Chapter 5—Indoor Air Pollutants and Toxic Materials

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-1

Indoor Air Pollution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-1

Biologic Pollutants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-1

Chemical Pollutants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-6

Toxic Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-13

Asbestos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-13

Lead . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-15

Arsenic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-19

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-20

Figure 5.1. Mold Growth in the Home . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-7

Figure 5.2. Home Carbon Monoxide Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-7

Figure 5.3. Environmental Tobacco Smoke and Children’s Exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-8

Figure 5.4. Wood Products Label . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-10

Figure 5.5. EPA Map of Radon Zones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-10

Figure 5.6. Radon Entry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-11

Figure 5.7. Home Radon Detectors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-12

Figure 5.9. Radon-resistant Construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-12

Figure 5.10. Arsenic Label. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-19

Healthy Housing Reference Manual 1

Contents
“Walking into a modern building can sometimes be

compared to placing your head inside a plastic bag that is

filled with toxic fumes.”

John Bower

Founder, Healthy House Institute 

Introduction

We all face a variety of risks to our health as we go about

our day-to-day lives. Driving in cars, flying in airplanes,

engaging in recreational activities, and being exposed to

environmental pollutants all pose varying degrees of risk.

Some risks are simply unavoidable. Some we choose to

accept because to do otherwise would restrict our ability

to lead our lives the way we want. Some are risks we

might decide to avoid if we had the opportunity to make

informed choices. Indoor air pollution and exposure to

hazardous substances in the home are risks we can do

something about.

In the last several years, a growing body of scientific

evidence has indicated that the air within homes and

other buildings can be more seriously polluted than the

outdoor air in even the largest and most industrialized

cities. Other research indicates that people spend

approximately 90% of their time indoors. Thus, for

many people, the risks to health from exposure to indoor

air pollution may be greater than risks from outdoor

pollution.

In addition, people exposed to indoor air pollutants for

the longest periods are often those most susceptible to

their effects. Such groups include the young, the elderly,

and the chronically ill, especially those suffering from

respiratory or cardiovascular disease [1]. 

Indoor Air Pollution

Numerous forms of indoor air pollution are possible in

the modern home. Air pollutant levels in the home

increase if not enough outdoor air is brought in to dilute

emissions from indoor sources and to carry indoor air

pollutants out of the home. In addition, high temperature and

humidity levels can increase the concentration of some

pollutants. Indoor pollutants can be placed into two

groups, biologic and chemical.

Biologic Pollutants

Biologic pollutants include bacteria, molds, viruses,

animal dander, cat saliva, dust mites, cockroaches, and

pollen. These biologic pollutants can be related to some

serious health effects. Some biologic pollutants, such as

measles, chickenpox, and influenza are transmitted

through the air. However, the first two are now

preventable with vaccines. Influenza virus transmission,

although vaccines have been developed, still remains of

concern in crowded indoor conditions and can be

affected by ventilation levels in the home. 

Common pollutants, such as pollen, originate from

plants and can elicit symptoms such as sneezing, watery

eyes, coughing, shortness of breath, dizziness, lethargy,

fever, and digestive problems. Allergic reactions are the

result of repeated exposure and immunologic

sensitization to particular biologic allergens. 

Although pollen allergies can be bothersome, asthmatic

responses to pollutants can be life threatening. Asthma is

a chronic disease of the airways that causes recurrent and

distressing episodes of wheezing, breathlessness, chest

tightness, and coughing [2]. Asthma can be broken

down into two groups based on the causes of an attack:

extrinsic (allergic) and intrinsic (nonallergic). Most

people with asthma do not fall neatly into either type,

but somewhere in between, displaying characteristics of

both classifications. Extrinsic asthma has a known cause,

such as allergies to dust mites, various pollens, grass or

weeds, or pet danders. Individuals with extrinsic asthma

produce an excess amount of antibodies when exposed to

triggers. Intrinsic asthma has a known cause, but the

connection between the cause and the symptoms is not

clearly understood. There is no antibody hypersensitivity

in intrinsic asthma. Intrinsic asthma usually starts in

adulthood without a strong family history of asthma.

Some of the known triggers of intrinsic asthma are

infections, such as cold and flu viruses, exercise and cold

air, industrial and occupational pollutants, food additives

and preservatives, drugs such as aspirin, and emotional

stress. Asthma is more common in children than in

adults, with nearly 1 of every 13 school-age children

having asthma [3]. Low-income African-Americans and

certain Hispanic populations suffer disproportionately,

with urban inner cities having particularly severe

problems. The impact on neighborhoods, school

systems, and health care facilities from asthma is severe

because one-third of all pediatric emergency room visits

are due to asthma, and it is the fourth most prominent

cause of physician office visits. Additionally, it is the

leading cause of school absenteeism—14 million school

Chapter 5: Indoor Air Pollutants and Toxic Materials

Healthy Housing Reference Manual 5-1
days lost each year—from chronic illness [4]. The U.S.

population, on the average, spends as much as 90% of its

time indoors. Consquently, allergens and irritants from

the indoor environment may play a significant role in

triggering asthma episodes. A number of indoor

environmental asthma triggers are biologic pollutants.

These can include rodents (discussed in Chapter 4),

cockroaches, mites, and mold.

Cockroaches

The droppings, body parts, and saliva of cockroaches can

be asthma triggers. Cockroaches are commonly found in

crowded cities and in the southern United States.

Allergens contained in the feces and saliva of cockroaches

can cause allergic reactions or trigger asthma symptoms. A

national study by Crain et al. [5] of 994 inner-city allergic

children from seven U.S. cities revealed that cockroaches

were reported in 58% of the homes. The Community

Environmental Health Resource Center reports that

cockroach debris, such as body parts and old shells,

trigger asthma attacks in individuals who are sensitized to

cockroach allergen [6]. Special attention to cleaning must

be a priority after eliminating the presence of cockroaches

to get rid of the presence of any allergens left that can be

asthma triggers.

House Dust Mites

Another group of arthropods linked to asthma is house

dust mites. In 1921, a link was suggested between

asthmatic symptoms and house dust, but it was not until

1964 that investigators suggested that a mite could be

responsible. Further investigation linked a number of mite

species to the allergen response and revealed that humid

homes have more mites and, subsequently, more allergens.

In addition, researchers established that fecal pellets

deposited by the mites accumulated in home fabrics and

could become airborne via domestic activities such as

vacuuming and dusting, resulting in inhalation by the

inhabitants of the home. House dust mites are distributed

worldwide, with a minimum of 13 species identified from

house dust. The two most common in the United States

are the North American house dust mite

(Dermatophagoides farinae) and the European house dust

mite (D. pteronyssinus). According to Lyon [7], house dust

mites thrive in homes that provide a source of food and

shelter and adequate humidity. Mites prefer relative

humidity levels of 70% to 80% and temperatures of 75°F

to 80°F (24°C to 27°C). Most mites are found in

bedrooms in bedding, where they spend up to a third of

their lives. A typical used mattress may have from

100,000 to 10 million mites in it. In addition, carpeted

floors, especially long, loose pile carpet, provide a

microhabitat for the accumulation of food and moisture

for the mite, and also provide protection from removal by

vacuuming. The house dust mite’s favorite food is human

dander (skin flakes), which are shed at a rate of

approximately 0.20 ounces per week. 

A good microscope and a trained observer are imperative

in detecting mites. House dust mites also can be detected

using diagnostic tests that measure the presence and

infestation level of mites by combining dust samples

collected from various places inside the home with

indicator reagents [7]. Assuming the presence of mites,

the precautions listed below should be taken if people

with asthma are present in the home:

• Use synthetic rather than feather and down pillows.

• Use an approved allergen barrier cover to enclose

the top and sides of mattresses and pillows and

the base of the bed.

• Use a damp cloth to dust the plastic mattress

cover daily.

• Change bedding and vacuum the bed base and

mattress weekly.

• Use nylon or cotton cellulose blankets rather than

wool blankets.

• Use hot (120°F–130°F [49°C–54°C]) water to

wash all bedding, as well as room curtains.

• Eliminate or reduce fabric wall hangings, curtains,

and drapes.

• Use wood, tile, linoleum, or vinyl floor covering

rather than carpet. If carpet is present, vacuum

regularly with a high-efficiency particulate air

(HEPA) vacuum or a household vacuum with a

microfiltration bag. 

• Purchase stuffed toys that are machine washable.

• Use fitted sheets to help reduce the accumulation

of human skin on the mattress surface.

HEPA vacuums are now widely available and have also

been shown to be effective [8]. A conventional vacuum

tends to be inefficient as a control measure and results in

a significant increase in airborne dust concentrations, but

can be used with multilayer microfiltration collection

5-2 Indoor Air Pollutants and Toxic Materials
bags. Another approach to mite control is reducing

indoor humidity to below 50% and installing central

air conditioning. 

Two products are available to treat house dust mites and

their allergens. These products contain the active

ingredients benzyl benzoate and tannic acid. 

Pets

According to the U.S. Environmental Protection Agency

(EPA) [9], pets can be significant asthma triggers because

of dead skin flakes, urine, feces, saliva, and hair. Proteins

in the dander, urine, or saliva of warm-blooded animals

can sensitize individuals and lead to allergic reactions or

trigger asthmatic episodes. Warm-blooded animals

include dogs, cats, birds, and rodents (hamsters, guinea

pigs, gerbils, rats, and mice). Numerous strategies, such as

the following, can diminish or eliminate animal allergens

in the home:

• Eliminate animals from the home.

• Thoroughly clean the home (including floors and

walls) after animal removal.

• If pets must remain in the home, reduce pet

exposure in sleeping areas. Keep pets away from

upholstered furniture, carpeted areas, and stuffed

toys, and keep the pets outdoors as much

as possible.

However, there is some evidence that pets introduced

early into the home may prevent asthma. Several studies

have shown that exposure to dogs and cats in the first

year of life decreases a child’s chances of developing

allergies [10] and that exposure to cats significantly

decreases sensitivity to cats in adulthood [11]. Many

other studies have shown a decrease in allergies and

asthma among children who grew up on a farm and were

around many animals [12].

Mold

People are routinely exposed to more than 200 species of

fungi indoors and outdoors [13]. These include moldlike

fungi, as well as other fungi such as yeasts and

mushrooms. The terms “mold” and “mildew” are

nontechnical names commonly used to refer to any fungus

that is growing in the indoor environment. Mold colonies

may appear cottony, velvety, granular, or leathery, and

may be white, gray, black, brown, yellow, greenish, or

other colors. Many reproduce via the production and

dispersion of spores. They usually feed on dead organic

matter and, provided with sufficient moisture, can live off

of many materials found in homes, such as wood,

cellulose in the paper backing on drywall, insulation,

wallpaper, glues used to bond carpet to its backing, and

everyday dust and dirt. 

Certain molds can cause a variety of adverse human

health effects, including allergic reactions and immune

responses (e.g., asthma), infectious disease (e.g.,

histoplasmosis), and toxic effects (e.g., aflatoxin-induced

liver cancer from exposure to this mold-produced toxin in

food) [14]. A recent Institute of Medicine (IOM) review

of the scientific literature found sufficient evidence for an

association between exposure to mold or other agents in

damp indoor environments and the following conditions:

upper respiratory tract symptoms, cough, wheeze,

hypersensitivity pneumonitis in susceptible persons, and

asthma symptoms in sensitized persons [15]. A previous

scientific review was more specific in concluding that

sufficient evidence exists to support associations between

fungal allergen exposure and asthma exacerbation and

upper respiratory disease [13]. Finally, mold toxins can

cause direct lung damage leading to pulmonary diseases

other than asthma [13]. 

The topic of residential mold has received increasing

public and media attention over the past decade. Many

news stories have focused on problems associated with

“toxic mold” or “black mold,” which is often a reference

to the toxin-producing mold, Stachybotrys chartarum. This

might give the impression that mold problems in homes

are more frequent now than in past years; however, no

good evidence supports this. Reasons for the increasing

attention to this issue include high-visibility lawsuits

brought by property owners against builders and

developers, scientific controversies regarding the degree to

which specific illness outbreaks are mold-induced, and an

increase in the cost of homeowner insurance policies due

to the increasing number of mold-related claims. Modern

construction might be more vulnerable to mold problems

because tighter construction makes it more difficult for

internally generated water vapor to escape, as well as the

widespread use of paper-backed drywall in construction

(paper is an excellent medium for mold growth when

wet), and the widespread use of carpeting. 

Allergic Health Effects. Many molds produce numerous

protein or glycoprotein allergens capable of causing

allergic reactions in people. These allergens have been

measured in spores as well as in other fungal fragments.

An estimated 6%–10% of the general population and

15%–50% of those who are genetically susceptible are

Healthy Housing Reference Manual 5-3
sensitized to mold allergens [13]. Fifty percent of the

937 children tested in a large multicity asthma study

sponsored by the National Institutes of Health showed

sensitivity to mold, indicating the importance of mold as

an asthma trigger among these children [16]. Molds are

thought to play a role in asthma in several ways. Molds

produce many potentially allergenic compounds, and

molds may play a role in asthma via release of irritants

that increase potential for sensitization or release of toxins

(mycotoxins) that affect immune response [13]. 

Toxics and Irritants. Many molds also produce

mycotoxins that can be a health hazard on ingestion,

dermal contact, or inhalation [14]. Although common

outdoor molds present in ambient air, such as

Cladosporium cladosporioides and Alternaria alternata, do

not usually produce toxins, many other different mold

species do [17]. Genera-producing fungi associated with

wet buildings, such as Aspergillus versicolor, Fusarium

verticillioides, Penicillium aiurantiorisen, and S. chartarum,

can produce potent toxins [17]. A single mold species

may produce several different toxins, and a given

mycotoxin may be produced by more than one species of

fungi. Furthermore, toxin-producing fungi do not

necessarily produce mycotoxins under all growth

conditions, with production being dependent on the

substrate it is metabolizing, temperature, water content,

and humidity [17]. Because species of toxin-producing

molds generally have a higher water requirement than do

common household molds, they tend to thrive only under

conditions of chronic and severe water damage [18]. For

example, Stachybotrys typically only grows under continuously

wet conditions [19]. It has been suggested that very

young children may be especially vulnerable to certain

mycotoxins [19,20]. For example, associations have been

reported for pulmonary hemorrhage (bleeding lung)

deaths in infants and the presence of S. chartarum [21–24]. 

Causes of Mold. Mold growth can be caused by any

condition resulting in excess moisture. Common moisture

sources include rain leaks (e.g., on roofs and wall joints);

surface and groundwater leaks (e.g., poorly designed or

clogged rain gutters and footing drains, basement leaks);

plumbing leaks; and stagnant water in appliances (e.g.,

dehumidifiers, dishwashers, refrigerator drip pans, and

condensing coils and drip pans in HVAC systems).

Moisture problems can also be due to water vapor

migration and condensation problems, including uneven

indoor temperatures, poor air circulation, soil air entry

into basements, contact of humid unconditioned air with

cooled interior surfaces, and poor insulation on indoor

chilled surfaces (e.g., chilled water lines). Problems can

also be caused by the production of excess moisture

within homes from humidifiers, unvented clothes dryers,

overcrowding, etc. Finished basements are particularly

susceptible to mold problems caused by the combination

of poorly controlled moisture and mold-supporting

materials (e.g., carpet, paper-backed sheetrock) [15].

There is also some evidence that mold spores from damp

or wet crawl spaces can be transported through air currents

into the upper living quarters. Older, substandard

housing low income families can be particularly prone to

mold problems because of inadequate maintenance (e.g.,

inoperable gutters, basement and roof leaks), overcrowding,

inadequate insulation, lack of air conditioning, and poor

heating. Low interior temperatures (e.g., when one or two

rooms are left unheated) result in an increase in the

relative humidity, increasing the potential for water to

condense on cold surfaces. 

Mold Assessment Methods. Mold growth or the

potential for mold growth can be detected by visual

inspection for active or past microbial growth, detection

of musty odors, and inspection for water staining or

damage. If it is not possible or practical to inspect a

residence, this information can be obtained using

occupant questionnaires. Visual observation of mold

growth, however, is limited by the fact that fungal

elements such as spores are microscopic, and that their

presence is often not apparent until growth is extensive

and the fact that growth can occur in hidden spaces (e.g.,

wall cavities, air ducts). 

Portable, hand-held moisture meters, for the direct

measurement of moisture levels in materials, may also be

useful in qualitative home assessments to aid in

pinpointing areas of potential biologic growth that may

not otherwise be obvious during a visual inspection [14]. 

For routine assessments in which the goal is to identify

possible mold contamination problems before

remediation, it is usually unnecessary to collect and

analyze air or settled dust samples for mold analysis

because decisions about appropriate intervention

strategies can typically be made on the basis of a visual

inspection [25]. Also, sampling and analysis costs can be

relatively high and the interpretation of results is not

straightforward. Air and dust monitoring may, however,

be necessary in certain situations, including 1) if an

individual has been diagnosed with a disease associated

with fungal exposure through inhalation, 2) if it is

suspected that the ventilation systems are contaminated,

or 3) if the presence of mold is suspected but cannot be

identified by a visual inspection or bulk sampling [26].

5-4 Indoor Air Pollutants and Toxic Materials
Generally, indoor environments contain large reservoirs of

mold spores in settled dust and contaminated building

materials, of which only a relatively small amount is

airborne at a given time. 

Common methods for sampling for mold growth include

bulk sampling techniques, air sampling, and collection of

settled dust samples. In bulk sampling, portions of

materials with visual or suspected mold growth (e.g., sections

of wallboard, pieces of duct lining, carpet segments, or

return air filters) are collected and directly examined to

determine if mold is growing and to identify the mold

species or groups that are present. Surface sampling in

mold contamination investigations may also be used

when a less destructive technique than bulk sampling is

desired. For example, nondestructive samples of mold may

be collected using a simple swab or adhesive tape [14]. 

Air can also be sampled for mold using pumps that pull

air across a filter medium, which traps airborne mold

spores and fragments. It is generally recommended that

outdoor air samples are collected concurrent with indoor

samples for comparison purposes for measurement of

baseline ambient air conditions. Indoor contamination

can be indicated by indoor mold distributions (both

species and concentrations) that differ significantly from

the distributions in outdoor samples [14]. Captured mold

spores can be examined under a microscope to identify

the mold species/groups and determine concentrations or

they can be cultured on growth media and the resulting

colonies counted and identified. Both techniques require

considerable expertise.

Dust sampling involves the collection of settled dust

samples (e.g., floor dust) using a vacuum method in

which the dust is collected onto a porous filter medium

or into a container. The dust is then processed in the

laboratory and the mold identified by culturing viable spores.

Mold Standards. No standard numeric guidelines exist

for assessing whether mold contamination exists in an

area. In the United States, no EPA regulations or

standards exist for airborne mold contaminants [26].

Various governmental and private organizations have,

however, proposed guidance on the interpretation of

fungal measures of environmental media in indoor

environments (quantitative limits for fungal

concentrations). 

Given evidence that young children may be especially

vulnerable to certain mycotoxins [18] and in view of the

potential severity or diseases associated with mycotoxin

exposure, some organizations support a precautionary

approach to limiting mold exposure [19]. For example,

the American Academy of Pediatrics recommends that

infants under 1 year of age are not exposed at all to

chronically moldy, water-damaged environments [18]. 

Mold Mitigation. Common intervention methods for

addressing mold problems include the following:

• maintaining heating, ventilating, and air

conditioning (HVAC) systems; 

• changing HVAC filters frequently, as

recommended by manufacturer;

• keeping gutters and downspouts in working order

and ensuring that they drain water away from the

foundation;

• routinely checking, cleaning, and drying drip pans

in air conditioners, refrigerators, and

dehumidifiers;

• increasing ventilation (e.g., using exhaust fans or

open windows to remove humidity when cooking,

showering, or using the dishwasher);

• venting clothes dryers to the outside; and 

• maintaining an ideal relative humidity level in the

home of 40% to 60%.

• locating and removing sources of moisture

(controlling dampness and humidity and repairing

water leakage problems);

• cleaning or removing mold-contaminated

materials;

• removing materials with severe mold growth; and

• using high-efficiency air filters.

Moisture Control. Because one of the most important

factors affecting mold growth in homes is moisture level,

controlling this factor is crucial in mold abatement

strategies. Many simple measures can significantly control

moisture, for example maintaining indoor relative

humidity at no greater than 40%–60% through the use

of dehumidifiers, fixing water leakage problems,

increasing ventilation in kitchens and bathrooms by using

exhaust fans, venting clothes dryers to the outside,

Healthy Housing Reference Manual 5-5
reducing the number of indoor plants, using air

conditioning at times of high outdoor humidity, heating

all rooms in the winter and adding heating to outside wall

closets, sloping surrounding soil away from building

foundations, fixing gutters and downspouts, and using a

sump pump in basements prone to flooding [27]. Vapor

barriers, sump pumps, and aboveground vents can also be

installed in crawlspaces to prevent moisture problems [28]. 

Removal and Cleaning of Mold-contaminated Materials.

Nonporous (e.g., metals, glass, and hard plastics) and

semiporous (e.g., wood and concrete) materials

contaminated with mold and that are still structurally

sound can often be cleaned with bleach-and-water

solutions. However, in some cases, the material may not

be easily cleaned or may be so severely contaminated that

it may have to be removed. It is recommended that

porous materials (e.g., ceiling tiles, wallboards, and

fabrics) that cannot be cleaned be removed and discarded

[29]. In severe cases, clean-up and repair of moldcontaminated buildings may be conducted using methods

similar to those used for abatement of other hazardous

substances such as asbestos [30]. For example, in

situations of extensive colonization (large surface areas

greater than 100 square feet or where the material is

severely degraded), extreme precautions may be required,

including full containment (complete isolation of work

area) with critical barriers (airlock and decontamination

room) and negative pressurization, personnel trained to

handle hazardous wastes, and the use of full-face

respirators with HEPA filters, eye protection, and

disposable full-body covering [26]. 

Worker Protection When Conducting Mold Assessment

and Mitigation Projects. Activities such as cleaning or

removal of mold-contaminated materials in homes, as well

as investigations of mold contamination extent, have the

potential to disturb areas of mold growth and release

fungal spores and fragments into the air. Recommended

measures to protect workers during mold remediation

efforts depend on the severity and nature of the mold

contamination being addressed, but include the use of

well fitted particulate masks or respirators that retain

particles as small as 1 micrometer or less, disposable

gloves and coveralls, and protective eyewear [31].

Following are examples of guidance documents for

remediation of mold contamination:

• New York City Department of Health and Mental

Hygiene. Guidelines on Assessment and

Remediation of Fungi in Indoor Environments

(available from URL: http://www.nyc.gov/html/

doh/html/epi/moldrpt1.shtml).

• American Conference of Governmental Industrial

Hygienists (ACGIH) 1999 document,

Biosaerosols: Assessment and Control (can be

ordered at URL http://www.acgih.org/home.htm). 

• American Industrial Hygiene Association (AIHA)

2004 document, Assessment, Remediation, and

Post-Remediation Verification of Mold in

Buildings (can be ordered at URL www.aiha.org)

• Environmental Protection Agency guidance, Mold

Remediation in Schools and Commercial Buildings

(includes many general principles also applicable

to residential mold mitigation efforts; available at

URL: http://www.epa.gov/iaq/molds/

mold_remediation.html)

• Environmental Protection Agency guidance, A

Brief Guide to Mold, Moisture, and Your Home

(for homeowners and renters on how to clean up

residential mold problems and how to prevent

mold growth; available at URL: http://www.epa.gov/

iaq/molds/images/moldguide.pdf) 

• Canada Mortgage and Housing Corporation,

Clean-up Procedures for Mold in Houses,

(provides qualitative guidance for mold

mitigation; can be ordered at URL:

https://www.cmhc-schl.gc.ca:50104/b2c/b2c/

init.do?language=en). 

Figure 5.1 shows mold growth in the home.

Chemical Pollutants

Carbon Monoxide 

Carbon monoxide (CO) is a significant combustion

pollutant in the United States. CO is a leading cause of

poisoning deaths [32]. According to the National Fire

Protection Association (NFPA), CO-related nonfire

deaths are often attributed to heating and cooking

equipment. The leading specific types of equipment

blamed for CO-related deaths include gas-fueled space

heaters, gas-fueled furnaces, charcoal grills, gas-fueled

ranges, portable kerosene heaters, and wood stoves.

As with fire deaths, the risk for unintentional CO death is

highest for the very young (ages 4 years and younger) and

the very old (ages 75 years and older). CO is an odorless,

colorless gas that can cause sudden illness and death. It is

5-6 Indoor Air Pollutants and Toxic Materials
a result of the incomplete combustion of carbon.

Headache, dizziness, weakness, nausea, vomiting, chest

pain, and confusion are the most frequent symptoms of

CO poisoning. According to the American Lung

Association (ALA) [33], breathing low levels of CO can

cause fatigue and increase chest pain in people with

chronic heart disease. Higher levels of CO can cause

flulike symptoms in healthy people. In addition,

extremely high levels of CO cause loss of consciousness

and death. In the home, any fuel-burning appliance that

is not adequately vented and maintained can be a

potential source of CO. The following steps should be

followed to reduce CO (as well as sulfur dioxide and

oxides of nitrogen) levels:

• Never use gas-powered equipment, charcoal grills,

hibachis, lanterns, or portable camping stoves in

enclosed areas or indoors.

• Install a CO monitor (Figure 5.2) in appropriate

areas of the home. These monitors are designed to

provide a warning before potentially lifethreatening levels of CO are reached.

• Choose vented appliances when possible and keep

gas appliances properly adjusted to decrease the

combustion to CO. (Note: Vented appliances are

always preferable for several reasons: oxygen levels,

carbon dioxide buildup, and humidity management).

• Only buy certified and tested combustion

appliances that meet current safety standards, as

certified by Underwriter’s Laboratories (UL),

American Gas Association (AGA) Laboratories, or

equivalent.

• Assure that all gas heaters

possess safety devices that

shut off an improperly

vented gas heater. Heaters

made after 1982 use a

pilot light safety system

known as an oxygen

depletion sensor. When

inadequate fresh air exists,

this system shuts off the

heater before large

amounts of CO can

be produced.

• Use appliances that have

electronic ignitions instead

of pilot lights. These

appliances are typically more energy efficient and

eliminate the continuous low-level pollutants

from pilot lights.

• Use the proper fuel in kerosene appliances. 

• Install and use an exhaust fan vented to the

outdoors over gas stoves.

• Have a trained professional annually inspect,

clean, and tune up central heating systems

(furnaces, flues, and chimneys) and repair them

as needed.

• Do not idle a car inside a garage.

The U.S. Consumer Product Safety Commission (CPSC)

recommends installing at least one CO alarm per household

near the sleeping area. For an extra measure of safety,

another alarm should be placed near the home’s heating

source. ALA recommends weighing the benefits of using

models powered by electrical outlets versus models powered by

batteries that run out of power and need replacing.

Battery-powered CO detectors provide continuous protection

and do not require recalibration in the event of a power

outage. Electric-powered systems do not provide protection

during a loss of power and can take up to 2 days to

recalibrate. A device that can be easily self-tested and reset

to ensure proper functioning should be chosen. The product

should meet Underwriters Laboratories Standard UL 2034.

Ozone

Inhaling ozone can damage the lungs. Inhaling small amounts

of ozone can result in chest pain, coughing, shortness of

breath, and throat irritation. Ozone can also exacerbate

Healthy Housing Reference Manual 5-7

Figure 5.1. Mold Growth in the Home Figure 5.2. Home Carbon

Monoxide Monitor

Source: U.S. Navy
chronic respiratory diseases such as asthma. Susceptibility

to the effects of ozone varies from person to person, but

even healthy people can experience respiratory difficulties

from exposure. 

According to the North Carolina Department of Health

and Human Services [34], the major source of indoor

ozone is outdoor ozone. Indoor levels can vary from 10% of

the outdoor air to levels as high as 80% of the outdoor air.

The Food and Drug Administration has set a limit of

0.05 ppm of ozone in indoor air. In recent years, there

have been numerous advertisements for ion generators that

destroy harmful indoor air pollutants. These devices create

ozone or elemental oxygen that reacts with pollutants.

EPA has reviewed the evidence on ozone generators and

states: “available scientific evidence shows that at

concentrations that do not exceed public health standards,

ozone has little potential to remove indoor air contaminants,”

and “there is evidence to show that at concentrations that

do not exceed public health standards, ozone is not

effective at removing many odor causing chemicals” [35].

Ozone is also created by the exposure of polluted air to

sunlight or ultraviolet light emitters. This ozone produced

outside of the home can infiltrate the house and react

with indoor surfaces, creating additional pollutants.

Environmental Tobacco Smoke or Secondhand Smoke

Like CO, environmental tobacco smoke (ETS; also

known as secondhand smoke), is a product of

combustion. The National Cancer Institute (NCI) [36],

states that ETS is the combination of two forms of smoke

from burning tobacco products:

• Sidestream smoke, or smoke that is emitted

between the puffs of a burning cigarette, pipe, or

cigar; and

• Mainstream smoke, or the smoke that is exhaled

by the smoker.

The physiologic effects of ETS are numerous. ETS can

trigger asthma; irritate the eyes, nose, and throat; and

cause ear infections in children, respiratory illnesses, and

lung cancer. ETS is believed to cause asthma by irritating

chronically inflamed bronchial passages. According to the

EPA [37], ETS is a Group A carcinogen; thus, it is a

known cause of cancer in humans. Laboratory analysis

has revealed that ETS contains in excess of

4,000 substances, more than 60 of which cause cancer

in humans or animals. The EPA also estimates that

approximately 3,000 lung cancer deaths occur each year

in nonsmokers due to ETS. Additionally, passive smoking

can lead to coughing, excess phlegm, and chest

discomfort. NCI also notes that spontaneous abortion

(miscarriage), cervical cancer, sudden infant death

syndrome, low birth weight, nasal sinus cancer, decreased

lung function, exacerbation of cystic fibrosis, and negative

cognitive and behavioral effects in children have been

linked to ETS [36].

The EPA [37] states that, because of their relative body

size and respiratory rates, children are affected by ETS

more than adults are. It is estimated that an additional

7,500 to 15,000 hospitalizations resulting from increased

respiratory infections occur in children younger than

18 months of age due to ETS exposure. Figure 5.3 shows

the ETS exposure levels in homes with children under age

7 years. The following actions are recommended in the

home to protect children from ETS:

• if individuals insist on smoking, increase

ventilation in the smoking area by opening

windows or using exhaust fans; and

• refrain from smoking in the presence of children

and do not allow babysitters or others who work

in the home to smoke in the home or near children.

Volatile Organic Compounds

In the modern home, many organic chemicals are used as

ingredients in household products. Organic chemicals

that vaporize and become gases at normal room

temperature are collectively known as VOCs.

Examples of common items that can release VOCs

include paints, varnishes, and wax, as well as in many

cleaning, disinfecting, cosmetic, degreasing, and hobby

products. Levels of approximately a dozen common

VOCs can be two to five times higher inside the home, as

opposed to outside, whether in highly industrialized areas

5-8 Indoor Air Pollutants and Toxic Materials

Figure 5.3. Environmental Tobacco Smoke and Children’s Exposure [37]
or rural areas. VOCs that frequently pollute indoor air

include toluene, styrene, xylenes, and trichloroethylene.

Some of these chemicals may be emitted from aerosol

products, dry-cleaned clothing, paints, varnishes, glues,

art supplies, cleaners, spot removers, floor waxes, polishes,

and air fresheners. The health effects of these chemicals

are varied. Trichlorethylene has been linked to childhood

leukemia. Exposure to toluene can put pregnant women

at risk for having babies with neurologic problems,

retarded growth, and developmental problems. Xylenes

have been linked to birth defects. Styrene is a suspected

endocrine disruptor, a chemical that can block or mimic

hormones in humans or animals. EPA data reveal that

methylene chloride, a common component of some paint

strippers, adhesive removers, and specialized aerosol spray

paints, causes cancer in animals [38]. Methylene chloride

is also converted to CO in the body and can cause

symptoms associated with CO exposure. Benzene, a

known human carcinogen, is contained in tobacco smoke,

stored fuels, and paint supplies. Perchloroethylene, a

product uncommonly found in homes, but common to

dry cleaners, can be a pollution source by off-gassing from

newly cleaned clothing. Environmental Media Services

[39] also notes that xylene, ketones, and aldehydes are

used in aerosol products and air fresheners. 

To lower levels of VOCs in the home, follow these steps:

• use all household products according to directions;

• provide good ventilation when using these products;

• properly dispose of partially full containers of old

or unneeded chemicals;

• purchase limited quantities of products; and

• minimize exposure to emissions from products

containing methylene chloride, benzene, and

perchlorethylene.

A prominent VOC found in household products and

construction products is formaldehyde. According to

CPSC [40], these products include the glue or adhesive

used in pressed wood products; preservatives in paints,

coating, and cosmetics; coatings used for permanent-press

quality in fabrics and draperies; and the finish on paper

products and certain insulation materials. Formaldehyde

is contained in urea-formaldehyde (UF) foam insulation

installed in the wall cavities of homes as an energy

conservation measure. Levels of formaldehyde increase

soon after installation of this product, but these levels

decline with time. In 1982, CPSC voted to ban UF foam

insulation. The courts overturned the ban; however, the

publicity has decreased the use of this product.

More recently, the most significant source of

formaldehyde in homes has been pressed wood products

made using adhesives that contain UF resins [41]. The

most significant of these is medium-density fiberboard,

which contains a higher resin-to-wood ratio than any

other UF pressed wood product. This product is generally

recognized as being the highest formaldehyde-emitting

pressed wood product. Additional pressed wood products

are produced using phenol-formaldehyde resin. The latter

type of resin generally emits formaldehyde at a

considerably slower rate than those containing UF resin.

The emission rate for both resins will change over time

and will be influenced by high indoor temperatures and

humidity. Since 1985, U.S. Department of Housing and

Urban Development (HUD) regulations (24 CFR 3280.308,

3280.309, and 3280.406) have permitted only the use of

plywood and particleboard that conform to specified

formaldehyde emission limits in the construction of

prefabricated and manufactured homes [42]. This limit was

to ensure that indoor formaldehyde levels are below 0.4 ppm. 

CPSC [40] notes that formaldehyde is a colorless, strongsmelling gas. At an air level above 0.1 ppm, it can cause

watery eyes; burning sensations in the eyes, nose, and

throat; nausea; coughing; chest tightness; wheezing; skin

rashes; and allergic reactions. Laboratory animal studies

have revealed that formaldehyde can cause cancer in

animals and may cause cancer in humans. Formaldehyde

is usually present at levels less than 0.03 ppm indoors and

outdoors, with rural areas generally experiencing lower

concentrations than urban areas. Indoor areas that

contain products that release formaldehyde can have levels

greater than 0.03 ppm. CPSC also recommends the

following actions to avoid high levels of exposure to

formaldehyde:

• Purchase pressed wood products that are labeled

or stamped to be in conformance with American

National Standards Institute criteria ANSI

A208.1-1993. Use particleboard flooring marked

with ANSI grades PBU, D2, or D3. Mediumdensity fiberboard should be in conformance with

ANSI A208.2-1994 and hardwood plywood with

ANSI/HPVA HP-1-1994 (Figure 5.4).

• Purchase furniture or cabinets that contain a high

percentage of panel surface and edges that are

laminated or coated. Unlaminated or uncoated

Healthy Housing Reference Manual 5-9
(raw) panels of pressed wood panel products will

generally emit more formaldehyde than those that

are laminated or coated.

• Use alternative products, such as wood panel

products not made with UF glues, lumber, or metal.

• Avoid the use of foamed-in-place insulation

containing formaldehyde, especially UF foam

insulation.

• Wash durable-press fabrics before use. 

CPSC also recommends the following actions to reduce 

existing levels of indoor formaldehyde:

• Ventilate the home well by opening doors and

windows and installing an exhaust fan(s).

• Seal the surfaces of formaldehyde-containing

products that are not laminated or coated with

paint, varnish, or a layer of vinyl or polyurethanelike materials.

• Remove products that release formaldehyde in the

indoor air from the home. 

Radon

According to the EPA [43], radon is a colorless, odorless

gas that occurs naturally in soil and rock and is a decay

product of uranium. The U.S. Geological Survey (USGS)

[44] notes that the typical uranium content of rock and

the surrounding soil is between 1 and 3 ppm. Higher

levels of uranium are often contained in rock such as

light-colored volcanic rock, granite, dark shale, and

sedimentary rock containing phosphate. Uranium levels

as high as 100 ppm may be present in various areas of the

United States because of these rocks. The main source of

high-level radon pollution in buildings is surrounding

uranium-containing soil. Thus, the greater the level of

uranium nearby, the greater the chances are that buildings

in the area will have high levels of indoor radon.

Figure 5.5 demonstrates the geographic variation in radon

levels in the United States. Maps of the individual states

and areas that have proven high for radon are available at

http://www.epa.gov/iaq/radon/ zonemap.html. A free

video is available from the U.S. EPA: call 1-800-438-

4318 and ask for EPA 402-V-02-003 (TRT 13.10).

Radon, according to the California Geological Survey

[45], is one of the intermediate radioactive elements

formed during the radioactive decay of uranium-238,

uranium-235, or thorium-232. Radon-222 is the radon

isotope of most concern to public health because of its

longer half-life (3.8 days). The mobility of radon gas is

much greater than are uranium and radium, which are

solids at room temperature. Thus, radon can leave rocks

and soil, move through fractures and pore spaces, and

ultimately enter a building to collect in high concentrations.

When in water, radon moves less than 1 inch before it

decays, compared to 6 feet or more in dry rocks or soil.

USGS [44] notes that radon near the surface of soil

typically escapes into the atmosphere. However, 

where a house is present, soil air often flows toward the

house foundation because of

5-10 Indoor Air Pollutants and Toxic Materials

Figure 5.4. Wood Products Label [42]

Figure 5.5. EPA Map of Radon Zones [43]

Zone 1: predicted average indoor radon screening level greater than

4 pCi/L [picocuries per liter] 

Zone 2: predicted average indoor radon screening level between 2 and

4 pCi/L 

Zone 3: predicted average indoor radon screening level less than 2 pCi/L 

Important: Consult the EPA Map of Radon Zones document [EPA-402-R93-071] before using this map. This document contains information on

radon potential variations within counties. 

EPA also recommends that this map be supplemented with any available

local data to further understand and predict the radon potential of a

specific area.
• differences in air pressure between the soil and the

house, with soil pressure often being higher;

• presence of openings in the house’s foundation; and

• increases in permeability around the basement

(if present).

Houses are often constructed with loose fill under a basement

slab and between the walls and exterior ground. This fill

is more permeable than the original ground. Houses

typically draw less than 1% of their indoor air from the

soil. However, houses with low indoor air pressures,

poorly sealed foundations, and several entry points for soil

air may draw up to 20% of their indoor air from the soil. 

USGS [44] states that radon may also enter the home

through the water systems. Surface water sources typically

contain little radon because it escapes into the air. In

larger cities, radon is released to the air by municipal

processing systems that aerate the water. However, in

areas where groundwater is the main water supply for

communities, small public systems and private wells are

typically closed systems that do not allow radon to escape.

Radon then enters the indoor air from showers, clothes

washing, dishwashing, and other uses of water. Figure 5.6

shows typical entry points of radon.

Health risks of radon stem from its breakdown into

“radon daughters,” which emit high-energy alpha

particles. These progeny enter the lungs, attach

themselves, and may eventually lead to lung cancer. This

exposure to radon is believed to contribute to between

15,000 and 21,000 excess lung cancer deaths in the

United States each year. The EPA has identified levels

greater than 4 picocuries per liter as levels at which

remedial action should be taken. Approximately 1 in

15 homes nationwide have radon above this level,

according to the U.S. Surgeon General’s recent advisory

[46]. Smokers are at significantly higher risk for radonrelated lung cancer. 

Radon in the home can be measured either by the

occupant or by a professional. Because radon has no odor

or color, special devices are used to measure its presence.

Radon levels vary from day to day and season to season.

Short-term tests (2 to 90 days) are best if quick results are

needed, but long-term tests (more than 3 months) yield

better information on average year-round exposure.

Measurement devices are routinely placed in the lowest

occupied level of the home. The devices either measure 

the radon gas directly or the daughter products. The

simplest devices are passive, require no electricity, and

include a charcoal canister, charcoal liquid scintillation

device, alpha tract detector, and electret ion detectors [47].

All of these devices, with the exception of the ion

detector, can be purchased in hardware stores or by mail.

The ion detector generally is only available through

laboratories. These devices are inexpensive, primarily used

for short-term testing, and require little to no training.

Active devices, however, need electrical power and include

continuous monitoring devices. They are customarily

more expensive and require professionally trained testers

for their operation. Figure 5.7 shows examples of the

charcoal tester (a; left) and the alpha tract detector (b; right). 

After testing and evaluation by a professional, it may be

necessary to lower the radon levels in the structure. The

Pennsylvania Department of Environmental Protection

[48] states that in most cases, a system with pipes and a

fan is used to reduce radon. This system, known as a subslab

depressurization system, requires no major changes to the

home. The cost typically ranges from $500 to $2,500 and

averages approximately $1,000, varying with geographic

region. The typical mitigation system usually has only one

pipe penetrating through the basement floor; the pipe also

may be installed outside the house. The Connecticut

Department of Public Health [49] notes that it is more

cost effective to include radon-resistant techniques while

constructing a building than to install a reduction system

in an existing home. Inclusion of radon-resistant

techniques in initial construction costs approximately

$350 to $500 [50]. Figure 5.8 shows examples of radonresistant construction techniques. 

Healthy Housing Reference Manual 5-11

Figure 5.6. Radon Entry [30]
A passive radon-resistant system has five major parts: 

1. A layer of gas-permeable material under the

foundation.

2. The foundation (usually 4 inches of gravel).

3. Plastic sheeting over the foundation, with all

openings in the concrete foundation floor sealed

and caulked.

4. A gas-tight, 3- or 4-inch vent pipe running from

under the foundation through the house to the roof.

5. A roughed-in electrical junction box for the future

installation of a fan, if needed. 

These features create a physical barrier to radon entry.

The vent pipe redirects the flow of air under the

foundation, preventing radon from seeping into the house.

Pesticides

Much pesticide use could be reduced if integrated pest

management (IPM) practices were used in the home.

IPM is a coordinated approach to managing roaches,

rodents, mosquitoes, and other pests that integrates

inspection, monitoring, treatment, and evaluation, with

special emphasis on the decreased use of toxic agents.

However, all pest management options, including natural,

biologic, cultural, and chemical methods, should be

considered. Those that have the least impact on health

and the environment should be selected. Most household

pests can be controlled by eliminating the habitat for the

pest both inside and outside, building or screening them

out, eliminating food and harborage areas, and safely

using appropriate pesticides if necessary.

EPA [51] states that 75% of U.S. households used at least

one pesticide indoors during the past year and that 80% of

most people’s exposure to pesticides occurs indoors.

Measurable levels of up to a dozen pesticides have been

found in the air inside homes. Pesticides used in and

around the home include products to control insects

(insecticides), termites (termiticides), rodents (rodenticides),

fungi (fungicides), and microbes (disinfectants). These

products are found in sprays, sticks, powders, crystals,

balls, and foggers.

Delaplane [52] notes that the ancient Romans killed

insect pests by burning sulfur and controlled weeds with

salt. In the 1600s, ants were controlled with mixtures of

honey and arsenic. U.S. farmers in the late 19th century

used copper actoarsenite (Paris green), calcium arsenate,

nicotine sulfate, and sulfur to control insect pests in field

crops. By World War II and afterward, numerous

pesticides had been introduced, including DDT, BHC,

aldrin, dieldrin, endrin, and 2,4-D. A significant factor

with regard to these pesticides used in and around the

home is their impact on children. According to a 2003

EPA survey, 47% of all households with children under

the age of 5 years had at least one pesticide stored in an

unlocked cabinet less than 4 feet off the ground. This is

within easy reach of children. Similarly, 74% of

households without children under the age of 5 also

stored pesticides in an unlocked cabinet less than 4 feet

off the ground. This issue is significant because 13% of all

pesticide poisoning incidents occur in homes other than

the child’s home. The EPA [53] notes a report by the

American Association of Poison Control Centers

indicating that approximately 79,000 children were

involved in common household pesticide poisonings or

exposures. 

The health effects of pesticides vary with the product.

However, local effects from most of the products will be

on eyes, noses, and throats; more severe consequences,

such as on the central nervous system and kidneys and on

Figure 5.7. Home Radon Dectectors [31]

Figure 5.8. Radon-resistant Construction [50]

5-12 Indoor Air Pollutants and Toxic Materials
cancer risks, are possible. The active and inert ingredients

of pesticides can be organic compounds, which can

contribute to the level of organic compounds in indoor

air. More significantly, products containing cyclodiene

pesticides have been commonly associated with

misapplication. Individuals inadvertently exposed during

this misapplication had numerous symptoms, including

headaches, dizziness, muscle twitching, weakness, tingling

sensations, and nausea. In addition, there is concern that

these pesticides may cause long-term damage to the liver

and the central nervous system, as well as an increased

cancer risk. Cyclodiene pesticides were developed for use

as insecticides in the 1940s and 1950s. The four main

cyclodiene pesticides—aldrin, dieldrin, chlordane, and

heptachlor—were used to guard soil and seed against

insect infestation and to control insect pests in crops.

Outside of agriculture they were used for ant control;

farm, industrial, and domestic control of fleas, flies, lice,

and mites; locust control; termite control in buildings, fences,

and power poles; and pest control in home gardens. No

other commercial use is permitted for cyclodiene or

related products. The only exception is the use of

heptachlor by utility companies to control fire ants in

underground cable boxes. 

An EPA survey [53] revealed that bathrooms and kitchens

are areas in the home most likely to have improperly stored

pesticides. In the United States, EPA regulates pesticides under

the pesticide law known as the Federal Insecticide, Fungicide,

and Rodenticide Act. Since 1981, this law has required

most residential-use pesticides to bear a signal word such

as “danger” or “warning” and to be contained in childresistant packaging. This type of packaging is designed to

prevent or delay access by most children under the age of

5 years. EPA offers the following recommendations for

preventing accidental poisoning:

• store pesticides away from the reach of children in

a locked cabinet, garden shed, or similar location;

• read the product label and follow all directions

exactly, especially precautions and restrictions;

• remove children, pets, and toys from areas before

applying pesticides;

• if interrupted while applying a pesticide, properly

close the package and assure that the container is

not within reach of children; 

• do not transfer pesticides to other containers that

children may associate with food or drink;

• do not place rodent or insect baits where small

children have access to them;

• use child-resistant packaging properly by closing

the container tightly after use;

• assure that other caregivers for children are aware

of the potential hazards of pesticides;

• teach children that pesticides are poisons and

should not be handled; and 

• keep the local Poison Control Center telephone

number available.

Toxic Materials

Asbestos

Asbestos, from the Greek word meaning “inextinguishable,”

refers to a group of six naturally occurring mineral fibers.

Asbestos is a mineral fiber of which there are several

types: amosite, crocidiolite, tremolite, actinolite,

anthrophyllite, and chrysotile. Chrysotile asbestos, also

known as white asbestos, is the predominant commercial

form of asbestos. Asbestos is strong, flexible, resistant to

heat and chemical corrosion, and insulates well. These

features led to the use of asbestos in up to 3,000 consumer

products before government agencies began to phase it

out in the 1970s because of its health hazards. Asbestos

has been used in insulation, roofing, siding, vinyl floor

tiles, fireproofing materials, texturized paint and

soundproofing materials, heating appliances (such as

clothes dryers and ovens), fireproof gloves, and ironing

boards. Asbestos continues to be used in some products,

such as brake pads. Other mineral products, such as talc

and vermiculite, can be contaminated with asbestos. 

The health effects of asbestos exposure are numerous and

varied. Industrial studies of workers exposed to asbestos in

factories and shipyards have revealed three primary health

risk concerns from breathing high levels of asbestos fibers:

lung cancer, mesothelioma (a cancer of the lining of the

chest and the abdominal cavity), and asbestosis (a condition in

which the lungs become scarred with fibrous tissue).

The risk for all of these conditions is amplified as the

number of fibers inhaled increases. Smoking also

enhances the risk for lung cancer from inhaling asbestos

fibers by acting synergistically. The incubation period (from

time of exposure to appearance of symptoms) of these

diseases is usually about 20 to 30 years. Individuals who

develop asbestosis have typically been exposed to high

levels of asbestos for a long time. Exposure levels to

asbestos are measured in fibers per cubic centimeter of air.

Most individuals are exposed to small amounts of asbestos

Healthy Housing Reference Manual 5-13
in daily living activities; however, a preponderance of

them do not develop health problems. According to the

Agency for Toxic Substances and Disease Registry

(ATSDR), if an individual is exposed, several factors

determine whether the individual will be harmed [54].

These factors include the dose (how much), the duration

(how long), and the fiber type (mineral form and

distribution). ATSDR also states that children may be

more adversely affected than adults [54]. Children breathe

differently and have different lung structures than adults;

however, it has not been determined whether these

differences cause a greater amount of asbestos fibers to

stay in the lungs of a child than in the lungs of an adult.

In addition, children drink more fluids per kilogram of

body weight than do adults and they can be exposed

through asbestos-contaminated drinking water. Eating

asbestos-contaminated soil and dust is another source of

exposure for children. Certain children intentionally eat

soil and children’s hand-to-mouth activities mean that all

young children eat more soil than do adults. Family

members also have been exposed to asbestos that was

carried home on the clothing of other family members

who worked in asbestos mines or mills. Breathing asbestos

fibers may result in difficulty in breathing. Diseases

usually appear many years after the first exposure to

asbestos and are therefore not likely to be seen in

children. But people who have been exposed to asbestos

at a young age may be more likely to contract diseases

than those who are first exposed later in life. In the small

number of studies that have specifically looked at asbestos

exposure in children, there is no indication that younger

people might develop asbestos-related diseases more

quickly than older people. Developing fetuses and infants

are not likely to be exposed to asbestos through the

placenta or breast milk of the mother. Results of animal

studies do not indicate that exposure to asbestos is likely

to result in birth defects. 

A joint document issued by CPSC, EPA, and ALA, notes

that most products in today’s homes do not contain

asbestos. However, asbestos can still be found in products

and areas of the home. These products contain asbestos

that could be inhaled and are required to be labeled as

such. Until the 1970s, many types of building products

and insulation materials used in homes routinely

contained asbestos. A potential asbestos problem both

inside and outside the home is that of vermiculite. According

to the USGS [55], vermiculite is a claylike material that

expands when heated to form wormlike particles. It is

used in concrete aggregate, fertilizer carriers, insulation,

potting soil, and soil conditioners. This product ceased

being mined in 1992, but old stocks may still be available.

Common products that contained asbestos in the past

and conditions that may release fibers include the following:

• Steam pipes, boilers, and furnace ducts insulated

with an asbestos blanket or asbestos paper tape.

These materials may release asbestos fibers if

damaged, repaired, or removed improperly.

• Resilient floor tiles (vinyl asbestos, asphalt, and

rubber), the backing on vinyl sheet flooring, and

adhesives used for installing floor tile. Sanding

tiles can release fibers, as may scraping or sanding

the backing of sheet flooring during removal.

• Cement sheet, millboard, and paper used as

insulation around furnaces and wood-burning

stoves. Repairing or removing appliances may

release asbestos fibers, as may cutting, tearing,

sanding, drilling, or sawing insulation.

• Door gaskets in furnaces, wood stoves, and coal

stoves. Worn seals can release asbestos fibers

during use.

• Soundproofing or decorative material sprayed on

walls and ceilings. Loose, crumbly, or waterdamaged material may release fibers, as will

sanding, drilling, or scraping the material.

• Patching and joint compounds for walls, ceilings,

and textured paints. Sanding, scraping, or drilling

these surfaces may release asbestos.

• Asbestos cement roofing, shingles, and siding.

These products are not likely to release asbestos

fibers unless sawed, drilled, or cut.

• Artificial ashes and embers sold for use in gasfired fireplaces in addition to other older

household products such as fireproof gloves,

stove-top pads, ironing board covers, and certain

hair dryers.

• Automobile brake pads and linings, clutch facings,

and gaskets. 

Homeowners who believe material in their home may be

asbestos should not disturb the material. Generally,

material in good condition will not release asbestos fibers,

and there is little danger unless the fibers are released and

inhaled into the lungs. However, if disturbed, asbestos

material may release asbestos fibers, which can be inhaled

into the lungs. The fibers can remain in the lungs for a

5-14 Indoor Air Pollutants and Toxic Materials
long time, increasing the risk for disease. Suspected

asbestos-containing material should be checked regularly

for damage from abrasions, tears, or water. If possible,

access to the area should be limited. Asbestos-containing

products such as asbestos gloves, stove-top pads, and

ironing board covers should be discarded if damaged or

worn. Permission and proper disposal methods should be

obtainable from local health, environmental, or other

appropriate officials. If asbestos material is more than

slightly damaged, or if planned changes in the home

might disturb it, repair or removal by a professional is

needed. Before remodeling, determine whether asbestos

materials are present. 

Only a trained professional can confirm suspected

asbestos materials that are part of a home’s construction. This

individual will take samples for analysis and submit them

to an EPA-approved laboratory.

If the asbestos material is in good shape and will not be

disturbed, the best approach is to take no action and

continue to monitor the material. If the material needs

action to address potential exposure problems, there are

two approaches to correcting the problem: repair and removal. 

Repair involves sealing or covering the asbestos material.

Sealing or encapsulation involves treating the material

with a sealant that either binds the asbestos fibers together

or coats the material so fibers are not released. This is an

approach often used for pipe, furnace, and boiler

insulation; however, this work should be done only by a

professional who is trained to handle asbestos safely.

Covering (enclosing) involves placing something over or

around the material that contains asbestos to prevent release

of fibers. Exposed insulated piping may be covered with a

protective wrap or jacket. In the repair process, the

approach is for the material to remain in position

undisturbed. Repair is a less expensive process than is removal. 

With any type of repair, the asbestos remains in place.

Repair may make later removal of asbestos, if necessary,

more difficult and costly. Repairs can be major or minor.

Both major and minor repairs must be done only by a

professional trained in methods for safely handling asbestos. 

Removal is usually the most expensive and, unless

required by state or local regulations, should be the last

option considered in most situations. This is because

removal poses the greatest risk for fiber release. However,

removal may be required when remodeling or making

major changes to the home that will disturb asbestos

material. In addition, removal may be called for if

asbestos material is damaged extensively and cannot be

otherwise repaired. Removal is complex and must be done

only by a contractor with special training. Improper

removal of asbestos material may create more of a

problem than simply leaving it alone. 

Lead

Many individuals recognize lead in the form often seen in

tire weights and fishing equipment, but few recognize its

various forms in and around the home. The MerriamWebster Dictionary [56] defines lead as “a heavy soft malleable

ductile plastic but inelastic bluish white metallic element

found mostly in combination and used especially in pipes,

cable sheaths, batteries, solder, and shields against

radioactivity.” Lead is a metal with many uses. It melts easily

and quickly. It can be molded or shaped into thin sheets

and can be drawn out into wire or threads. Lead also is

very resistant to weather conditions. Lead and lead

compounds are toxic and can present a severe hazard to

those who are overexposed to them. Whether ingested or

inhaled, lead is readily absorbed and distributed

throughout the body.

Until 1978, lead compounds were an important component

of many paints. Lead was added to paint to promote

adhesion, corrosion control, drying, and covering. White

lead (lead carbonate), linseed oil, and inorganic pigments

were the basic components for paint in the 18th and 19th

centuries, and continued until the middle of the 20th century.

Lead was banned by CPSC in 1978. Lead-based paint was

used extensively on exteriors and interior trim-work, window

sills, sashes, window frames, baseboards, wainscoting,

doors, frames, and high-gloss wall surfaces, such as those

found in kitchens and bathrooms. The only way to determine

which building components are coated with lead paint is

through an inspection for lead-based paint. Almost all

painted metals were primed with red lead or painted with

lead-based paints. Even milk (casein) and water-based

paints (distemper and calcimines) could contain some

lead, usually in the form of hiding agents or pigments.

Varnishes sometimes contained lead. Lead compounds also

were used as driers in paint and window-glazing putty. 

Lead is widespread in the environment. People absorb

lead from a variety of sources every day. Although lead

has been used in numerous consumer products, the most

important sources of lead exposure to children and others

today are the following:

• contaminated house dust that has settled on

horizontal surfaces,

• deteriorated lead-based paint,

Healthy Housing Reference Manual 5-15
• contaminated bare soil, 

• food (which can be contaminated by lead in the

air or in food containers, particularly leadsoldered food containers), 

• drinking water (from corrosion of plumbing

systems), and 

• occupational exposure or hobbies.

Federal controls on lead in gasoline, new paint, food

canning, and drinking water, as well as lead from industrial air

emissions, have significantly reduced total human exposure

to lead. The number of children with blood lead levels above

10 micrograms per deciliter (μg/dL), a level designated as

showing no physiologic toxicity, has declined from

1.7 million in the late 1980s to 310,000 in 1999–2002.

This demonstrates that the controls have been effective,

but that many children are still at risk. CDC data show

that deteriorated lead-based paint and the contaminated

dust and soil it generates are the most common sources of

exposure to children today. HUD data show that the

number of houses with lead paint declined from 64 million

in 1990 to 38 million in 2000 [57].

Children are more vulnerable to lead poisoning than are

adults. Infants can be exposed to lead in the womb if

their mothers have lead in their bodies. Infants and

children can swallow and breathe lead in dirt, dust, or

sand through normal hand-to-mouth contact while they

play on the floor or ground. These activities make it easier

for children to be exposed to lead. Other sources of

exposure have included imported vinyl miniblinds,

crayons, children’s jewelry, and candy. In 2004, increases

in lead in water service pipes were observed in Washington,

D.C., accompanied by increases in blood lead levels in

children under the age of 6 years who were served by the

water system [58].

In some cases, children swallow nonfood items such as

paint chips. These may contain very large amounts of lead,

particularly in and around older houses that were painted

with lead-based paint. Many studies have verified the

effect of lead exposure on IQ scores in the United States.

The effects of lead exposure have been reviewed by the

National Academy of Sciences [59]. 

Generally, the tests for blood lead levels are from drawn

blood, not from a finger-stick test, which can be unreliable if

performed improperly. Units are measured in micrograms

per deciliter and reflect the 1991 guidance from the Centers

of Disease Control [60]: 

• Children: 10 μg/dL (level of concern)—find

source of lead;

• Children: 15 μg/dL and above—environmental

intervention, counseling, medical monitoring;

• Children: 20 μg/dL and above—medical treatment;

• Adults: 25 μg/dL (level of concern)—find source

of lead; and 

5-16 Indoor Air Pollutants and Toxic Materials

Lead in paint. Differing methods report results in differing units. Lead is considered a potential hazard if

above the following levels, but can be a hazard at lower levels if improperly handled. Below are the current

action levels identified by HUD [62] and EPA (40 CFR Part 745):

Lab analysis of samples: 

5,000 milligram per kilogram (mg/kg) or 5,000 parts per million (ppm) 

0.5% lead by weight.

X-ray fluorescence: 

1 milligram per square centimeter (mg/cm2)

Lead in dust: Lead in soil: 

Floors, 40 micrograms per square foot (μg/ft2) High-contact bare play areas: 400 ppm 

Window sills, 250 μg/ft2 Other yard areas: 1,200 ppm

Window troughs, 400 μg/ft2 (clearance only)

Action Levels for Lead
• Adults: 50 μg/dL—Occupational Safety and

Health Administration (OSHA) standard for

medical removal from the worksite.

Adults are usually exposed to lead from occupational

sources (e.g., battery construction, paint removal) or at

home (e.g., paint removal, home renovations). 

In 1978, CPSC banned the use of lead-based paint in

residential housing. Because houses are periodically

repainted, the most recent layer of paint will most likely

not contain lead, but the older layers underneath

probably will. Therefore, the only way to accurately

determine the amount of lead present in older paint is to

have it analyzed. 

It is important that owners of homes built before 1978 be

aware that layers of older paint can contain a great deal of

lead. Guidelines on identifying and controlling lead-based

paint hazards in housing have been published by HUD [61]. 

Controlling Lead Hazards

The purpose of a home risk assessment is to determine,

through testing and evaluation, where hazards from lead

warrant remedial action. A certified inspector or risk

assessor can test paint, soil, or lead dust either on-site or

in a laboratory using methods such as x-ray fluorescence

(XRF) analyzers, chemicals, dust wipe tests, and atomic

absorption spectroscopy. Lists of service providers are

available by calling 1-800-424-LEAD. Do-it-yourself test

kits are commercially available; however, these kits do not

tell you how much lead is present, and their reliability at

detecting low levels of lead has not been determined.

Professional testing for lead in paint is recommended.

The recommended sampling method for dust is the

surface wet wipe. Dust samples are collected from

different surfaces, such as bare floors, window sills, and

window wells. Each sample is collected from a measured

surface area using a wet wipe, which is sent to a

laboratory for testing. Risk assessments can be fairly lowcost investigations of the location, condition, and severity

of lead hazards found in house dust, soil, water, and

deteriorating paint. Risk assessments also will address

other sources of lead from hobbies, crockery, water, and

work environments. These services are critical when

owners are seeking to implement measures to reduce

suspected lead hazards in housing and day-care centers or

when extensive rehabilitation is planned. 

HUD has published detailed protocols for risk

assessments and inspections [61].

It is important from a health standpoint that future tenants,

painters, and construction workers know that lead-based

paint is present, even under treated surfaces, so they can

take precautions when working in areas that will generate

lead dust. Whenever mitigation work is completed, it is

Healthy Housing Reference Manual 5-17

Deteriorated lead-based paint: Paint known to contain lead above the regulated level that shows signs of

peeling, chipping, chalking, blistering, alligatoring, or otherwise separating from its substrate. 

Dust removal: The process of removing dust to avoid creating a greater problem of spreading lead particles;

usually through wet or damp collection and use of HEPA vacuums.

Hazard abatement: Long-term measures to remove the hazards of lead-based paint through replacement of

building components, enclosure, encapsulation, or paint removal. 

Interim control: Short-term methods to remove lead dust, stabilize deteriorating painted surfaces, treat

friction and impact surfaces that generate lead dust, and repaint surfaces. Maintenance can ensure that

housing remains lead-safe. 

Lead-based paint: Any existing paint, varnish, shellac, or other coating that is equal to or greater than

1.0 milligrams per square centimeter (mg/cm2) or greater than 0.5% by weight (5,000 ppm, 5,000

micrograms per gram [μg/g], or 5,000 milligrams per kilogram [mg/kg]). For new paint, CPSC has

established 0.06% as the maximum amount of lead allowed in new paint. Lead in paint can be measured by

x-ray fluorescence analyzers or laboratory analysis by certified personnel and approved laboratories. 

Risk assessment: An on-site investigation to determine the presence and condition of lead-based paint,

including limited test samples and an evaluation of the age, condition, housekeeping practices, and uses of a

residence. 

Definitions Related to Lead
important to have a clearance test using the dust wipe

method to ensure that lead-laden dust generated during

the work does not remain at levels above those established

by the EPA and HUD. Such testing is required for

owners of most housing that is receiving federal financial

assistance, such as Section 8 rental housing. A building or

housing file should be maintained and updated whenever

any additional lead hazard control work is completed.

Owners are required by law to disclose information about

lead-based paint or lead-based paint hazards to buyers or

tenants before completing a sales or lease contract [62].

All hazards should be controlled as identified in a

risk assessment.

Whenever extensive amounts of lead must be removed

from a property, or when methods of removing toxic

substances will affect the environment, it is extremely

important that the owner be aware of the issues surrounding

worker safety, environmental controls, and proper disposal.

Appropriate architectural, engineering, and environmental

professionals should be consulted when lead hazard

projects are complex. 

Following are brief explanations of the two approaches for

controlling lead hazard risks. These controls are

recommended by HUD in HUD Guidelines for the

Evaluation and Control of Lead-Based Paint Hazards in

Housing [61], and are summarized here to focus on

special considerations for historic housing: 

Interim Controls. Short-term solutions include thorough

dust removal and thorough washdown and cleanup, paint

film stabilization and repainting, covering of leadcontaminated soil, and informing tenants about lead

hazards. Interim controls require ongoing maintenance

and evaluation. 

Hazard Abatement. Long-term solutions are defined as

having an expected life of 20 years or more and involve

permanent removal of hazardous paint through chemicals,

heat guns, or controlled sanding or abrasive methods;

permanent removal of deteriorated painted features

through replacement; removal or permanent covering of

contaminated soil; and the use of enclosures (such as

drywall) to isolate painted surfaces. The use of specialized

encapsulant products can be considered as permanent

abatement of lead. 

Reducing and controlling lead hazards can be successfully

accomplished without destroying the character-defining

features and finishes of historic buildings. Federal and

state laws generally support the reasonable control of leadbased paint hazards through a variety of treatments,

ranging from modified maintenance to selective substrate

removal. The key to protecting children, workers, and the

environment is to be informed about the hazards of lead,

to control exposure to lead dust and lead in soil and lead

paint chips, and to follow existing regulations. 

The following summarizes several important regulations

that affect lead-hazard reduction projects. Owners should

be aware that regulations change, and they have a

responsibility to check state and local ordinances as well.

Care must be taken to ensure that any procedures used to

release lead from the home protect both the residents and

workers from lead dust exposure.

Residential Lead-Based Paint Hazard Reduction Act of

1992, Title X [62]. Part of the Housing and Community

Development Act of 1992 (Public Law 102-550) [63]. It

established that HUD issue Guidelines for the Evaluation

and Control of Lead-Based Paint Hazards in Housing [61]

to outline risk assessments, interim controls, and

abatement of lead-based paint hazards in housing. Title X

calls for the reduction of lead in federally supported

housing. It outlines the federal responsibility toward its

own residential units and the need for disclosure of lead

in residences, even private residences, before a sale. Title X

also required HUD to establish regulations for federally

assisted housing (24 CFR Part 35) and EPA to establish

standards for lead in paint, dust, and soil, as well as

standards for laboratory accreditation (40 CFR Part 745).

EPA’s residential lead hazard standards are available at

http://www.epa.gov/lead/leadhaz.htm.

Interim Final Rule on Lead in Construction (29 Code of

Federal Regulations [CFR] 1926.62) [64]. Issued by

OSHA, these regulations address worker safety, training,

and protective measures. The regulations are based in part

on personal-air sampling to determine the amount of lead

dust exposure to workers. 

State Laws. States generally have the authority to regulate

the removal and transportation of lead-based paint and

the generated waste through the appropriate state

environmental and public health agencies. Most

requirements are for mitigation in the case of a leadpoisoned child, for protection of children, or for oversight

to ensure the safe handling and disposal of lead waste.

When undertaking a lead-based paint reduction program,

it is important to determine which laws are in place that

may affect the project.

5-18 Indoor Air Pollutants and Toxic Materials
Local Ordinances. Check with local health departments,

poison control centers, and offices of housing and

community development to determine whether any laws

require compliance by building owners. Determine

whether projects are considered abatements and will

require special contractors and permits. 

Owner’s Responsibility. Owners are ultimately

responsible for ensuring that hazardous waste is properly

disposed of when it is generated on their own sites.

Owners should check with their state government to

determine whether an abatement project requires a

certified contractor. Owners should establish that the

contractor is responsible for the safety of the crew, to

ensure that all applicable laws are followed, and that

transporters and disposers of hazardous waste have

liability insurance as a protection for the owner. The

owner should notify the contractor that lead-based paint

may be present and that it is the contractor’s

responsibility to follow appropriate work practices to

protect workers and to complete a thorough cleanup to

ensure that lead-laden dust is not present after the work is

completed. Renovation contractors are required by EPA

to distribute an informative educational pamphlet

(Protect Your Family from Lead in Your Home) to

occupants before starting work that could disturb leadbased paint (http://www.epa.gov/lead/

leadinfo.htm#remodeling).

Arsenic

Lead arsenate was used legally up to 1988 in most of the

orchards in the United States. Often 50 applications or

more of this pesticide were applied each year. This toxic

heavy metal compound has accumulated in the soil

around houses and under the numerous orchards in the

country, contaminating both wells and land. These

orchards are often turned into subdivisions as cities

expand and sprawl occurs. Residues from the pesticide

lead arsenate, once used heavily on apple, pear, and other

orchards, contaminate an estimated 70,000 to 120,000 acres

in the state of Washington alone, some of it in areas

where agriculture has been replaced with housing,

according to state ecology department officials and others. 

Lead arsenate, which was not banned for use on food

crops until 1988, nevertheless was mostly replaced by the

pesticide dichlorodiphenyltrichloroethane (DDT) and its

derivatives in the late 1940s. DDT was banned in the

United States in 1972, but is used elsewhere in the world. 

For more than 20 years, the wood industry has infused

green wood with heavy doses of arsenic to kill bugs and

prevent rot. Numerous studies show that arsenic sticks to

children’s hands when they play on treated wood, and it is

absorbed through the skin and ingested when they put

their hands in their mouths. Although most uses of

arsenic wood treatments were phased out by 2004, an

estimated 90% of existing outdoor structures are made of

arsenic-treated wood [65].

In a study conducted by the University of North Carolina

Environmental Quality Institute in Asheville, wood

samples were analyzed and showed that 

• Older decks and play sets (7 to 15 years old) that

were preserved with chromated copper arsenic

expose people to just as much arsenic on the

wood surface as do newer structures (less than

1 year old). The amount of arsenic that testers

wiped off a small area of wood about the size of a

4-year-old’s handprint typically far exceeds what

EPA allows in a glass of water under the Safe

Drinking Water Act standard. Figure 5.9 shows a

safety warning label placed on wood products. 

• Arsenic in the soil from two of every five

backyards or parks tested exceeded EPA’s

Superfund cleanup level of 20 ppm. 

Arsenic is not just poisonous in the short term, it causes

cancer in the long term. Arsenic is on EPA’s short list of

chemicals known to cause cancer in humans. According to the

National Academy of Sciences, exposure to arsenic causes

lung, bladder, and skin cancer in humans, and is suspected as

a cause of kidney, prostate, and nasal passage cancer. 

Healthy Housing Reference Manual 5-19

Figure 5.9. Arsenic Label 
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5-22 Indoor Air Pollutants and Toxic Materials
54. Agency for Toxic Substances and Disease Registry.

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56. Merriam-Webster, Inc. Merriam-Webster dictionary. Springfield, MA: Merriam-Webster, Inc.; no

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58. Centers for Disease Control and Prevention.

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62. US Department of Housing and Urban

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disclosurerule/index.cfm. 

63. Residential Lead-Based Paint Hazard Reduction

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shows high levels of arsenic on old wood.

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Group; 2002. Available from URL:

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Healthy Housing Reference Manual 5-23
5-24 Indoor Air Pollutants and Toxic Materials