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FSN 1500 Week 10
Indoor Air Quality
Foreword
The quality of the air we breathe is both a personal health and a major economic issue
Most people don’t consider how vital the quality of their indoor air is to their health, so today we’ll focus on some important indoor air quality concerns
Indoor Air Quality
The average Westerner spends about 90% of their life indoors!
Studies have shown that indoor air may be 10 - 100 times more polluted than outdoor air!
Indoor Air Quality
Some indoor air quality concerns include: radon, the combustion pollutants and asbestos.
Indoor Air Quality (Radon)
Radon - colorless, odorless, radioactive gas formed by the radioactive transformation of uranium in soil and rock.
238U ---> 222Rn + heat + 4 4 He (alpha particles) (see next slide)
Example of Radioactive Decay
http://www.ndt-ed.org/EducationResources/HighSchool/Radiography/radioactivedecay.htm
Indoor Air Quality (Radon)
Radon gas has a natural tendency to seep upward through cracks in rocks and soil pore spaces; it may even rise as a dissolved gas in groundwater
Radon enters a dwelling through cracks in the foundation or concrete slab, through porous construction materials (e.g., concrete), through uncapped sumps and floor drains and through gaps between utilities and the structure’s walls and floors (see figure)
The uranium content in soils and rocks and the amount of radon released does vary
Indoor Air Quality (Radon)
However, nearly every rock and soil type emits some level of radon so every structure contains some level of radon
The U.S. Environmental Protection Agency (EPA) and the American Lung Association contend that moderate to long-term exposure to elevated levels of indoor radon and its radioactive byproducts is the second-leading cause of lung cancer
Indoor Air Quality (Radon)
According to the EPA and the U.S. National Cancer Institute, cigarette smoking is responsible for approximately 85% of lung cancer cases and prolonged exposure to radon and its byproducts is responsible for approximately 10% of lung cancer cases
Indoor Air Quality (Radon)
How could radon or its byproducts induce lung cancer? The key concern is the alpha particles and their potential to mutate the DNA of the lung wall cells.
The alpha particle is not very energetic; its penetration power is not great - even a few centimeters of air dampens its energy significantly (see figure)
Penetration energies of different types of nuclear radiation
Indoor Air Quality (Radon)
However, if the alpha particle gets released into our lung cavity, some alpha particles may have enough energy to penetrate the first few millimeters of the lung wall and cause mutations in these cells
When the radon gas enters our dwellings it mixes well with the other air gases; when you inhale you could be inhaling some radon atoms
Indoor Air Quality (Radon)
What’s the chance of a radon atom undergoing radioactive decomposition and releasing an alpha particle while in your lungs? For the average adult only about a 1 in 15,000 chance!
Why so low a chance? We need to examine the residence time of the radon in the lungs and its half-life.
Indoor Air Quality (Radon)
Most of any adult’s inhalation gases only reside in the lungs about 30 seconds before they’re exhaled or absorbed
Half-life: the time it takes one half of a substance’s atoms to radioactively transform
The measured half-life of radon is about 3.8 days
Indoor Air Quality (Radon)
The 1 in 15,000 chance I mentioned earlier results from the short residence time of the radon in the lungs compared to the significantly longer radon half-life
So why the concern over radon exposure possibly inducing lung cancer?
The key: radon decomposes to two radioactive solids - polonium-218 and polonium-214
Indoor Air Quality (Radon)
Polonium-218 and polonium-214 have a tendency to adhere to aerosols (e.g., dust and smoke particles) and be drawn into the lungs
Polonium-218 has a half-life of about 3 minutes, polonium-214 half-life is even shorter; these elements decompose by emitting an alpha particle
Indoor Air Quality (Radon)
The lung residence time for aerosols in the average adult is 30 minutes. Comparing the residence time and polonium half-lives, is it likely that alpha particles will be released into the lung wall?
Inexpensive, fairly accurate tests have been developed to measure air radon levels but not polonium levels; we assume the higher the air radon level the higher the polonium levels
Indoor Air Quality (Radon)
Indoor air radon levels are typically measured in units of picoCuries per liter (pCi/L); the picoCurie is a measure of radioactivity, the liter a measure of air volume
1 pCi/L corresponds to 133 radon atom disintegrations in 1 liter of air in 1 hour
Indoor Air Quality (Radon)
The U.S. EPA and other health agencies suggest that structures with levels at 4 pCi/L or greater have remediation work conducted
The World Health Organization’s action level for remediation is 2 pCi/L
The following tables illustrate the relative death risks for nonsmokers and smokers from long-term radon exposure
Radon LevelIf 1,000 people who never
smoked were exposed to this level over a lifetime*...
The risk of cancer from radon exposure compares to**...
WHAT TO DO:
20 pCi/LAbout 36 people could get lung cancer
35 times the risk of drowning Fix your home
10 pCi/LAbout 18 people could get lung cancer
20 times the risk of dying in a home fire
Fix your home
8 pCi/LAbout 15 people could get lung cancer
4 times the risk of dying in a fall Fix your home
4 pCi/LAbout 7 people could get lung cancer
The risk of dying in a car crash Fix your home
2 pCi/LAbout 4 person could get lung cancer
The risk of dying from poisonConsider fixing between 2 and 4 pCi/L
1.3 pCi/LAbout 2 people could get lung cancer
(Average indoor radon level)(Reducing radon levels below 2 pCi/L is difficult.)
0.4 pCi/L (Average outdoor radon level)
Note: If you are a former smoker, your risk may be higher.* Lifetime risk of lung cancer deaths from EPA Assessment of Risks from Radon in Homes (EPA 402-R-03-003).** Comparison data calculated using the Centers for Disease Control and Prevention's 1999-2001 National Center for Injury Prevention and Control Reports.
Radon LevelIf 1,000 people who smoked were exposed to this level
over a lifetime*...
The risk of cancer from radon exposure compares to**...
WHAT TO DO:Stop smoking and...
20 pCi/LAbout 260 people could get lung cancer
250 times the risk of drowning Fix your home
10 pCi/LAbout 150 people could get lung cancer
200 times the risk of dying in a home fire
Fix your home
8 pCi/LAbout 120 people could get lung cancer
30 times the risk of dying in a fall Fix your home
4 pCi/LAbout 62 people could get lung cancer
5 times the risk of dying in a car crash
Fix your home
2 pCi/LAbout 32 people could get lung cancer
6 times the risk of dying from poison
Consider fixing between 2 and 4 pCi/L
1.3 pCi/LAbout 20 people could get lung cancer
(Average indoor radon level)
(Reducing radon levels below 2 pCi/L is difficult.)
0.4 pCi/LAbout 3 people could get lung cancer
(Average outdoor radon level)
Note: If you are a former smoker, your risk may be lower.* Lifetime risk of lung cancer deaths from EPA Assessment of Risks from Radon in Homes (EPA 402-R-03-003).** Comparison data calculated using the Centers for Disease Control and Prevention's 1999-2001 National Center for Injury Prevention and Control Reports.
Indoor Air Quality (Radon)
Indoor air radon levels as high as 3500 pCi/L have been measured; the outdoor average level is 0.2 – 0.4 pCi/L
All indoor air pollution risks (not just radon) are increased when we live under “closed house” (windows and doors sealed tightly and doors infrequently opened) conditions (i.e., winter, portions of spring and fall)
Indoor Air Quality (Radon)
The radon lung cancer risk is further enhanced if significant aerosol production occurs within the dwelling
If your structure contained elevated radon levels, how could you possibly reduce these levels?
Two broad approaches: 1) improve cross-ventilation by natural or artificial means (e.g., sub-slab suction)
Indoor Air Quality (Radon)
2) Seal or cover the radon entryways as effectively as possible (e.g., caulking, application of gas-impermeable paints, installation of water permeable/gas impermeable sump and floor drains)
There are also preconstruction radon mitigation techniques which can be employed (see figure for summary)
A = bed of permeable gravel (preconstruction)
B = gas impermeable sheeting (preconstruction)
C = caulk cracks and utility openings (usually post construction)
D = Sub-slab ventilation pipe (usually post construction)
E = ventilation fan
Indoor Air Quality (Radon)
A dozen or so states now require indoor air radon testing to be conducted before any commercial or residential structure is sold.
How is this issue affected by Michigan's (mid-1990s) enacted real estate transfer disclosure statement?
Be forewarned: there is still much controversy, perhaps unresolvable, concerning what radon and radon byproduct exposure levels are necessary to significantly increase lung cancer risk.
Indoor Air Quality (Radon)
Why the controversy? The only actual human data we have is from studies of underground uranium miners, typically exposed to higher radon and radon byproduct levels for longer periods than the average adult
There is definitely a linear (positive) relationship between radon exposure and lung cancer incidence for underground uranium miners
Indoor Air Quality (Radon)
Can the risk relationship be linearly extrapolated to lower exposure levels and times to establish the lung cancer risk for the general population? The U.S. EPA thinks this is a valid approach - it employs what is called a “linear” dose-response model (see figure)
Actual Data
Linear Model
Threshold Model
Dose(Radon/Byproduct Exposure)
Res
pons
e(L
ung
Can
cer
Inci
denc
e)
Indoor Air Quality (Radon)
Some groups have argued that the appropriate dose-response model is the “threshold” model (see previous figure); this suggests the lung cancer risk wouldn’t increase until a certain, somewhat elevated combination of radon level and exposure time was exceeded.
Why may we never be able to answer which model is more appropriate? Why should we care?
Indoor Air Quality (Radon)
Broadly: we will likely never have the clinical data to conclusively decide whether the linear or threshold dose-response model is more appropriate - yet we must try to make risk assessments for substance exposures!
This issue illustrates the political and economic aspects of science and how the layperson could be mislead (see figures)
Detroit News 3/19/93
Indoor Air Quality (Radon)
In 1998 the U.S. National Cancer Institute scientists published a report that evaluated eight previous studies on over 10,000 people in five countries
Using a linear model approach, they estimated a 14% increased chance of lung cancer for a person living in a residence for 30 years that has air radon levels of 4 pCi/L
Indoor Air Quality (Radon)
What’s the status of the indoor air radon problem in Michigan? There are definitely “geographic hot spots” where elevated levels of indoor radon have been measured
See the following figures - more detailed information is available from the state (Department of Natural Resources), federal government (EPA) and the American Lung Association
Source: U.S. EPA, 2005
> 4 pCi/LHigh Potential
ModeratePotential
2-4 pCi/L
< 2 pCi/LLow Potential
Michigan Radon Potential Map
Indoor Air Quality (Radon)
While the U.S. EPA and U.S. Geological Survey suggest that only 6% of U.S. households host air radon levels > 4 pCi/L; note from the previous slides and your handout that some geographic regions may have a much higher percentage of households whose air radon levels exceed 4 pCi/L
Indoor Air Quality (Radon)
• Short-term (days) and long-term (months) air radon test kits are available; make sure the kits are EPA approved
• A very good long-term (90 days to year) test kit: Accustar Alpha Track AT 100 (~$20 and available at Amazon.com)
Indoor Air Quality (Combustion Pollutants) Combustion Pollutants - air pollutants resulting
when fossil fuels or other carbon-containing fuels, or volatile organic compounds, are inadequately combusted (e.g., not enough oxygen present) or the combustion gases are insufficiently vented
Major sources: wood stoves, fireplaces, coal stoves, gas appliances (water heaters, cooking ranges, clothes dryers, kerosene heaters, camping cook stoves)
Example: 2 C(s) + O2(g) 2 CO(9) (carbon monoxide)
Indoor Air Quality (Combustion Pollutants) Carbon monoxide (CO) - short term, the most
dangerous of the combustion pollutants; about 1100 people in the U.S., on the average, die each year from accidental CO poisoning (early 1990’s Journal of the American Medical Association report)
CO bonds about 250 times more effectively than oxygen to the hemoglobin molecule in your blood; the oxygen starvation to your organs can result in death!
Indoor Air Quality (Combustion Pollutants) CO is a colorless,
odorless gas; for the average adult, exposure to 400 ppm (parts per million) concentrations of CO for two hours results in death
Be aware of low-level CO exposure symptoms: flu-like symptoms, disorientation, headaches, fatigue
Indoor Air Quality (Combustion Pollutants) Health agencies suggest each home have one
or more CO monitors; the monitors are available in two types: passive and active
Passive monitors require no power source (battery or electrical cord) and typically consist of a small, mountable disk whose surface changes color as CO gases of different concentrations pass over the disk (see figure)
Indoor Air Quality (Combustion Pollutants) Although passive monitors are cheap, they are
useless unless you are visually monitoring them Active monitors are available that use a battery,
electrical cord, or both, power source See handout (and figures), some very good
active monitors are now available for sale
Indoor Air Quality (Combustion Pollutants)
The most versatile active CO monitors have two power sources (electrical and battery backup) and provide a digital readout of CO levels (see figure)
Indoor Air Quality (Combustion Pollutants)
Why would health and safety officials urge that all electrically powered CO detectors be equipped with a backup battery? (see figure)
12/18/2006
Indoor Air Quality (Combustion Pollutants)
Consumer advocacy groups (e.g., Consumer Reports) periodically rates CO monitors (see figure)
Indoor Air Quality (Combustion Pollutants)
Listen to the news or periodically scan the Internet - like any other product, some CO detectors have been recalled by their manufacturers for failing to accurately detect harmful levels of CO or for being too sensitive (yielding false alarms)
Recent News
Note the
recent law
Oakland Press3/20/09
Be Aware
Any enclosed space (automobiles, boats, tents, hotel rooms) could be a location for carbon monoxide poisoning
Indoor Air Quality (Combustion Pollutants) Nitrogen dioxide (NO2) and sulfur dioxide (SO2)
combustion pollutants combine with air water vapor to create respirable acidic sulfuric and nitric acid aerosols
The acidic aerosols cause upper respiratory irritation; the sulfuric acid aerosols are threatening to people with asthma, allergies or lung diseases like chronic bronchitis
Indoor Air Quality (Combustion Pollutants) Formaldehyde - pungent gas (a volatile organic
compound); found in many household products including foam insulation; resins in particleboard, fiberboard and plywood paneling; some carpeting, upholstery and drapery fabric; and some plastics
Exposure is commonly associated with eye, nose and throat irritation; coughing, skin rashes, headaches, nausea, vomiting and nosebleeds
Indoor Air Quality (Combustion Pollutants)
The EPA has classified formaldehyde as a probable human carcinogen (likely lower risk)
Indoor Air Quality (Asbestos)
Asbestos - collective name for two families of minerals that are flexible, fire-resistant and durable; one group of minerals is quite fibrous and the other typically consists of small, brittle needles (see figure)
Indoor Air Quality (Asbestos)
Problem: most forms of asbestos can exist as microscopic, respirable particles that can remain airborne for long periods
Inhalation of asbestos particles, especially the needlelike forms, cause lung tissue scarring and is linked to several types of cancer (lung (mesothelioma), stomach)
Indoor Air Quality (Asbestos)
The asbestos fibers become airborne typically as the product containing them (e.g., pipe insulation) decomposes or is fragmented (may happen accidentally or during remodeling or demolition)
Unfortunately, health problems may not become apparent until 15-40 years after prolonged exposure
Indoor Air Quality (Asbestos)
Most homes built prior to 1975 probably contain some asbestos in floor or ceiling tiles, wall and pipe insulation, wallboard and attic insulation (see figure)
Indoor Air Quality (Asbestos)
Local connection? Up to 700,000 Michigan homeowners (12/6/04 Detroit Free Press, page B1) may have attic insulation which contains easily fragmented asbestos
The insulation has the product name Zonolite and contains a mineral called vermiculite which is contaminated with the more dangerous form of asbestos
This product was even produced in a Dearborn, MI processing plant from 1966-1990
Indoor Air Quality (Asbestos)
The U.S. is not the only country facing this indoor air quality problem.
Indoor Air Quality (Asbestos)
During the late 1970s U.S. federal and state regulations required removal of identified asbestos-bearing materials - studies found that large amounts of asbestos became airborne during removal of the materials and that these fibers remained airborne for months
Indoor Air Quality (Asbestos)
Today, encapsulation of asbestos-bearing materials by sealants or enclosure construction is thought to be safer; removal still done but it increases risk of accidental exposure
Be aware; this is still a relevant issue
Related Issue
During the 1950s and 1960s millions of tons of asbestos waste were dumped into the Great Lakes - this has raised concern over whether ingestion of asbestos particles in drinking water could cause stomach cancers
Indoor Air Quality
Relatively inexpensive home test kits exist for the indoor air pollutants we discussed; contact the American Lung Association or regional U.S. EPA office for direction
Indoor air quality is both a health and a business economic issue: some buildings have been abandoned or closed for costly renovations because of associated “sick building syndrome”
Indoor Air Quality
Related note: the U.S. Centers for Disease Control and Prevention stated in 2012 that an estimated 25 million Americans have asthma
One possible contributing factor? More airtight house construction resulting in less cross-ventilation and an increased exposure to indoor air pollutants?