Molds can produce other secondary metabolites (see list in table below) such as

antibiotics and mycotoxins. Antibiotics are isolated from mold (and some bacterial)

cultures and some of their bacteriotoxic or bacteriostatic properties are exploited

medicinally to combat infections.

Mycotoxins are also products of secondary metabolism of molds. They are not essential

to maintaining the life of the mold cell in a primary way (at least in a friendly world),

such as obtaining energy or synthesizing structural components, informational molecules

or enzymes. They are products whose function seems to be to give molds a competitive

advantage over other mold species and bacteria. Mycotoxins are nearly all cytotoxic,

disrupting various cellular structures such as membranes, and interfering with vital

cellular processes such as protein, RNA and DNA synthesis. Of course they are also toxic

to the cells of higher plants and animals, including humans.

Mycotoxins vary in specificity and potency for their target cells, cell structures or cell

processes by species and strain of the mold that produces them. Higher organisms are

not specifically targeted by mycotoxins, but seem to be caught in the crossfire of the

biochemical warfare among mold species and molds and bacteria vying for the same

ecological niche.

Not all molds produce mycotoxins, but numerous species do (including some found

indoors in contaminated buildings). Toxigenic molds vary in their mycotoxin production

depending on the substrate on which they grow (Jarvis, 1990). The spores, with which

the toxins are primarily associated, are cast off in blooms that vary with the mold's

diurnal, seasonal and life cycle stage (Burge, 1990; Yang, 1995). The presence of

competitive organisms may play a role, as some molds grown in monoculture in the

laboratory lose their toxic potency (Jarvis, 1995). Until relatively recently, mold poisons

were regarded with concern primarily as contaminants in foods.

More recently concern has arisen over exposure to multiple mycotoxins from a mixture of

mold spores growing in wet indoor environments. Health effects from exposures to such

mixtures can differ from those related to single mycotoxins in controlled laboratory

exposures. Indoor exposures to toxigenic molds resemble field exposures of animals

more closely than they do controlled experimental laboratory exposures. Animals in

controlled laboratory exposures are healthy, of the same age, raised under optimum

conditions, and have only the challenge of known doses of a single toxic agent via a

single exposure route. In contrast, animals in field exposures are of mixed ages, and

states of health, may be living in less than optimum environmental and nutritional

conditions, and are exposed to a mixture of toxic agents by multiple exposure routes.

Exposures to individual toxins may be much lower than those required to elicit an

adverse reaction in a small controlled exposure group of ten animals per dose group. The

effects from exposure may therefore not fit neatly into the description given for any

single toxin, or the effects from a particular species, of mold. Field exposures of animals

to molds (in contrast to controlled laboratory exposures) show effects on the immune

system as the lowest observed adverse effect. Such immune effects are manifested in

animals as increased susceptibility to infectious diseases (Jakab et al., 1994). It is

important to note that almost all mycotoxins have an immunosuppressive effect,

although the exact target within the immune system may differ. Many are also cytotoxic,

so that they have route of entry effects that may be damaging to the gut, the skin or the

lung. Such cytotoxicity may affect the physical defense mechanisms of the respiratory

tract, decreasing the ability of the airways to clear particulate contaminants (including

bacteria or viruses), or damage alveolar macrophages, thus preventing clearance of

contaminants from the deeper lung. The combined result of these activities is to increase

the susceptibility of the exposed person to infectious disease, and to reduce his defense

against other contaminants. They may also increase susceptibility to cancer.

Because indoor samples are usually comprised of a mixture of molds and their spores, it

has been suggested that a general test for cytotoxicity be applied to a total indoor

sample to assess the potential for hazard as a rough assessment (Gareis, 1995).

The following summary of toxins and their targets is adapted from Smith and Moss

(1985), with a few additions from the more recent literature. While this compilation of

effects does not describe the effects from multiple exposures, which could include

synergistic effects, it does give a better idea of possible results of mycotoxin exposure to

multiple molds indoors.

from lung, e. g., aflatoxin, satratoxin, roridins).

necrosis, fibrosis: aflatoxin; caustic effects on mucous membranes: T-2 toxin;

anorexia: vomitoxin.

tremorgens, trichothecenes.

e. g., trichothecenes.

zearalenone.

It should be noted that not all mold genera have been tested for toxins, nor have all

species within a genus necessarily been tested. Conditions for toxin production vary with

cell and diurnal and seasonal cycles and substrate on which the mold grows, and those

conditions created for laboratory culture may differ from those the mold encounters in its

environment. Toxicity can arise from exposure to mycotoxins via inhalation of mycotoxincontaining

mold spores or through skin contact with the toxigenic molds (Forgacs, 1972;

Croft et al., 1986; Kemppainen et al., 1988 -1989). A number of toxigenic molds have

been found during indoor air quality investigations in different parts of the world. Among

the genera most frequently found in numbers exceeding levels that they reach outdoors

1992; Hirsh and Sosman, 1976; Verhoeff et al., 1992; Miller et al., 1988; Gravesen et

al., 1999).

Some Common Mycotoxins and the Organisms that Produce them

Deoxynivalenol

diacetate

Deoxynivalenol

monoacetate

Deoxynivalenol

diacetate

Deoxynivalenol

monoacetate

Fungi are ubiquitous to the environment and primarily saprophytic, using nonliving

organic material as a nutrient source for growth and reproduction. Many of these

saprophytes can colonize organic water-damaged building materials. During the digestion

process fungi secrete enzymes into the nutrient source to break down complex

compounds into simpler compounds, which are taken up by the fungi and digested. The

digested nutrients are classified into two categories, primary and secondary metabolites.

The primary metabolites consist of cellulose and other compounds that are used for

energy to grow and reproduce.

The secondary metabolites, called mycotoxins, are produced to give fungi a competitive

edge against other microorganisms, including other fungi. There are over 200 recognized

mycotoxins, however, the study of mycotoxins and their health effects on humans is in

its infancy and many more are waiting to be discovered. Many mycotoxins are harmful to

humans and animals when inhaled, ingested or brought into contact with human skin.

Mycotoxins can cause a variety of short term as well as long-term health effects, ranging

from immediate toxic response to potential long-term carcinogenic and teratogenic

effects. Symptoms due to exposure to mycotoxins include dermatitis, cold and flu

symptoms, sore throat, headache, fatigue, diarrhea, and impaired or altered immune

function, which may lead to opportunistic infection. Historically, mycotoxins have been a

persistent problem to farmers and the animal husbandry industry in Eastern Europe and

developing countries. Mycotoxins are a known agent in biological warfare as a moderate

illness compared to the other biologicals.

Recently, however, research has implicated many toxin-producing fungi, such as

problems and building related illnesses. Inhalation of mycotoxin producing fungi in

contaminated buildings is the most significant exposure, however, dermal contact from

handling contaminated materials and the chance of ingesting toxin containing spores

through eating, drinking and smoking is likely to increase exposure in a contaminated

environment. Recent advances in technology have given laboratories the ability to test

for specific mycotoxins without employing cost-prohibitive gas chromatography or high

performance liquid chromatography techniques. Currently, surface, bulk, food and feeds,

and air samples can be analyzed relatively inexpensively for the following mycotoxins:

Aflatoxin is one of the most potent carcinogens known to man and has been linked to

a wide variety of human health problems. The FDA has established maximum

allowable levels of total aflatoxin in food commodities at 20 parts per billion. The

maximum level for milk products is even lower at 0.5 parts per billion. Primarily

Ochratoxin is damaging to the kidneys and liver and is also a suspected carcinogen.

There is also evidence that it impairs the immune system.

deadly toxins. If ingested in sufficient quantity, T-2 toxin can severely damage the

entire digestive tract and cause rapid death due to internal hemorrhage. T-2 has

been implicated in the human diseases alimentary toxic aleukia and pulmonary

hemosiderosis. Damage caused by T-2 toxin is often permanent.

found in corn and corn-based products, with recent outbreaks of veterinary

mycotoxicosis occurring in Arizona, Indiana, Kentucky, North Carolina, South

Carolina, Texas and Virginia. The animals most affected were horses and swine,

resulting in dozens of deaths. Fumonisin toxin causes "crazy horse disease", or

leukoencephalomalcia, a liquefaction of the brain. Symptoms include blindness, head

butting and pressing, constant circling and ataxia, followed by death. Chronic lowlevel

exposure in humans has been linked to esophageal cancer. The American

Association of Veterinary Laboratory Diagnosticians (AAVLD) advisory levels for

fumonisin in horse feed is 5 ppm.

Vomitoxin, chemically known as Deoxynivalenol, a tricothecene mycotoxin, is

outbreaks of acute gastrointestinal illness in humans. The FDA advisory level for

vomitoxin for human consumption is 1 ppm.

similar in chemical structure to the female sex hormone estrogen and targets the

reproductive organs.

Other mycotoxins of clinical significance are as follows:

damage, vasodilatation, and bronchial constriction are some of the health effects

associated with this toxin.

toxin is abortogenic in animals and is believed to alter immune system function and

makes affected individuals more susceptible to opportunistic infection.

genera of fungi. It is believed to cause hemorrhaging in the brain and lungs and is

usually associated with apple and grape spoilage.

- Penicillic acid, roquefortine, cyclopiazonic acid, verrucosidin, rubratoxins A and B,

PR toxin, luteoskyrin, cychlochlorotine, rugulosin, erythroskyrine, secalonic acid D,

viridicatumtoxin, kojic acid, xanthomegnin, viomellein, chaetoglobosin C, echinulin,

flavoglaucin, versicolorin A, austamide, maltoyzine, aspergillic acid, paspaline,

aflatrem, fumagillin nigragillin chlamydosporol, isotrichodermin and many more.

As discussed there are many mycotoxins that can cause adverse health effects and

even death in humans. The synergistic effect of exposure to multiple mycotoxins

simultaneously is very poorly understood. Even more poorly understood are the byproducts

of mycotoxin degradation, particularly under the influence of strong

oxidizing agents such as sodium hypochlorite and/or ozone, agents frequently used

or misused by remediation personnel in the industry. More research is required in

this field to better understand the relationship of fungal contamination, mycotoxin

production on building substrates and building related disease.

Endotoxin is the name given to a group of heat stabile lipopolysaccharide molecules

present in the cell walls of gram-negative bacteria that have a certain characteristic

toxic effect. The lipid portion of each molecule is responsible for its toxicity and can

vary between bacterial species and even from cell to cell. When inhaled, endotoxin

creates an inflammatory response in humans that may result in fever, malaise,

alterations in white blood cell counts, headache, respiratory distress and even death.

It is common to the environment due to the ubiquitous nature of Gram-negative

bacteria. Exposure to elevated levels of endotoxin primarily occurs through exposure

to aerosols from specific reservoirs such as cotton mills, wastewater treatment

facilities, air washers, humidifiers and any other occupational settings where Gramnegative

bacteria can flourish.

In addition to their roles as irritants and allergens, many fungi produce toxic

chemical constituents (Kendrick, 1992; Miller, 1992; Wyllie and Morehouse, 1977).

Samson and co-workers (1996) defined mycotoxins as "fungal secondary metabolites

that in small concentrations are toxic to vertebrates and other animals when

introduced via a natural route". These compounds are non-volatile and may be

sequestered in spores and vegetative mycelium or secreted into the growth

substrate. The mechanism of toxicity of many mycotoxins involves interference with

various aspects of cell metabolism, producing neurotoxic, carcinogenic or teratogenic

effects (Rylander, 1999). Other toxic fungal metabolites such as the cyclosporins

exert potent and specific toxicity on the cellular immune system (Hawksworth et al.,

1995); however, most mycotoxins are known to possess immunosuppressant

properties that vary according to the compound (Flannigan and Miller, 1994).

Indeed, the toxicity of certain fungal metabolites such as aflatoxin, ranks them

among the most potently toxic, immunosuppressive and carcinogenic substances

known (ibid.). There is unambiguous evidence that ingestion exposure as well as

exposures by the inhalation pathway have been correlated with outbreaks of human

and animal mycotoxicoses (Abdel-Hafez and Shoreit, 1985; Burg et al., 1982; Croft

et al. , 1986; Hintikka, 1978; Jarvis, 1986; Norbick et al. , 1990; Sorenson et al.,

1987; Schiefer, 1986). Several common mycotoxigenic indoor fungi and their

respective toxins are listed.

During exponential growth, many fungi release low molecular weight, volatile organic

compounds (VOCs) as products of secondary metabolism. These compounds

comprise a great diversity of chemical structure, including ketones, aldehydes and

alcohols as well as moderately to highly modified aromatics and aliphatics. Cultural

studies of some common household moulds suggests that the composition of VOCs

remains qualitatively stable over a range of growth media and conditions (Sunesson

et al. , 1995). Furthermore, the presence of certain marker compounds common to

multiple species, such as 3-methylfuran, may be monitored as a proxy for the

presence of a fungal amplifier (Sunesson et al. , 1995). This method has been

suggested as a means of monitoring fungal contamination in grain storage facilities

(B?rjesson et al. , 1989; 1990; 1992; 1993).

Limited evidence suggests that exposure to low concentrations of VOCs may induce

respiratory irritation independent of exposure to allergenic particulate (Koren et al.,

1992). Volatile organic compounds may also arise through indirect metabolic effects.

A well-known example of this is the fungal degradation of urea formaldehyde foam

insulation.

Fungal colonization of this material results in the cleavage of urea from the polymer,

presumably to serve as a carbon or nitrogen source for primary metabolism. During

this process formaldehyde is evolved as a derivative, contributing to a decline in IAQ

(Bissett, 1987).

The present study was conceived with two primary objectives. First, this investigation

shall characterize the fungal biodiversity of house dust. This work shall investigate

correlations between dustborne fungal species, and examine the ecological similar of

positively associated taxa based on the hypothesis that positively associated dustborne

fungi are likely to share habitat characteristics.

From this, a second hypothesis follows that mechanisms that permit the entry or

concentration a given species will tend to facilitate the entry of other positively correlated

taxa. A second objective of this research is to assess the extent of genotypic variability in