Radon (Rn) is an odorless and colorless (inert), radioactive gas, produced by the decay of radium, that is, by the change in the composition of the nucleus of the radium atom with the emission of radiation. Radium, in turn, is produced by successive decays of uranium, present in small quantities throughout the earth's crust.
Its isotope (the isotopes of a chemical element are atoms with the same number of protons, 86 in the case of radon, but with a different atomic mass, therefore with a different number of neutrons) most widespread in the internal air of buildings is 222Rn It decays within a few days (halves its concentration in 3.8 days) emitting radiation alpha ionizing agents (particles composed of two protons and two neutrons) and forming the so-called radon decay products or children of radon (isotopes, also radioactive, of polonium, lead and bismuth).
Sources of exposure
Radon is found in every soil and rock, albeit in very different quantities depending on some of their characteristics such as the concentration of uranium, permeability, the presence of fractures / faults, etc.
Radon continually escapes from the ground, dispersing into the open air (where the concentration, consequently, is very low) or penetrating buildings and, in general, closed places. Inside them, therefore, the concentration of radon can be high.
In general, the mechanism that allows radon to penetrate indoors is the small pressure difference that exists between the inside of the buildings and the outside, due to the difference in temperature between the (warmer) interior of the building and the outside. exterior (colder). In this way a sort of chimney effect is created which produces a suction of the gases present in the ground, including radon, towards the interior of the building.
Although the soil is the main source of radon found in the internal air, various building materials obtained from rocks or soils, such as those obtained from volcanic rocks, are also sources of radon. The water from wells can constitute a " additional source of radon.
Radon and exposure levels
The unit of measurement of radon concentration, according to the International System (SI), is the Becquerel per cubic meter (Bq / m3), where the Becquerel (Bq) is the unit of measurement of the activity of a radioactive substance and 1 Bq represents 1 radioactive decay per second.
The concentration of radon outdoors is typically low and, in any case, does not exceed a few tens of Bq / m3, because the radon that escapes from the ground is diluted in a very large volume of air. In closed places (houses, offices, schools etc.), on the other hand, the concentration typically varies from a few tens to a few hundreds of Bq / m3, but it can also reach much higher values (thousands of Bq / m3).
The concentration of radon is not constant over time: it is generally higher at night and in winter and lower during day and summer, but these variability can be very different from one building to another. Consequently, to evaluate the risks for the health of exposure to radon, it is necessary to measure the average value over a year, as also required by current legislation, while short-term measures are completely useless.
Radon, in fact, does not produce immediate toxic effects, unless it is present above certain thresholds, but carcinogenic effects that occur over very long times (even decades). They are all the more probable the greater the exposure to the gas. To assess it, the annual average concentration must be measured.
Effects on human health
As for the effects that radon has on human health, it is now known that exposure to radon increases the likelihood of contracting lung cancer.
The World Health Organization (WHO), through the International Agency for Research on Cancer (IARC), has classified radon in Group 1, the one that contains substances with an "evident ability to cause cancer (carcinogenicity) on the based on epidemiological studies on humans (120 out of 1003 analyzed by the IARC, as of April 18, 2018, Agents classified by the IARC monographs, v. 1-123). In the same group there are also cigarette smoke and asbestos.
The risk of cancer is proportional to the overall exposure accumulated over time: it is given by the average concentration of the gas over the exposure time. Consequently, long-term exposures to medium-low concentrations (such as those at home) rather than short-term exposures at higher concentrations (such as, for example, those in the workplace and, even more so, those in places visited occasionally).
The number of lung cancers attributable to radon exposure in Italy was assessed by the Istituto Superiore di Sanità (ISS) - on the basis of the most recent epidemiological studies, radon concentration data representative of the exposure of the Italian population in homes and of the overall mortality from lung cancer - equal to:
- Approximately 3200 cases each year (the estimate ranges from a minimum of approximately 1100 to a maximum of approximately 5700, in relation to the inevitable uncertainties of epidemiological studies)
- About 10% of all lung cancer deaths in Italy, the percentage varies from region to region, from 4% to 16%, mainly in relation to the average levels of radon concentration
Most lung cancers attributable to radon involve smokers (and to a lesser extent ex-smokers) due to the multiplicative effect of radon and tobacco use.
For non-smokers, exposure to radon is a major risk factor for lung cancer.
Other possible effects of radon exposure on health have been studied, for example, an increased risk of leukemia, but to date there are no firm conclusions as the risk for other effects is still much lower than that of developing cancer. pulmonary and, therefore, more difficult to ascertain through epidemiological studies.
Actions of prevention and rehabilitation and legislation
It is possible, and usually inexpensive, to reduce the concentration of radon in the air inside buildings by reducing the entry of radon from the ground. This can be done through various technical measures, for example by sucking the air from the ground below the house through a small electric pump connected to simple pipes and conveying it towards the outside, where it is dispersed.
These and other technical measures to reduce the entry of radon can be applied preventively during the construction of buildings (or renovations that involve the part of the building in contact with the ground) and, in this case, they are even cheaper and more effective than intervening in an already built building.
Since 2001, the Italian legislation provides for the control of radon concentration only in the workplace, including schools.
Preventive actions during the construction phase of buildings are not currently mandatory in Italy but in 2008 they were recommended by the scientific committee of the National Radon Plan and are required by the new European directive on radiation protection (2013/59 / Euratom). It also contains provisions regarding radon in homes and stricter protection from radon in workplaces. Italy has not yet implemented this European directive.
Higher Institute of Health (ISS). Radon protection
World Health Organization (WHO). Ionizing radiation. Radon
World Health Organization (WHO). Radon and health