Linear no-threshold model

From Wikipedia, the free encyclopedia

Different assumptions on the extrapolation of the cancer risk vs. radiation dose to low-dose levels, given a known risk at a high dose:
(A) supra-linearity, (B) linear
(C) linear-quadratic, (D) hormesis

The linear no-threshold model (LNT) is a model used in radiation protection to quantify radiation exposure and set regulatory limits. It is most frequently used to calculate the probability of radiation induced cancer at both high doses where epidemiology studies support its application but, controversially, it likewise finds applications in calculating the effects of low doses, a dose region that is fraught with much less statistical confidence in its predictive power but that nonetheless has resulted in major personal and policy decisions in regards to public health. The model assumes that the long-term, biological damage caused by ionizing radiation (essentially the cancer risk) is directly proportional to the dose. This allows the summation by dosimeters of all radiation exposure, without taking into consideration dose levels or dose rates. In other words, radiation is always considered harmful with no safety threshold, and the sum of several very small exposures are considered to have the same effect as one larger exposure (response linearity).

One of the organizations for establishing recommendations on radiation protection guidelines internationally, the UNSCEAR, recommended in 2014 policies that do not agree with the Linear No-Threshold model at exposure levels below background levels of radiation to the UN General Assembly from the Fifty-Ninth Session of the Committee. Its recommendation states that "the Scientific Committee does not recommend multiplying very low doses by large numbers of individuals to estimate numbers of radiation-induced health effects within a population exposed to incremental doses at levels equivalent to or lower than natural background levels." This is a reversal from previous recommendations by the same organization.

There are three active (2016) challenges to the LNT model currently being considered by the US Nuclear Regulatory Commission. One was filed by Nuclear Medicine Professor Carol Marcus of UCLA, who calls the LNT model scientific "baloney".

Whether the model describes the reality for small-dose exposures is disputed. It opposes two competing schools of thought: the threshold model, which assumes that very small exposures are harmless, and the radiation hormesis model, which claims that radiation at very small doses can be beneficial. Because the current data are inconclusive, scientists disagree on which model should be used. Pending any definitive answer to these questions and the precautionary principle, the model is sometimes used to quantify the cancerous effect of collective doses of low-level radioactive contaminations, even though it estimates a positive number of excess deaths at levels that would have had zero deaths, or saved lives, in the two other models. Such practice has been condemned by the International Commission on Radiological Protection.

The LNT model is sometimes applied to other cancer hazards such as polychlorinated biphenyls in drinking water.

Origins

Increased Risk of Solid Cancer with Dose for A-bomb survivors, from BEIR report. Notably this exposure pathway occurred from essentially a massive spike or pulse of radiation, a result of the brief instant that the bomb exploded, which while somewhat similar to the environment of a CT scan, it is wholly unlike the low dose rate of living in a contaminated area such as Chernobyl, were the dose rate is orders of magnitude smaller. However LNT does not consider dose rate and is an unsubstantiated one size fits all approach based solely on total absorbed dose. When the two environments and cell effects are vastly different. Likewise, it has also been pointed out that bomb survivors inhaled carcinogenic benzopyrene from the burning cities, yet this is not factored in.

 

The association of exposure to radiation with cancer had been observed as early as 1902, six years after the discovery of X-ray by Wilhelm Röntgen and radioactivity by Henri Becquerel. In 1927, Hermann Muller demonstrated that radiation may cause genetic mutation. He also suggested mutation as a cause of cancer. Muller, who received a Nobel Prize for his work on the mutagenic effect of radiation in 1946, asserted in his Nobel Lecture, "The Production of Mutation", that mutation frequency is "directly and simply proportional to the dose of irradiation applied" and that there is "no threshold dose".

The early studies were based on relatively high levels of radiation that made it hard to establish the safety of low level of radiation, and many scientists at that time believed that there may be a tolerance level, and that low doses of radiation may not be harmful. A later study in 1955 on mice exposed to low dose of radiation suggest that they may outlive control animals. The interest in the effect of radiation intensified after the dropping of atomic bombs on Hiroshima and Nagasaki, and studies were conducted on the survivors. Although compelling evidence on the effect of low dosage of radiation was hard to come by, by the late 1940s, the idea of LNT became more popular due to its mathematical simplicity. In 1954, the National Council on Radiation Protection and Measurements (NCRP) introduced the concept of maximum permissible dose. In 1958, United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) assessed the LNT model and a threshold model, but noted the difficulty in acquiring "reliable information about the correlation between small doses and their effects either in individuals or in large populations". The United States Congress Joint Committee on Atomic Energy (JCAE) similarly could not establish if there is a threshold or "safe" level for exposure, nevertheless it introduced the concept of "As Low As Reasonably Achievable" (ALARA). ALARA would become a fundamental principle in radiation protection policy that implicitly accepts the validity of LNT. In 1959, United States Federal Radiation Council (FRC) supported the concept of the LNT extrapolation down to the low dose region in its first report.

By the 1970s, the LNT model had become accepted as the standard in radiation protection practice by a number of bodies. In 1972, the first report of National Academy of Sciences (NAS) Biological Effects of Ionizing Radiation (BEIR), an expert panel who reviewed available peer reviewed literature, supported the LNT model on pragmatic grounds, noting that while "dose-effect relationship for x rays and gamma rays may not be a linear function", the "use of linear extrapolation . . . may be justified on pragmatic grounds as a basis for risk estimation." In its seventh report of 2006, NAS BEIR VII writes, "the committee concludes that the preponderance of information indicates that there will be some risk, even at low doses".

Radiation precautions and public policy

Radiation precautions have led to sunlight being listed as a carcinogen at all sun exposure rates, due to the ultraviolet component of sunlight, with no safe level of sunlight exposure being suggested, following the precautionary LNT model. According to a 2007 study submitted by the University of Ottawa to the Department of Health and Human Services in Washington, D.C., there is not enough information to determine a safe level of sun exposure at this time.

If a particular dose of radiation is found to produce one extra case of a type of cancer in every thousand people exposed, LNT projects that one thousandth of this dose will produce one extra case in every million people so exposed, and that one millionth of the original dose will produce one extra case in every billion people exposed. The conclusion is that any given dose equivalent of radiation will produce the same number of cancers, no matter how thinly it is spread.

The model is simple to apply: a quantity of radiation can be translated into a number of deaths without any adjustment for the distribution of exposure, including the distribution of exposure within a single exposed individual. For example, a hot particle embedded in an organ (such as lung) results in a very high dose in the cells directly adjacent to the hot particle, but a much lower whole-organ and whole-body dose. Thus, even if a safe low dose threshold was found to exist at cellular level for radiation induced mutagenesis, the threshold would not exist for environmental pollution with hot particles, and could not be safely assumed to exist when the distribution of dose is unknown.

The linear no-threshold model is used to extrapolate the expected number of extra deaths caused by exposure to environmental radiation, and it therefore has a great impact on public policy. The model is used to translate any radiation release, like that from a "dirty bomb", into a number of lives lost, while any reduction in radiation exposure, for example as a consequence of radon detection, is translated into a number of lives saved. When the doses are very low, at natural background levels, in the absence of evidence, the model predicts via extrapolation, new cancers only in a very small fraction of the population, but for a large population, the number of lives is extrapolated into hundreds or thousands, and this can sway public policy.

A linear model has long been used in health physics to set maximum acceptable radiation exposures.

The United States-based National Council on Radiation Protection and Measurements (NCRP), a body commissioned by the United States Congress, recently released a report written by the national experts in the field which states that, radiation's effects should be considered to be proportional to the dose an individual receives, regardless of how small the dose is. 

A 1958 analysis of two decades of research on the mutation rate of 1 million lab mice showed that six major hypotheses about ionizing radiation and gene mutation were not supported by data. Its data was used in 1972 by the Biological Effects of Ionizing Radiation I committee to support the LNT model. However, it has been claimed that the data contained a fundamental error that was not revealed to the committee, and would not support the LNT model on the issue of mutations and may suggest a threshold dose rate under which radiation does not produce any mutations. The acceptance of the LNT model has been challenged by a number of scientists, see controversy section below.

Fieldwork

The LNT model and the alternatives to it each have plausible mechanisms that could bring them about, but definitive conclusions are hard to make given the difficulty of doing longitudinal studies involving large cohorts over long periods. 

A 2003 review of the various studies published in the authoritative Proceedings of the National Academy of Sciences concludes that "given our current state of knowledge, the most reasonable assumption is that the cancer risks from low doses of x- or gamma-rays decrease linearly with decreasing dose."

A 2005 study of Ramsar, Iran (a region with very high levels of natural background radiation) showed that lung cancer incidence was lower in the high-radiation area than in seven surrounding regions with lower levels of natural background radiation. A fuller epidemiological study of the same region showed no difference in mortality for males, and a statistically insignificant increase for females. 

A 2009 study by researchers that looks at Swedish children exposed to fallout from Chernobyl while they were fetuses between 8 and 25 weeks gestation concluded that the reduction in IQ at very low doses was greater than expected, given a simple LNT model for radiation damage, indicating that the LNT model may be too conservative when it comes to neurological damage. However, in medical journals, studies detail that in Sweden in the year of the Chernobyl accident, the birth rate, both increased and shifted to those of "higher maternal age" in 1986. More advanced maternal age in Swedish mothers was linked with a reduction in offspring IQ, in a paper published in 2013. Neurological damage has a different biology than cancer. 

In a 2009 study cancer rates among UK radiation workers were found to increase with higher recorded occupational radiation doses. The doses examined varied between 0 and 500 mSv received over their working lives. These results exclude the possibilities of no increase in risk or that the risk is 2-3 times that for A-bomb survivors with a confidence level of 90%. The cancer risk for these radiation workers was still less than the average for persons in the UK due to the healthy worker effect.

A 2009 study focusing on the naturally high background radiation region of Karunagappalli, India concluded: "our cancer incidence study, together with previously reported cancer mortality studies in the HBR area of Yangjiang, China, suggests it is unlikely that estimates of risk at low doses are substantially greater than currently believed." A 2011 meta-analysis further concluded that the "Total whole body radiation doses received over 70 years from the natural environment high background radiation areas in Kerala, India and Yanjiang, China are much smaller than [the non-tumour dose, "defined as the highest dose of radiation at which no statistically significant tumour increase was observed above the control level"] for the respective dose-rates in each district."

In 2011 an in vitro time-lapse study of the cellular response to low doses of radiation showed a strongly non-linear response of certain cellular repair mechanisms called radiation-induced foci (RIF). The study found that low doses of radiation prompted higher rates of RIF formation than high doses, and that after low-dose exposure RIF continued to form after the radiation had ended.

In 2012 a historical cohort study of >175 000 patients without previous cancer who were examined with CT head scans in UK between 1985 and 2002 was published. The study, which investigated leukaemia and brain cancer, indicated a linear dose response in the low dose region and had qualitative estimates of risk that were in agreement with the Life Span Study (Epidemiology data for low-linear energy transfer radiation). 

In 2013 a data linkage study of 11 million Australians with more than 680,000 people exposed to CT scans between 1985 and 2005 was published. The study confirmed the results of the 2012 UK study for leukaemia and brain cancer but also investigated other cancer types. The authors conclude that their results were generally consistent with the linear no threshold theory.

Controversy

The LNT model has been contested by a number of scientists. It is been claimed that the early proponent of the model Hermann Joseph Muller intentionally ignored an early study that did not support the LNT model when he gave his 1946 Nobel Prize address advocating the model.

It is also argued that LNT model had caused an irrational fear of radiation. In the wake of the 1986 Chernobyl accident in Ukraine, Europe-wide anxieties were fomented in pregnant mothers over the perception enforced by the LNT model that their children would be born with a higher rate of mutations. As far afield as the country of Denmark, hundreds of excess induced abortions were performed on the healthy unborn, out of this no-threshold fear. Following the accident however, studies of data sets approaching a million births in the EUROCAT database, divided into "exposed" and control groups were assessed in 1999. As no Chernobyl impacts were detected, the researchers conclude "in retrospect the widespread fear in the population about the possible effects of exposure on the unborn was not justified". Despite studies from Germany and Turkey, the only robust evidence of negative pregnancy outcomes that transpired after the accident were these elective abortion indirect effects, in Greece, Denmark, Italy etc., due to the anxieties created.

In very high dose radiation therapy, it was known at the time that radiation can cause a physiological increase in the rate of pregnancy anomalies, however, human exposure data and animal testing suggests that the "malformation of organs appears to be a deterministic effect with a threshold dose" below which, no rate increase is observed. A review in 1999 on the link between the Chernobyl accident and teratology (birth defects) concludes that "there is no substantive proof regarding radiation‐induced teratogenic effects from the Chernobyl accident". It is argued that the human body has defense mechanisms, such as DNA repair and programmed cell death, that would protect it against carcinogenesis due to low-dose exposures of carcinogens.

Ramsar, located in Iran, is often quoted as being a counter example to LNT. Based on preliminary results, it was considered as having the highest natural background radiation levels on Earth, several times higher than the ICRP-recommended radiation dose limits for radiation workers, whilst the local population did not seem to suffer any ill effects. However, the population of the high-radiation districts is small (about 1800 inhabitants) and only receive an average of 6 millisieverts per year, so that cancer epidemiology data are too imprecise to draw any conclusions. On the other hand, there may be non-cancer effects from the background radiation such as chromosomal aberrations or female infertility.

A 2011 research of the cellular repair mechanisms support the evidence against the linear no-threshold model. According to its authors, this study published in the Proceedings of the National Academy of Sciences of the United States of America "casts considerable doubt on the general assumption that risk to ionizing radiation is proportional to dose". 

However, a 2011 review of studies addressing childhood leukaemia following exposure to ionizing radiation, including both diagnostic exposure and natural background exposure, concluded that existing risk factors, excess relative risk per Sv (ERR/Sv), is "broadly applicable" to low dose or low dose-rate exposure.

Several expert scientific panels have been convened on the accuracy of the LNT model at low dosage, and various organizations and bodies have stated their positions on this topic:

Support

• In 2004 the United States National Research Council (part of the National Academy of Sciences) supported the linear no threshold model and stated regarding Radiation hormesis:

  The assumption that any stimulatory hormetic effects from low doses of ionizing radiation will have a significant health benefit to humans that exceeds potential detrimental effects from the radiation exposure is unwarranted at this time.

• In 2005 the United States National Academies' National Research Council published its comprehensive meta-analysis of low-dose radiation research BEIR VII, Phase 2. In its press release the Academies stated:

The scientific research base shows that there is no threshold of exposure below which low levels of ionizing radiation can be demonstrated to be harmless or beneficial.

• The National Council on Radiation Protection and Measurements (a body commissioned by the United States Congress). endorsed the LNT model in a 2001 report that attempted to survey existing literature critical of the model.
• The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) wrote in its 2000 report

  Until the [...] uncertainties on low-dose response are resolved, the Committee believes that an increase in the risk of tumour induction proportionate to the radiation dose is consistent with developing knowledge and that it remains, accordingly, the most scientifically defensible approximation of low-dose response. However, a strictly linear dose response should not be expected in all circumstances.

• the United States Environmental Protection Agency also endorses the LNT model in its 2011 report on radiogenic cancer risk:

  Underlying the risk models is a large body of epidemiological and radiobiological data. In general, results from both lines of research are consistent with a linear, no-threshold dose (LNT) response model in which the risk of inducing a cancer in an irradiated tissue by low doses of radiation is proportional to the dose to that tissue.

Oppose

A number of organisations disagree with using the Linear no-threshold model to estimate risk from environmental and occupational low-level radiation exposure:

• The French Academy of Sciences (Académie des Sciences) and the National Academy of Medicine (Académie Nationale de Médecine) published a report in 2005 (at the same time as BEIR VII report in the United States) that rejected the Linear no-threshold model in favor of a threshold dose response and a significantly reduced risk at low radiation exposure:

In conclusion, this report raises doubts on the validity of using LNT for evaluating the carcinogenic risk of low doses (< 100 mSv) and even more for very low doses (< 10 mSv). The LNT concept can be a useful pragmatic tool for assessing rules in radioprotection for doses above 10 mSv; however since it is not based on biological concepts of our current knowledge, it should not be used without precaution for assessing by extrapolation the risks associated with low and even more so, with very low doses (< 10 mSv), especially for benefit-risk assessments imposed on radiologists by the European directive 97-43.

• The Health Physics Society's position statement first adopted in January 1996, as revised in July 2010, states:

In accordance with current knowledge of radiation health risks, the Health Physics Society recommends against quantitative estimation of health risks below an individual dose of 5 rem (50 mSv) in one year or a lifetime dose of 10 rem (100 mSv) above that received from natural sources. Doses from natural background radiation in the United States average about 0.3 rem (3 mSv) per year. A dose of 5 rem (50 mSv) will be accumulated in the first 17 years of life and about 25 rem (250 mSv) in a lifetime of 80 years. Estimation of health risk associated with radiation doses that are of similar magnitude as those received from natural sources should be strictly qualitative and encompass a range of hypothetical health outcomes, including the possibility of no adverse health effects at such low levels.

• The American Nuclear Society recommended further research on the Linear No Threshold Hypothesis before making adjustments to current radiation protection guidelines, concurring with the Health Physics Society's position that:

  There is substantial and convincing scientific evidence for health risks at high dose. Below 10 rem or 100 mSv (which includes occupational and environmental exposures) risks of health effects are either too small to be observed or are non-existent.

Intermediate

The US Nuclear Regulatory Commission takes the intermediate position that "accepts the LNT hypothesis as a conservative model for estimating radiation risk", but noting that "public health data do not absolutely establish the occurrence of cancer following exposure to low doses and dose rates — below about 10,000 mrem (100 mSv). Studies of occupational workers who are chronically exposed to low levels of radiation above normal background have shown no adverse biological effects."

Mental health 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 radiation 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 the 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 the 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".

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. It is "only nuclear radiation that bears a huge psychological burden — for it carries a unique historical legacy".

Mobile phone radiation and health

From Wikipedia, the free encyclopedia

The effect of mobile phone radiation on human health is a subject of interest and study worldwide, as a result of the enormous increase in mobile phone usage throughout the world. As of 2015, there were 7.4 billion subscriptions worldwide, though the actual number of users is lower as many users own more than one mobile phone. Mobile phones use electromagnetic radiation in the microwave range (450–3800 MHz and 24–80 GHz in 5G mobile). Other digital wireless systems, such as data communication networks, produce similar radiation.

The World Health Organization states that "A large number of studies have been performed over the last two decades to assess whether mobile phones pose a potential health risk. To date, no adverse health effects have been established as being caused by mobile phone use." In a 2018 statement, the FDA said that "the current safety limits are set to include a 50-fold safety margin from observed effects of Radio-frequency energy exposure".

Exposure

A cell phone is a wireless portable telephone that connects to the telephone network by radio waves exchanged with a local antenna and automated transceiver called a cellular base station (cell site or cell tower). The service area served by each provider is divided into small geographical areas called cells, and all the cell phones in a cell communicate with that cell's antenna. Both the cell phone and the cell tower have radio transmitters which communicate with each other. Since in a cellular network the same radio channels are reused every few cells, cellular networks use low power transmitters to avoid radio waves from one cell spilling over and interfering with a nearby cell using the same frequencies. 

Cell phones are limited to a equivalent isotropic radiated power (EIRP) radiated power output of 3 watts, and the network continuously adjusts the phone transmitter to the lowest power consistent with good signal quality, reducing it to as low as one milliwatt when near the cell tower. Cell phone tower channel transmitters usually have an EIRP power output of around 50 watts. Even when it is not being used, unless it is turned off, a cell phone periodically emits radio signals on its control channel, to keep contact with its cell tower and for functions like handing off the phone to another tower if the user crosses into another cell. When the user is making a call, the cell phone transmits a signal on a second channel which carries the user's voice. Existing 2G, 3G, and 4G networks use frequencies in the UHF or low microwave bands, 600 MHz to 3.5 GHz. Many household wireless devices such as Wifi networks, garage door openers, and baby monitors use other frequencies in this same frequency range. 

Radio waves decrease rapidly in intensity by the inverse square of distance as they spread out from a transmitting antenna. So the cell phone transmitter, which is held close to the user's face when talking, is a much greater source of human exposure than the cell tower transmitter, which is typically at least hundreds of meters away from the public on a cell tower. A user can reduce their exposure by using a headset and keeping the cell phone itself further away from their body. 

Next generation 5G cellular networks, which began deploying in 2019, use higher frequencies in or near the millimeter wave band, 24 to 52 GHz. Millimeter waves are absorbed by atmospheric gases so 5G networks will use smaller cells than previous cellular networks, about the size of a city block. Instead of a cell tower, each cell will use an array of multiple small antennas mounted on existing buildings and utility poles. In general, millimeter waves penetrate less deeply into biological tissue than microwaves, and are mainly absorbed within the first centimeter of the body surface.

Effects studied

Blood–brain barrier

A 2010 review stated that "The balance of experimental evidence does not support an effect of 'non-thermal' radiofrequency fields" on the permeability of the blood-brain barrier, but noted that research on low frequency effects and effects in humans was sparse. A 2012 study of low-frequency radiation on humans found "no evidence for acute effects of short-term mobile phone radiation on cerebral blood flow".

Cancer

There is no strong or consistent evidence that mobile phone use increases the risk of getting brain cancer or other head tumors. The United States National Cancer Institute points out that "Radiofrequency energy, unlike ionizing radiation, does not cause DNA damage that can lead to cancer. Its only consistently observed biological effect in humans is tissue heating. In animal studies, it has not been found to cause cancer or to enhance the cancer-causing effects of known chemical carcinogens." The majority of human studies have failed to find a link between cell phone use and cancer. In 2011 a World Health Organization working group classified cell phone use as "possibly carcinogenic to humans". The CDC states that no scientific evidence definitively answers whether cell phone use causes cancer.

In a 2018 statement, the FDA said that "the current safety limits are set to include a 50-fold safety margin from observed effects of radiofrequency energy exposure".

An analysis of an "eagerly anticipated" study using rats and mice by the National Toxicology Program indicates that due to such issues as the inconsistent appearances of "signals for harm" within and across species and the increased chances of false positives due to the multiplicity of tests, the positive results seen are more likely due to random chance. The full results of the study were released in February 2018.

Male fertility

A decline in male sperm quality has been observed over several decades. Studies on the impact of mobile radiation on male fertility are conflicting, and the effects of the radiofrequency electromagnetic radiation (RF-EMR) emitted by these devices on the reproductive systems are currently under active debate. A 2012 review concluded that "together, the results of these studies have shown that RF-EMR decreases sperm count and motility and increases oxidative stress". A 2017 study of 153 men that attended an academic fertility clinic in Boston, Massachusetts found that self-reported mobile phone use was not related to semen quality, and that carrying a mobile phone in the pants pocket was not related to semen quality.

Electromagnetic hypersensitivity

Some users of mobile phones and similar devices have reported feeling various non-specific symptoms during and after use. Studies have failed to link any of these symptoms to electromagnetic exposure. In addition, EHS is not a recognised medical diagnosis.

Glucose metabolism

According to the National Cancer Institute, two small studies exploring whether and how cell phone radiation affects brain glucose metabolism showed inconsistent results.

Base stations

Cellular Mobile and UHF Antenna Tower with multiple Antennas

 

Experts consulted by France considered it was mandatory that the main antenna axis should not to be directly in front of a living place at a distance shorter than 100 metres. This recommendation was modified in 2003 to say that antennas located within a 100-metre radius of primary schools or childcare facilities should be better integrated into the cityscape and was not included in a 2005 expert report. The Agence française de sécurité sanitaire environnementale (fr) as of 2009, says that there is no demonstrated short-term effect of electromagnetic fields on health, but that there are open questions for long-term effects, and that it is easy to reduce exposure via technological improvements.

Safety standards and licensing

In order to protect the population living around base stations and users of mobile handsets, governments and regulatory bodies adopt safety standards, which translate to limits on exposure levels below a certain value. There are many proposed national and international standards, but that of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) is the most respected one, and has been adopted so far by more than 80 countries. For radio stations, ICNIRP proposes two safety levels: one for occupational exposure, another one for the general population. Currently there are efforts underway to harmonise the different standards in existence.

Radio base licensing procedures have been established in the majority of urban spaces regulated either at municipal/county, provincial/state or national level. Mobile telephone service providers are, in many regions, required to obtain construction licenses, provide certification of antenna emission levels and assure compliance to ICNIRP standards and/or to other environmental legislation. 

Many governmental bodies also require that competing telecommunication companies try to achieve sharing of towers so as to decrease environmental and cosmetic impact. This issue is an influential factor of rejection of installation of new antennas and towers in communities. 

The safety standards in the US are set by the Federal Communications Commission (FCC). The FCC has based its standards primarily on those standards established by the National Council on Radiation Protection and Measurements (NCRP) a Congressionally chartered scientific organization located in the WDC area and the Institute of Electrical and Electronics Engineers (IEEE), specifically Subcommittee 4 of the "International Committee on Electromagnetic Safety". 

Switzerland has set safety limits lower than the ICNIRP limits for certain "sensitive areas" (classrooms, for example).

Lawsuits

In the US, personal injury lawsuits have been filed by individuals against cellphone manufacturers (including Motorola, NEC, Siemens, and Nokia) on the basis of allegations of causation of brain cancer and death. In US federal courts, expert testimony relating to science must be first evaluated by a judge, in a Daubert hearing, to be relevant and valid before it is admissible as evidence. In a 2002 case against Motorola, the plaintiffs alleged that the use of wireless handheld telephones could cause brain cancer and that the use of Motorola phones caused one plaintiff's cancer. The judge ruled that no sufficiently reliable and relevant scientific evidence in support of either general or specific causation was proffered by the plaintiffs, accepted a motion to exclude the testimony of the plaintiffs' experts, and denied a motion to exclude the testimony of the defendants' experts.

Two separate cases in Italy, in 2009 and 2017, resulted in pensions being awarded to plaintiffs who had claimed their benign brain tumors were the result of prolonged mobile phone use in professional tasks, for 5–6 hours a day, which they ruled different from non-professional use.

Precautions

Precautionary principle

In 2000, the World Health Organization (WHO) recommended that the precautionary principle could be voluntarily adopted in this case. It follows the recommendations of the European Community for environmental risks. 

According to the WHO, the "precautionary principle" is "a risk management policy applied in circumstances with a high degree of scientific uncertainty, reflecting the need to take action for a potentially serious risk without awaiting the results of scientific research." Other less stringent recommended approaches are prudent avoidance principle and as low as reasonably practicable. Although all of these are problematic in application, due to the widespread use and economic importance of wireless telecommunication systems in modern civilization, there is an increased popularity of such measures in the general public, though also evidence that such approaches may increase concern. They involve recommendations such as the minimization of cellphone usage, the limitation of use by at-risk population (e.g., children), the adoption of cellphones and microcells with as low as reasonably practicable levels of radiation, the wider use of hands-free and earphone technologies such as Bluetooth headsets, the adoption of maximal standards of exposure, RF field intensity and distance of base stations antennas from human habitations, and so forth. Overall, public information remains a challenge as various health consequences are evoked in the literature and by the media, putting populations under chronic exposure to potentially worrying information.

Precautionary measures and health advisories

In May 2011, the World Health Organization's International Agency for Research on Cancer announced it was classifying electromagnetic fields from mobile phones and other sources as "possibly carcinogenic to humans" and advised the public to adopt safety measures to reduce exposure, like use of hands-free devices or texting.

Some national radiation advisory authorities, including those of Austria, France, Germany, and Sweden, have recommended measures to minimize exposure to their citizens. Examples of the recommendations are:

• Use hands-free to decrease the radiation to the head.
• Keep the mobile phone away from the body.
• Do not use telephone in a car without an external antenna.

The use of "hands-free" was not recommended by the British Consumers' Association in a statement in November 2000, as they believed that exposure was increased. However, measurements for the (then) UK Department of Trade and Industry and others for the French Agence française de sécurité sanitaire environnementale [fr] showed substantial reductions. In 2005, Professor Lawrie Challis and others said clipping a ferrite bead onto hands-free kits stops the radio waves travelling up the wire and into the head.

Several nations have advised moderate use of mobile phones for children. A journal by Gandhi et al. in 2006 states that children receive higher levels of Specific Absorption Rate (SAR). When 5- and 10-year olds are compared to adults, they receive about 153% higher SAR levels. Also, with the permittivity of the brain decreasing as one gets older and the higher relative volume of the exposed growing brain in children, radiation penetrates far beyond the mid-brain.

Bogus products

Products have been advertised that claim to shield people from EM radiation from cell phones; in the US the Federal Trade Commission published a warning that "Scam artists follow the headlines to promote products that play off the news – and prey on concerned people."

According to the FTC, "there is no scientific proof that so-called shields significantly reduce exposure from electromagnetic emissions. Products that block only the earpiece – or another small portion of the phone – are totally ineffective because the entire phone emits electromagnetic waves." Such shields "may interfere with the phone's signal, cause it to draw even more power to communicate with the base station, and possibly emit more radiation." The FTC has enforced false advertising claims against companies that sell such products.

Non-ionizing radiation

From Wikipedia, the free encyclopedia

Different types of electromagnetic radiation

 

Non-ionizing (or non-ionising) radiation refers to any type of electromagnetic radiation that does not carry enough energy per quantum (photon energy) to ionize atoms or molecules—that is, to completely remove an electron from an atom or molecule. Instead of producing charged ions when passing through matter, non-ionizing electromagnetic radiation has sufficient energy only for excitation, the movement of an electron to a higher energy state. Ionizing radiation which has a higher frequency and shorter wavelength than nonionizing radiation, has many uses but can be a health hazard; exposure to it can cause burns, radiation sickness, cancer, and genetic damage. Using ionizing radiation requires elaborate radiological protection measures which in general are not required with nonionizing radiation.

The region at which radiation becomes considered as "ionizing" is not well defined, since different molecules and atoms ionize at different energies. The usual definitions have suggested that radiation with particle or photon energies less than 10 electronvolts (eV) be considered non-ionizing. Another suggested threshold is 33 electronvolts, which is the energy needed to ionize water molecules. The light from the Sun that reaches the earth is largely composed of non-ionizing radiation, since the ionizing far-ultraviolet rays have been filtered out by the gases in the atmosphere, particularly oxygen. The remaining ultraviolet radiation from the Sun causes molecular damage (for example, sunburn) by photochemical and free-radical-producing means.

Different biological effects are observed for different types of non-ionizing radiation. The upper frequencies of non-ionizing radiation near these energies (much of the spectrum of UV light and some visible light) are capable of non-thermal biological damage, similar to ionizing radiation. Health debate therefore centers on the non-thermal effects of radiation of much lower frequencies (microwave, millimeter and radiowave radiation). The International Agency for Research on Cancer recently stated that there could be some risk from non-ionizing radiation to humans. But a subsequent study reported that the basis of the IARC evaluation was not consistent with observed incidence trends. This and other reports suggest that there is virtually no way that results on which the IARC based its conclusions are correct. The Bioinitiative Report 2012 makes the claim that there are significant health risk associated with low frequency non-ionizing electromagnetic radiation. This report claims that statistically significant increases in cancer among those exposed to even low power levels, low frequency, non-ionizing radiation. There is considerable debate on this matter. Currently regulatory bodies around the world have not seen the need to change current safety standards.

Mechanisms of interaction with matter, including living tissue

Near ultraviolet, visible light, infrared, microwave, radio waves, and low-frequency radio frequency (longwave) are all examples of non-ionizing radiation. By contrast, far ultraviolet light, X-rays, gamma-rays, and all particle radiation from radioactive decay are ionizing. Visible and near ultraviolet electromagnetic radiation may induce photochemical reactions, or accelerate radical reactions, such as photochemical aging of varnishes or the breakdown of flavoring compounds in beer to produce the "lightstruck flavor". Near ultraviolet radiation, although technically non-ionizing, may still excite and cause photochemical reactions in some molecules. This happens because at ultraviolet photon energies, molecules may become electronically excited or promoted to free-radical form, even without ionization taking place. 

The occurrence of ionization depends on the energy of the individual particles or waves, and not on their number. An intense flood of particles or waves will not cause ionization if these particles or waves do not carry enough energy to be ionizing, unless they raise the temperature of a body to a point high enough to ionize small fractions of atoms or molecules by the process of thermal-ionization. In such cases, even "non-ionizing radiation" is capable of causing thermal-ionization if it deposits enough heat to raise temperatures to ionization energies. These reactions occur at far higher energies than with ionizing radiation, which requires only a single particle to ionize. A familiar example of thermal ionization is the flame-ionization of a common fire, and the browning reactions in common food items induced by infrared radiation, during broiling-type cooking. 

The energy of particles of non-ionizing radiation is low, and instead of producing charged ions when passing through matter, non-ionizing electromagnetic radiation has only sufficient energy to change the rotational, vibrational or electronic valence configurations of molecules and atoms. This produces thermal effects. The possible non-thermal effects of non-ionizing forms of radiation on living tissue have only recently been studied. Much of the current debate is about relatively low levels of exposure to radio frequency (RF) radiation from mobile phones and base stations producing "non-thermal" effects. Some experiments have suggested that there may be biological effects at non-thermal exposure levels, but the evidence for production of health hazard is contradictory and unproven. The scientific community and international bodies acknowledge that further research is needed to improve our understanding in some areas. Meanwhile the consensus is that there is no consistent and convincing scientific evidence of adverse health effects caused by RF radiation at powers sufficiently low that no thermal health effects are produced.

Health risks

Non-ionizing radiation hazard sign

 

Non-ionizing radiation can produce non-mutagenic effects such as inciting thermal energy in biological tissue that can lead to burns. In 2011, the International Agency for Research on Cancer (IARC) from the World Health Organization (WHO) released a statement adding radiofrequency electromagnetic fields (including microwave and millimeter waves) to their list of things which are possibly carcinogenic to humans.

In terms of potential biological effects, the non-ionizing portion of the spectrum can be subdivided into:

1. The optical radiation portion, where electron excitation can occur (visible light, infrared light)
2. The portion where the wavelength is smaller than the body. Heating via induced currents can occur. In addition there are claims of other adverse biological effects. Such effects are not well understood and even largely denied. (MW and higher-frequency RF).
3. The portion where the wavelength is much larger than the body, and heating via induced currents seldom occurs (lower-frequency RF, power frequencies, static fields).

The above effects have only been shown to be due to heating effects. At low power levels where there is no heating affect, the risk of cancer is not significant.

	Source	Wavelength	Frequency	Biological effects
UVA	Black light, Sunlight	318–400 nm	750–950 THz	Eye: photochemical cataract; skin: erythema, including pigmentation
Visible light	Sunlight, fire, LEDs, light bulbs, lasers	400–780 nm	385–750 THz	Eye: photochemical & thermal retinal injury; skin: photoaging
IR-A	Sunlight, thermal radiation, incandescent light bulbs, lasers, remote controls	780 nm – 1.4 µm	215–385 THz	Eye: thermal retinal injury, thermal cataract; skin: burn
IR-B	Sunlight, thermal radiation, incandescent light bulbs, lasers	1.4–3 µm	100–215 THz	Eye: corneal burn, cataract; skin: burn
IR-C	Sunlight, thermal radiation, incandescent light bulbs, far-infrared laser	3 µm – 1 mm	300 GHz – 100 THz	Eye: corneal burn, cataract; heating of body surface
Microwave	Mobile/cell phones, microwave ovens, cordless phones, millimeter waves, airport millimeter scanners, motion detectors, long-distance telecommunications, radar, Wi-Fi	1 mm – 33 cm	1–300 GHz	Heating of body tissue
Radio-frequency radiation	Mobile/cell phones, television, FM, AM, shortwave, CB, cordless phones	33 cm – 3 km	100 kHz – 1 GHz	Heating of body tissue, raised body temperature
Low-frequency RF	Power lines	>3 km	<100 font="" khz="" nbsp="">	Cumulation of charge on body surface; disturbance of nerve & muscle responses
Static field	Strong magnets, MRI	Infinite	0 Hz (technically static fields are not "radiation")	Electric charge on body surface

Types of non-ionizing electromagnetic radiation

Near ultraviolet radiation

Ultraviolet light can cause burns to skin and cataracts to the eyes. Ultraviolet is classified into near, medium and far UV according to energy, where near and medium ultraviolet are technically non-ionizing, but where all UV wavelengths can cause photochemical reactions that to some extent mimic ionization (including DNA damage and carcinogenesis). UV radiation above 10 eV (wavelength shorter than 125 nm) is considered ionizing. However, the rest of the UV spectrum from 3.1 eV (400 nm) to 10 eV, although technically non-ionizing, can produce photochemical reactions that are damaging to molecules by means other than simple heat. Since these reactions are often very similar to those caused by ionizing radiation, often the entire UV spectrum is considered to be equivalent to ionization radiation in its interaction with many systems (including biological systems).

For example, ultraviolet light, even in the non-ionizing range, can produce free radicals that induce cellular damage, and can be carcinogenic. Photochemistry such as pyrimidine dimer formation in DNA can happen through most of the UV band, including much of the band that is formally non-ionizing. Ultraviolet light induces melanin production from melanocyte cells to cause sun tanning of skin. Vitamin D is produced on the skin by a radical reaction initiated by UV radiation. 

Plastic (polycarbonate) sunglasses generally absorb UV radiation. UV overexposure to the eyes causes snow blindness, common to areas with reflective surfaces, such as snow or water.

Visible light

Light, or visible light, is the very narrow range of electromagnetic radiation that is visible to the human eye (about 400–700 nm), or up to 380–750 nm. More broadly, physicists refer to light as electromagnetic radiation of all wavelengths, whether visible or not.

High-energy visible light is blue-violet light with a higher damaging potential.

Infrared

Infrared (IR) light is electromagnetic radiation with a wavelength between 0.7 and 300 micrometers, which equates to a frequency range between approximately 1 and 430 THz. IR wavelengths are longer than that of visible light, but shorter than that of terahertz radiation microwaves. Bright sunlight provides an irradiance of just over 1 kilowatt per square meter at sea level. Of this energy, 527 watts is infrared radiation, 445 watts is visible light, and 32 watts is ultraviolet radiation.

Microwave

Microwaves are electromagnetic waves with wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz (0.3 GHz) and 300 GHz. This broad definition includes both UHF and EHF (millimeter waves), and various sources use different boundaries. In all cases, microwave includes the entire SHF band (3 to 30 GHz, or 10 to 1 cm) at minimum, with RF engineering often putting the lower boundary at 1 GHz (30 cm), and the upper around 100 GHz (3mm). Applications include cellphone (mobile) telephones, radars, airport scanners, microwave ovens, earth remote sensing satellites, and radio and satellite communications.

Radio waves

Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Like all other electromagnetic waves, they travel at the speed of light. Naturally occurring radio waves are made by lightning, or by astronomical objects. Artificially generated radio waves are used for fixed and mobile radio communication, broadcasting, radar and other navigation systems, satellite communication, computer networks and innumerable other applications. Different frequencies of radio waves have different propagation characteristics in the Earth's atmosphere; long waves may cover a part of the Earth very consistently, shorter waves can reflect off the ionosphere and travel around the world, and much shorter wavelengths bend or reflect very little and travel on a line of sight.

Very low frequency (VLF)

Very low frequency or VLF is the radio frequencies (RF) in the range of 3 to 30 kHz. Since there is not much bandwidth in this band of the radio spectrum, only the very simplest signals are used, such as for radio navigation. Also known as the myriameter band or myriameter wave as the wavelengths range from ten to one myriameter (an obsolete metric unit equal to 10 kilometers).

Extremely low frequency (ELF)

Extremely low frequency (ELF) is the range of radiation frequencies from 300 Hz to 3 kHz. In atmosphere science, an alternative definition is usually given, from 3 Hz to 3 kHz. In the related magnetosphere science, the lower frequency electromagnetic oscillations (pulsations occurring below ~3 Hz) are considered to be in the ULF range, which is thus also defined differently from the ITU Radio Bands.

Thermal radiation

Thermal radiation, a common synonym for infra-red when it occurs at temperatures commonly encountered on Earth, is the process by which the surface of an object radiates its thermal energy in the form of electromagnetic waves. Infrared radiation that one can feel emanating from a household heater, infra-red heat lamp, or kitchen oven are examples of thermal radiation, as is the IR and visible light emitted by a glowing incandescent light bulb (not hot enough to emit the blue high frequencies and therefore appearing yellowish; fluorescent lamps are not thermal and can appear bluer). Thermal radiation is generated when the energy from the movement of charged particles within molecules is converted to the radiant energy of electromagnetic waves. The emitted wave frequency of the thermal radiation is a probability distribution depending only on temperature, and for a black body is given by Planck's law of radiation. Wien's displacement law gives the most likely frequency of the emitted radiation, and the Stefan–Boltzmann law gives the heat intensity (power emitted per area).

Parts of the electromagnetic spectrum of thermal radiation may be ionizing, if the object emitting the radiation is hot enough (has a high enough temperature). A common example of such radiation is sunlight, which is thermal radiation from the Sun's photosphere and which contains enough ultraviolet light to cause ionization in many molecules and atoms. An extreme example is the flash from the detonation of a nuclear weapon, which emits a large number of ionizing X-rays purely as a product of heating the atmosphere around the bomb to extremely high temperatures.

As noted above, even low-frequency thermal radiation may cause temperature-ionization whenever it deposits sufficient thermal energy to raises temperatures to a high enough level. Common examples of this are the ionization (plasma) seen in common flames, and the molecular changes caused by the "browning" in food-cooking, which is a chemical process that begins with a large component of ionization.

Black-body radiation

Black body radiation is radiation from an idealized radiator that emits at any temperature the maximum possible amount of radiation at any given wavelength. A black body will also absorb the maximum possible incident radiation at any given wavelength. The radiation emitted covers the entire electromagnetic spectrum and the intensity (power/unit-area) at a given frequency is dictated by Planck's law of radiation. A black body at temperatures at or below room temperature would thus appear absolutely black as it would not reflect any light. Theoretically a black body emits electromagnetic radiation over the entire spectrum from very low frequency radio waves to X-rays. The frequency at which the black-body radiation is at maximum is given by Wien's displacement law.