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Content Cleaning | Fungus of the month: Fusarium

Content Cleaning

By Dr. Harriet Burge

We are often asked if building contents should be discarded as part of mold remediation. The short answer is "NO". A slightly longer answer is "Not normally" and we are now back into the commonly found gray area of mold remediation.

The goal of mold remediation is to remove active fungal growth and its products from a contaminated space. In most cases this can be done without actually removing the contents of the space. Unfortunately, some investigators are recommending that ALL building contents be removed and discarded.

This often results in enormous economic losses that are usually unnecessary. Here are a few guidelines to aid in deciding whether or not something needs to be discarded.

1. Water must be removed, and the problem that allowed the water to be present must be corrected. Otherwise, no amount of mold remediation will solve the problem.

2. Non-porous materials can always be cleaned, even if surface mold growth is present. In these cases, the mold is growing on dust, oil, soap film, or other nutrients attached to the surface of the material. Soap, water, and a little elbow grease will readily remove this kind of contamination. This is common practice when mold grows on shower tiles or in the refrigerator. This principle extends to television sets, metal or plastic furniture, ceramic or vinyl flooring, composition and granite counter tops, etc.

3. Wood can be cleaned unless the fungal growth is rotting the wood. This only occurs when wood has been wet for a long period of time. The blue, green and black powdery molds often seen on wood surfaces are not rotting the wood. As with non-porous materials, the fungi are growing on dust, wax, oils or other nutrients on the wood surface and can be removed with soap and water.

4. Removable soft materials can always be cleaned if the only contamination is from spores released from growth occurring elsewhere. Mattresses can be thoroughly vacuumed and covered in allergen-proof encasings. Upholstered furniture can be professionally cleaned. Drapery can be dry cleaned or washed. Rugs can be professionally cleaned, which involves immersion in soapy water followed by thorough rinsing and rapid drying. Clothing can be washed or dry-cleaned. If the soft material has been wetted and fungi are actually growing on the fibers, then decisions will have to be made about how valuable the object actually is. It is usually worth trying to clean all but the most grossly contaminated materials.

5. Fixed soft materials that have not become wet, and are contaminated only with spores can be cleaned in place either by occupants or professionals. Thorough vacuuming of furniture and installed carpeting is often sufficient. If mold growth within the space has been extensive, professional cleaners can more effectively remove residual spores using high powered suction with rapid drying. If fixed soft materials have become wet and mold has grown within the fibers, then they probably will have to be discarded. This may include gypsum board, wallpaper, and upholstered furniture. Again, good professional cleaning may be sufficient and is certainly worth trying, especially if a material is extremely valuable. Note that people with severe allergies are usually advised not to have upholstered furniture, carpeting or rugs, or draperies that require dry cleaning; and they should always use mattress and pillow encasings.

These cleaning approaches should also remove most of the odors caused by active fungal growth. Residual odors may be caused by undiscovered growth, bacterial growth, or other factors and correctly identifying the source is not always easy. Airing outdoors is the traditional approach to removing residual odors from mattresses, rugs, and clothing. The ultraviolet light and ozone (as well as other chemicals present outdoors) effectively destroy the chemicals that cause these odors. Ozone and ultraviolet use indoors is more problematic. Ozone is routinely used by fire restoration specialists to remove combustion odors. These remediations are always done in unoccupied spaces, and require high ozone concentrations. Obviously, if odors cannot be removed, the object may have to be discarded.

These suggestions are supported by the USEPA in moldguide.pdf and moldremediation.pdf, both available on the EPA website (www.epa.gov). They are also supported by the New York City Guidelines for Mold Remediation (http://www.ci.nyc.ny.us/html/doh/html/epi/moldrpt1.html#remed).


Fungus of the Month: Fusarium

By Dr. Payam Fallah

The genus Fusarium has a worldwide distribution. There are approximately 50 species in this genus, some of which can cause diseases in plants (e.g. agricultural, horticultural, and ornamental). Certain species within this genus are considered to be post-harvest pathogens of seeds and cereals, in particular barely and corn.

A few of the Fusarium species have been recovered in indoor environments from a variety of substrates which include: cooling units of air-conditioning systems, soil, carpet, drywall papers, mattress dust, polyurethane foam, cotton from duct liner insulation, metal working fluids, wood, and a variety of fruits. As suggested by this extensive list, Fusarium grows on a wide variety of substrates and continues to show up on very unusual and unexpected substrates. Some of the species commonly found include F. culmorum, F. solani, F. moniliforme, and F. oxysporum.

Identification of almost all Fusarium to species level using morphological based taxonomy can only be done in culture. One of the most striking characters of this genus is the ability of some species to produce two kinds of spores (or conidia), macro-conidia and micro-conidia. The macro-conidia of the fusaria can easily be identified on spore traps and tape lifts. These spores are "banana" shaped, colorless, and typically have multiple septa (or cross walls). An important morphological feature of these spores is the presence of a foot-cell (Fig. 1). In the absence of this characteristic, it is very difficult to identify the spores and they can be mistakenly identified as some of the ascospores that are commonly found in the air. The micro-conidia are also colorless, but much smaller, and usually posses one or two septa. If recovered on a spore trap, the micro-conidia are impossible to identify and only culturable sampling can provide an accurate and reliable identification. Micro-conidia of Fusarium (sometimes referred to as an acremonial phase) may be confused with Acremonium.

In culture, Fusarium species often produce a distinct soluble pigment that can vary from pink to purple in coloration. Occasionally, this soluble pigment can be detected on the actual substrates that Fusarium colonizes, such as drywall paper. It is important to note that the presence of the color alone cannot provide a reliable identification. Generally, the colonies of the fusaria are slimy and, therefore, less frequently aerosolized. The slimy texture is a characteristic also seen in genera such as Stachybotrys, Trichoderma, and Acremonium. Like these fungi, the primary means of dissemination by the fusaria is by water splash and insects. Spores can potentially become airborne once they are dried. Because Fusarium can colonize indoor building materials and is not commonly airborne, it can be considered a "marker spore" and recovery of it in an indoor environment suggests an indoor water problem and fungal growth.

Fusarium species are known to cause type I allergies (hay fever, asthma). One type of mycotoxin produced by this fungus is known as zearalenone. Zearalenone has been patented as a growth stimulant in animals and has a potential application as an oral contraceptive, in addition to being recognized as an anabolic steroid (<1ppm). Fusarium graminearum is used for the production of quorn (a mycoprotein) for human consumption. The product contains many fibers and is used in pies in the United Kingdom and some other countries.

Fig. 1. Macro-conidia (spores) of a Fusarium species showing the distinct characteristic know as a foot-cell.

Microphoto of Fusarium species Macro-conidia spores


This article was originally published on May 2005.