Radon gas and lung cancer: origin and solutions

Medina, Marc; Nilsson, Jenny; Bosch; Marçal.

INTRODUCTION

Recent studies identify radon gas as the leading cause of lung cancer among non-smokers. There is scientific agreement on the risk to human health posed by exposure to high concentrations of radon gas over long periods of time. This gas, which is not detectable without special measuring equipment, is colorless and odorless and originates naturally in the subsoil, and is responsible for much of the radiation we receive throughout our lives.

In 2005, the WHO published a manual focusing on residential exposure to radon and its impact from a public health perspective. In 2013, the European Union established basic safety standards for protection against hazards arising from exposure to ionizing radiation. Among others, it sets national reference levels for indoor radon concentrations, as well as the adoption of appropriate measures to limit the intrusion of radon gas into buildings.

In Spain, the latest modification of the Technical Building Code (CTE) has addressed the issue of radon gas, both in the construction of new buildings (prevention) and in existing buildings (mitigation or correction), by requiring protective measures against potential exposure to radon gas, incorporating a new section in the basic health document (Protection against exposure to radon) and setting a maximum reference level.

WHAT IS RADON GAS?

Radon is a noble gas that is generated in the radioactive decay chain of radium, which, in turn, comes from uranium. These two elements are naturally present in the earth’s crust in varying concentrations, depending on the composition of rocks and soils, the origin of sediments and the existence and location of aquifers. In addition, radon in its decay process also generates radioactive particles.

As a gas, it can move through the earth’s crust and even be diluted in water. The vapors generated move to the surface, reaching the outside environment and quickly diluting in the air, while if they move into an enclosed and poorly ventilated space such as the interior of a building, it tends to accumulate and can become a problem. Inside buildings, radon can be inhaled by people and thus damage cellular structures and even cause cancer.

ORIGIN OF RADON GAS

Radon comes from the soil; the type or origin of the soil will determine the presence of compounds that generate radon gas. Soils with a high uranium content, such as those coming from igneous (granite) and metamorphic (slate and schist) rocks, but also the sediments coming from them or aquifers associated with this type of rocks/soils, produce a large amount of radon. Regardless of whether the rock has more or less presence of radon or its precursor compounds, radon emanation is conditioned by the fracturing or permeability of the rock/soil; it is higher in very fractured rocks than in compact rocks, or in porous soils (sands and gravels) than in less permeable soils (clays).

In order to identify and regulate areas with potential influence of this gas, the Ministry of Development has prepared a zoning map where municipalities are classified according to the potential presence of radon. Zone I municipalities have values between one and two times the reference level and zone II municipalities have values higher than two times the reference level. Thus, the national territory is zoned in 3 classifications according to the potential influence of radon by the concentration of its precursor elements.

Groundwater in contact with rocks or sediments containing these compounds may harbor a concentration of dissolved radon. In this case, its consumption directly from springs or wells, without adequate aeration, could lead to a release of the radon gas contained in the water. Since radon dissipates rapidly on contact with air, if surface water is used for drinking, this risk is minimal or negligible.

Finally, a certain presence of precursor compounds has been detected in building materials due to their origin (clay, sand, etc.), so that they could contribute, to some extent, to the increase in the average radon concentration inside buildings.

HOW DOES IT AFFECT US?

Radon present in the subsoil can penetrate into the interior of buildings through cracks and joints in building envelopes in contact with the ground (basement walls, floor slabs, etc.), and even through pores in the building’s construction materials.

Since radon comes from the subsoil, the highest concentrations in a building will be located in the lower floors, such as basements and first floors. The density of the gas is also higher than that of air, so once it has reached the interior of buildings, it will accumulate on the first floors.

The radon accumulated in these areas comes into contact with people through inhalation, reaching the lungs. This is the main problem that has been identified and for which the scientific and health community is on alert. Finding measures to control and minimize the impact that radon can have on health is the main challenge we face.

WHAT DOES THE NEW REGULATORY FRAMEWORK ENTAIL?

The latest modification of the Technical Building Code (CTE) has incorporated the consideration of mitigation/elimination measures in areas potentially affected by the presence of radon. The projects affected are those of new construction, changes in the use of buildings or in the habitability of premises, renovations, extensions, etc. in the municipalities located in zones 1 and 2.

CONTROL MEASURES

A first approach to evaluate the presence of radon gas in buildings, regardless of whether or not they are located in the area of influence, and to propose, if necessary, measures to prevent the impact on people’s health, could be the planning of detection and identification campaigns through gas sampling and laboratory analysis.

There are different techniques for determining the presence of radon gas. Detectors with point measurement can be used, if a quick diagnosis is required to identify radon entry points, or constant measurement detectors, which are used to obtain average annual intrusion values. For the latter case, there are detectors with integrated measurement and meters with continuous measurement.

As mentioned above, the arrival of radon to people inside buildings depends on its concentration in the subsoil, as well as on other factors related to the location of the terrain, the construction characteristics of the building, the weather and the behavior of the users. Factors such as humidity, atmospheric pressure, temperature and time of year influence the presence and concentration of radon by modifying the parameters that determine vapor intrusion. The associated diagnosis should consider, as far as possible, the factors that could be influencing both the potential presence of the gas and the routes of contact with the receptors (people). It is therefore necessary to plan appropriate diagnostic and control campaigns.

PREVENT AND/OR MITIGATE INTRUSION

Once we have identified whether we are in areas of influence of the gas or diagnosed its presence through the corresponding measurement campaigns, it is necessary to propose appropriate measures to mitigate the intrusion of radon gas and minimize its influence on people.

Different solutions are proposed to mitigate the intrusion of radon gas inside existing buildings, as well as the adoption of preventive measures in newly constructed buildings to prevent or minimize the potential intrusion of the gas. The degree of intervention and/or the preventive measures to be applied will depend on the degree of affection in the study area, requiring different measures according to the regulations, depending on the classification of the municipality. It is therefore necessary to evaluate each specific scenario, proposing appropriate measurement, control and diagnostic campaigns and, depending on the results and the application of the regulations to each case, propose the appropriate control and/or mitigation measures.

Examples of measures to prevent or mitigate vapor intrusion include:

• Protective barriers (A) of low/low permeability between the ground and the buildings, limiting the passage of gases coming from the subsoil. The barrier may be of a foil type or other barrier of proven effectiveness. The main characteristic of the barrier is its radon diffusion coefficient, which must be sufficiently low to limit the exhalation of radon from the ground into the premises/buildings, taking into account its thickness.

• Air chamber (B) between the ground and the habitable premises of the building, intended to mitigate the entry of the gas. The air chamber must be ventilated and separated from the living quarters by an enclosure without cracks, fissures or discontinuities between the construction elements and systems that could allow radon to pass through.

In those cases where protection must be increased, an additional protective barrier may be placed in addition to a vapor mitigation system, such as:

• Ventilated containment space (B) located between the ground and the premises to be protected, to mitigate the entry of radon from the ground into the habitable premises by means of natural or mechanical ventilation.
• Soil depressurization system (C) to extract the gases contained in the soil under the building, preventing them from accumulating at the base of the building and eventually penetrating through cracks or pores into the interior of the premises.
• Increase ventilation rates, through a forced extraction system and air renewal in vulnerable areas (E).

For mitigation in existing buildings, the sealing of cracks (D), crevices, joints and joints, as well as an improvement in the ventilation of living spaces (E) can be considered. In this case, a prior study of the presence of radon gas, using detectors with point measurement method is essential for a quick diagnosis and identification of radon entry points: cracks, gaps or discontinuities in the enclosures in contact with the ground that have been previously identified in the visual inspection of the building.

In any case, the application of these systems requires a certain degree of specialization in their installation, since the guarantee of their effectiveness depends not only on the choice of a suitable system but also on careful execution.

Addressing the above problems is a challenge for research, industry and environmental consultancy, and underlines the need to continue working and researching in the same direction to safeguard the health of our society, as well as to demand changes in environmental regulation that allow us to address the new paradigms that have arisen.