RADIATION

Radiation is everywhere. Life would not exist on Earth without radiation from the sun. Additionally, many important technological activities are based on radiation, such as radio and telecommunications. Another type of radiation is used for producing X-ray images in industrial and medical applications. Radiation is also emitted as a side effect from various technological activities. Some types of radiation are known to be harmful to human beings and need to be carefully managed. Other types are not believed to be dangerous, but are a source of worry among the general public. An example is possible radiation risks from power lines, cellular phones, and cellular base stations, which since the 1980s have received considerable media attention.

Protection of humans and the environment from the harmful effects of radiation is called radiation protection. The field of radiation protection evaluates scientific knowledge of adverse health effects from radiation and influences legislation and regulations for protection. The field is complex and involves intricate ethical problems. Lauriston S. Taylor, one of the pioneers of radiation protection during the early 1900s, once said, "Radiation protection is not only a matter for science. It is a problem of philosophy, morality and the utmost wisdom" (1980, p. 854).

It is important to distinguish between ionizing and nonionizing radiation. The biological effects of the two types of radiation are very different, as are therefore the methods of protection. Radiation is ionizing if the energy of the radiation suffices to remove an electron from an atom to create an ion. Conversely, if the energy does not suffice to create ions it is called nonionizing.

Nonionizing Radiation

The most important types of nonionizing radiation are electromagnetic and consist of electric and magnetic waves propagating at the speed of light. Electromagnetic radiation comes from both natural and technological sources and has different properties depending on the frequency of the electromagnetic waves. Low-frequency electromagnetic fields and radio waves come from electric appliances, power lines, radio and television broadcasting, and natural sources such as thunderstorms. Microwaves are used in microwave ovens, radar, and telecommunications. Infrared radiation, visible light, and ultraviolet radiation are emitted from the sun, artificial light, and other technical applications. Electromagnetic radiation with frequencies above visible light has enough energy to change chemical bonds and cause ionizations. Ultraviolet radiation lies on the borderline between nonionizing and ionizing radiation, but is usually considered nonionizing.

The biological effects of nonionizing electromagnetic radiation depend on the frequency and the intensity of the radiation. Low-frequency electromagnetic fields and radio waves pass through human bodies without any apparent effects, but can induce electrical currents and stimulate human nerve cells at high intensities. Microwaves cannot penetrate far into human bodies, but high intensities can cause heating of tissue and burn injuries to the skin. Infrared radiation and visible light can produce surface heating and cause harm to the eye in high intensities. Ultraviolet radiation cannot penetrate the skin, but is known to cause skin cancers.

Claims that low-frequency electromagnetic fields and microwaves can cause cancer are controversial. These types of radiation have insufficient energy to damage the DNA directly, and no other mechanism is known through which they could cause cancer. The prevailing scientific view is that these types of radiation are unlikely to cause cancer. Other effects, such as reduced fertility, memory loss, and fatigue, have been reported, but there is no consistent evidence for these kinds of adverse health effects.

International and national recommendations on exposure limits for nonionizing radiation are based on guidelines from the International Commission on Non-Ionizing Radiation Protection (ICNIRP). The ICNIRP is a nongovernmental organization officially recognized by the World Health Organization (WHO), the International Labour Organization (ILO), and the European Union (EU). The ICNIRP recommends exposure limits for different types of nonionizing radiation. The exposure limits are set with a margin of safety to the level at which health effects occur. The ICNIRP guidelines are based on scientifically verified health effects of nonionizing radiation. Potential, but not proven, hazards are not used as a basis for the limits.

The most important ethical issue regarding nonionizing radiation concerns how to deal with potential health hazards that are scientifically controversial. Examples include the possible risks of radiation from power lines and cellular base stations. Typical exposure levels in these cases are substantially lower than the exposure limits recommended by the ICNIRP, but they do introduce new exposures into society and, in the case of cell phones, such exposures are centered around sensitive parts of the human body. Thus, some countries have, in addition to the recommended exposure limits, adopted precautionary strategies for managing possible hazards from nonionizing radiation. These strategies include the use of prudent avoidance and the precautionary principle.

Prudent avoidance can be defined as a general reduction of needless exposure. This means taking simple, easily achievable, low-cost measures, even in the absence of a demonstrable health hazard. Prudent refers to expenditures and does not include any requirement for assessment of the potential health benefits of adopted measures. In practice, this means that the location of new facilities can be influenced by prudent considerations, but need not be modified, because this would involve higher costs. Prudent avoidance can also take the form of voluntary measures, for example, to recommend that manufacturers of mobile phones minimize radiation exposure to the head.

The precautionary principle is not a single, well-defined principle, but the basic idea is that measures against a possible hazard ought to be taken even if evidence for the existence of the hazard does not suffice to be treated as a scientific fact. It is usually thought that the application of the precautionary principle should be science-based and should reference plausible explanations for possible mechanisms for hazards. A common further requirement is that precautionary measures should be temporary and subject to review when further knowledge is gathered. Because scientific evidence and plausible mechanisms are missing for possible risks of low levels of nonionizing electromagnetic radiation, it has been argued that the precautionary principle is inappropriate for these types of radiation.

Adopting precautionary approaches are not unproblematic. What level of precaution should be taken, and what should be the basis for the decision? The WHO has argued that precautionary approaches regarding non-ionizing electromagnetic radiation should be adopted with care, and under the condition that scientific assessments of risk and science-based exposure limits are not undermined by arbitrary precautionary approaches.

Ionizing Radiation

Radiation is ionizing if it has enough energy to ionize atoms and molecules. There are two types of ionizing radiation: high-frequency electromagnetic radiation and particle radiation. Examples of ionizing electromagnetic radiation include gamma rays and X rays. Most particle radiation is ionizing. Common types of particle radiation are alpha (helium nuclei), beta (electrons), neutron, and proton radiation.

Ionizing radiation originates from both nonhuman and human sources. Nonhuman or natural sources of ionizing radiation are cosmic rays and naturally occurring radioactive substances in Earth's crust, the human body, air, water, and food. The level of natural exposure varies around the globe, and cosmic radiation is more intense at higher altitudes. The total exposure from all natural sources is called natural background radiation. The natural background radiation is by far the greatest contributor to human exposure to ionizing radiation.

Some human activities can enhance the exposure from natural sources. Examples include radon gas from the soil that concentrates in buildings, mining, and the combustion of fossil fuels that contain radioactive substances. Aircraft passengers and crew are subject to higher levels of cosmic radiation at flight altitudes. Environmental contamination by radioactive residues come from atmospheric nuclear weapons tests (performed between 1945 and 1980), the Chernobyl accident (1986), and the operation of nuclear power plants. These activities contribute only a small fraction of the global average exposure to ionizing radiation.

The largest human-made exposures to ionizing radiation stem from medical procedures. Medical exposures include diagnostic exposures (such as X-ray examinations) and therapeutic exposures (as in tumor treatment). Occupational exposure to ionizing radiation affects workers in industry, medicine, and research. The level of occupational exposure is generally similar to that of the average natural exposure. A few percent of workers are exposed to radiation levels several times greater than the average natural exposure. A comparison between the average exposures from different sources of ionizing radiation is listed in Table 1.

The biological effects of ionizing radiation are generally well known. Ionizing radiation can cause cell death and acute harm to organs if sufficient numbers of cells are damaged. Another type of damage occurs in cells that are modified. This may lead to inheritable genetic changes and the development of cancer, which may manifest itself decades after exposure. Acute effects

occur if the radiation dose is substantial (as in accidents), while it is believed that cancer and hereditary effects may be caused by the modification of a single cell. As the dose increases, the probability of these effects also increases.

The effects and penetration of ionizing radiation depend on the type of radiation. Exposure from ionizing radiation is therefore quantified by the effective dose, which is a measure that takes the type of radiation into account. The unit for the effective dose is the sievert (Sv). One sievert is a very large dose, and it is common to express the effective dose in millisieverts instead (1 mSv = 0.001 Sv). Sometimes the unit rem is used instead (1 rem = 0.01 Sv).

Epidemiological data argue for a linear relation between the dose and the cancer risk from ionizing radiation for intermediate dose levels. A linear dose–effect relation means that an increase in dose implies a corresponding increase in effect. Because of statistical limitations, the dose–effect relation cannot be determined for low doses. Therefore, the risks of low-dose ionizing radiation must be estimated based on knowledge of biological mechanisms that cause or inhibit cancer and inheritable defects. The dose–effect relation for low doses is important, because the exposure to the public or in normal work situations are in ranges where the risk is uncertain (below 50 mSv).

It is especially important to know if there is a threshold for the dose–effect relation for ionizing radiation. If there is no threshold, there is a (small) risk associated with even very low exposure levels. The prevailing scientific consensus, represented by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), is that a threshold is unlikely and that a linear dose–effect relationship for small doses is consistent with current knowledge about the mechanisms by which ionizing radiation causes harmful effects. This view is challenged by those who believe that there is a threshold (and thus no risk) for very low doses of ionizing radiation. Some even argue for a positive effect called hormesis at very low levels.

Setting Standards

Radiation protection from ionizing radiation is generally the same all over the world, because of the profound influence of the International Commission on Radiological Protection (ICRP), a nongovernmental organization whose recommendations are used by both national radiation protection authorities and international organizations as a basis for more detailed guidelines. The ICRP works under the assumption that the risk of cancer and hereditary effects from low doses of ionizing radiation is without a threshold and that the dose–effect relation is linear—the so-called linear, no threshold assumption. This approach to the risks of low-dose ionizing radiation can be seen as precautionary, although the assumption is supported by scientific knowledge.

The 1990 ICRP recommendations are based on a system of three principles: justification, optimization, and dose limitation. The justification principle states that no additional dose should be tolerated unless there is an associated benefit to the exposed individuals or to society that outweighs the detriment. Though the principle may seem obvious, its application gives rise to complex ethical issues. The concepts of benefit and detriment are difficult to define, and calculations are often associated with great uncertainties and errors. Other ethical issues include how the benefit for society can be weighed against the detriment to individuals, issues of free and informed consent, and who should make the decisions (for example, stakeholders or experts).

According to the optimization principle, total exposure should be kept as low as reasonably achievable (or ALARA), with economic and social factors taken into account. (Based on the acronym, this principle is sometimes called the ALARA principle.) What is reasonable depends on economic considerations, which means that doses need not be lowered further if the economic cost would be too high. The principle is thus a trade-off between economics and protection. Cost–benefit analysis has often been applied for optimization of protection, although the ICRP stresses that it is only one possible method.

The optimization principle does not consider the distribution of doses among individuals. A strict application of the principle may thus, at least in theory, lead to a situation in which a few individuals are exposed to substantially higher doses than others. The optimization principle can be seen as utilitarian or consequentialist, focusing on total rather than individual effects.

The dose-limitation principle requires that individual doses not exceed unacceptable levels. This principle can be seen as deontological, because it implies a duty to protect individuals from undue harm. In many cases, the optimization principle and the dose-limitation principle coincide, but there can be cases in which the two principles conflict. In the ICRP system such conflicts are resolved by first applying the dose-limitation principle and after that the optimization principle, deontology before utility.

Under the common assumption that cancer and hereditary effects do not have a threshold, a dose limit (above zero) cannot yield a completely safe level. The dose limits should, according to the ICRP, be regarded as the boundary to unacceptable doses, and protection should essentially be due to the optimization principle. As a dose limit cannot yield a wholly safe dose, a decision on a dose limit will always involve value judgments and ethical considerations. What is acceptable or not is a complex ethical issue, and judgments are not necessarily the same in all contexts.

The dose limits recommended by the ICRP are 1 mSv per year for the public and 20 mSv per year for occupational exposure. A special question regarding dose limits is why it is acceptable for workers to be exposed to higher risks than the public. This is an ethically problematic issue, not just for radiation protection. Arguments that have been used are that the limit for the general public concerns exposure for the whole life and not just the working life, and that the public includes children and other more susceptible individuals. Workers may also be informed of their exposure levels and thus voluntarily accept them, whereas the public has no alternative.

An important concept in radiation protection from ionizing radiation is the collective dose. The collective dose is defined as the mean dose for each individual in an exposed population multiplied by the number of individuals. There has been considerable controversy over what influence the value of the collective dose should have. Considerable collective doses can arise from exposure to large populations even if the dose to each individual is very low. This may be the case in global contamination from radioactive substances (such as in atmospheric nuclear weapons tests) or in contamination that stretches very far into the future. If the risk of cancer from ionizing radiation is proportional to the dose and without a threshold, it follows that the expected number of cancer cases is proportional to the collective dose. In spite of this, it has been argued that small individual doses should not pose a problem even if the collective dose is great.

Arguments to the effect that "risks ought to be disregarded if they are sufficiently small" are called de minimis arguments. Common arguments for calling risks de minimis are that they are trivial compared to other risks humans accept, that they are trivial in comparison to natural risks, or that they have to be disregarded in order to avoid the allocation of unreasonably large economic resources to investigate or manage them. It has often been claimed that risks with a probability on the order of magnitude of one in a million or smaller are de minimis. Nevertheless, such a general de minimis level is ethically problematic because it would allow many small risks that in combination may yield a large risk for an individual. Furthermore, many small risks to many people may also yield a large total effect. For example, exposing each of ten million persons to an independent risk of death of one per million yields ten expected fatalities. Also, the mathematical "law of large numbers" yields that the actual outcome will be around ten fatalities.

Another ethical problem in radiation protection arises from the long-term management of radioactive waste. Radioactive materials may be dangerous for hundreds of thousands of years, and mistakes made now may affect future generations. This problem is not exclusive to radioactive waste, because many other technological activities have consequences reaching far into future; examples include emissions that may lead to global climate change and damage to the ozone layer. The discussion regarding radioactive waste is nevertheless important, because many countries have not made final decisions for long-term management of the radioactive waste from nuclear reactors and/or nuclear weapons. The problem of distant future effects poses intriguing ethical problems. What is the moral status of future, nonexisting individuals and what duties do persons today have toward them? The International Atomic Energy Agency (IAEA) is of the opinion that radioactive waste should be managed in such a way that predicted impacts on the health of future generations will not be greater than today and that no undue burden is imposed on future generations.

PER WIKMAN

SEE ALSO Chernobyl;Hormesis;International Commission on Radiological Protection;Regulatory Toxicology.

BIBLIOGRAPHY

International Atomic Energy Agency (IAEA). (1996). Radiation Protection and the Safety of Radiation Sources. Vienna: Author. The foundation document of the IAEA system of protection.

International Commission on Non-Ionizing Radiation Protection (ICNIRP). (1998). "Guidelines for Limiting Exposure to Time-Varying Electric, Magnetic, and Electromagnetic Fields (Up to 300 GHz)." Health Physics 74(4): 494–522. Describes the rationale for the ICNIRP guidelines for limiting exposure to electromagnetic fields.

International Commission on Non-Ionizing Radiation Protection (ICNIRP). (2001). "Review of the Epidemiologic Literature on EMF and Health." Environmental Health Perspectives 109(suppl. 6): 911–933. An authoritative overview of the knowledge base for the risks from electromagnetic fields.

International Commission on Non-Ionizing Radiation Protection (ICNIRP). (2002). "General Approach to Protection against Non-Ionizing Radiation." Health Physics 82(4): 540–548. The foundation document of the ICNIRP system of protection.

International Commission on Radiological Protection (ICRP). (1992). 1990 Recommendations of the International Commission on Radiological Protection. Oxford: Pergamon Press. The foundation document of the ICRP 1990 system of protection that has had a profound influence on radiation protection internationally.

Lindell, Bo. (1985). Concepts of Collective Dose in Radiological Protection: A Review for the Committee on Radiation Protection and Public Health of the OECD Nuclear Energy Agency. Paris: Organisation for Economic Co-operation and Development, Nuclear Energy Agency. A detailed guide to the concept of collective dose, and related ethical issues.

Silini, Giovanni. (1992). "Ethical Issues in Radiation Protection: The 1992 Sievert Lecture." Health Physics 63(2): 139–148. Reviews ethical issues that have been considered in the development of radiation protection from ionizing radiation.

Sowby, David, and Jack Valentin. (2003). "Forty Years On: How Radiological Protection Has Evolved Internationally." Journal of Radiological Protection 23(2): 157–171. An overview of international organizations in radiation protection and the development of the ICRP recommendations since 1950.

Taylor, Lauriston S. (1980). "Some Nonscientific Influences on Radiation Protection Standards and Practice: The 1980 Sievert Lecture." Health Physics 39(6): 851–874. A classic text on more philosophical aspects of radiation protection by one of the first members of ICRP.

United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR). (2000). Sources and Effects of Ionizing Radiation: UNSCEAR 2000 Report to the General Assembly, with Scientific Annexes. 2 vols. New York: United Nations. An authoritative overview of the knowledge base for the risks from ionizing radiation.

Wikman, Per. (2004). "Trivial Risks and the New Radiation Protection System." Journal of Radiological Protection 24(1): 3–11. Examines ethical and philosophical aspects of a novel way of thinking in radiation protection.