Is Black Mold Toxic?

It should be noted, however, that not all black mold is toxic and that not all toxic mold is black. In fact, there are over 400,000 different types of mold and many of them are black in color of which only a portion have been identified. Black mold and/or toxic mold are terms often used in reference to Stachybotrys, (stack-ee-bot-ris) aka: Stachybotrys chartarum, aka: Stachybotrys atra.

Many fungi (e.g., species of Aspergillus, Penicillium, Fusarium, Trichoderma, and Memnoniella) in addition to Stachybotrys can produce potent mycotoxins, some of which are identical to compounds produced by Stachybotrys. For this reason, Stachybotrys cannot be treated as uniquely toxic in indoor environments.

OVERVIEW:

Virtually everyone has some type of mold or another somewhere in their home. Although not all types are toxic, it is sometimes difficult to distinguish types without lab testing. Black molds can develop from water seepage, and while toxic mold is less common than other mold species, it is not rare. For that reason, it is imperative to treat and remove all molds as if they are potentially harmful. Regardless of the type of mold found, a home containing mold is not essentially a healthy home.

The notoriety of Stachybotrys leads some to believe that is the only “toxic mold”. That is not true. 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 are Aspergillus, Penicillium, Stachybotrys, and Cladosporium (Burge, 1986; Smith et al., 1992; Hirsh and Sosman, 1976; Verhoeff et al., 1992; Miller et al., 1988; Gravesen et al., 1999). Penicillium, Aspergillus and Stachybotrys toxicity, especially as it relates to indoor exposures, are discussed briefly in the paragraphs along the right.

Summary of Stachybotrys:

Stachybotrys has a different make up than most other molds and does not produce airborne spore as easily as other molds. If you were to physically touch a spot of black mold, it would feel slimy and would smear on the area. Areas and substances where black mold can be found include water soaked wood, ceiling tiles, wall paneling, cardboard, even items made of cotton. Black mold can grow on drywall and insulation and can infest areas in the floors, walls and ceilings.
Moisture is essential to the growth of black mold, and when it is wet it is shiny in appearance.

If and when you are contemplating clean up of black mold, there are two important considerations:

1. Know what you are dealing with.
If you were told you have an animal in your house, your first question would be, “What kind of animal?” Based on the answer, you will know the best way to “suit up” for the encounter. If you know you have a kitty-cat, you may need a pair of gloves to keep from getting scratched. If you know you have a lion, you might want a whip, a chair, and a pistol just in case. Same with mold. If you are going to clean up some common allergenic molds you will need a cheap dust mask and a pair of rubber gloves. If you are going to clean up toxic mold, you will need an expensive respirator and other protective gear. Perhaps you will want to set up a containment area to keep toxic mold spores from contaminating other areas of your home. Taping off vents and duct work can help prevent the spread of toxic spores into the HVAC system as well.

2. Verify the extent of the problem.
Many of the indoor mold problems you will encounter are the direct result of water intrusion, i.e. improper drainage and irrigation, plumbing leaks, rain and condensation issues. After discovering the root of the problem and correcting it, you may be able to clean the area with bleach depending on the scope of the contamination. In the even you choose to do the clean up yourself, it is important to understand that bleach is only good for cleaning mold off of a surface. It should not be used for cleaning mold that is deeply embedded. Bleach dries too quickly to penetrate deep enough into wood or drywall to reach embedded mold, therefore, it does not always reach mold that is embedded beyond the surface. For that reason, after or instead of cleaning with bleach, use a mildewcide (not a fungicide) disinfect cleaner to penetrate deep into contaminated construction materials to kill embedded mold. After this you must take care to thoroughly dry the cleaned area. If there is any trace of mold left behind, it is only a matter of time before you will repeating the entire process. One way to be sure your clean up is effective is to have the cleaned materials re-tested by your inspector.

3. Hiring a Contractor
If you choose to have a contractor clean up the contamination, there are a couple of important matters for you to consider:

a) Only hire experience Mold Remediation Contractors. There are many fine and well established remodeling companies around who do great remodeling work but are not well experienced in mold remediation. Remodeling contractors who are not remediation specialist can make a bad situation absolutely horrible with their lack of mold experience.

b) Insist on references of customers who's jobs are at least one year old. A mold clean up job can look really great right after its finished. But if it isn't done correctly the problem can come back much worse than before within six months to a year.

c) Never allow your contractor to conduct his own post-remediation clearance testing.

PENICILLIUM:
Penicillium species have been shown to be fairly common indoors, even in clean environments, but can be problematic when indoor spore levels are higher than outdoors (Burge, 1986; Miller et al., 1988; Flannigan and Miller, 1994). Spores have the highest concentrations of mycotoxins, although the vegetative portion of the mold, the mycelium, can also contain the poison. The viability of spores is not essential to toxicity. In other words, a dead spore can still be a source of toxin.

ASPERGILLUS:
Aspergillus species are also fairly prevalent in problem buildings. This genus contains several toxigenic species, among which the most important are, A. parasiticus, A. flavus, and A. fumigatus. Aflatoxins produced by the first two species are among the most extensively studied mycotoxins. They are among the most toxic substances known, being acutely toxic to the liver, brain, kidneys and heart, and with chronic exposure, potent carcinogens of the liver. They are also teratogenic (Smith and Moss, 1985; Burge, 1986). Symptoms of acute aflatoxicosis are fever, vomiting, coma and convulsions (Smith and Moss, 1985). A. flavus is found indoors in tropical and subtropical regions, and occasionally in specific environments such as flowerpots. A. fumigatus has been found in many indoor samples. A more common aspergillus species found in wet buildings is A. versicolor, where it has been found growing on wallpaper, wooden floors, fibreboard and other building material. A. versicolor does not produce aflatoxins, but does produce a less potent toxin, sterigmatocystin, an aflatoxin precursor (Gravesen et al., 1994). While symptoms of aflatoxin exposure through ingestion are well described, symptoms of exposure such as might occur in most moderately contaminated buildings are not know, but are undoubtedly less severe due to reduced exposure. However, the potent toxicity of these agents advise that prudent prevention of exposures are warranted when levels of aspergilli indoors exceed outdoor levels by any significant amount. A. fumigatus has been found in many indoor samples. This mold is more often associated with the infectious disease aspergillosis, but this species does produce poisons for which only crude toxicity tests have been done (Betina, 1989). Recent work has found a number of tremorgenic toxins in the conidia of this species (Land et al., 1994). A. ochraceus produces ochratoxins (also produced by some penicillia as mentioned above). Ochratoxins damage the kidney and are carcinogenic (Smith and Moss, 1985).

STACHYBOTRYS:
Stachybotrys chartarum (atra) has been much discussed in the popular press and has been the subject of a number of building related illness investigations. It is a mold that is not readily measured from air samples because its spores, when wet, are sticky and not easily aerosolized. Because it does not compete well with other molds or bacteria, it is easily overgrown in a sample, especially since it does not grow well on standard media (Jarvis, 1990). Its inability to compete may also result in its being killed off by other organisms in the sample mixture. Thus, even if it is physically captured, it will not be viable and will not be identified in a cultured sample media, even though it is present in the environment and those who breathe it can have toxic exposures. For that reason, it is prudent to take a surface sample, such as tape or bulk, whenever evidence of black mold is found. This organism has a high moisture requirement, so it grows vigorously where moisture has accumulated from roof or wall leaks, or chronically wet areas from plumbing leaks. It is often hidden within the building envelope and inside wall cavities. When Stachybotrys is found in an air sample, it should be searched out in walls or other hidden spaces, where it is likely to be growing in abundance. This mold has a very low nitrogen requirement, and can grow on wet hay and straw, paper, wallpaper, ceiling tiles, carpets, insulation material (especially cellulose-based insulation).

Stachybotrys is a specific family (genus) of mold that is present in the environment. Out-of-doors stachybotrys molds help to decay organic matter. One particular species known as stachybotrys atra (sometimes known as stachybotrys chartarum) is prone to growth indoors. This mold is normally dark brown or black in color. It can look slimy, sooty, or even like grayish white strands depending on the amount of moisture available and the length of time it has been growing. It is important to remember that many other common indoor molds can look similar to stachybotrys (including cladosporium, aspergillus, alternaria, and drechslera), so testing is critical to conclusively identify stachybotrys in a building. Stachybotrys mold needs the proper conditions in order to grow, including moisture, a nutrient source, temperature, and time. Standing water or a relative humidity of 90% or higher is necessary for stachybotrys to start germination and grow. However, once the stachybotrys begins to grow it can continue to propagate even if the surface water source dries up and the relative humidity falls to 70%. The nutrient sources that best support stachybotrys are those with a high cellulose content. As such, stachybotrys thrives on natural materials such as hay, straw, and wood chips, as well as building materials such as ceiling tile, drywall, paper vapor barriers, wallpaper, insulation backing, cardboard boxes, and paper files. Stachybotrys survives a wide variation in temperature and grows most proficiently in temperatures that humans consider warm to moderately hot. It tends to develop more slowly than many other molds—one to two weeks after moisture intrusion as compared to one to two days for molds like aspergillus, penicillium, or cladosporium. Despite its slow start, stachybotrys usually develops into the dominant mold if the conditions are favorable, eventually crowding out other mold types that may have colonized the material first.

Like many other molds, stachybotrys can spread both through the generation of spores and the growth of root-like structures called mycelia. Stachybotrys spores grow in clusters at the end of stem-like structures known as hyphae. The spores do not easily disperse into the air if the colonized material is wet, as the spores are held together by a sticky/slimy coating. Distribution through the air is possible when the mold dries out or is disturbed. Because of this danger of the airborne dispersion of spores, all cleaning and removal of stachybotrys mold should be done using appropriate controls.

Stachybotrys has a high moisture requirement, so it grows vigorously where moisture has accumulated from roof or wall leaks, or chronically wet areas from plumbing leaks. It is often hidden within the building envelope. When S. chartarum is found in an air sample, it should be searched out in walls or other hidden spaces, where it is likely to be growing in abundance. This mold has a very low nitrogen requirement, and can grow on wet hay and straw, paper, wallpaper, ceiling tiles, carpets, insulation material (especially cellulose-based insulation). It also grows well when wet filter paper is used as a capturing medium.

S. chartarum has a well-known history in Russia and the Ukraine, where it has killed thousands of horses, which seem to be especially susceptible to its toxins. These toxins are macrocyclic trichothecenes. They cause lesions of the skin and gastrointestinal tract, and interfere with blood cell formation. (Sorenson, 1993). Persons handling material heavily contaminated with this mold describe symptoms of cough, rhinitis, burning sensations of the mouth and nasal passages and cutaneous irritation at the point of contact, especially in areas of heavy perspiration, such as the armpits or the scrotum (Andrassy et al., 1979).

One case study of toxicosis associated with macrocyclic trichothecenes produced by S. chartarum in an indoor exposure, has been published (Croft et al., 1986), and has proven seminal in further investigations for toxic effects from molds found indoors. In this exposure of a family in a home with water damage from a leaky roof, complaints included (variably among family members and a maid) headaches, sore throats, hair loss, flu symptoms, diarrhea, fatigue, dermatitis, general malaise, psychological depression. (Croft et al, 1986; Jarvis, 1995).