Indoor Mold Characteristics

Molds are a type of fungi that may be found throughout the natural
environment. Fungi are a large and diverse class of microorganisms
that live on organic nutrients. In nature they play an important role in
the natural breakdown of dead organic matter.

Like most fungi, the majority of molds reproduce by producing spores,
which are microscopic cells, usually between 2-20 microns and oblong
shaped, and can become airborne very easily. These spores then can
attach to surfaces that are wet and new growths called colonies may
then form if the right conditions are present. These ideal conditions
include high humidity (usually over 65% relative humidity) or moisture
content. Ideal temperature range for mold growth is between 50 and 90
degrees Fahrenheit (10-32 Celsius). No mold is able to grow in the
absence of moisture. When the spores settle on a surface and begin to
germinate they produce a branching network called hyphae. The mold
then begins digesting the surface that they are growing on in order to
survive.

The problem with molds start when they are found in excessive
amounts in the indoor environment. Because they are so small, mold
spores can easily be brought indoors on clothing, pets, shoes etc. The
spores may also enter a building through open doors, windows, or
ventilation systems. It is impossible and impractical to attempt to
eliminate all indoor molds, but it is necessary to prevent significant
accumulation.

Mold growths may be detected visibly by discovering growths that
appear cottony, velvety, granular, or leathery that may first appear as
stains or discolorations. These growths may differ in color, varying
between white, gray, brown, black, yellow, green, or fluorescent. The
other common indicator that there is a mold problem may be the
detection of a musty or moldy odor, caused by volatile organic
compounds. This method may help when there is a case of hidden
mold, which may occur behind wallpaper or ceiling tiles, and is not
noticeably visible.

It is estimated that there are around one hundred common indoor mold
types that have the potential to be hazardous to one’s health in a wide
variety of ways. The most common molds encountered include:
Alternaria, Aspergillus, Cladosporium, Memnoniella Mucor, Penicillium,
and Stachybotrys (also known as “toxic black mold”).

Stachybotrys is a greenish-black mold that may have whitish edges.
When wet it appears slimy. Stachybotrys can be found worldwide, is
widespread in North America and is commonly found indoors. This
particular mold is found only on cellulose products, such as can be
found in wood, wallpaper, sheet-rock, ceiling tiles, insulation, etc.
Stachybotrys will not grow on tiles or concrete. Constant moisture is
required for growth of Stachybotrys. Mycotoxins, toxic chemicals
released by toxigenic fungi, can be found in the spores of
Stachybotrys, or on mold fragments. When wet the spores are not
easily aerosolized, but when released into the air, they can easily be
inhaled and cause health effects. The ideal conditions for toxin
production include about 55% relative humidity and fluctuating
temperatures. Because it thrives on cellulose materials, leaks behind
walls, under floors, or above ceilings may serve as ideal environments
for significant growth.

Certain species of Penicillium are pathogenic, causing severe sickness
in humans.

There are over 150 species in the Aspergillus genus, only a few of
which may be found indoors or may be potentially pathogenic, or
harmful to the health of humans and animals. This genus is found
world-wide, and is especially common in the Northern Hemisphere in
autumn and winter. Most people are naturally immune to the effects of
Aspergillis, but when disease occurs, it may take on several forms.
Aspergillus produces many well known toxins such as aflatoxins,
ochratoxins, and sterigmatocystin. Aflatoxin from Aspergillus flavus
and A. parasiticus are associated with stored peanuts and grains.

Cladosporium is the most common of the “black molds.” It produces a
black pigment that is useful in protection from Ultraviolet light, which
may explain why it is so common in nature. Certain species in this
genus are pathogenic, but no major mycotoxins are associated with
Cladosporium.

Mold related problems have been on the rise. One potential cause for
this may be that there have been changes in the construction industry
since the 1970’s. The methods and materials have changed, resulting in
the homes not “breathing” and the trapping of moisture vapors.

Exposure Pathway

The two most common pathways for exposure are inhalation and
dermal contact. Another possible pathway would include accidental
ingestion.

Exposure by inhalation may occur when people become exposed to
allergens produced by the mold. This type of exposure usually occurs
when spores, fragments, or mold products (such as mycotoxins)
become airborne, such as if the mold becomes damaged or disturbed.
This is the most common type of exposure.

Dermal exposure may occur if people accidental come into contact with
the mold, or if they are attempting to clean the infested area without
proper safety equipment.

Reactions by any pathway may be immediate or delayed, depending on
the sensitivity of the individual.

People at greater risk for experiencing hazardous health effects include
infants and children, the elderly, and anyone who is immune deficient,
such as caused by chemotherapy or disease.

Fate and Transport of Molds

Mold needs four basic components in order to grow and survive: a
temperature range above 40 degrees F and below 100 degrees F, mold
spores, a nutrient base, and moisture.

Molds produce tiny spores for reproduction. Spores penetrate through
indoor and outdoor air continuously; they land on damp surfaces and
begin growing and digesting whatever they land on in order to survive.
Spores can prosper on wood, paper, carpet, soil, plants, and fabrics.
Dirt on these surfaces can provide additional nutrients for spore
growth. Moisture also plays a major part in mold growth; an increase in
moisture will cause mold to grow excessively. To control and eliminate
mold growth, moisture must be minimal.

Molds can be detrimental and beneficial, depending on the
environment. They are always unwelcome and unhelpful in homes. It
causes staining and musty odors. Molds are detrimental to health; they
cause eye, skin, and respiratory tract irritation. They can be poisonous
if ingested or inhaled. Molds can be beneficial in some cases. They are
helpful in decomposing organic matter and in increasing availability to
plants.

What Types of People and Buildings are at Risk for Mold Exposure?

The keys to mold growth in a home are relative humidity and
temperature. Molds grow bests in cool, damp areas of a building.
Therefore, people most at risk for mold exposure are those that live in
houses with moisture problems or that have experienced flood
damage. Indoor humidity above 60% can promote mold growth. In
particular, a leaky foundation or plumbing may be indications of a
potential (or already existent) mold problem.
© 2007, American Mold Investigations All Rights Reserved
www.americanmoldinvestigations.com