Comparison of Methyl Benzoate and Ergosterol for the Quantification of Mold in Indoor Buildings and Materials

Over the last few years there have been many school and business closures related to mold and bacteria buildup, which have affected the health of the occupants. Mold growth has been potentially linked to poor air quality and public ill health, under what has generally been referred to as sick building syndrome. Because occupants tend to spend many hours in buildings, prolonged exposure to low mold concentrations (<50 ng/L) can be problematic, even to those who are not thought to be in the most susceptible portion (elderly, the infirm, children) of the population. It has been demonstrated that fungal metabolites can be easily adsorbed to respirable airborne particles and lysed through the lungs.1

Although classical methods of mold detection exist (culture studies, ergosterol analysis, total fatty acids), such methods in their current form tend to be expensive, laboratory intensive, and/or are not applicable to air analysis. Hence, a more assessable and cost-effective method to detect mold in indoor air and buildings is desired.

During mold growth, microbial volatile organic compounds (MVOCs) are out-gassed to the surrounding air, and detection of individual components is possible; however, there are many metabolites in the variety of molds found in indoor building materials.2 The employment of a biomarker, or particular compound, that is easier to detect but is indicative of other more difficult analytes has been investigated, though the uses of markers are not totally without difficulties.

In the study of molds in buildings, certain MVOCs have been suggested as useful indicators of hidden microbial damage.3 A scheme has been developed for interpreting the results of indoor MVOC concentrations,2,3 and fine-tuning of this original work has been ongoing. 4–6 An assortment of (40+) primary indicators have included: 1-octen-3-ol, dimethyl disulfide, 2-pentanol, 2-methylisoborneol, and sometimes 3-methyl-1-butanol, and secondary indicators: 2-hexanone, 2-heptanone, 2-methyl-1-propanol, 1-decanol, 3-octanol, 3-octanone, and methyl benzoate. It is likely that no one biomarker will be able to assess the presence (or not) of mold within a building or its air. A useful adage is “the higher the number of indicators detected, the more reliable the interpretation.”

Although nearly all MVOCs are produced by microbes, their evolution rates are also dependent upon the molds’ growth rates, which can vary on different building materials. Further, molds do not grow continuously; they have rest periods and/or can decompose through autolysis. For this reason, it is important that biomarkers be standardized to known amounts of mold so that their responses can be checked. One way to do this is to compare the amounts of an MVOC emitted to ergosterol analysis, which indicates the number of cells in the mold. As an example, methyl benzoate output, as a potential biomarker, is assessed by comparison to ergosterol amounts.

The analysis method for methyl benzoate uses solid-phase microextraction (SPME) as its sample preparation and extraction technique, coupled to gas chromatography-mass spectroscopy (GC-MS), a technique used for quantification of semivolatile analytes, and is compared to ergosterol extraction and subsequent analysis by liquid chromatography with UV-VIS detection. This article presents some preliminary results with optimized conditions in the development of these methods.

Materials and methods

Ergosterol (85%), methyl benzoate (>99%) from Sigma-Aldrich (Mississauga, Ontario, Canada), and conditioned (manufacturers’ guidelines) 70-μm Carbowax/DVB–stableflex SPME fibers from Supelco (Bellefonte, PA) were used.

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