Radon Dangers: Deadly Lung Cancer, Other Cancers, and Stroke
According to
Phys.org:
“Radon gas pollution is the second leading cause of lung
cancer in the United States, claiming an estimated 21,000 lives per year
(220,000 globally), with exposure linked to multiple other risks such as breast
cancer, stroke and stomach cancer.”
At radon concentrations above 148 Bq/m3, the EPA recommends
mitigation efforts. The World Health Organization
set a new recommended radon reference level in 2009 of 2.7 pCi/L for residences
and the U.S. The President’s Cancer Panel issued its “Reducing Environmental
Cancer Risk: What We Can Do Now” in 2010. It encourages the EPA to consider
lowering its current “action level” (the level at which remedial action
is recommended) of 4 pCi/L for radon exposure.
Phys.org:
“Regulations adopted in 35 states have mandated radon
measurement and disclosure during property transactions, with tens of millions
being recorded in the last few decades. The accumulated data provides an
opportunity for revisiting the distribution of radon risk around the country.”
Radon gets into the lining of the lungs and over time causes
lung cancer. Radon-sourced lung cancer has also been identified at high levels
among underground miners. Children are especially vulnerable to lung effects
from radon. According to Web MD:
“Children may be especially vulnerable to radon’s health
risks. That’s because their lungs have a different size and shape compared to
those of adults. Children also breathe at a faster rate. Those factors mean
that children get higher doses of radon when they breathe it in. It remains
unclear whether this leads to higher rates of lung cancer, but some experts
estimate that children could have twice the risk of lung cancer as adults
exposed to the same amount of radon.”
The vast majority of exposure to dangerous levels of radon
gas occurs in homes. According to the EPA, “Radon in homes causes more
deaths than fires, drownings, and airplane crashes combined.” More people
die from lung cancer than any other cancer and radon gas is the second highest
cause of cancer after smoking, making it the number one lung cancer cause for
non-smokers. RadonSeal suggests that people who spend more time in basements where
radon leaks in are more likely to develop cancer than those who don’t. The damage
from radon decay products is concentrated on the bronchial epithelial cells in
the immediate area where alpha particles are trapped or deposited. Radon gas also
enters the bloodstream where it can be trapped and possibly lead to other
cancers including breast cancer and leukemia. There is also a possibility of
radon causing genetic damage.
There is some controversy
about the risks of low-level radiation. However, the EPA radon gas action limits
are considered to be valid by most scientists. RadonSeal notes that it is likely
radon that causes cancer among smokers as well since it it the only known constituent
that has caused cancer by itself in the lab. The EPA Radon Potential Map is shown below:
“Lung cancer rates among men kept climbing from a rarity
in 1930 (4/100,000 per year) to the No. 1 cancer killer in 1980 (72/100,000) in
spite of an almost 20 percent reduction in smoking. But during the same period,
the level of polonium-210 in American tobacco had tripled. This coincided with
the increase in the use of phosphate fertilizers by tobacco growers – calcium
phosphate ore accumulates uranium and slowly releases radon gas.”
Humans spend 70-75%
of their time indoors, children even more. Humans receive more radiation from
radon than from all other sources combined. This is because radon is a radioactive gas.
Radon Geochemistry
Radon gas is
generated in the subsurface by the radioactive decay of the element radium, which
is itself derived from the decay of the element uranium. Radon gas further decays
to solid lead as shown below.
The U.S
Geological Survey (USGS) notes:
“Radon levels in outdoor air, indoor air, soil air, and
ground water can be very different. Outdoor air ranges from less than 0.1 pCi/L
to about 30 pCi/L, but it probably averages about 0.2 pCi/L. Radon in indoor
air ranges from less than 1 pCi/L to about 3,000 pCi/L, but it probably
averages between 1 and 2 pCi/L. Radon in soil air (the air that occupies the
pores in soil) ranges from 20 or 30 pCi/L to more than 100,000 pCi/L; most
soils in the United States contain between 200 and 2,000 pCi of radon per liter
of soil air. The amount of radon dissolved in ground water ranges from about
100 to nearly 3 million pCi/L.”
Uranium in rocks is the source of radon gas. All rocks have
some uranium. The average is between 1 and 3 parts per million (ppm). In
general, the uranium content of a soil is dependent on the uranium content of
the parent rock from which the soil is derived. Some types of rocks have higher
than average uranium content, including light-colored volcanic rocks, granites,
dark shales, sedimentary rocks that contain phosphate, and metamorphic rocks
derived from these rocks. These rocks and their corresponding soils could have
as much as 100ppm of uranium. These rocks of higher uranium content occur in
various parts of the U.S. Buildings in areas with these rocks of higher uranium
content tend to have higher radon gas levels as well, but there are exceptions.
One reason for less radon gas in high uranium areas is better sealing of the
building against entry of gases from the ground. The graphic below shows that
most of the radon gas generated by rocks remains in the mineral grains. Between
10 and 50% of the radon gas typically escapes into the pore spaces of the rock.
If the pore space is dry the gas may become embedded in a nearby mineral grain.
If the pore space contains water the radon is more likely to remain in that
pore space.
Radon gas will
travel upward, especially through more permeable soils. It may become embedded
in the soil and then likely decay to lead, or it may escape into the atmosphere.
Because gases move less readily in impermeable soils like clays, they may
become trapped or embedded by the impermeable layer. Thus, the layer that effectively
seals in the gas. Similarly, foundation sealing is one way that radon gas is prevented
or mitigated. Radon moves slower in water than in air space. On average it
moves 1 inch in water-saturated soil and 6 feet in dry soil in the time it
takes for most of it to decay. Thus, radon tends to travel faster and further
in dry soils. Thus, an important variable for radon gas concentration is the
permeability of the soil or rock. Intergranular permeability and especially
fracture permeability in rock can help maximize total gas entry into a building
as can dry soil.
USGS:
“For these reasons, homes in areas with drier, highly
permeable soils and bedrock, such as hill slopes, mouths and bottoms of
canyons, coarse glacial deposits, and fractured or cavernous bed- rock, may
have high levels of indoor radon. Even if the radon content of the air in the
soil or fracture is in the normal range (200-2,000 pCi/L), the permeability of
these areas permits radon-bearing air to move greater distances before it
decays and thus contributes to high indoor radon.”
Radon entry into buildings
“Radon moving through soil pore spaces
and rock fractures near the surface of the earth usually escapes into the
atmosphere. Where a house is present, however, soil air often flows toward its foundation
for three reasons: differences in air pressure between the soil and the house,
the presence of openings in the house's foundation, and increases in
permeability around the basement (if one is present).”
“In
constructing a house with a basement, a hole is dug, footings are set, and
coarse gravel is usually laid down as a base for the basement slab. Then, once
the basement walls have been built, the gap between the basement walls and the ground
outside is filled with material that often is more permeable than the original
ground. This filled gap is called a disturbed zone.”
“The air
pressure in the ground around most houses is often greater than the air
pressure inside the house. Thus, air tends to move from the disturbed zone and
gravel bed into the house through openings in the house's foundation. All house
foundations have openings such as cracks, utility entries, seams between
foundation walls and slabs, sumps, permeable foundation materials, and
uncovered soil in crawl spaces and basements.”
“Most houses
draw less than one percent of their indoor air from the soil; the remainder
comes from outdoor air, which is generally quite low in radon. Houses with low
indoor air pressures, poorly sealed foundations, and several entry points for soil
air, however, may draw as much as 20 percent of their indoor air from the soil.
Even if the soil air has only moderate levels of radon, levels inside the house
may be very high.”
It is important that the mitigation system does not cause the collected and further concentrated radon gas to be sucked back into the home. EPA recommendations to prevent this are shown below.
Radon may also be
present in water, particularly in groundwater. Municipal water systems may aerate
the water, and gases can also bubble out through time so that any radon gas is
usually gone before it reaches consumers. It is present in very small amounts
in common building materials – rock, brick, and concrete.
In order to evaluate the potential for dangerous
concentrations of radon gas, one should first determine the proximity to source
rocks via geology. Next, any other post-deposition events that redistributed
rock should be understood. The permeability of the spaces between the source rocks
and the surface should be determined. And finally, soil saturation should be determined.
Below, from the 1992 USGS book on the Geology of Radon, are two sections of an
aero-radioactivity map of the U.S. that measures surface uranium concentrations
via aircraft flying grid patterns. Superimposed on that are shown different areas
where radon gas has been found in higher concentrations along with the different
geological sources and additional factors. For instance, the Ohio Shale which
outcrops in central Ohio was redistributed by the movement of glaciers so that
the radioactivity was spread over a larger area of the state. It is a radon gas
hotspot based on direct indoor measurements nationwide. It is one of the
hotspots in a populated area as well.
Radon Sampling in Soils, Homes, and Buildings
Soil Vapor Sampling
The way to gather
data about radon gas is to gather and analyze soil vapor samples. Soil vapor
contains a composite of different soil gases such as CO2 and biological decay
gases. Measurement of radon in soils is similar to measuring
it in buildings. Both methods measure the alpha particles produced by the decay
of the radon in the air. One method, designed for long-term sampling at
intervals is shown below.
USGS:
“Soil-air methods require specialized equipment because
soil-air data are sensitive to many conditions and factors, such as the depth
of measurement. Radon levels vary widely in the top 2 to 3 feet of soil because
of variations in soil moisture and the amount of radon that escapes to the atmosphere.
Making measurements at 3 feet or deeper avoids many of the problems related to near-surface
conditions, but it may be difficult in some soils.”
USDA -Natural Resources Conservation Service Soil Surveys now
often contain important data about soil permeability, which can be used to high-grade
vulnerable areas.
USGS:
“By careful examination and correlation, scientists can
evaluate the effects of varying geology and soils on actual readings of indoor
radon. The indoor radon information can be used as an additional aid to create
a radon potential map or it can be used as a way of expressing the radon potential
of areas mapped by the geologist. However, differences in house construction
also can cause variations in the indoor radon levels.”
Home or Building Sampling: Short-Term, Long-Term, In-Water
Testing, and DIY Test Kits
Residential radon
gas sampling can be done with do-it-yourself test kits. There is short-term
testing and long-term testing. As Radon Test Kits.com notes long-term tests are
much more accurate and reliable than short-term tests. However, short-term
tests can indicate whether long-term tests are warranted.
As shown below, radon
levels can vary drastically between short-term and long-term testing. In general,
short-term tests have a wider range of results. The reasons the readings vary
so much in time are discussed below by Radon Test Kits.com:
“During a single day, the concentration of radon gas in
indoor air varies widely and may easily double or triple. Moreover, it
fluctuates greatly from day to day, week to week, and season to season.”
“Radon gas is drawn from the ground into homes by
differences in concentration, air pressure, and temperature. This force largely
depends on the weather and ground conditions outdoors. The indoor radon level
is thus affected by barometric pressure, strong winds, rain-soaked ground, snow
cover, the season, heating and A/C systems, house construction, open windows,
etc.”
The variability and
ranges in concentrations between short-term and long-term tests is shown for a
home over a two-year period in the graph and table below. Long-term tests are
typically done over a period of 3 to 12 months, evening out the wild daily,
weather-dependent, and season swings in concentrations often encountered with
short-term tests.
The EPA has
developed standards, protocols, and strategies for radon testing. Below are
some testing methods and strategy flow charts from an early EPA manual.
Radon Prevention and Mitigation Methods
One method of radon
prevention and mitigation is deep-penetrating concrete sealers for basements. Company
RadonSeal has been the leader in providing these sealing products, also called
RadonSeal. They have two types: standard basement dealer for poured concrete
less than 20-years and outdoor concrete less than 2-years old, and a higher
strength sealer used for more porous concrete and blocks. Recommended for
concrete and cinder blocks, poured concrete older than 20-years, and outdoor
concrete older than 2-years. They note that it “contains ZERO VOCs, is
solvent-free, does not off-gas, is non-toxic, and is a noncorrosive concrete
sealer.” RadonSeal is also very good at waterproofing and should be applied
especially in areas where radon is a concern. It also protects and extends the
life of basement concrete. It should be applied on walls and floors before
finishing or painting. The benefits of RadonSeal are shown below.
Aside from concrete
basement sealing, other radon mitigation methods can be classified as fan-based
or passive. Different methods are suited to different applications and materials.
The table below shows a variety of radon mitigation strategies, some based on
fans and ventilation, some based on suction and depressurization, and some based
on preventing gas entry such as sealers and caulking. Of course, utilizing both
sealing and ventilation systems can be a comprehensive mitigation solution. A
plastic vapor barrier under a house or in a crawl space can retard or slow radon
gas movement but it still diffuses.
A New U.S. National Map of Radon Concentrations
Researchers from
Harvard T.H. Chan School of Public Health have assembled a national database
with millions of multi-day indoor radon measurements from 2001 to 2021. This
enables an updated and improved nationwide map of radon gas concentration
levels, as shown below. The findings from the study include:
“25% of the U.S. population may be exposed to radon
concentrations exceeding 148 Bq/m3, a level associated with cancer risks.”
However, there is debate about the level of radon that is
dangerous so those numbers may overestimate the dangers.
The new map is
based on 6 million direct measurements, many required for property sale disclosures.
Geogenic Radon Potential Maps and Risk Assessment
Models
A February 2024
paper in Science of the Total Environment offered new perspectives on radon risk
assessment based on machine learning analysis of the different variables
affecting indoor radon exposure. The authors developed a radon hazard indicator
based on machine learning number crunching the different variables. They call
it the Geogenic Radon Potential (GRP).
The GRP is characterised by the interaction of three
natural processes
• Background Radon Source (BRS) represents the process
that produces Rn through the natural decay of uranium (U) and thorium (Th)
(220Rn), which are present in rocks and soils.
• Tectonically Enhanced Radon (TER, Benà et al., 2022)
accounts for processes that allow radon to migrate more easily towards the
surface through permeable pathways (e.g., faults and fractures in the crust)
from deeper sources, caused by increased stress and pressure conditions
associated with tectonic activity.
• Surface Radon Exhalation (SRE) is the process by which
radon gas is released from the ground into the atmosphere. SRE considers
variables affecting radon movement in the shallow soil up to the
soil/atmosphere interface (e.g., land morphology, soil permeability,
atmospheric pressure, humidity, and temperature). This quantity of radon
represents the amount that could potentially enter buildings, although BRS and
TER are the dominant geological radon sources.
The authors developed a radon hazard indicator based on machine
learning number crunching the different variables. They call it the Geogenic
Radon Potential (GRP). The first graph below shows the risk model. Below in the second graph are the different variables that were analyzed in
the modeling to derive the mapping. I have done similar types of composite
mapping in oil & gas geology, with varying weights and emphases attributed to
each variable. Another way of graphing the attributes of the model is via a
SHAP diagram as shown in the third figure below.
This method of
mapping can isolate areas with high hazard risks, known as Radon Priority Areas
(RPAs). The maps below are from the target study area of the project in the
Pusteria Valley in the Alps of Italy and Austria.
References:
Comparison
Of Radon Mitigation Methods. RadonSeal. Radon Mitigation Methods - Comparison
Radon:
How It Can Affect Your Health. Matt McMillen and Zilpah Sheikh, MD. Web MD. August 7, 2024.
Radon Gas Exposure & Poisoning:
Symptoms, Health Effects, Prevention
The
Geology of Radon. James K. Otton. U.S. Geological Survey. 1992. report.pdf
A new
perspective in radon risk assessment: Mapping the geological hazard as a first
step to define the collective radon risk exposure. Eleonora Benà, Giancarlo
Ciotoli, Eric Petermann, Peter Bossew, Livio Ruggiero, Luca Verdi, Paul Huber,
Federico Mori, Claudio Mazzoli, and Raffaele Sassi. Science of The Total Environment. Volume
912, 20 February 2024, 169569. A new perspective in radon risk
assessment: Mapping the geological hazard as a first step to define the
collective radon risk exposure - ScienceDirect
How
Radon Gas Sneaks into Homes. RadonSeal. Radon in Homes from Soil, Water and Even Air.
There
is no Safe Radon Level! RadonSeal. Radon Levels: None is safe in Homes | RadonSeal
Radon
Standards of Practice. U.S. EPA. Radon Standards of Practice | US EPA
How
Radon Causes Lung Cancer. RadonSeal. How Radon Gas Endangers People in Their Own Homes
National
Consensus Standards for Every Building Type. AARST Consortium on National Radon
Standards. AARST Radon Standards
Protocols
For Radon And Radon Decay Product Measurements In Homes. U.S. EPA. May 1993. PROTOCOLS FOR RADON AND RADON DECAY PRODUCT
MEASUREMENTS IN HOMES
Improved
radon gas mapping finds nearly 25% of Americans living in highest risk areas. Justin
Jackson. Phys.org. January 21, 2025. Improved radon gas mapping finds
nearly 25% of Americans living in highest risk areas
High-resolution
national radon maps based on massive indoor measurements in the United States. Longxiang
Li, Brent A. Coull, Carolina L. Zilli Vieira, and Petros Koutrakis. PNAS. 122
(3) e2408084121. January 14, 2025. High-resolution national radon maps
based on massive indoor measurements in the United States | PNAS
Detailed
Radon County Statistics. Ohio Department of Health. County+Statistics+up+to+September+2020.pdf
Geometric
Mean of Indoor Radon Concentrations in Ohio Counties. Ohio Department of
Health. Ohio+Map+of+Concentration.pdf
Radon
and Radioactivity – Facts and Controversies. RadonSeal. Amazing Facts and Arguments about Radon and
Radioactivity
Are
Short-Term Radon Test Kits Worth It? Freeradontestkits.com. Are Short-Term Radon Test Kits
Accurate? Are Long-Term Test Kits Better?
DIY
Teat Kits. RadonSeal. Radon Test Kits Archives | RadonSeal
RadonSeal
Deep-Penetrating Concrete Sealers. RadonSeal. Basement Sealer - Radon Mitigation
and Waterproofing
