A Regional Comparison of Mold Spore Concentrations Outdoors and Inside “Clean” and “Mold Contaminated” Southern California Buildings

Abstract

A total of 625 buildings and outdoor locations in the San Diego, California, area were monitored using the Allergenco Sampl-Air MK-3 impaction sampler or the Zefon Air-O-Cell slit bioaerosol cassette. Locations were classified by rigid criteria as clean commercial, commercial with mold growth, clean residential, residential with water staining, and residential with mold growth. In addition, coastal and inland outdoor locations were measured. Seven categories (total spores, Ascospores/Basidiospores, Cladosporium, Smut/Myxomycetes-like, Aspergillus/Penicillium (AS/PE), Alternaria, and Unidentified/Other) were detected frequently enough that maximum likelihood estimate techniques could be used to determine distribution parameters and, thus, treat these as continuous variables. For total counts (no nondetectables) an analysis of variance was used to examine differences in location means. For the other categories Land's confidence limits were generated and visually compared for differences among locations. For 12 other categories (Curvularia, Dreschlera, Epicoccum, Fusarium, Mildew-like, Pithomyces, Rusts, Stachybotrys, Stemphyllium, Torula, Ulocladium, and Zygomycetes-like), detection generally occurred in less than 10% of samples. These genera were treated as dichotomous (detect/nondetect) data, and Chi-square analyses differentiated between locations. For total counts, values were significantly different on the order of clean < outdoor < moldy. There was a large difference between the moldy and other location classes. For AS/PE, moldy location means were clearly higher than those for clean buildings and outdoors, although the clean and outdoor means could not be differentiated. For all other genera the results tend to indicate little or no ability to discriminate location. For example, there were no differences in the probabilities of detecting Stachybotrys among the various locations. In our study only total counts, usually driven by AS/PE concentrations, had value in determining whether a building is mold contaminated employing our set of rigorous location classification criteria.

A Comparison of Replicate Field Samples Collected with the Bi-Air, Air-O-Cell, and Graesby-Andersen N6 Bioaerosol Samplers

“…A ratio of 100 was the highest BA:AOC ratio detected for a series of four replicate samples. In addition, the low frequency of detection of Chaetomium in AOC samples reported in previous studies by Baxter et al (2005) and Foto et al (2005) was consistent with the results of the current study. The results for Asp/Pen clusters and Chaetomium spores suggested that the AOC, and possibly similar slit impaction samplers, may substantially under-report average spore concentrations under some field conditions.…”

“…Baxter et al indicated that for AOC samples, Asp/Pen spores were one of the more frequently encountered spores in contaminated indoor environments (Baxter et al 2005). The minimum Asp/Pen concentration detected in the AOC samples in Table 4 was 4,800 spores/m 3 .…”

“…Slit impaction samplers such as the Air-O-Cell (AOC) cassette are one of the most commonly used methods for collecting airborne fungal spores (Chen et al 2004;Baxter et al 2005). They are simple to use, easy to analyze, and cost effective.…”

“…McGrath et al (1999) reported that complaint buildings frequently had high airborne concentrations of Penicillium species, while Cladosporium was usually dominant in buildings with few complaints. Similarly, Baxter et al (2005) concluded that indoor concentrations of airborne Aspergillus/Penicillium (Asp/Pen) like spores, as compared to other spore types, had the most utility in determining whether a building was contaminated with mold. These studies suggested that airborne concentrations of Asp/Pen like spores may be useful in differentiating clean from contaminated indoor environments.…”

“…In the study by Baxter et al (2005), the AOC samples were collected in moldy residential properties located in southern California. Asp/Pen spores were reported in 92% of the samples, Stachybotrys in 16% of the samples, and Chaetomium spores were not reported, suggesting they were either not detected or only detected in a small percentage of samples.…”