Moldy Claims - Mycotoxins
Mycotoxins: Basic Evidence
Mycotoxins Generally
Carcinogenic Mycotoxins
Organic Dust Toxic Syndrome
Mycotoxins Generally
Many, but not all, molds are capable of producing another category of substances that are blamed for a multitude of problems and thus are the source of much of the alarm associated with molds. Called “mycotoxins,” those substances are not required in the complete life cycle of the mold and are produced unpredictably even by those species (“toxigenic species”) that are capable of producing them. A variety of environmental factors, including age of the colony, available nutrition and water, and competition with other species, influence whether mycotoxins are produced at all and, if produced, what kinds and to what extent. The wide variability on the part of toxigenic species to produce, or fail to produce, mycotoxins has been shown both in laboratory studies and by testing naturally growing environmental samples. Thus, even if a species of mold that is capable of producing mycotoxins grows in an indoor environment, it does not necessarily follow that mycotoxins will be produced.
Unlike microbial volatile organic compounds, mycotoxins do not evaporate into the air but remain in the mold colony where they are produced and in the substrate the colony grows upon. Also unlike microbial volatile organic compounds, mycotoxins do not dissipate when active mold growth ceases. If mycotoxins are produced, they remain in place even after the mold is inactive or dead. These facts mean that when mycotoxins are produced, human exposure requires either direct skin contact with or ingestion (eating) of the moldy material, or inhalation (breathing in) of particles in the air that carry mycotoxins with them. In homes, offices and schools, only the inhalation route of exposure has potential to be meaningful. See Hendry and Cole, supra note 20; Pasanen, A.-L. et al., Laboratory experiments on membrane filter sampling of airborne mycotoxins produced by Stachybotrys atra Corda, Atmospheric Environment 27A(1):9-13 (1993); Schiefer, H.B. Mycotoxins in indoor air: a critical toxicological viewpoint, Indoor Air 90:167-172 (1990); WHO, Selected mycotoxins: ochratoxins, trichothecenes, ergot, Environmental Health Criteria 105 (World Health Organization (WHO), Geneva, Switzerland 1990), at 30, 77, 169.
Most of what is known about the health effects of mycotoxins comes from veterinary and human illnesses caused by eating moldy foods. Episodes of acute toxicity are infrequent in developed nations, but experience demonstrates that mycotoxins consumed in the diet can cause severe, even fatal, health effects. The precise dose (amount) of mycotoxin required to produce these health effects is not known, but it seems clear that the dose in these episodes has been very high. See Ciegler, A. and Bennett, J.W., Mycotoxins and mycotoxicoses, BioScience 30(8):512-515 (1980); Ciegler, A. et al., supra note 20; Drobotko, V.G. Stachybotryotoxicosis: a new disease of horses and humans, Am. Rev. Soviet Med. 2(3):238-242 (1945); Forgacs, J. and Carll, W.T. Mycotoxicoses, Adv. Vet. Sci. 7:273-382 (1962 ); Pohland, A.E. Mycotoxins in review, Food Addit. Contam. 10(1):17-28 (1993).
Andersen, B. et al., Characterization of Stachybotrysfrom water-damaged buildings based on morphology, growth, and metabolic production, Mycologia 94(3):392-403 (2002); Burge, H.A., Fungi: toxic killers or unavoidable nuisances? Ann. Allergy Asthma Immunol. 87(6 Suppl 3):52-56 (2001); Ciegler, A. et al. Mycotoxins: occurrence in the environment, 1-50 in Mycotoxins and N-nitroso compounds: environmental risks, Vol. I,(R.C. Shank, ed.) (CRC Press, Inc., Boca Raton, FL 1981); Hendry, K.M. and Cole, E.C., A review of mycotoxins in indoor air, J. Toxicol. Environ. Health 38(2):183-198 (1993); Jarvis, B.B. et al., Study of toxin production by isolates of Stachybotrys chartarum and Memnoniella echinata isolated during a study of pulmonary hemosiderosis in infants, Appl. Environ. Microbiol. 64(10): 3620-3625 (1998); Nikulin, M., et al., Stachybotrys atra growth and toxin production in some building materials and fodder under different relative humidities, Appl. Environ. Microbiol. 60(9):3421-3424 (1994); NRC, Protection against trichothecene mycotoxins, National Research Council (NRC) (National Academy Press, Washington, D.C. 1983); Rao, C.Y., Toxigenic fungi in the indoor environment 46-1 to 46-17 in Indoor Air Quality Handbook(J.D. Spengler et al., eds.) (McGraw Hill, New York, NY 2001); Smith, J.E. et al., Cytotoxic fungal spores in the indoor atmosphere of the damp domestic environment, FEMS Microbiol. Lett. 79(1-3):337-343 (1992); Tobin, R.S. et al., Significance of fungi in indoor air: report of a working group, Can. J. Public Health 78(Suppl 2):S1-S14 (1987); Tuomi, T. et al., Mycotoxins in crude building materials from water-damaged buildings, Appl. Environ. Microbiol. 66(5):1899-1904 (2000); Vesper, S.J. et al., Hemolysis, toxicity, and randomly amplified polymorphic DNA analysis of Stachybotrys chartarum strains, Appl. Environ. Microbiol. 65(7):3175-3181 (1999).
Even if cancer-causing mycotoxins were being produced by molds growing indoors, the exposure levels and therefore any risk of cancer would be very low, and certainly lower than that encountered in dusty agricultural and grain-handling environments. Epidemiologic studies of workers with occupational inhalation exposure to dusts containing aflatoxin have suggested an increased cancer risk, See Hayes, R.B. et al., Aflatoxin exposures in the industrial setting: an epidemiological study of mortality, Food Chem. Toxicol. 22(1):39-43 (1984); Olsen, J.H. et al., Cancer risk and occupational exposure to aflatoxins in Denmark, Br. J. Cancer 58(3):392-396 (1988). but these studies have had weak predictive power and were not in agreement on the specific kinds of cancer they associated with exposure. The International Agency for Research on Cancer (IARC) has evaluated the evidence pertaining to numerous mycotoxins but only the aflatoxins have been classified as human carcinogens, while others were either “possibly” carcinogenic to humans or could not be classified as to cancer risk. IARC, Some Traditional Herbal Medicines, Some Mycotoxins, Naphthalene and Styrene 82 (2002); IARC, Some Naturally Occurring Substances: Food Items and Constituents, Heterocyclic Aromatic Amines and Mycotoxins 56 (1993).
Similarly, the U.S. National Toxicology Program classifies aflatoxin as “known” to cause human cancer and ochratoxin A as “reasonably anticipated” to cause human cancer. See Report on Carcinogens, U.S. Department of Health and Human Services, Public Health Service, National Toxicology Program (2002).
Agricultural workers who inhale high concentrations of dusts generated from silage and stored grains sometimes experience the acute illnesses “pulmonary mycotoxicosis,” “grain fever,” “silo unloader’s lung,” or “organic dust toxic syndrome.” Workers experience these illnesses, a high fever with breathing difficulty, following hours of heavy dust exposure. The exact cause of these illnesses has not been established, but they appear not to be allergic in nature. The mixed dusts the farm workers are exposed to contain the organic debris from the stored agricultural products along with fungi and bacteria and their associated mycotoxins, endotoxins and glucans. Dust exposures associated with these illnesses are high enough to obscure clear vision, and spore counts have been measured in the range of 1 billion to 10 billion spores per cubic meter of air, more than 1000 times higher than the most extreme conditions encountered in a moldy indoor environment. See Brinton, W.T. et al. An outbreak of organic dust toxic syndrome in a college fraternity, JAMA 258(9):1210-1212 (1987); Di Paolo, N. et al., Inhaled mycotoxins lead to acute renal failure, Nephrol Dial Transplant 9 Suppl 4:116-120 (1994); Emanuel, D.A. et al., Pulmonary mycotoxicosis, Chest 67(3):293-297 (1975); Lacey and Crook, supra note 8; Malmberg, P. et al., Exposure to microorganisms associated with allergic alveolitis and febrile reactions to mold dust in farmers, Chest 103(4):1202-1209 (1993); May, J.J. et al., A study of silo unloading the work environment and its physiologic effects, Am. J. Ind. Med. 10:318 (1986); Preventing organic dust toxic syndrome, NIOSH Alert National Institute for Occupational Safety and Health (NIOSH), NIOSH Publication No. 94-102 (1994); Pratt, D.S. and May, J. J. Feed-associated respiratory illness in farmers, Arch. Environ. Health 39(1):43-48 (1984).
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