MOLD TRAINING: AWARENESS
FUNGI
The edible mushroom has much in common with the mold that
forms on stale bread and old cantaloupe – and bathroom mildew and
mold. All these life forms belong to the Kingdom FUNGI – a diverse
group of more than 100,000 known species. Fungi are heterotophs –
meaning that they absorb their food through the wall and membrane.
They reproduce by means of spores which may be produced sexually
or asexually. Their main purpose on
earth is to break down dead materials.
Without fungi, the earth would be full of
dead things – leaves, trees, insects,
animals, etc. Life as we know it could
not exist without fungi. The same
powerful digestive enzymes that enable
fungi to decompose wastes and dead
organisms also permit them to reduce
wood, fiber, and food into their elemental components with
great efficiency. Various molds produce incalculable damage
to stored goods and building materials each year. These same
molds cause considerable damage to the structural soundness
of personal housing, public buildings, and commercial
structures while compromising the health of many of those
people who build, reside, work in, or visit these structures.
Fungi are classified into three major divisions based on the characteristics of the sexual
spores and fruiting bodies:
1. Zygomycota (black bread mold is a common example);
2. Ascomycota (includes some yeasts, powdery mildews, most of the bluegreen, red, and brown molds, and edible morels and truffles [over 30,000
species in this division]); and
3. Basidiomycota (includes the most familiar of the fungi-mushrooms, toadstools, bracket fungi, puff balls, and some plant parasites such as rusts and
smuts).3
3
The three division names may used in specie descriptions of fungi. See “Glossary” and “Broad
Classes of Reactions to Allergenic, Pathogenic, or Toxic Mold and Allergens” at the end of this handout.
Introduction To Mold
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MOLD TRAINING: AWARENESS
Molds are simple, microscopic organisms whose purpose in the ecosystem is to break
down dead materials. Molds can be found on plants, dry leaves, and just about every other
organic material. People have found some molds to be useful, such as those used to make
antibiotics, beer, cheese, and wine. Some molds are known to be highly toxic when
ingested, such as types that invade grains and peanuts. Still others cause adverse health
effects such as asthma or allergic reactions when their reproductive spores are inhaled.
Most molds found indoors came from the outdoors. The spores float in on air currents
and find a suitable spot to grow. Spores are lightweight and can travel on air currents. If
mold spores land on a suitable surface, they will begin to grow. Molds need three things
to thrive –
Moisture
Z
Food
Surface to Grow On
Molds can be seen throughout homes and other buildings. You can easily find some in
most bathrooms. Mold growth can often be seen in the form of discoloration and can be
many colors – white, orange, pink, green, black, or brown. When molds are present in
large quantities (called colonies), they can cause health problems in some people. Molds
can generally be divided in three groups based on their effects –
1. Allergenic
2. Infectious
3. Toxic
Allergenic molds are normally not dangerous, but they can cause allergic or asthmatic
symptoms such as wheezing or runny nose. These molds do not usually produce lifethreatening health effects and they are likely to affect those who are already allergic or
asthmatic. Indoor fungal allergens probably affect fewer people than do allergens
from cats, mites, or cockroaches; yet, significant portions (10-32%) of all asthmatics
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Introduction To Mold
MOLD TRAINING: AWARENESS
are sensitive to fungi. These
include those encountered in
buildings, such as Penicillium
(pen-ih-sill-ee-um), Aspergillus
(as-per-jil-lus), Cladosporium
(clad-oh-spore-ee-um), and
Alternaria (all-tur-nair-ee-ah).
Infectious/Pathogenic mold can
cause serious health effects in
persons with suppressed immune
systems, those taking chemotherapy, or in those with HIV/
AIDS. Opportunistic fungal
Where there is mold, there’s usually more than one – Aspergillus,
pathogens (disease-causing
Cladosporium, and Penicillium are in this room.
organisms) such as Aspergillus are
common in indoor air. A normal, healthy individual can
probably resist infection by these organisms regardless of dose,
although high exposure may cause hypersensitivity pneumonitis.
However, any mold that can grow at body temperature can
become a pathogen in an immuno-compromised individual.
Toxins (poisons) from mold can cause serious health
effects in almost anyone. These agents are fungal metabolites
that have toxic effects ranging from short-term irritation to
Aspergillus Fumigatus Colony
immuno-suppression and even cancer. Virtually all the
Forming Unit (CFU)
information related to diseases caused by mycotoxins concerns
ingestion of contaminated food. However, mycotoxins are contained in some kinds of
fungal spores and these spores can enter the body through the respiratory tract. Skin is
another route of entry for mycotoxins. Toxins of several fungi have caused cases of severe
dermatosis. Exposure to mycotoxin-producing fungi should be minimized. (See pages 5
- 6 for more information.)
Body Plan of a Fungus
The body structures of fungi vary in complexity, ranging from single-celled yeasts to
multi-cellular mold.4 Most fungi consist of long, branched thread-like strings (or
4
No body structure pictures or artwork are provided in this Guide because of the variety of mold
structures. “Mycelium” is a term you might encounter if you research molds listed in a sampling report.
Introduction To Mold
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MOLD TRAINING: AWARENESS
filaments) of cells called hyphae (singular, hypha). Hyphae form a tangled mass or tissuelike group known as mycelium. The web-like mold seen on bread consists of the mycelia
of mold colonies. What is not seen is the extensive mycelia that grows down into the bulk
of the bread. The color of the mold comes from the reproductive spores which are
produced in large numbers on the mycelia. Some hyphae are divided by walls, called
septa (singular, septum), into individual cells containing one or more nuclei while other
hyphae are undivided by septa and are something like a large, multi-nucleated giant cell.
The whole fungus body is referred to as a thallus.
Most fungi, particularly those that cause illness in humans, are dimorphic
– they have two forms. They can change from the yeast form to the mold
form in response to changes in temperature, nutrients (food), or other
environmental factors.
Mold Metabolism and Growth
Fungi grow best in dark, moist habitats but they are found universally
wherever organic material is available. Moisture is necessary for their
growth and they can obtain water from the atmosphere as well as from the
medium upon which they live. When the environment becomes very dry,
fungi survive by going into a resting stage – dormant – or by producing
spores that are resistant to dessication – drying out.
When a fungal spore comes into contact with an appropriate substrate, perhaps wet
carpet or drywall, it germinates and begins to grow. A thread-like hypha emerges from
the tiny spore and soon a tangled mat of hyphae infiltrates the substrate while other
hyphae extend up into the air. Cells of the hyphae secrete enzymes into the substrate,
degrading its organic compounds into small molecules that the fungus can absorb. Fungi
are efficient at converting nutrients into new cell material. If adequate amounts of
nutrients are available, then fungi are able to store them in the mycelium.
The Life Cycle of Molds
Fungal reproduction occurs in a variety ways: asexually by fission (cell division),
budding, or most commonly by spore formation; or sexually by means that are
characteristic of each group. Two types of reproductive structures are found in fungi –
Sporangia produce spores (as in most molds) and gametangia produce gametes (eggs
4
Introduction To Mold
MOLD TRAINING: AWARENESS
and sperm). The focus of this Guide is on spore formation because mold spore exposure
is responsible for most health effects.
Spores are usually produced on hyphae that project up into the air above the food
source. This arrangement permits the spores to be blown by the wind and distributed to
new areas. Fungal spores are stationary, unmoving cells which rely on wind (and animals)
for dispersal. We do not normally see the bulk of the mold organism which is an almost
invisible network of hyphae buried out of sight in the rotting material it invades. What we
do see is the upper body of hyphae that produces spores.
HEALTH EFFECTS OF MOLD EXPOSURE
Everyone is exposed to mold in some concentration in the outdoor air. Indoor exposure
to molds is not healthy to anyone. In particular, those people with allergies, existing
respiratory conditions, or suppressed immune systems are especially susceptible to health
problems from mold exposure. Additionally, infants and children, pregnant women and
the elderly can be sensitive to the effects of mold exposure. Some molds are more
hazardous than others. As humans vary greatly in their chemical make-up, so does the
body’s reaction to mold exposure. For some people, a small number of mold spores can
cause health problems. For others, it may take many more.
Mold exposure health effects are attributed to two components: 1) mold spores and 2)
mold toxins. Mold spores cause health problems when they become airborne and are
inhaled in large numbers. Remember, mold spores are the reproductive units of mold.
Under certain metabolic conditions, many fungi produce mycotoxins – natural organic
compounds that initiate a toxic response in humans. While some mycotoxins have been
found to be associated with hyphae, the primary mode of human exposure to
mycotoxins is inhalation of spores and mold-contaminated material. Molds that are
important potential producers of toxins indoors are certain species of
Fusarium (few-sair-ee-um), Penicillium, and Aspergillus. In water damaged
buildings, Stachybotrys (stack-ee-bau-tris) chartarum and Aspergillus
versicolor may also produce toxic metabolites.
However, isolation of a toxigenic fungus from a
building does not imply the presence of mycotoxin
since the physical conditions necessary for
mycotoxin production are very specific and they
are often different from those required for growth Green Wheat
blighted (turned
of the parent mold. Likewise, failure to produce
grey/white) by
Aspergillus Versicolor CFU toxins in vitro (in a culture dish) does not mean
Fusarium
that a mold known to be toxigenic will not produce toxins in a field situation.
Introduction To Mold
5
MOLD TRAINING: AWARENESS
There are many symptoms of mold exposure. Remember, the extent to which symptoms
appear depends on the sensitivity of the exposed person. Allergic reactions are the most
common mold-related symptoms and they typically include –
1. Respiratory problems (such as wheezing and difficulty breathing),
2. Nasal and Sinus congestion,
3. Sinusitis,5
4. Burning, Watery, Reddened Eyes or Blurry Vision,
5. Sore Throat,
6. Nose and Throat Irritation,
7. Shortness of Breath, and
8. Skin irritation.
Other, less common, health effects are –
9. Nervous System problems (headaches, memory loss, and moodiness),
10. Aches and Pains, and
11. Fever.
If you have any of these symptoms and the symptoms are reduced or completely
gone when you leave the job, chances are you have been exposed to some sort of allergen,
quite possibly mold.
5
Sinusitis simply means inflammation of the sinuses, but this gives little indication of the misery
and pain this condition can cause. Chronic sinusitis, sinusitis that persists for at least 3 weeks, affects an
estimated 32 million people in the United States. Sinusitis has its own localized pain signals, depending
upon the particular sinus affected. Headache upon awakening in the morning is characteristic of sinus
involvement. Pain when the forehead over the frontal sinuses is touched may indicate inflammation of the
frontal sinuses. Infection in the maxillary sinuses can cause the upper jaw and teeth to ache and the
cheeks to become tender to the touch. Since the ethmoid sinuses are near the tear ducts in the corner of
the eyes, inflammation of these cavities often causes swelling of the eyelids and tissues around the eyes,
and pain between the eyes. Ethmoid inflammation also can cause tenderness when the sides of the nose
are touched, a loss of smell, and a stuffy nose. Although the sphenoid sinuses are less frequently affected,
infection in this area can cause earaches, neck pain, and deep aching at the top of the head.
However, most patients with sinusitis have pain or tenderness in several locations, and symptoms
usually do not clearly define which sinuses are inflamed. Other symptoms of sinusitis can include fever,
weakness, tiredness, a cough that may be more severe at night, and runny nose or nasal congestion. In
addition, drainage of mucus from the sphenoids (or other sinuses) down the back of the throat (postnasal
drip) can cause a sore throat and can irritate the membranes lining the larynx (upper windpipe). On rare
occasions, acute sinusitis can result in brain infection and serious complications.
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Introduction To Mold
MOLD TRAINING: AWARENESS
MOLD AND INDOOR AIR QUALITY
While occupational exposure to pollutants such asbestos fibers is known to cause a
variety of cancers and coal dust is known to cause pneumoconiosis (black lung),
consequences of exposure to air contaminants, especially bioaerosols6 are not yet fully
understood.
In the 1970s and ‘80s, microbial contamination was identified as the primary cause for
poor air quality in only 5% of more than 500 IAQ (indoor air quality) investigations
conducted by NIOSH (National Institute for Occupational Safety and Health – 1989).
During the ‘90s, the percentage of mold-related IAQ cases increased dramatically
(between 35% - 50%).7
Some mold problems are obvious – you will see it growing – if you are lucky. Others
are not so obvious. If you can see mold or if there is a musty odor, there probably is a
mold problem. Areas that are wet, or have been wet because of flooding, leaky
plumbing, leaky roofing, or areas that are humid (such as bathrooms and laundry rooms)
are most likely to have mold growth. Look for signs of previous water damage. Visible
mold growth may be found underneath wall paper, baseboards, carpet, behind walls, in
attic spaces, in basements, or it may be evident by discolored plaster or drywall. It you
don’t see mold, it could still be growing in areas you cannot see, such as duct work for a
heating/cooling system or in a wall space.
The first course of action is to determine why the mold is growing.
Investigate any areas that are damp. Mold will grow on any surface that
provides moisture and food.
6
Bioaerosols are extremely small living organisms or fragments of living things suspended in the
air. Dust mites, molds, fungi, spores, pollen, bacteria, viruses, amoebas, fragments of plant materials, and
human and pet dander (skin which has been shed) are some examples. They cannot be seen without a
magnifying glass or microscope.
7
The increase can be partially attributed to a shift from chemical contaminant-based
investigations to an approach combining evaluation of physical, chemical, and micro-biological
constituents of indoor air environments.
Introduction To Mold
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MOLD TRAINING: AWARENESS
PREVENTION AND CONTROL
Although we do not fully understand how and when indoor mold affects human health,
we do have enough evidence to recommend controlling mold in indoor environments. The
most effective method of source control is the elimination of moisture that supports
mold growth. This may involve the fixing of leaking pipes, windows or roofs, directing
rainfall or drainage away from exterior walls, or increasing insulation. Using fans or
opening windows may also be helpful. Ventilation systems, especially those in large
commercial buildings, should be properly maintained and examined periodically for mold
contamination.
When underlying moisture sources cannot be readily eliminated, air conditioners
and dehumidifiers can help control relative humidity. When using dehumidifiers, water
collection traps should be cleaned routinely as these are another source of mold growth.
Visible mold can be removed by disinfection with a chlorine bleach solution mixed as
1 part bleach to 10 parts water.8
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On non-porous surfaces. Using diluted bleach may be a greater hazard than the mold itself.
Using a commercial fungicide (mold killer) or a fungistat (mold inhibitor) requires careful planning and
application, usually only after other control measures have failed. Some biocides are considered
pesticides and some states require that only registered pesticide applicators apply these products in
schools, commercial buildings, and homes. Make sure anyone applying a biocide is properly licensed
where required.
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Introduction To Mold