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Detection of gaseous effluents and by-products of fungal growth that affect environments (RP-1243).

INTRODUCTION

It is well known that fungal growth produces emissions as a result of secondary metabolic processes (Horner and Miller 2003). These microbial volatile organic compounds (MVOCs) represent a variety of chemical classes including alcohols, amines, aldehydes, ketones, sulfides, and many other hydrocarbons (Claeson et al. 2006; Lancker et al. 2008). Therefore, in order to effectively apply MVOC analysis to building investigations, MVOCs that are identified as mold-indicators must be unique. In other words, the MVOCs should not be among the hundreds of common chemicals that emit from building materials and consumer products but should be specific indicators of mold growth. While the literature contains studies that have been performed to identify MVOC emissions on building materials contaminated with mold, many of them do not reference the use of un-inoculated materials (negative controls); thus, it is not clear that these measured emissions are from the mold itself. Also critical to the success of a MVOC sampling paradigm are parameters associated with MVOC levels such as ventilation rates and amounts of mold growth; previous studies suggest that indoor emissions may be diluted too quickly to reliably detected (Schleibinger et al. 2005; Schleibinger et al. 2008). Identification of specific target compounds may provide an opportunity to increase the sensitivity of the analytical method and detect MVOCs when even a minimal amount of mold is present. Hence, extremely important and novel components of this research are the determination and validation of an MVOC sampling and analysis method.

The objectives of this research were (1) to develop a database of MVOCs that are associated with types of mold growth found in problem building environments and that would be useful in determining the presence of hidden mold growing in indoor environments and (2) to accurately determine MVOC emissions from building materials inoculated with mold and exposed under simulated realistic environmental conditions (temperature, relative humidity, and ventilation air change rate).

METHODS

First, to identify and quantify specific MVOCs associated with certain organisms grown on different materials, selected species were grown and isolated in laboratory glass vessels for static studies. Following growth and incubation of the molds, air samples were obtained from the glass vessels using a passive volatile-organic-compound (VOC) collection technique and analyzed using thermal desorption-gas chromatography/mass spectrometry (GC/MS). Specific emissions were identified using a mass spectrometric database of common indoor contaminants and MVOCs. Potential marker compounds were chosen for specific mold types based on the uniqueness and levels of the identified MVOCs.

Second, dynamic chamber studies were used to accurately determine MVOC emissions from building materials inoculated with mold and exposed under realistic environmental conditions (temperature, relative humidity, and ventilation air change rate). Inoculated materials were placed into environmentally controlled chambers operating under dynamic conditions. Chamber air was sampled using an active VOC collection technique and was analyzed using the VOC analysis method previously described.

Procurement of Mold-Contaminated Building Materials--Static Studies and Dynamic Chamber Studies

Six mold species, typical to water-damaged buildings, were selected for use in static studies: Stachybotrys chartarum, Cladosporium sphaerospermum, Chaetomium globosum, Eurotium amstelodami, Aspergillus versicolor (tested in duplicate), and Aspergillus sydowii. S. chartarum is widely publicized as a mold of great concern from a health standpoint, and C. globosum is commonly found in water-damaged environments. Furthermore, the two molds are often found together in the environment. Based on these factors and on results from the static studies, only S. chartarum and C. globosum were used in subsequent dynamic chamber studies.

Cultures were freshly obtained from a commercial laboratory conducting analysis of air samples on mold-colonized building samples. Isolated cultures of each organism were plated onto appropriate growth media. S. chartarum, C. globosum, and C. sphaerospermum were cultivated on PDA. CY20S was used for A. sydowii and E. amstelodami. A. versicolor was grown on B-malt. The inoculated plates were incubated at 25[degrees]C for 5 to 7 days or until after sufficient colonization and sporulation. Each organism was harvested and suspended in 0.01% Tween 80 with 0.1% peptone (PepTween). Suspensions were vortexed for 2 min and then centrifuged for 20 min at a minimum 3500 rpm. The pellet in each tube was washed twice and was suspended in sterile 0.9% NaCl. The number of spores per milliliter of stock suspension was counted using a Hemocytometer and microscope. Then each stock suspension was diluted to yield the final desired suspension concentration. The population of this suspension was verified by means of a standard plate count. These solutions for each test organism were used to inoculate the building materials.

Four building materials were selected for use in the static studies based on common problem building materials found in building investigations: paper-faced drywall (gypsum board), fibrous ceiling tile, kraft paper (as used for facing insulation batts), and oriented strand board (OSB). OSB did not sufficiently support mold growth, perhaps due to the high aldehyde levels that typically emit from new manufactured wood products and that may be toxic to molds; this material was not chosen for subsequent dynamic chamber studies. While ceiling tile is often a source of mold growth in buildings, its installation and use often is easily accessible for visual inspection of mold on either side of this material. Since one purpose of MVOC sampling is targeted at identifying hidden mold growth, then the use of ceiling tiles as substrates for further study did not seem reasonable. Kraft paper and gypsum wallboard met two key criteria for MVOC study: 1) they readily support mold growth in problem indoor environments, and 2) they are installed and used in buildings in a manner that results in the subsequent mold growth being concealed. Based on the prevalent use of gypsum wallboard in buildings, its potential to account for mold coverage (in square footage) in problem environments is significant. Since it has the potential to be a significant host for hidden mold growth, gypsum wall-board was chosen as the subject substrate for the dynamic chamber studies.

For the static studies, all test materials were cut to fit into each 3 in. by 5 in. test container, a glass jar with a Teflon-lined lid. The sample coupons ranged in size from 1 in. by 1 in. to 2 in. by 3 in. Materials were sterilized in dry heat for 2 hr at 121[degrees]C and inoculated separately with 2 mL of a 7.0x[10.sup.5] to 2.0x[10.sup.6] spores/mL inoculum of each separate fungal culture. Thirty-two test environments were created; sample sets of each of four types of building materials were moistened and inoculated separately with each of six test organisms (one in duplicate) plus one un-inoculated control and were then incubated for three weeks at 25[degrees]C.

Methods from the static studies were optimized for application to dynamic chamber studies. In preparation for these dynamic studies, test materials were evaluated weekly to determine the general rate of fungal colonization per test organism and material type. Materials were visually assessed and growth was rated according to the following scale: "0" = no visual growth observed, "1" = trace amount of growth observed (less than 10% coverage of material surface), "2" = light growth observed (11-30% coverage of material surface), "3" = moderate growth observed (31-60% coverage of material surface) and "4" = heavy growth observed (61-100% coverage of material surface). Periodic visual inspection of the test containers ensured that they contained sufficient moisture to sustain growth of the fungal species; 0.9% NaCl was added to containers as needed.

For the dynamic chamber studies, 1.2 cm thick (nominal 1/2-inch) commercial gypsum wall-board panels were cut into coupons approximately 30 cm x 30 cm. Five sets of wallboard coupons were prepared with each set consisting of five replicates (a total of 25 pieces). All panels were wetted by submersion in 18 megohm purified water for 30 min and were subsequently air-dried for 30 min prior to use (to minimize drainage of inoculum from the surface). Four sets were then inoculated with aqueous suspensions of spores (1-2x[10.sup.5] CFU/mL) of either C. globosum, S. chartarum, or a mixture of the two molds. Panels were sprayed with a manual atomizer. Inoculated panels were incubated at room temperature in a humid chamber (approximately 100% RH) for either nine days (light growth) or 16 days (heavy growth) before loading into the dynamic environmental chambers for further evaluation. The control (uninoculated) panels were wetted and dried in an identical manner to the inoculated panels, immediately prior to loading into the chambers. The five treatment sets (5 coupons each) were (1) control (uninoculated), (2) light growth of mixed molds, (3) heavy growth of mixed molds, (4) heavy growth of C. globosum, and (5) heavy growth of S. chartarum.

Sampling of VOCs from Static Test Containers

VOCs were passively collected from setup through the end of one-, two-, and three-week incubation periods for each of the fungus/building material combinations. Air was passively collected onto a solid sorbent (Tenax[R] TA). Stainless steel sorbent tubes (3) were affixed to lids that were cored with three holes. One open end of the tube was exposed to the atmosphere in the container; the other end of the tube was sealed with a cap.

For population verification, a sample from each test container was removed at the appropriate time period and used to determine the fungal population per weight of material. Organisms from each material were harvested in PepTween, serial-diluted, plated onto appropriate media, and incubated at 25[degrees]C for four to seven days.

Exposure controls were established for the static studies. In order to better distinguish building material emissions from true MVOCs, the six species (plus one uninoculated control) were also cultivated on appropriate growth media in specially prepared "French Squares," whereby media was applied to four sides of this square vessel. Samples acquired from these vessels were considered positive controls. A sample of the atmosphere in these vessels was measured after eight days of exposure.

Sampling for VOCs and Target MVOCs from Dynamic Environmental Chambers

The exposed area of inoculated wallboard was approximately 1 [m.sup.2] resulting in a material-to-air-volume-loading ratio of approximately 10 [m.sup.2]/[m.sup.3]. Environmental chamber operation and control measures complied with ASTM Standards D 5116-97 (ASTM 1997). Using a combination of vapor phase and solid media filtration, dehumidified supply air to the chamber was stripped of formaldehyde, VOCs, particles, and other contaminants so that any contaminant backgrounds in the empty chamber were below strict levels of < 10 [micro]g/[m.sup.3] TVOC, < 10 [micro]g/[m.sup.3] total particles, < 2 [micro]g/[m.sup.3] formaldehyde, and < 2 [micro]g/[m.sup.3] for any individual VOC. Air supply to the chambers was maintained at 23[degrees]C [+ or -] 2[degrees]C and 50% RH [+ or -] 5% RH.

The background from the empty chamber was measured prior to loading panels into the chamber. After an overnight equilibration period set at a minimum air change rate of 0.4 ACH to concentrate the sample for analysis of the headspace, duplicate air samples were collected onto Tenax[R] sorbent tubes. Then the air change rate was adjusted to 0.8 ACH followed by a 4-hr re-equilibration period in the chamber. The 0.8 ACH rate was chosen to represent a typical commercial building ventilation rate. Duplicate air samples were collected at 0.8 ACH. Repeat samples were collected at both 0.4 ACH and 0.8 ACH rates.

Chamber air was sampled over an approximately 90-min period for a total volume of approximately 18 L or 24 L. Both low-volume (18 L) and high-volume (24 L) air samples were collected on two consecutive days of growth. Different volumes were used to allow collection of VOCs across a broad range of vapor pressure.

Analytical Methodology for VOCs

Collected samples were thermally desorbed into the GC/MS. Instrumentation included a Per-kin-Elmer Turbo Matrix ATD or ATD 400 Thermal Desorption System, a Hewlett-Packard 5890 Series II or 6890 Series Gas Chromatograph, and a Hewlett-Packard 5971 or 5973 Mass Selective Detector GC/MS.

The sorbent collection technique, separation and detection analysis methodology was adapted from techniques presented by the USEPA and other researchers. The technique followed EPA Method IP-1B, generally applicable to C5-C16 organic chemicals with boiling points ranging from 35[degrees]C to 230[degrees]C (Bertoni et al. 1981; Bruner et al. 1978; Mangani et al. 1982; Winberry et al. 1990). The detection limit was 0.5 [micro]g/[m.sup.3] for most individual VOCs and total VOCs (TVOCs). The detection limit for MVOCs was 0.2 [micro]g/[m.sup.3]. The relative standard deviation of duplicate samples was acceptable if it was less than 20% and typically it fell between 10 and 15%. Analytical error was estimated at less than 20% based on historical accuracy and precision data. Chamber and laboratory blanks are routinely analyzed as part of the overall laboratory quality assurance program. Spiked sorbent tubes with a second sorbent tube connected in series were evaluated to ensure that all MVOCs were retained on the collection media at the flow rates used and at the concentration levels expected.

Individual VOCs (IVOC) were separated and detected by GC/MS. VOCs were calibrated to authentic standards for the MVOC quantitation procedure and to toluene for the IVOC quantitation procedure.

The data was analyzed first using a target list approach for 23 known MVOCs. The advantages of this analysis were a very low detection limit and ease with which target compounds from analytical and environmental noise could be identified. Individual VOCs were identified using a specialized indoor air mass spectral database. This database consists of mass spectral information and method-specific retention time information generated by analyzing authentic standards of compounds commonly found in the indoor environment. Other compounds were identified with less certainty using a general mass spectral library available from the National Institute of Standards and Technology (NIST). This library contained mass spectral characteristics of more than 75,000 compounds as made available from NIST, the USEPA, and the National Institutes of Health (NIH). A match was first pursued in the indoor air database, which included data for the gas chromatographic retention time of the compound in addition to the mass spectrum. This additional information increased confidence in the identifications from the indoor air database from identifications using only the NIST/EPA/NIH mass spectral library.

The target list MVOCs that were specifically analyzed included 3-methylfuran, 2-methyl-1-propanol, 1-butanol, 3-methyl-2-butanol, 2-pentanol, 3-methyl-1-butanol, dimethyl disulfide, ethyl isobutyrate, 2-hexanone, 2-heptanone, 5-methyl-3-heptanone, 1-octen-3-ol, 3-octanone, 3-octanol, 2-pentylfuran, 2-octen-1-ol, 2-methoxy-3-1(methylethyl)pyrazine, 2-nonanone, fenchone, 2-methylisoborneol, alpha-terpineol, geosmin, thujopsene, anisole, and isopropyl acetate. Other VOCs detected in the analysis scan were also identified to assess their potential as useable MVOCs.

Target MVOCs were detected and each was quantified to its own authentic standard with a multipoint (5) calibration curve (minimum [r.sup.2] = 0.985). The measured MVOC concentrations were within the upper limit of the calibration curve. The total MVOC (TMVOC) concentrations were determined by adding the measured responses of all individual MVOCs. Analysis of calibration curves and samples were performed using Hewlett Packard EnviroQuant analytical software. Individual MVOC and TMVOC values are reported in nanogram per cubic meter. A detection limit for each specific individual MVOC was approximately 200 ng/[m.sup.3] (equivalent to 0.2 [micro]g/[m.sup.3]).

Calculation Methods

Emission factors for MVOCs, in nanograms released per area of mold-colonized material ([m.sup.2]), were calculated using Equation 1, assuming a constant emission process.

EF = Chamber Concentration x N/L (1)

where

EF = emission factor, ng/[m.sup.2]*h

N = air change rate, [m.sup.3]/h

L = product loading, [m.sup.2]/[m.sup.3]

Room air concentrations were estimated using Equation 2, assuming a well-mixed environment and no sinks.

Room Air Concentration = EF x Area/(N x Vol) (2)

where

Area = area of mold coverage, [m.sup.2]

Vol = room volume in, [m.sup.3]

RESULTS

Identification of Mold Specific MVOCs--Static Studies

Of the six fungal species studied, the three of greatest significance to indoor mold investigations and with the most interesting MVOC potential (apparently unique MVOC patterns and/or troublesome growth locations) were S. chartarum, A. versicolor, and C. globosum. Key MVOCs were detected emitting from these molds: dimethyldisulfide, isopropyl acetate, and methoxyben-zene (Figure 1) from S. chartarum; 1-Octen-3-ol, 3-Octanone, 5-Methyl-3-heptanone and geos-min from C. globosum; 1-Phenylethanone, 2-Ethylfuran, 2-Ethyl-2-hexenal, 3-Methylbutanal, and dimethyldisulfide from A. versicolor. Identified MVOCs were two times greater than the positive control.

[FIGURE 1 OMITTED]

Mold growth on building products was found to produce a variety of MVOCs. However, only a limited number could be considered "markers" for specific mold types. Over two-dozen different MVOCs were identified. Measurements of the VOCs produced in the controlled growth vessels were compared to those obtained from mold growing on building materials. Some common MVOCs were found to be consistent among the various growth media, including well-known MVOCs that are frequently reported in the literature, such as 3-methylfuran, 1-octen-3-ol, and 3-octanone.

Comparison of MVOCs generated by different molds growing on various building materials yielded interesting results one of which was the persistent presence and identification of methoxybenzene (anisole) associated with the growth of S. chartarum. This MVOC was present in large amounts from three primary building materials that supported the growth of S. chartarum: gypsum wallboard, porous ceiling tile, and kraft paper. Methoxybenzene was also found in the headspace volume of S. chartarum growing on B-malt culture medium. Methoxybenzene was not found to be a significant MVOC emission from any of the additional molds studied. Methoxybenzene appeared to be useful as a unique indicator MVOC for the growth and presence of S. chartarum in building environments.

MVOC results indicated that 1-octen-3-ol and 3-octanone were found to be consistent measurable indicators of C. globosum growing on ceiling tile and kraft paper; however, 1-octen-3-ol was not found from C. globosum growing on gypsum wallboard.

Dimethyldisulfide appeared to be a good MVOC indicator for both S. chartarum and A. versi-color. Other interesting emissions that were not in the background included 3-methylbutanal, 2-ethyl-1-furan, phenyl ethanone, and a well-known MVOC, 3-methylfuran. 2-Ethyl-2-hexenal may be related to the linoleic acid metabolite and was found in many samples.

Identification of MVOCs from Stachybotrys and Chaetomium on Gypsum in Simulated Realistic Conditions--Dynamic Chamber Studies

Analytical results obtained from the environmental chamber testing of inoculated materials showed consistency with results obtained in the former vessel study. The specific MVOC previously identified, methoxybenzene (or anisole), was also found in the chamber studies (Table 1). This compound appeared to be an exclusive emission of S. chartarum and was found to be emitting at significant levels from inoculated wallboard. Significantly similar compounds were found to be emitting as well, including dimethoxybenzene and methylmethoxybenzene. The levels of these specific MVOCs as measured among the colonized materials showed the pattern visible in Figure 2. The two compounds that appear to be selective emissions from C. globosum include benzothiazole and menthol are shown in Figure 3.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]
Table 1. MVOC Concentrations (ng/[m.sup2]) from Dynamic Chamber Studies

Compound                Light Growth  Heavy   Chaetomium  Stachybotrys
                                      Growth   Globosum    Chartarum

l-Butanol                   1,089       187     1,157        279

l-Octen-3-ol                1,040       404      632         647

2-Heptanone                  725        340      563         309

2-Hexanone                   513         ND      324          ND

2-Methoxy-3-                  ND         ND       ND          ND
l(methylethyl)pyrazine

2-Methyl-1 -propanol         551         ND      275          93

2-Methylisoborneol            ND         ND       ND          ND

2-Nonanone                    ND         ND       ND          ND

2-Octen-1-ol                  ND         ND       ND          ND

2-Pentanol                    ND         ND      147          ND

2-Pentylfuran                247        188      203         212

3-Methyl-1-butanol            ND         ND       ND          ND

3-Methyl-2-butanol           676         ND      591          ND

3-Methylfuran               55.0         ND       ND          ND

3-Octanol                    547        197     1,063        137

3-Octanone                  8,952      6,314    9,039       5,506

5-Methyl-3-heptanone          ND         ND       ND          ND

Anisole                     9,221      1,357      ND        1,245

Borneol                       ND        509     1,011        699

Dimethyl disulfide           225        275      175         214

Ethyl isobutyrate             ND         ND       ND          ND

Fenchone                      ND         ND      294         109

Geosmin                       ND         ND       ND          ND

Isopropyl acetate           1,106      2,914    1,471        503

Thujopsene                    ND         ND       ND          ND

[alpha]-Terpineol           1,172       794     1,199       1,088

Total Microbial VOCs       26,119     13,479   18,144      11,041
(TMVOCs)

ND = Not detected


Chamber testing also identified a number of other MVOCs emitting from the colonized gypsum wallboard materials. Analytical results of the original target list of MVOCs and description of the associated mold substrate inoculation are provided in Table 1. A review of all measured emitting VOCs indicated that the inoculated materials released a broader range than the original target list of MVOCs.

Higher levels were generally found in the light-growth test substrate. Those MVOCs with consistent emissions among all inoculations included 1-butanol, 1-octen-3-ol, 2-heptanone, 2-pentyl-furan, 3-octanol, 3-octanone, dimethyl disulfide, isopropyl acetate and [alpha]-terpineol. Anisole, or methoxybenzene, was the only MVOC observed exclusively in S. chartarum inoculates.

MVOCs that were present in mold-colonized samples but not present to any extent in the control samples are graphed in Figure 4.

[FIGURE 4 OMITTED]

DISCUSSION

Numerous MVOCs are released from active mold growth and appear to be dependent on the type of mold and building-material substrate (Gao and Martin 2002; Claeson et al. 2002; Lancker et al. 2008). In initial studies, dimethyldisulfide appeared to be a good MVOC indicator for both S. chartarum and A. versicolor. This compound is believed to be a derivative of the sulfur-containing amino acid methionine (Wessen et al. 2001). Although this compound is a common bacterial emission and is therefore not unique to A. versicolor, its presence in an indoor environment certainly indicates a biological source. Isopropyl acetate was detected from S. chartarum; acetate is considered the most important precursor in the biosynthesis of volatile fungal metabolites (Larsen 1998) and many different acetate esters have been identified as fungal emissions.

Initial findings that S. chartarum is a major producer of methoxybenzene, and C. globosum is not, is consistent with the dynamic-chamber-study finding that this MVOC appears to be exclusively emitted by S. chartarum. Additionally, the much higher emission factor of methoxybenzene in the "light-growth mixed molds" sample than in the "heavy-growth mixed molds" sample could be due to more rapid production during the initial growth period, with heavy visible growth of molds indicative of senescence. Perhaps more likely, the large amount of dimethoxy-benzene found in the "heavy-growth S. chartarum" may indicate that methoxybenzene is an intermediate in a synthetic pathway towards a different compound. Supporting this metabolic intermediate theory is the presence of the related compound methylmethoxybenzene. Methoxy-benzene has not been reported in the literature as an important MVOC, but some related compounds have been described. For example, Bjurman et al. (1997) found 4-allylanisole from Penicillium on pinewood; Fischer et al. (1999) found 1-methoxy-3-methylbenzene (one isomer of methylmethoxybenzene) to be exclusively produced by Penicillium expansum.

MVOCs 1-octen-3-ol and 3-octanone, found in the emissions from C. globosum, are unique compounds not found in typical indoor environments or from common building material. These are likely to come from metabolic processes involving linoleic acid (Matsui et al. 2003). Although chamber studies clearly indicate that benzothiazole and menthol are associated with C. globosum growth, initial studies indicated their presence in some control samples. This may have been the result of contamination or may indicate the wetter wallboard material itself as a source. More conclusive studies are required to solidify the likelihood of benzothiazole and menthol as C. globosum-specific MVOCs.

The findings from the broader range of detected MVOCs in the chamber studies (Table 1) further establish that molds produce a wide range of chemical metabolites and that these compounds can be identified and measured analytically. Some of these MVOCs were also found to be emitting from the control set of gypsum wallboard at low levels. This may be the result of a difference in the preparation of the wallboard, as the wallboard for the control was wetted immediately prior to loading in the environmental chamber. Conversely, the test samples were wetted 9 to 16 days prior to loading. Because of the difference in preparation of control and test samples, the findings of MVOCs in the control sample should not invalidate the results of the test samples. All reported results were corrected for low levels found in the control samples.

Interestingly, findings from the control data show that wetting the paper covering the gypsum wallboard releases water-soluble MVOCs. In this case, the wetting process may trigger the release of MVOCs that were absorbed in the gypsum wallboard. These findings may also indicate that building materials, such as wet gypsum wallboard may emit detectable levels of MVOCs prior to installation even in the absence of visible mold growth. This may be the result of moisture exposure during or after manufacturing and prior to use in buildings.

Many VOCs of potential microbial origin were found to emit from the building materials. However, they were not good candidates for the purpose of this study, which was to find compounds that could be used as specific markers for microbial growth. Some of them were known MVOCs but were in the negative controls as well as the mold-contaminated samples. Examples of this include 2-hexanone, 2-heptanone, and 2- pentylfuran. In some cases known MVOCs were at high levels in the mold-contaminated samples and not in the controls, but they were known to be common material-related VOCs. Examples include styrene and ethanol. In some cases, interesting VOCs were found that, while they are not currently known to be MVOCs, their presence in the samples and not the control blanks indicated they might be unique markers. However, the levels were so low that their detection in actual environments would be unlikely.

This research study provides a firm foundation for continuation of additional MVOC research. It is recommended that additional research efforts be focused on the following areas: (1) prioritization of building substrates for further study, (2) identification and validation of additional mold-specific MVOC markers, and (3) building surveys.

CONCLUSION

This research study found numerous MVOCs released from active mold growth and developed a list of these MVOCs with the potential to be useful in determining the presence of hidden mold growing in problem indoor environments. Specific MVOC emissions resulting from mold growth on building materials were dependent on both the type of mold and the specific host substrate, as seen in other studies (Claeson et al 2002, Gao and Martin 2002, Schleibinger et al 2005, Lancker et al, 2008). The majority of these MVOCs are associated with a variety of mold types. Certain mold selective MVOCs were identified including methoxybenzene for Stachy-botrys chartarum; benzothiazole and menthol were identified as potential indicators for Chaetomium globosum. Methoxybenzene (as anisole) was earlier reported as uniquely emitted from S. chartarum by Wilkins et al. (2000) but Gao and Martin (2002) looked specifically at S. charta-rum and did not detect this MVOC. The discrepancy between these earlier reports is not resolved by the current work, but the production of methoxybenzene from S. chartarum is confirmed and in the present study also appears unique to S. chartarum, as reported by Wilkins et al (2000).

This was an extensive study to develop a database of MVOCs that might be practical in identifying the presence of mold growth in buildings. In order to be usable in these situations, an MVOC has one of the following characteristics: unique, predictable and detectable. The compound should not be frequently emitted from other common indoor air pollution sources. Its presence needs to be predictably observed in an environment with sustained mold growth. The MVOC needs to be emitted at a rate that will result in detectable levels for an amount of mold coverage.

This research study showed that many MVOCs could be identified as being generated from mold growth, but only a small number of the compounds have been shown to be effective in field/building studies. In this study one MVOC, methoxybenzene (also known as anisole), was found to be effective and reliable under the specific requirements stated above and could be potentially quite useful to indoor air researchers and investigators for the following reasons. It is specific for Stachybotrys chartarum, a mold of great public concern and an excellent ecological indicator. It is emitted when growing on gypsum wallboard, one of the substrates that most warrants a non-destructive investigative technique such as MVOC sampling. It also appears to emit from S. chartarum growing on other building materials, including ceiling tiles and Kraft paper. It is a very unique chemical and not commonly associated with general VOC product emissions. This uniqueness is based on comparison to an indoor air VOC database containing over 15 years of data and thousands of air analyses from indoor environments and material emissions. Although in modern mechanically ventilated buildings, dilution remains a challenge to detecting any MVOCs, the confirmation that methoxybenzene is consistently associated with the growth of S. chartarum does provide a useful candidate for a specific marker for mold growth due to water damage.

ACKNOWLEDGMENT

The authors would like to thank ASHRAE for their support with ASHRAE Research Grant 1243-TRP.

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Received January 12, 2009; accepted December 4, 2009

This paper is based on findings resulting from ASHRAE Research Project RP-1243.

Stephany Mason is technical director and W. Elliot Horner is principal consultant at Air Quality Sciences, Inc. in Marietta, GA. Don Cortes is laboratory director for STAT Analysis in Chicago, IL.

Stephey Mason, PhD

Associate Member ASHRAE

W. Elliot Horner, PhD

Don Cortes, PhD
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Author:Mason, Stephany; Cortes, Don; Horner, W.Elliot
Publication:HVAC & R Research
Article Type:Report
Geographic Code:1USA
Date:Mar 1, 2010
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