|Enviromental Protection Agency - Toxic Mold|
Children's Health Initiative: Toxic MoldOutbreaks of the fungi Stachybotrys chartarum (S. chartarum) are under investigation for an association with the deaths of infants in Cleveland, Ohio, and serious health problems in other areas of the U.S. Although not widely found, Stachybotrys chartarum has been studied for the last 20 years. The following is documented.
The following is background information, current research, and research needs.
The past twenty years have brought the recognition that an important factor in the health of people in indoor environments is the dampness of the buildings in which they live and work. Furthermore, it is now appreciated that the principal biology responsible for the health problems in such building are fungi rather than bacteria or viruses. Although fungi in this context have been traditionally viewed as allergens (and, in unusual circumstances, pathogens), data have accumulated to show that the adverse health effects resulting from inhalation of fungal spores are due to multiple factors. One factor associated with certain fungi is small molecular toxins (mycotoxins) produced by these fungi. Traditionally, mycotoxins are held to be important in human and animal health because of their production by toxigenic-fungi-associated food and feed. However, mycotoxins tend to concentrate in fungal spores, and thus present a potential hazard to those inhaling airborne spores. Toxigenic spores strongly affect alveolar macrophage function and pose a threat to those exposed. Reports have indicated that Stachybotrys chartarum, Aspergillus versicolor, and several toxigenic species of Penicillium are potentially hazardous, especially when the air-handling systems have become heavily contaminated.
Perhaps the most hazardous of the toxigenic fungi found in wet buildings is S. chartarum, a fungus known to produce the very potent cytotoxic macrocyclic trichothenes along with a variety of immunosuppressants and endothelin receptor antagonists mycotoxins. This fungus was investigated for its association with the serious health problems of a family living in a water-damaged home in Chicago and has been implicated in several cases of building-related illness. A cluster of cases of acute pulmonary hemorrhage/hemosiderosis was reported in Cleveland, Ohio, where 27 infants from homes that suffered flood damage became sick (nine deaths) with the illness starting in January 1993.
Although a great deal of literature describes fungi growing on a variety of building and structural materials that resulted in contamination of buildings and sick individuals, information on what environmental conditions permitted their growth has been limited. Starting in 1991, EPA has conducted research into the environmental conditions that permit building material colonization by fungi and the subsequent development of contamination sources. The focus has been on evaluating material properties, climate conditions, and microorganism interactions that contribute to materials serving as microecological habitats fostering fungal colonization, amplification, and dissemination. To better understand when fungal growth occurs, we developed a static chamber method for evaluating the various environmental conditions. These chambers were designed to provide controlled environments that can simulate differing conditions of temperature and relative humidity that the materials might be exposed to in a building. Over the last five years, a variety of building materials and fungi have been evaluated using this static chamber method and it is in the process of being transitioned to a Standard Guide for ASTM International.
One of the most significant technical results from this project is that the effect of relative humidity is indirect and that very small amounts of moisture, well below those commonly cited, will permit growth. The amount of moisture required for fungal growth can vary depending upon the material and the organism. S. chartarum requires high levels of moisture (effective relative humidity required for S. chartarum growth would be 94%) and cellulose-containing materials for growth.
Biological agents do not have to be alive to cause allergic, toxic, or inflammatory responses; however, the organisms that are sources of indoor biological contamination are living, multiplying organisms. One approach to limiting exposure is to reduce the levels of biological contamination. Antimicrobial agents, called fungicides or biocides, have long been used to control, prevent, and remediate microbial growth for many different applications in the environment. The potential for antimicrobials and antimicrobial treatments including encapsulants to reduce exposure to S. chartarum will be investigated by EPA. Both static and dynamic chamber experiments will be run using new and used building materials with and without antimicrobial treatment and encapsulants/sealants.
Aerosolization/Emission of Fungal Spores
Although it is known that fungi growing on surfaces are capable of generating particulate (spore) and gas phase (VOC) emissions, the actual impact on the indoor environment has not been determined quantitatively for most organisms because there is little information on the dynamics of fungal spore release from the contaminated surfaces. For example, what is the significance of 10 m2 of Stachybotrys chartarum growing on ceiling tile? That fungi growing or deposited on surfaces become aerosolized is well known. Indeed, sporulating fungi depend on aerosol emission for propagation. Recent experiments with A. versicolor and P. chrysogenum have started to elucidate some of the relationships between commonly measured indoor environmental parameters and fungal emissions. Documenting the production of spores and mycotoxins by S. chartarum will assist in determining the magnitude of the health threat in the indoor environment that is posed by these emissions.
Many factors affect the emission and dissemination of fungi into the indoor air from the contaminated source. A clear understanding of the factors, such as activity (translational energy), air flow, and relative humidity, that enable and/or promote emission is required. High humidity is important for those active release mechanisms that depend on rupture of turgid cells, while tissue desiccation in low humidity is important to another class of release mechanisms. The reported experiments have generally been conducted under equilibrium conditions in simple systems, however, and the impact of the indoor microenvironment has not been considered.
The objective of this work will be the measurement of emission factors for fungi growing on common building materials. To that end, we will investigate the emissions and dissemination characteristics of a variety of S. chartarum on different materials under differing conditions (i.e., humidity, temperature, air-flow, mechanical factors). The experiments will be performed using the Dynamic Microbial Test Chamber. Tests will be conducted under known, favorable growth conditions and under known flow conditions. Environmental conditions (temperature, relative humidity, and air flow rate) will be controlled, and experiments will be conducted at a range of conditions. Air samples will be collected using real-time instruments (optical particle counters, or OPCs) or integrated samples such as filter mass samples, microbial filters, or microbial impactors. The measurements will be made periodically, depending on the organism's growth rate, emission rate, and type of measurement. Surface microbial samples will also be collected directly or through the glove wall. Contact plates may be appropriate for some materials, while others may be better sampled by pre-cutting portions of the material to allow extraction. Amounts appropriate to the emission will be selected. Particle measurements will be conducted at multiple locations within the chamber to quantitate dispersion.
Model to Predict Indoor Air Quality (IAQ) Impact
Chamber studies at specified environmental conditions will yield emission rates unique for S. chartarum. However, to relate the emission rates to actual exposure, an IAQ model will be used which can estimate concentration and potential exposure, as is done with other indoor air contaminants. The model to be used will be the RISK IAQ Model for Windows, a completely mixed room model incorporating source/sink behavior that can generate concentration and exposure estimates as a function of time. The ventilation flows (none or limited outdoor air up to 5%) and pollutant emission rates can be set as desired for each modeled room. A variety of building types will be modeled, from a home completely sealed or with average air exchange rates to a centralized HVAC system in an apartment environment.
Concentration profiles and exposure levels will be calculated for an infant, child, and adult. Once the emission rates are known, the RISK Model is a useful tool in predicting exposure.
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