northern Hemisphere. Plot of atmospheric ¹⁴C, New Zealand and Austria. The New Zealand curve is representative for the Southern Hemisphere, the Austrian curve is representative for the Northern Hemisphere. 

 

Radioactive contamination can be due to a variety of causes. It may occur due to release of radioactive gases, liquids or particles. For example, if a radionuclide used in nuclear medicine is spilled (accidentally or, as in the case of the Goiânia accident, through ignorance), the material could be spread by people as they walk around. 

Radioactive contamination may also be an inevitable result of certain processes, such as the release of radioactive xenon in nuclear fuel reprocessing. In cases that radioactive material cannot be contained, it may be diluted to safe concentrations. For a discussion of environmental contamination by alpha emitters please see actinides in the environment. 

Nuclear fallout is the distribution of radioactive contamination by the 520 atmospheric nuclear explosions that took place from the 1950s to the 1980s. 

In nuclear accidents, a measure of the type and amount of radioactivity released,such as from a reactor containment failure, is known as the source term. The United States Nuclear Regulatory Commission defines this as "Types and amounts of radioactive or hazardous material released to the environment following an accident."

Contamination does not include residual radioactive material remaining at a site after the completion of decommissioning. Therefore, radioactive material in sealed and designated containers is not properly referred to as contamination, although the units of measurement might be the same.

Containment

Large industrial glovebox in the nuclear industry

 

Containment is the primary way of preventing contamination being released into the environment or coming into contact or being ingested by humans.

Being within the intended Containment differentiates radioactive material from radioactive contamination. When radioactive materials are concentrated to a detectable level outside a containment, the area affected is generally referred to as "contaminated".

There are a large number of techniques for containing radioactive materials so that it does not spread beyond the containment and become contamination. In the case of liquids this is by the use of high integrity tanks or containers, usually with a sump system so that leakage can be detected by radiometric or conventional instrumentation.

Where material is likely to become airborne, then extensive use is made of the glovebox, which is a common technique in hazardous laboratory and process operations in many industries. The gloveboxes are kept under a slight negative pressure and the vent gas is filtered in high efficiency filters, which are monitored by radiological instrumentation to ensure they are functioning correctly.

Naturally occurring radioactivity

A variety of radionuclides occur naturally in the environment. Elements like uranium and thorium, and their decay products, are present in rock and soil. Potassium-40, a primordial nuclide, makes up a small percentage of all potassium and is present in the human body. Other nuclides, like carbon-14, which is present in all living organisms, are continuously created by cosmic rays. 

These levels of radioactivity pose little danger but can confuse measurement. A particular problem is encountered with naturally generated radon gas which can affect instruments which are set to detect contamination close to normal background levels and can cause false alarms. Because of this skill is required by the operator of radiological survey equipment to differentiate between background radiation and the radiation which emanates from contamination.

Naturally occurring radioactive materials (NORM) can be brought to the surface or concentrated by human activities like mining, oil and gas extraction and coal consumption.

Control and monitoring of contamination

G-M counters being used as gamma survey monitors, seeking radioactive satellite debris

 

Radioactive contamination may exist on surfaces or in volumes of material or air, and specialist techniques are used to measure the levels of contamination by detection of the emitted radiation.

Contamination monitoring

Contamination monitoring depends entirely upon the correct and appropriate deployment and utilisation of radiation monitoring instruments.

Surface contamination

Surface contamination may either be fixed or "free". In the case of fixed contamination, the radioactive material cannot by definition be spread, but its radiation is still measurable. In the case of free contamination there is the hazard of contamination spread to other surfaces such as skin or clothing, or entrainment in the air. A concrete surface contaminated by radioactivity can be shaved to a specific depth, removing the contaminated material for disposal.

For occupational workers controlled areas are established where there may be a contamination hazard. Access to such areas is controlled by a variety of barrier techniques, sometimes involving changes of clothing and foot wear as required. The contamination within a controlled area is normally regularly monitored. Radiological protection instrumentation (RPI) plays a key role in monitoring and detecting any potential contamination spread, and combinations of hand held survey instruments and permanently installed area monitors such as Airborne particulate monitors and area gamma monitors are often installed. Detection and measurement of surface contamination of personnel and plant is normally by Geiger counter, scintillation counter or proportional counter. Proportional counters and dual phosphor scintillation counters can discriminate between alpha and beta contamination, but the Geiger counter cannot. Scintillation detectors are generally preferred for hand held monitoring instruments, and are designed with a large detection window to make monitoring of large areas faster. Geiger detectors tend to have small windows, which are more suited to small areas of contamination.

Exit monitoring

The spread of contamination by personnel exiting controlled areas in which nuclear material is used or processed is monitored by specialised installed exit control instruments such as frisk probes, hand contamination monitors and whole body exit monitors. These are used to check that persons exiting controlled areas do not carry contamination on their body or clothes.

In the United Kingdom the HSE has issued a user guidance note on selecting the correct portable radiation measurement instrument for the application concerned. This covers all radiation instrument technologies, and is a useful comparative guide for selecting the correct technology for the contamination type. 

The UK NPL publishes a guide on the alarm levels to be used with instruments for checking personnel exiting controlled areas in which contamination may be encountered. Surface contamination is usually expressed in units of radioactivity per unit of area for alpha or beta emitters. For SI, this is becquerels per square meter (or Bq/m²). Other units such as picoCuries per 100 cm² or disintegrations per minute per square centimeter (1 dpm/cm² = 167 Bq/m²) may be used.

Airborne contamination

The air can be contaminated with radioactive isotopes in particulate form, which poses a particular inhalation hazard. Respirators with suitable air filters, or completely self-contained suits with their own air supply can mitigate these dangers. 

Airborne contamination is measured by specialist radiological instruments that continuously pump the sampled air through a filter. Airborne particles accumulate on the filter and can be measured in a number of ways:

1. The filter paper is periodically manually removed to an instrument such as a "scaler" which measures any accumulated radioactivity.
2. The filter paper is static and is measured in situ by a radiation detector.
3. The filter is a slowly moving strip and is measured by a radiation detector. These are commonly called "moving filter" devices and automatically advance the filter to present a clean area for accumulation, and thereby allow a plot of airborne concentration over time.

Commonly a semiconductor radiation detection sensor is used that can also provide spectrographic information on the contamination being collected. 

A particular problem with airborne contamination monitors designed to detect alpha particles is that naturally occurring radon can be quite prevalent and may appear as contamination when low contamination levels are being sought. Modern instruments consequently have "radon compensation" to overcome this effect.

Internal human contamination

Radioactive contamination can enter the body through ingestion, inhalation, absorption, or injection. This will result in a committed dose of radiation.

For this reason, it is important to use personal protective equipment when working with radioactive materials. Radioactive contamination may also be ingested as the result of eating contaminated plants and animals or drinking contaminated water or milk from exposed animals. Following a major contamination incident, all potential pathways of internal exposure should be considered.

Successfully used on Harold McCluskey, chelation therapy and other treatments exist for internal radionuclide contamination.

Decontamination

Cleaning up contamination results in radioactive waste unless the radioactive material can be returned to commercial use by reprocessing. In some cases of large areas of contamination, the contamination may be mitigated by burying and covering the contaminated substances with concrete, soil, or rock to prevent further spread of the contamination to the environment. If a person's body is contaminated by ingestion or by injury and standard cleaning cannot reduce the contamination further, then the person may be permanently contaminated.

Contamination control products have been used by the U.S. Department of Energy (DOE) and the commercial nuclear industry for decades to minimize contamination on radioactive equipment and surfaces and fix contamination in place. "Contamination control products" is a broad term that includes fixatives, strippable coatings, and decontamination gels. A fixative product functions as a permanent coating to stabilize residual loose/transferable radioactive contamination by fixing it in place; this aids in preventing the spread of contamination and reduces the possibility of the contamination becoming airborne, reducing workforce exposure and facilitating future deactivation and decommissioning (D&D) activities. Strippable coating products are loosely adhered paint-like films and are used for their decontamination abilities. They are applied to surfaces with loose/transferable radioactive contamination and then, once dried, are peeled off, which removes the loose/transferable contamination along with the product. The residual radioactive contamination on the surface is significantly reduced once the strippable coating is removed. Modern strippable coatings show high decontamination efficiency and can rival traditional mechanical and chemical decontamination methods. Decontamination gels work in much the same way as other strippable coatings. The results obtained through the use of contamination control products is variable and depends on the type of substrate, the selected contamination control product, the contaminants, and the environmental conditions (e.g., temperature, humidity, etc.).

Some of the largest areas committed to be decontaminated are in the Fukushima Prefecture, Japan. The national government is under pressure to clean up radioactivity due to the Fukushima nuclear accident of March 2011 from as much land as possible so that some of the 110,000 displaced people can return. Stripping out the key radioisotope threatening health (caesium-137) from low level waste could also dramatically decrease the volume of waste requiring special disposal. A goal is to find techniques that might be able to strip out 80 to 95% of the caesium from contaminated soil and other materials, efficiently and without destroying the organic content in the soil. One being investigated is termed hydrothermal blasting. The caesium is broken away from soil particles and then precipitated with ferric ferricyanide (Prussian blue). It would be the only component of the waste requiring special burial sites. The aim is to get annual exposure from the contaminated environment down to one millisievert (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.

To help with protection of people living in geographical areas which have been radioactively contaminated the International Commission on Radiological Protection has published a guide: "Publication 111 – Application of the Commission’s Recommendations to the Protection of People Living in Long-term Contaminated Areas after a Nuclear Accident or a Radiation Emergency".

Contamination hazards

Periodic table with elements colored according to the half-life of their most stable isotope.

 

  Elements which contain at least one stable isotope.

  Radioactive elements: the most stable isotope is very long-lived, with half-life of over four million years.

  Radioactive elements: the most stable isotope has half-life between 800 and 34.000 years.

  Radioactive elements: the most stable isotope has half-life between one day and 130 years.

  Highly radioactive elements: the most stable isotope has half-life between several minutes and one day.

  Extremely radioactive elements: the most stable isotope has half-life less than several minutes.

Low-level contamination

The hazards to people and the environment from radioactive contamination depend on the nature of the radioactive contaminant, the level of contamination, and the extent of the spread of contamination. Low levels of radioactive contamination pose little risk, but can still be detected by radiation instrumentation. If a survey or map is made of a contaminated area, random sampling locations may be labeled with their activity in becquerels or curies on contact. Low levels may be reported in counts per minute using a scintillation counter. 

In the case of low-level contamination by isotopes with a short half-life, the best course of action may be to simply allow the material to naturally decay. Longer-lived isotopes should be cleaned up and properly disposed of, because even a very low level of radiation can be life-threatening when in long exposure to it. 

Facilities and physical locations that are deemed to be contaminated may be cordoned off by a health physicist and labeled "Contaminated area." Persons coming near such an area would typically require anti-contamination clothing ("anti-Cs").

High-level contamination

High levels of contamination may pose major risks to people and the environment. People can be exposed to potentially lethal radiation levels, both externally and internally, from the spread of contamination following an accident (or a deliberate initiation) involving large quantities of radioactive material. The biological effects of external exposure to radioactive contamination are generally the same as those from an external radiation source not involving radioactive materials, such as x-ray machines, and are dependent on the absorbed dose. 

When radioactive contamination is being measured or mapped in situ, any location that appears to be a point source of radiation is likely to be heavily contaminated. A highly contaminated location is colloquially referred to as a "hot spot." On a map of a contaminated place, hot spots may be labeled with their "on contact" dose rate in mSv/h. In a contaminated facility, hot spots may be marked with a sign, shielded with bags of lead shot, or cordoned off with warning tape containing the radioactive trefoil symbol. 

The radiation warning symbol (trefoil)

 

Alpha radiation consists of helium-4 nucleus and is readily stopped by a sheet of paper. Beta radiation, consisting of electrons, is halted by an aluminium plate. Gamma radiation is eventually absorbed as it penetrates a dense material. Lead is good at absorbing gamma radiation, due to its density.

 

The hazard from contamination is the emission of ionising radiation. The principal radiations which will be encountered are alpha, beta and gamma, but these have quite different characteristics. They have widely differing penetrating powers and radiation effect, and the accompanying diagram shows the penetration of these radiations in simple terms. For an understanding of the different ionising effects of these radiations and the weighting factors applied, see the article on absorbed dose.

Radiation monitoring involves the measurement of radiation dose or radionuclide contamination for reasons related to the assessment or control of exposure to radiation or radioactive substances, and the interpretation of the results. The methodological and technical details of the design and operation of environmental radiation monitoring programmes and systems for different radionuclides, environmental media and types of facility are given in IAEA Safety Standards Series No. RS–G-1.8 and in IAEA Safety Reports Series No. 64.

Health effects of contamination

Biological effects

Radioactive contamination by definition emits ionizing radiation, which can irradiate the human body from an external or internal origin.

External irradiation

This is due to radiation from contamination located outside the human body. The source can be in the vicinity of the body or can be on the skin surface. The level of health risk is dependent on duration and the type and strength of irradiation. Penetrating radiation such as gamma rays, X-rays, neutrons or beta particles pose the greatest risk from an external source. Low penetrating radiation such as alpha particles have a low external risk due to the shielding effect of the top layers of skin. See the article on sievert for more information on how this is calculated.

Internal irradiation

Radioactive contamination can be ingested into the human body if it is airborne or is taken in as contamination of food or drink, and will irradiate the body internally. The art and science of assessing internally generated radiation dose is Internal dosimetry. 

The biological effects of ingested radionuclides depend greatly on the activity, the biodistribution, and the removal rates of the radionuclide, which in turn depends on its chemical form, the particle size, and route of entry. Effects may also depend on the chemical toxicity of the deposited material, independent of its radioactivity. Some radionuclides may be generally distributed throughout the body and rapidly removed, as is the case with tritiated water. 

Some organs concentrate certain elements and hence radionuclide variants of those elements. This action may lead to much lower removal rates. For instance, the thyroid gland takes up a large percentage of any iodine that enters the body. Large quantities of inhaled or ingested radioactive iodine may impair or destroy the thyroid, while other tissues are affected to a lesser extent. Radioactive iodine-131 is a common fission product; it was a major component of the radioactivity released from the Chernobyl disaster, leading to nine fatal cases of pediatric thyroid cancer and hypothyroidism. On the other hand, radioactive iodine is used in the diagnosis and treatment of many diseases of the thyroid precisely because of the thyroid's selective uptake of iodine.

The radiation risk proposed by the International Commission on Radiological Protection (ICRP) predicts that an effective dose of one sievert (100 rem) carries a 5.5% chance of developing cancer. Such a risk is the sum of both internal and external radiation dose.

The ICRP states "Radionuclides incorporated in the human body irradiate the tissues over time periods determined by their physical half-life and their biological retention within the body. Thus they may give rise to doses to body tissues for many months or years after the intake. The need to regulate exposures to radionuclides and the accumulation of radiation dose over extended periods of time has led to the definition of committed dose quantities". The ICRP further states "For internal exposure, committed effective doses are generally determined from an assessment of the intakes of radionuclides from bioassay measurements or other quantities (e.g., activity retained in the body or in daily excreta). The radiation dose is determined from the intake using recommended dose coefficients".

The ICRP defines two dose quantities for individual committed dose:

Committed equivalent dose, H _T(t) is the time integral of the equivalent dose rate in a particular tissue or organ that will be received by an individual following intake of radioactive material into the body by a Reference Person, where t is the integration time in years. This refers specifically to the dose in a specific tissue or organ, in a similar way to external equivalent dose.

Committed effective dose, E(t) is the sum of the products of the committed organ or tissue equivalent doses and the appropriate tissue weighting factors W_T, where t is the integration time in years following the intake. The commitment period is taken to be 50 years for adults, and to age 70 years for children. This refers specifically to the dose to the whole body, in a similar way to external effective dose.

Social and psychological effects

A 2015 report in Lancet explained that serious impacts of nuclear accidents were often not directly attributable to radiation exposure, but rather social and psychological effects. The consequences of low-level radiation are often more psychological than radiological. Because damage from very-low-level radiation cannot be detected, people exposed to it are left in anguished uncertainty about what will happen to them. Many believe they have been fundamentally contaminated for life and may refuse to have children for fear of birth defects. They may be shunned by others in their community who fear a sort of mysterious contagion.

Forced evacuation from a radiological or nuclear accident may lead to social isolation, anxiety, depression, psychosomatic medical problems, reckless behavior, even suicide. Such was the outcome of the 1986 Chernobyl nuclear disaster in Ukraine. A comprehensive 2005 study concluded that "the mental health impact of Chernobyl is the largest public health problem unleashed by the accident to date". Frank N. von Hippel, a U.S. scientist, commented on 2011 Fukushima nuclear disaster, saying that "fear of ionizing radiation could have long-term psychological effects on a large portion of the population in the contaminated areas". Evacuation and long-term displacement of affected populations create problems for many people, especially the elderly and hospital patients.

Such great psychological danger does not accompany other materials that put people at risk of cancer and other deadly illness. Visceral fear is not widely aroused by, for example, the daily emissions from coal burning, although, as a National Academy of Sciences study found, this causes 10,000 premature deaths a year in the US population of 317,413,000. Medical errors leading to death in U.S. hospitals are estimated to be between 44,000 and 98,000. It is "only nuclear radiation that bears a huge psychological burden – for it carries a unique historical legacy".

Iodine in biology

From Wikipedia, the free encyclopedia

Iodine is an essential trace element in biological systems. It has the distinction of being the heaviest element commonly needed by living organisms as well as the second-heaviest known to be used by any form of life (only tungsten, a component of a few bacterial enzymes, has a higher atomic number and atomic weight). It is a component of biochemical pathways in organisms from all biological kingdoms, suggesting its fundamental significance throughout the evolutionary history of life. 

Iodine is critical to the proper functioning of the vertebrate endocrine system, and plays smaller roles in numerous other organs, including those of the digestive and reproductive systems. An adequate intake of iodine-containing compounds is important at all stages of development, especially during the fetal and neonatal periods, and diets deficient in iodine can present serious consequences for growth and metabolism.

Functions

Thyroid

In vertebrate biology, iodine's primary function is as a constituent of the thyroid hormones, thyroxine (T4) and triiodothyronine (T3). These molecules are made from addition-condensation products of the amino acid tyrosine, and are stored prior to release in an iodine-containing protein called thyroglobulin. T4 and T3 contain four and three atoms of iodine per molecule, respectively; iodine accounts for 65% of the molecular weight of T4 and 59% of T3. The thyroid gland actively absorbs iodine from the blood to produce and release these hormones into the blood, actions which are regulated by a second hormone, called thyroid-stimulating hormone (TSH), which is produced by the pituitary gland. Thyroid hormones are phylogenetically very old molecules which are synthesized by most multicellular organisms, and which even have some effect on unicellular organisms. 

Thyroid hormones play a fundamental role in biology, acting upon gene transcription mechanisms to regulate the basal metabolic rate. T3 acts on small intestine cells and adipocytes to increase carbohydrate absorption and fatty acid release, respectively. A deficiency of thyroid hormones can reduce basal metabolic rate up to 50%, while an excessive production of thyroid hormones can increase the basal metabolic rate by 100%. T4 acts largely as a precursor to T3, which is (with minor exceptions) the biologically active hormone.

Via the thyroid hormones, iodine has a nutritional relationship with selenium. A family of selenium-dependent enzymes called deiodinases converts T4 to T3 (the active hormone) by removing an iodine atom from the outer tyrosine ring. These enzymes also convert T4 to reverse T3 (rT3) by removing an inner ring iodine atom, and also convert T3 to 3,3'-Diiodothyronine (T2) by removing an inner ring atom. Both of the latter products are inactivated hormones which have essentially no biological effects and are quickly prepared for disposal. A family of non-selenium-dependent enzymes then further deiodinates the products of these reactions. 

Selenium also plays a very important role in the production of glutathione, the body's most powerful antioxidant. During the production of the thyroid hormones, hydrogen peroxide is produced in large quantities, and therefore high iodine in the absence of selenium can destroy the thyroid gland (often described as a sore throat feeling); the peroxides are neutralized through the production of glutathione from selenium. In turn, an excess of selenium increases demand for iodine, and deficiency will result when a diet is high in selenium and low in iodine.

Extrathyroidal iodine

Sequence of 123-iodide human scintiscans after an intravenous injection, (from left) after 30 minutes, 20 hours, and 48 hours. A high and rapid concentration of radio-iodide is evident in cerebrospinal fluid (left), gastric and oral mucosa, salivary glands, arterial walls, ovary and thymus. In the thyroid gland, I-concentration is more progressive, also in a reservoir (from 1% after 30 minutes, and after 6, 20 h, to 5.8% after 48 hours, of the total injected dose.

 

A pheochromocytoma tumor is seen as a dark sphere in the center of the body (it is in the left adrenal gland). The image is by MIBG scintigraphy, showing the tumor by radiation from radioiodine in the MIBG. Two images are seen of the same patient from front and back. The image of the thyroid in the neck is due to unwanted uptake of radioiodine from a radioactive iodine-containing medication by the thyroid gland in the neck. Accumulation at the sides of the head is from salivary gland uptake of iodide. Radioactivity is also seen from uptake by the liver, and excretion and accumulation in the bladder.

 

The human body contains about 15–20 mg of iodine, mostly concentrated in thyroid tissue (70–80%). Extra-thyroidal iodine exists in several other organs, including the mammary glands, eyes, gastric mucosa, cervix, cerebrospinal fluid, arterial walls , ovary and salivary glands. In the cells of these tissues the iodide ion (I⁻) enters directly by the sodium-iodide symporter (NIS). Different tissue responses for iodine and iodide occur in the mammary glands and the thyroid gland of rats. The role of iodine in mammary tissue is related to fetal and neonatal development, but its role in the other tissues is not well known. It has been shown to act as an antioxidant and antiproliferant in various tissues that can uptake iodine. Molecular iodine (I₂) has been shown to have a suppressive effect on benign and cancerous neoplasias.

The U.S. Food and Nutrition Board and Institute of Medicine recommended daily allowance of iodine ranges from 150 micrograms per day for adult humans to 290 micrograms per day for lactating mothers. However, the thyroid gland needs no more than 70 micrograms per day to synthesize the requisite daily amounts of T4 and T3. The higher recommended daily allowance levels of iodine seem necessary for optimal function of a number of other body systems, including lactating breasts, gastric mucosa, salivary glands, oral mucosa, arterial walls, thymus, epidermis, choroid plexus and cerebrospinal fluid, among others.

Other functions

Iodine and thyroxine have also been shown to stimulate the spectacular apoptosis of the cells of the larval gills, tail and fins during metamorphosis in amphibians, as well as the transformation of their nervous system from that of the aquatic, herbivorous tadpole into that of the terrestrial, carnivorous adult. The frog species Xenopus laevis has proven to be an ideal model organism for experimental study of the mechanisms of apoptosis and the role of iodine in developmental biology.

Moreover, iodine can add to double bonds of docosahexaenoic acid and arachidonic acid of cellular membranes, making them less reactive to free oxygen radicals.

Dietary recommendations

The U.S. Institute of Medicine (IOM) updated Estimated Average Requirements (EARs) and Recommended Dietary Allowances (RDAs) for iodine in 2000. For people age 14 and up, the iodine RDA is 150 μg/day; the RDA for pregnant women is 220 μg/day and the RDA during lactation is 290 μg/day. For children 1–8 years, the RDA is 90 μg/day; for children 8–13 years, 130 μg/day. As a safety consideration, the IOM sets tolerable upper intake levels (ULs) for vitamins and minerals when evidence is sufficient. The UL for iodine for adults is 1,100 μg/day. This UL was assessed by analyzing the effect of supplementation on thyroid-stimulating hormone. Collectively, the EARs, RDAs, AIs and ULs are referred to as Dietary Reference Intakes (DRIs).

The European Food Safety Authority (EFSA) refers to the collective set of information as Dietary Reference Values, with Population Reference Intake (PRI) instead of RDA, and Average Requirement instead of EAR; AI and UL are defined the same as in the United States. For women and men ages 18 and older, the PRI for iodine is set at 150 μg/day; the PRI during pregnancy or lactation is 200 μg/day. For children ages 1–17 years, the PRI increases with age from 90 to 130 μg/day. These PRIs are comparable to the U.S. RDAs with the exception of that for lactation. The EFSA reviewed the same safety question and set its adult UL at 600 μg/day, which is a bit more than half the U.S. value. Notably, Japan reduced its adult iodine UL from 3,000 to 2,200 µg/day in 2010, but then increased it back to 3,000 µg/day in 2015.

For U.S. food and dietary supplement labeling purposes, the amount in a serving is expressed as a percent of Daily Value (%DV). For iodine specifically, 100% of the Daily Value is considered 150 μg, and this figure remained at 150 μg in the May 27, 2016 revision. A table of the old and new adult Daily Values is provided at Reference Daily Intake. The original deadline to be in compliance was July 28, 2018, but on September 29, 2017, the FDA released a proposed rule that extended the deadline to January 1, 2020 for large companies and January 1, 2021 for small companies.

As of 2000, the median observed intake of iodine from food in the United States was 240 to 300 μg/day for men and 190 to 210 μg/day for women. In Japan, consumption is much higher due to the frequent consumption of seaweed or kombu kelp. The average daily intake in Japan ranges from 1,000 to 3,000 μg/day; previous estimates suggested an average intake as high as 13,000 μg/day.

Food sources

Natural sources of iodine include many marine organisms, such as kelp and certain seafood products, as well as plants grown on iodine-rich soil. Iodized salt is fortified with iodine. According to a Food Fortification Initiative 2016 report, 130 countries have mandatory iodine fortification of salt and an additional 10 have voluntary fortification.

Deficiency

Worldwide, iodine deficiency affects two billion people and is the leading preventable cause of mental retardation. Mental disability is a result which occurs primarily when babies or small children are rendered hypothyroidic by a lack of dietary iodine (new hypothyroidism in adults may cause temporary mental slowing, but not permanent damage).

In areas where there is little iodine in the diet, typically remote inland areas and semi-arid equatorial climates where no marine foods are eaten, iodine deficiency also gives rise to hypothyroidism, the most serious symptoms of which are epidemic goitre (swelling of the thyroid gland), extreme fatigue, mental slowing, depression, weight gain, and low basal body temperatures.

The addition of iodine to table salt (so-called iodized salt) has largely eliminated the most severe consequences of iodine deficiency in wealthier nations, but deficiency remains a serious public health problem in the developing world. Iodine deficiency is also a problem in certain areas of Europe; in Germany, an estimated one billion dollars in healthcare costs is spent each year in combating and treating iodine deficiency.

Iodine and cancer risk

• Breast cancer. The mammary gland actively concentrates iodine into milk for the benefit of the developing infant, and may develop a goiter-like hyperplasia, sometimes manifesting as fibrocystic breast disease, when iodine level is low. Studies indicate that iodine deficiency, either dietary or pharmacologic, can lead to breast atypia and increased incidence of malignancy in animal models, while iodine treatment can reverse dysplasia, with elemental iodine (I₂) having been found to be more effective in reducing ductal hyperplasias and perilobular fibrosis in iodine-deficient rats than iodide (I⁻). On the observation that Japanese women who consume iodine-rich seaweed have a relatively low rate of breast cancer, iodine is suggested as a protection against breast cancer. Iodine is known to induce apoptosis in breast cancer cells. Laboratory evidence has demonstrated an effect of iodine on breast cancer that is in part independent of thyroid function, with iodine inhibiting cancer through modulation of the estrogen pathway. Gene array profiling of the estrogen responsive breast cancer cell line shows that the combination of iodine and iodide alters gene expression and inhibits the estrogen response through up-regulating proteins involved in estrogen metabolism. Whether iodine/iodide will be useful as an adjuvant therapy in the pharmacologic manipulation of the estrogen pathway in women with breast cancer has not been determined clinically.
• Gastric cancer. Some researchers have found an epidemiologic correlation between iodine deficiency, iodine-deficient goitre, and gastric cancer; a decrease in the death incidence from stomach cancer after iodine-prophylaxis. In the proposed mechanism, the iodide ion functions in gastric mucosa as an antioxidant reducing species that detoxifies poisonous reactive oxygen species, such as hydrogen peroxide.

Precautions and toxicity

Elemental iodine

Elemental iodine is an oxidizing irritant, and direct contact with skin can cause lesions, so iodine crystals should be handled with care. Solutions with high elemental iodine concentration such as tincture of iodine are capable of causing tissue damage if use for cleaning and antisepsis is prolonged. Although elemental iodine is used in the formulation of Lugol's solution, a common medical disinfectant, it becomes triiodide upon reacting with the potassium iodide used in the solution and is therefore non-toxic. Only a small amount of elemental iodine will dissolve in water, and adding potassium iodide allows a much larger amount of elemental iodine to dissolve through the reaction of I2-I3. This allows Lugol's iodine to be produced in strengths varying from 2% to 15% iodine. 

Elemental iodine (I₂) is poisonous if taken orally in large amounts; 2–3 grams is a lethal dose for an adult human. Potassium iodide, on the other hand, has a median lethal dose (LD₅₀) that is relatively high in several other animals: in rabbits, it is 10 g/kg; in rats, 14 g/kg, and in mice, 22 g/kg. The tolerable upper intake level for iodine as established by the Food and Nutrition Board is 1,100 µg/day for adults. The safe upper limit of consumption set by the Ministry of Health, Labor and Welfare in Japan is 3,000 µg/day.

The biological half-life of iodine differs between the various organs of the body, from 100 days in the thyroid, to 14 days in the kidneys and spleen, to 7 days in the reproductive organs. Typically the daily urinary elimination rate ranges from 100 to 200 µg/L in humans. However, the Japanese diet, high in iodine-rich kelp, contains 1,000 to 3,000 µg of iodine per day, and research indicates the body can readily eliminate excess iodine that is not needed for thyroid hormone production. The literature reports as much as 30,000 µg/L (30 mg/L) of iodine being safely excreted in the urine in a single day, with levels returning to the standard range in a couple of days, depending on seaweed intake. One study concluded the range of total body iodine content in males was 12.1 mg to 25.3 mg, with a mean of 14.6 mg. It is presumed that once thyroid-stimulating hormone is suppressed, the body simply eliminates excess iodine, and as a result, long-term supplementation with high doses of iodine has no additional effect once the body is replete with enough iodine. It is unknown if the thyroid gland is the rate-limiting factor in generating thyroid hormone from iodine and tyrosine, but assuming it is not, a short-term loading dose of one or two weeks at the tolerable upper intake level may quickly restore thyroid function in iodine-deficient patients.

Iodine vapor is very irritating to the eye, to mucous membranes, and in the respiratory tract. Concentration of iodine in the air should not exceed 1 mg/m³ (eight-hour time-weighted average). 

When mixed with ammonia and water, elemental iodine forms nitrogen triiodide, which is extremely shock-sensitive and can explode unexpectedly.

Iodide ion

Excessive iodine intake presents symptoms similar to those of iodine deficiency. Commonly encountered symptoms are abnormal growth of the thyroid gland and disorders in functioning, as well as in growth of the organism as a whole. Iodide toxicity is similar to (but not the same as) toxicity to ions of the other halogens, such as bromides or fluorides. Excess bromine and fluorine can prevent successful iodine uptake, storage and use in organisms, as both elements can selectively replace iodine biochemically. 

Excess iodine may also be more cytotoxic in combination with selenium deficiency. Iodine supplementation in selenium-deficient populations is theoretically problematic, partly for this reason. Selenocysteine (abbreviated as Sec or U, in older publications also as Se-Cys) is the 21st proteinogenic amino acid, and is the root of iodide ion toxicity when there is a simultaneous insufficiency of biologically available selenium. Selenocysteine exists naturally in all kingdoms of life as a building block of selenoproteins.

Hypersensitivity reactions to iodine-containing compounds

Some people develop a hypersensitivity to compounds of iodine but there are no known cases of people being directly allergic to elemental iodine itself. Notable sensitivity reactions that have been observed in humans include:

• The application of tincture of iodine may cause a rash.
• Some cases of reaction to povidone-iodine (Betadine) have been documented to be a chemical burn.
• Eating iodine-containing foods, especially seafood products such as shellfish, may cause hives.

Medical use of iodine compounds (i.e. as a contrast agent) can cause anaphylactic shock in highly sensitive patients, presumably due to sensitivity to the chemical carrier. Cases of sensitivity to iodine compounds should not be formally classified as iodine allergies, as this perpetuates the erroneous belief that it is the iodine to which patients react, rather than to the specific allergen. Sensitivity to iodine-containing compounds is rare but has a considerable effect given the extremely widespread use of iodine-based contrast media.