Mold: The Whole Picture
by Ellen McCrady
Mold is fascinating, despite the fact that it can be destructive and unhealthy, even deadly sometimes. For me it is an intellectual challenge, almost like playing a magical game of chess with an opponent who can become invisible, change into an animal and back again at will, or continue making his moves after he is obviously dead.
(This is not as imaginative as it sounds. Some mold can change at will into a form with a different species name. It can even change into yeast, and back again. Its color and other visible features depend on the temperature of its environment and what it has been eating. The toxins and volatile organic compounds released by the organism continue to affect competing species, including humans, after the mold itself is dead.)
We know what mold can do to collections, but this is just the tip of the iceberg. Mold is also a problem in medicine and public health, agriculture, composting operations, indoor air quality, building construction, historic preservation, and even social history. Considering all these together, its importance is immense, and a growing amount of research in many of these fields reflects this. A conference on mold in any one of these fields attracts specialists from other fields, and an intense cross-disciplinary exchange of information can result, which is quite stimulating.
Knowledge about mold is not only fascinating and important, but it is scarce in our field of library and archive preservation. People who care for collections have to cope with the aftermath of floods, chronic mold growth in their collection, and building-related illnesses, often without expert advice. When the situation calls for administrative action and expenditure of money, as all three of these examples do, who can they call upon to put their case before administrators? We need more bridges linking us with fields where research is done or expert services performed, to help us find knowledgeable people to advise us.
One final reason why I have roused myself to prepare this series on mold: The house I bought here in Austin seven years ago has had a mold problem. The chimney and fireplace smelled of mold; so did the area behind the clothes dryer; and the wooden deck and the clapboard siding were rotten.
Then a few years ago I started getting allergic reactions to the mold toxins in the air, and my memory, balance and ability to concentrate were affected. I knew I had to get rid of as much mold as I could. I had the deck replaced, several rotten windowsills repaired, the chimney capped, the dryer vent replaced, and the drainage around the edge of the house improved. I had two exhaust fans installed (including one at the top of the chimney), began leaving windows open a crack here and there, and (most important) began setting the air conditioning to a warmer temperature to minimize condensation on the outside of the house. Finally, I bought an air purifier for my bedroom. My memory, balance, concentration, and the quality of my sleep have all improved noticeably.
The moisture problem is still not under control, because the house “sweats” visibly on summer mornings like a glass of ice tea and the air is sometimes bad despite all the improvements. The rotten siding and possibly some insulation and structural members still need to be treated or replaced. That will be Phase Two.
Topics to be Covered in Later Instalments
Definition and assessment of mold problems
Cleanup, reconstruction, treatment
Sources of water or mold around buildings
Correcting construction flaws and building conditions that encourage mold growth
Effect of mold on human health
Sources of information
Mold in Human History
The Ergot Epidemic
In her book, Poisons of the Past: Molds, Epidemics, and History, Mary Kilbourne Matossian (a history professor) presents overwhelming evidence that the population of Europe was held down for 500 years by endemic mold-induced food poisoning called ergot or ergotism. Although most sources attribute this long epidemic to fungi in the genus Claviceps, she also gives credit to the genus Fusarium. Both genera infected rye kernels before and after harvest, producing toxic, long-acting alkaloids (e.g., ergotamine).
In northern Europe the poor, who lived on rye bread and little else, were the most affected. Women miscarried and children died frequently. Those who survived childhood had chronic illnesses, gangrene, and mental disturbances. Their hallucinations and seizures were interpreted as witchcraft, possession, or divine inspiration. No one knew that their diet was responsible for their misfortune. Not until wheat and potatoes began to replace rye did the epidemic abate.
Wealthy households were never affected as much as poor households, because their servants prepared the grain as gruel, boiling it over a fire for about a half hour, which broke down the toxin. They also enjoyed a more diverse diet, including meat and white bread.
Ergot was responsible for the low birth rate and high death rate in Europe from perhaps as early as 1250 to 1750. It even provided occasion for the Salem witch trials, because the early settlers of Massachusetts planted rye, ate rye bread, and experienced hallucinations and seizures just as the Europeans did. Even as late as 1945, ergotism was still retarding the population growth of Russia.
As a strong influence on population and quality of life in Europe for half a millenium, mold had a massive effect on the course of history. (Matossian’s book is fascinating! You can buy it for $23.90 from Books Now by calling 1-800-266-5766, ext. 1494.)
The Irish Potato Famine
The potato was introduced to northern Europe in the 1700s, and is credited with the quadrupling of Ireland’s population between 1740 and 1840, because it could support three or four more people per acre than wheat could. The potato blight came in 1845 and returned at intervals thereafter, causing widespread famine and the loss of half Ireland’s population by emigration and starvation in a period of 47 years. This time the mold did not sicken people, as the ergot had, but it killed the plants that provided them with food. The result was an Irish diaspora.
Public Health Measures in Biblical Times
The very first mention of mold and mold cleanup is in the Bible: Leviticus, Ch. 13, verses 1-46 (isolation or purification of people with skin diseases); verses 47-59 (mildewed clothing must be burned); and Ch. 14, verses 33-48 (mildew “with greenish or reddish depressions” on the inside wall of a house). The rabbi did inspections and acted as the public health officer.
The mildewed walls were to be remedied, according to Chapter 14, by tearing out the contaminated stones and throwing them into “an unclean place outside the town,” then scraping the remaining inside walls and throwing the scrapings in an unclean place. The old stones are replaced with new, the house is replastered and then monitored to see whether the trouble recurs. (In previous translations, the rather vague word used for any skin disease was translated as “leprosy.” This translation uses “mildew,” but the word should not be taken too literally.)
The text can be found on the International Bible Society’s web site, http://bible.gospelcom.net/cgi-bin/bible.
Mold and the Good Things in Life
Food and drink fermented by mold have been prepared almost everywhere in the world, since before written records began: mead (fermented honey), wine, beer, cheese and more.
In medicine, certain toxins produced by molds to deter rival microorganisms have been put to use by humans: penicillin and ergotamine, for instance. Ergotamine is now sometimes prescribed for migraine headaches, because it causes overdilated arteries in the brain to contract, thus relieving the pain.
There are other ways in which molds have been useful to people, but none of them relate to preservation of collections, so we will move on.
Fungus is the umbrella term for mold, mildew, mushrooms, yeasts, and puffballs. Fungi have a kingdom all to themselves, like plants and animals. What they all have in common, for starters, is that all their cells have one or more nuclei, and none of them have chlorophyll, so they can’t make their own carbohydrates.
Mildew is a popular term for visible mold in the home, but mycologists use it only for the molds that infect plants, like downy mildew.
The term mold applies to the microscopic members of this kingdom whose lifestyle involves putting out root-like rhizomes, releasing spores, and living in colonies. Although they are handicapped by their lack of chlorophyll and their inability to move around, they have compensated in a number of ways by their metabolic and reproductive versatility.
If they find themselves in a less than ideal situation (say, on an agar plate, away from their favorite food, with too much or too little light, the wrong temperature), they are likely to switch to a nonsexual method of reproduction (one not involving swapping or combining of genetic material) for the duration. This can make them hard to identify, since species are classified by their sexual characteristics (e.g., kind of spore cell wall, spore-producing cells, and sacs that store cells).
There is some evidence that fungi are responsible for foxing on the paper of old books, despite the fact that the brown spots don’t look like mold colonies. A reason offered for their drab appearance is that the dry interior of a book is not an ideal growth environment, even for xerotolerant or xerophyllic species.
Any given mold species may be able to reproduce by two or more different methods: budding off from mycelial fragments, or release of sexual spores, asexual spores and conidia.
Conidia are asexual spores that are not formed inside a sporangium (sac), but by budding out or converting from an existing cell. They provide the organism with a way of producing rapidly and cheaply. They are produced in great numbers by fungi in the class Ascomycetes. Species in this class also produce sexual spores in abundance, within specialized cells called asci.
An example of a species with reproductive versatility is Penicillium brevicompactum, which can hybridize on its own, even though it is known as an asexual fungus.
Whenever a fungus formerly thought to be only an asexual form is found to be the same as a sexual form with another name, the name of the asexual form is supposed to be dropped, so that both forms can have the same species name. However that may be, the chapter in the ACGIH handbook that is written by Burge and Otten provides separate names for both forms of nine genera (e.g., Emericella for the sexual form and Aspergillus for the asexual form).
If all this seems confusing, I have accomplished my purpose: to demonstrate that we would do better to focus on more familiar, practical applications, and leave mold species identification to the experts. In fact, I intend to recommend leaving several additional matters to the experts when they come up in future installments.
We still have to be able to generalize about mold when we are dealing with a situation or talking with each other, of course, but we should always be aware of mold species’ complexity and variety.
A few generalizations that I have seen in the literature or heard at meetings are presented below. They may contradict each other, either because so much is still unknown, or because the experts disagree, or because one is addressing a general audience and the other is addressing a professional audience. Then come some references to websites that provide both general information and specific information on characteristics of mold species. Seven books on mold are listed at the end of the Literature section.
The ideal mold environment is 32°-104°F, pH 3 to 8. The relative humidity is less important than the dew point or the water activity (free water) of the substrate. Requirements for air and light vary. Some fungi prefer a temperature range between 15° and 30°C; others below 0°C; and others prefer 35° to 50°C. [i.e., some like it below freezing; some like it as warm as 122°F; and some like it in between].
Different solutions [to the mold problem] in turn create diverse habitats for mold growth. Indeed, moulds are endowed with a miscellaneous enzymatic arsenal; as a result, there is almost no habitat that they cannot colonize. Even in dry climates with advanced ventilation or air-conditioning technologies, fungi will still find what they need to grow and reproduce.
Since fungi cannot make their own carbohydrates like plants do, they have to eat foods containing carbon; also, complex nitrogen compounds, and many elements, e.g., phosphorus, sulfur, manganese, and probably also copper and iron, since foxing spots often contain minute fragments of these metals. They release enzymes to digest cellulose, protein, and fats. Certain species are used in the paper industry to digest lignin in wood chips, leaving the cellulose intact. Molds can grow on virtually any substrate, including jet fuel, paint, rubber, textiles, electrical equipment, glass and stainless steel. Sometimes, as in the case of glass and steel, the nourishment offered by the substrate is only the dirt and grease on its surface.
Airborne fungi have spores that vary from three or four micrometers to 60 micrometers. Since one micrometer [micron] is only one millionth of a meter, spores cannot be seen without a good microscope. Spores may remain viable for a matter of minutes to many years; those of Aspergillus and Penicillium sometimes remain viable for over 12 years, air-dry at room temperature.
Release of spores is encouraged by a change in the relative humidity for some fungi. Release mechanisms that depend on rupture of moist, swollen cells are activated by a high RH. This is true of spores from Penicillium and Aspergillus, two of the most common indoor genera of mold. The number of spores in the air can be multiplied a hundredfold or more by foot traffic, use of vacuum machines and other cleaning equipment, or a higher level of ventilation. Most molds are not poisonous, but since there is always a mix of species, one cannot rule out the presence of toxins in a growth of mold.
Almost all mycotoxins are either airborne particulates or compounds produced in the tissues of the host by means of genetic material brought in by the spore. Some are able to suppress the human immune system.
There are hundreds of known or suspected mycotoxins, but the list could turn out to be in the thousands. Several have gained some notoriety, for instance Aflatoxin B1 and Satratoxin H. The species of a given genus may produce only one type of toxin (e.g., Aspergillus species, which produce only aflatoxins) or they may produce many (e.g., Penicillium species, which produce more than 100). Sometimes they will fail to produce their toxins in the lab, and sometimes they produce in the lab but not necessarily in the field. In addition to toxins, some molds produce synergizers (sometimes called potentiators) which exaggerate the effect of toxins; one of these synergizers is ethanol. Synergizers may be harmless in themselves. The smell of mold comes from the volatile organic compounds (VOCs) produced by the organism. Opinion differs on whether they are toxic or not. A 1988 study by J. David Miller et al. identified seven VOCs from a culture of Penicillium fellutanum, by GC-MS analysis. They included pentane, heptane, octane, 2 hexanone, and undecane. Over 500 VOCs from various fungi have been identified.
Indoor fungi are often xerotolerant or xerophyllic (tolerating or preferring low humidities), though the whole spectrum is present.
Websites & Listservs
Univ. of Minnesota, Environmental Health & Safety. A “Fungal Glossary” gives basic facts and references for five pages of genera & species.
Environmental Microbiology Laboratory. Gives lots of specific information on 40 or so mold genera; not very accurate regarding Stachybotrys.
Eastern NY Occupational & Environmental Health Center. Gives ordering info for Bioaerosols Conf. proceedings, 1994 & 1998.
Mycology Online. Provides links to Mycological Resources on the Internet, Really Big Index to Mycology Resources on the Internet, The Classification of Fungal Genera, Index of Fungi, and other sites.
Author: Tom Volk, U. Wisc., La Crosse. Good on basic stuff; lovely pictures; fun to read because of his contagious enthusiasm.
[I am indebted to Dr. Phil Morey for his comments and suggestions on this instalment -Ed.]