By Kelly A. Reynolds, MSPH, Ph.D.
In the point-of-use/point-of-entry (POU/POE) industry, questions frequently arise regarding the relationship of pathogenic fungi and drinking water. Although fungi are ubiquitous in the environment—found in soil, air and water—drinking water is typically not a direct link to pathogenic fungal infections but rather an indirect contributor, since water is a key ingredient in the successful proliferation of the organisms.
Background on fungi
Fungi include yeast, mold, mildew and mushrooms. These organisms, commonly found throughout the world, are estimated to compose approximately 25 percent of the Earth’s biomass. While that may seem high, keep in mind that these often play an important role in decomposition of dead organic matter from trees to animals. Nearly 100,000 species have been identified and scientists estimate that another 1.4 million species are in existence. Fungi have adapted to grow over a wide range of environmental niches and are able to colonize just about any surface, provided moisture is present.
Most fungi reproduce via the production of microscopic spores, from which branching structures, or hyphae, develop. Atop the hypha, a cup-like structure—known as the sporocarp—holds the reproductive mass of spores. Fungal spores vary in size from 1 to 100 microns and enable fungi to survive harsh conditions whether they travel or lie dormant. Spores are very lightweight and can easily be dispersed by air. Fungal spores are common in the environment, averaging approximately 1-to-2 × 104 per cubic meter of outdoor air, varying greatly due to season or geographical location.
Fungi are also beneficial organisms, used to make medicines and industrially important chemicals or serve as an indirect or direct food source. Relative to the number of fungi identified, few are pathogenic to animals, plants and humans. Approximately 200 fungi are known to cause diseases in vertebrates.
Prevalence of indoor molds
Entering homes via open doors and windows, or on clothing, shoes and pets, molds are most problematic when they colonize indoor environments, growing only in the presence of moisture. Every home is subject to moisture problems, either due to leakage (flooding, pipes bursting, overflows) or routine activities (showering, watering indoor plants, cooking). See Table 1 for detail. According to 1998 U.S. Census Bureau data, 10.9 million U.S. homes—or 16 percent—had leakage from inside during the last 12 months and 16.9 million (21 percent) had leakage from outside. It’s estimated that approximately 30 percent of all buildings will have indoor air quality problems associated with mold during their existence. Molds are easily distributed indoors due to natural breezes, heating/ventilation and cooling systems, humidifiers and active movement. In addition to the adverse health effects, structural damage due to mold colonization indoors can be devastating.
Molds are known to cause a variety of health effects, including mild skin infections to severe allergic reactions to lung disease, cancer, organ failure, neurological disorders and death. In addition, molds are also suspected of being associated with Sudden Infant Death Syndrome (SIDS), stillbirths, infertility problems and hormonal imbalances (see Table 2). Many fungi are problematic whether the organisms are living or dead. Mold toxins are so potent that most of the research in this area has been conducted by the U.S. Department of Defense due to the concern for their use as biological warfare agents.
Like plants, fungi have cell walls, primarily composed of polysaccharides, with glucan being the most prevalent component. Cell wall components, called exopolysaccharides (EPS), can cause allergenic reactions in humans. In addition, as a by-product of fungal growth, some fungi during their metabolic processes produce chemicals known as microbial volatile organic compounds (MVOCs) and mycotoxins. Secondary fungal metabolites—such as EPS, glucan, MVOCs and mycotoxins—have all been associated with human disease.
The most common health effect of mold is allergic disease. Allergic diseases have greatly increased worldwide over the last 30 years. More than 50 million Americans (or about 20 percent of the total population) suffer from hay fever, asthma or other allergic diseases. The allergy and asthma “epidemic” costs an estimated $6.5 billion in medical and indirect costs with $3.5 million to lost workdays and $2 million to school days each year. Adverse effects associated with mold may be immediate or delayed for years. Almost all microbial allergens are fungal in origin and any one fungal species may produce dozens of allergens.
The most common indoor molds are Cladosporium, Penicillium, Aspergillus (primarily associated with allergic reactions), headaches, itchy eyes, rashes and respiratory problems, but also known to produce mycotoxins, resulting in chemical toxigenic responses. Perhaps the most disconcerting indoor mold is Stachybotrys chartarum (aka S. atra). This mold, even in small doses, is associated with severe, often irreversible neurologic conditions, lung disease and death. Currently, there’s no accurate information about how often Stachybotrys chartarum is found in buildings and homes. While it’s less common than other mold species, it isn’t considered rare.
Everyone is potentially at risk of pathogenic fungi and many fungal infections don’t respond to treatment and can have fatal consequences. In addition, immunocompromised populations (i.e., children, elderly and the chronically ill) are at increased risk for mold infections and a more serious outcome of disease. Early exposure of children to molds may predispose them to chronic health problems in the future.
Minimizing mold exposures
Although it’s recognized that fungal spores cause allergenic reactions, little is known about exposure thresholds, survival and proliferation factors in the indoor environment. The level of mold needed to make people sick varies with the individual. For some, a relatively small number of spores can illicit health problems, for others it takes an extremely large dose. In general, if the mold is visible or odiferous, it should be eliminated.
Although the U.S. Environmental Protection Agency (USEPA) has consistently ranked indoor air pollution among the top five environmental risks to public health, there are currently no federal regulations or standards for airborne mold contaminants. Indoor mold and moisture represent a public health issue that’s inadequately addressed by building, health or housing codes.
As a rule, fungal growth in homes or businesses shouldn’t be ignored and measures of removal and decontamination need to be applied at the first sign of contamination. The most important primary need for elimination of mold in buildings is to remove the moisture source and reduce the contaminant via routine cleaning and disinfecting.
In more than 65 percent of surveyed homes in the United States, residents report they live in a damp environment. Dampness has been a significant factor in the prevalence of respiratory and other illnesses in children. Preventing a home from becoming moldy is far easier (and cheaper) than trying to eliminate a fungal colonization. A 10 percent household bleach solution appears to be sufficient for disinfecting mold on indoor surfaces. Numerous commercial products are also widely available for disinfecting molds on non-porous surfaces. Carpeting and other porous material should be carefully removed. Exposure to molds during remediative procedures can be 10-to-1,000 times higher than background levels. In severe situations, respirators and protective clothing may be necessary. Rapid cleanup of water-damaged homes can help to minimize the growth and spread of fungal contaminants as can routine and diligent house cleaning.
Drinking water isn’t directly associated with pathogenic mold infections. Conventional methods of municipal drinking water treatment aimed at removing protozoan, viral and bacterial pathogens are also adequate for mold removal. By-products of such treatments, however, may be associated with adverse effects either due to aesthetic offense and/or impaired health (i.e., the presence of residual chlorine disinfectant). Many POU treatment systems are beneficial not only for the direct removal of waterborne human pathogens but also for the removal of prior chemical treatments.
About the author
Dr. Kelly A. Reynolds is a research scientist at the University of Arizona with a focus on development of rapid methods for detecting human pathogenic viruses in drinking water. She holds a master of science degree in public health (MSPH) from the University of South Florida and doctorate in microbiology from the University of Arizona. Reynolds also has been a member of the WC&P Technical Review Committee since 1997.
EXTRA: Mold discovered in bottled water
Elan Natural Waters, of Blairsville, Ga., voluntarily recalled “Elan Natural Waters Natural Drinking Water” in late August after laboratory tests indicated the presence of mold and yeast. Union County Bottlers, of Blairsville, bottled the products for the company. The water was packaged in 500 milliliter bottles with pull-up tops. All bottles have package codes that begin with 1FAF1.