Coreen A. Robbins

Health Effects of Mycotoxins in Indoor Air: A Critical Review

Industrial hygienists (IHs) are called upon to investigate exposures to mold in indoor environments, both residential and commercial. Because exposure standards for molds or mycotoxins do not exist, it is important for the industrial hygienist to have a broad knowledge of the potential for exposure and health effects associated with mold in the indoor environment. This review focuses on the toxic effects of molds associated with the production of mycotoxins, and the putative association between health effects due to mycotoxin exposure in the indoor environment. This article contains background information on molds and mycotoxins, and a brief summary and review of animal exposure studies, case reports, and epidemiological studies from the primary literature concerning inhalation of mycotoxins or potentially toxin-producing molds. The relevance of the findings in the reviewed articles to exposures to mold in indoor, non-agricultural environments is discussed. Although evidence was found of a relationship between high levels of inhalation exposure or direct contact to mycotoxin-containing molds or mycotoxins, and demonstrable effects in animals and health effects in humans, the current literature does not provide compelling evidence that exposure at levels expected in most mold-contaminated indoor environments is likely to result in measurable health effects. Even though there is general agreement that active mold growth in indoor environments is unsanitary and must be corrected, the point at which mold contamination becomes a threat to health is unknown. Research and systematic field investigation are needed to provide an understanding of the health implications of mycotoxin exposures in indoor environments.

Risk from inhaled mycotoxins in indoor office and residential environments.

Mycotoxins are known to produce veterinary and human diseases when consumed with contaminated foods. Mycotoxins have also been proposed to cause adverse human health effects after inhalation exposure to mold in indoor residential, school, and office environments. Epidemiologic evidence has been inadequate to establish a causal relationship between indoor mold and nonallergic, toxigenic health effects. In this article, the authors model a maximum possible dose of mycotoxins that could be inhaled in 24 h of continuous exposure to a high concentration of mold spores containing the maximum reported concentration of aflatoxins B1 and B2, satratoxins G and H, fumitremorgens B and C, verruculogen, and trichoverrols A and B. These calculated doses are compared to effects data for the same mycotoxins. None of the maximum doses modeled were sufficiently high to cause any adverse effect. The model illustrates the inefficiency of delivery of mycotoxins via inhalation of mold spores, and suggests that the lack of association between mold exposure and mycotoxicoses in indoor environments is due to a requirement for extremely high airborne spore levels and extended periods of exposure to elicit a response. This model is further evidence that human mycotoxicoses are implausible following inhalation exposure to mycotoxins in mold-contaminated home, school, or office environments.

End User Exposures to Man-Made Vitreous Fibers: I. Installation of Residential Insulation Products

Abstract An investigation was undertaken to develop a comprehensive characterization of end user exposures to residential man-made vitreous fiber insulation products in terms useful for future study of potential health outcomes. Nearly 1200 air samples were collected and analyzed gravimetrically or by phase contrast microscopy or scanning electron microscopy to describe worker exposure in eight homogeneous exposure groups defined by man-made vitreous fiber product and occupation. These samples represent the exposure of 99 different workers insulating 107 different houses in 11 states in the eastern and central United States. Gravimetric and fiber count exposure concentrations are reported in terms of task length and full shift time-weighted averages (TWAs). Results of this study indicate mean task length airborne fiber concentrations determined by phase contrast microscopy (PCM) using the National Institute for Occupational Safety and Health (NIOSH) Method 7400 “B” rules to be less than 1.0 fibers/cm3 for...

The Concentration of No Toxicologic Concern (CoNTC) and Airborne Mycotoxins

The threshold of toxicologic concern (TTC) concept was developed as a method to identify a chemical intake level that is predicted to be without adverse human health effects assuming daily intake over the course of a 70-yr life span. The TTC values are based on known structure–activity relationships and do not require chemical-specific toxicity data. This allows safety assessment (or prioritization for testing) of chemicals with known molecular structure but little or no toxicity data. Recently, the TTC concept was extended to inhaled substances by converting a TTC expressed in micrograms per person per day to an airborne concentration (ng/m3), making allowance for intake by routes in addition to inhalation and implicitly assuming 100% bioavailability of inhaled toxicants. The resulting concentration of no toxicologic concern (CoNTC), 30 ng/m3, represents a generic airborne concentration that is expected to pose no hazard to humans exposed continuously throughout a 70-yr lifetime. Published data on the levels of mycotoxins in agricultural dusts or in fungal spores, along with measured levels of airborne mycotoxins, spores, or dust in various environments, were used to identify conditions under which mycotoxin exposures might reach the CoNTC. Data demonstrate that airborne concentrations of dusts and mold spores sometimes encountered in agricultural environments have the potential to produce mycotoxin concentrations greater than the CoNTC. On the other hand, these data suggest that common exposures to mycotoxins from airborne molds in daily life, including in the built indoor environment, are below the concentration of no toxicologic concern.

Controlled Study of Mold Growth and Cleaning Procedure on Treated and Untreated Wet Gypsum Wallboard in an Indoor Environment

The basis for some common gypsum wallboard mold remediation practices was examined. The bottom inch of several gypsum wallboard panels was immersed in bottled drinking water; some panels were coated and others were untreated. The panels were examined and tested for a period of 8 weeks. This study investigated: (a) whether mold growth, detectable visually or with tape lift samples, occurs within 1 week on wet gypsum wallboard; (b) the types, timing, and extent of mold growth on wet gypsum wallboard; (c) whether mold growth is present on gypsum wallboard surfaces 6 inches from visible mold growth; (d) whether some commonly used surface treatments affect the timing of occurrence and rate of mold growth; and (e) if moldy but dried gypsum wallboard can be cleaned with simple methods and then sealed with common surface treatments so that residual mold particles are undetectable with typical surface sampling techniques. Mold growth was not detected visually or with tape lift samples after 1 week on any of the wallboard panels, regardless of treatment, well beyond the 24–48 hours often mentioned as the incubation period. Growth was detected at 2 weeks on untreated gypsum. Penicillium, Cladosporium, and Acremonium were early colonizers of untreated panels. Aspergillus, Epicoccum, Alternaria, and Ulocladium appeared later. Stachybotrys was not found. Mold growth was not detected more than 6 inches beyond the margin of visible mold growth, suggesting that recommendations to remove gypsum wallboard more than 1 foot beyond visible mold are excessive. The surface treatments resulted in delayed mold growth and reduced the area of mold growth compared with untreated gypsum wallboard. Results showed that simple cleaning of moldy gypsum wallboard was possible to the extent that mold particles beyond “normal trapping” were not found on tape lift samples. Thus, cleaning is an option in some situations where removal is not feasible or desirable. In cases where conditions are not similar to those of this study, or where large areas may be affected, a sample area could be cleaned and tested to verify that the cleaning technique is sufficient to reduce levels to background or normal trapping. These results are generally in agreement with laboratory studies of mold growth on, and cleaning of, gypsum wallboard.

Growth of Mold on Fiberglass Insulation Building Materials—A Review of the Literature

An exhaustive search of the literature on the growth of mold on fiberglass insulation materials was conducted. Because of the paucity of published material, both peer-reviewed and non-peer-reviewed articles were included. The literature indicates that fiberglass can serve as a support matrix for the collection of debris which, when moist, have the capability of supporting the growth of mold. Further, binding and paper-based moisture barriers from fiberglass resins are also capable of supporting the growth of mold when moist.

End-user exposures to synthetic vitreous fibers: II. Fabrication and installation fabrication of commercial products

This article summarizes the results of exposure monitoring conducted during the installation and fabrication of commercial synthetic vitreous fiber (SVF) products. Included in this investigation were fiberglass duct insulation and construction applications (duct board, duct liner, and duct wrap), pipe and vessel insulation, batt insulation for prefabricated homes, and general fiberglass products. Commercial mineral wool products sampled as a part of this investigation included ceiling tiles, building safing, and loose insulation for prefabricated homes. A total of 520 valid air samples were collected as a part of this investigation and were analyzed using gravimetric, phase contrast microscopy (PCM), or scanning electron microscopy (SEM). Airborne fiber-size distributions were also determined for a subset of samples collected for SEM analysis. As a result of the task-based sampling strategy used in this study, sample times reflect exposures over the time the person was actually engaged in SVF-related work activities, and exposure results are therefore presented as task-length averages (TLAs). Thirty-five total dust samples were collected as a part of this investigation, resulting in 14 TLAs ranging from 0.3 to 7.6 mg/m3. A total of 125 PCM-based TLAs were collected, with the mean TLA time for all product and occupation categories ranging from 277 to 443 minutes. The mean PCM-based TLAs for all product/occupations were below 1.0 f/cm3, ranging from 0.04 to 0.68 f/cm3. A total of 116 SEM TLAs were determined. Average SEM-based TLA concentrations were slightly lower than the PCM-based estimates and ranged from <0.01 to 0.16 f/cm3. The geometric mean fiber diameters for commercial products and occupations sampled as a part of the investigation ranged from 0.8 microm to 1.9 microm. Geometric mean fiber length varied by a factor of approximately three, ranging from 9.5 microm to 29.5 microm.

Comparison of Size Characteristics of Fibers Found on Sample Filters and Cassette Cowls from Personal Samples of Airborne Man-Made Mineral Fibers

Abstract National Institute for Occupational Safety and Health Method 7400 is commonly used to evaluate airborne exposures to man-made mineral fibers (MMMFs). Although recent evidence suggests that current methods for collecting air samples may be biased due to fiber deposition on the inside of the sampling-cassette extension cowl, few data are available on the mechanism of deposition, the number of fibers deposited on the cowl, or potential bias in size selection associated with this deposition. The length and diameter distributions of fiber populations collected on the air-sample filters were compared to those deposited on the inside of the electrically conductive extension cowl. The samples were collected during insulation of residential buildings with pneumatically conveyed loose-fill insulation. Two different filters recommended for sample collection in the World Health Organization Reference Method for MMMFs were used. It was determined that a significantly different fiber-size distribution is deriv...

The effect of vapor polarity and boiling point on breakthrough for binary mixtures on respirator carbon

This research evaluated the effect of the polarity of a second vapor on the adsorption of a polar and a nonpolar vapor using the Wheeler model. To examine the effect of polarity, it was also necessary to observe the effect of component boiling point. The 1% breakthrough time (1% tb), kinetic adsorption capacity (W(e)), and rate constant (kv) of the Wheeler model were determined for vapor challenges on carbon beds for both p-xylene and pyrrole (referred to as test vapors) individually, and in equimolar binary mixtures with the polar and nonpolar vapors toluene, p-fluorotoluene, o-dichlorobenzene, and p-dichlorobenzene (referred to as probe vapors). Probe vapor polarity (0 to 2.5 Debye) did not systematically alter the 1% tb, W(e), or kv of the test vapors. The 1% tb and W(e) for test vapors in binary mixtures can be estimated reasonably well, using the Wheeler model, from single-vapor data (1% tb +/- 30%, W(e) +/- 20%). The test vapor 1% tb depended mainly on total vapor concentration in both single and binary systems. W(e) was proportional to test vapor fractional molar concentration (mole fraction) in mixtures. The kv for p-xylene was significantly different (p < or = 0.001) when compared according to probe boiling point; however, these differences were apparently of limited importance in estimating 1% tb for the range of boiling points tested (111 to 180 degrees C). Although the polarity and boiling point of chemicals in the range tested are not practically important in predicting 1% tb with the Wheeler model, an effect due to probe boiling point is suggested, and tests with chemicals of more widely ranging boiling point are warranted. Since the 1% tb, and thus, respirator service life, depends mainly on total vapor concentration, these data underscore the importance of taking into account the presence of other vapors when estimating respirator service life for a vapor in a mixture.