The 100 percent difference.

For many IAQ laboratory methods, there are currently no published standards. Notably, no standard method exists for the analysis of fungal spores in indoor air, and there is a diverse range of analytical approaches and statistical analyses of data. Laboratories typically analyze anywhere from 15 percent to 100 percent of the sample from spore trap cassettes, and, depending on the nature of the sample, the percentage analyzed can have a significant effect on the final results.

Aerotech P & K conducted a study to identify significant differences, if any, between two common analytical approaches used for spore trap cassettes. Fifty-five Zefon Air-O-Cell[R] cassette samples were analyzed via both the 15 percent and the 100 percent counting methods, and the results were compared. These samples, which were taken in various indoor and outdoor environments, were analyzed by degreed analysts with at least two years of experience. The results were compiled, and several interesting observations were made when the data were compared.

In outdoor air samples, the data show relatively little influence from method selection. In sharp contrast, air samples from indoor environments often contain aggregate fungal conidia and other multi-spore structures; the data show significant differences between the two methods.

When compared with a reading based on 100 percent of the sample, the 15 percent technique failed to detect Stachybotrys in 9 percent of the samples. The 100 percent counting method detected at least one Stachybotrys spore in five of the samples analyzed, whereas the 15 percent method detected zero Stachybotrys in the entire project. With Stachybotrys and other specific moisture indicator genera commonly being a target of interest in both analysis and remediation efforts, it would be beneficial to use a 100 percent counting method.

In addition, 18 percent of the samples were skewed because of heterogeneous deposition of spores. When the 15 percent method detected spores in samples with only a few chains or clumps of spores, the extrapolation calculations made a huge impact on the final results. For example, when a chain of five Cladosporium spores is detected in the 15 percent count, the extrapolation is 467 Cladosporium per cubic meter. The same number of spores counted with the 100 percent method is calculated at only 67 Cladosporium per cubic meter. Conversely, if there are a few scattered chains throughout the sample trace, but only one of these chains is detected in the 15 percent technique, the calculated results will be much higher (and more accurate) with the 100 percent counting method.

Samples with low spore concentrations showed variation in results as well. For example, the 15 percent counting method missed five or more genera in 25 percent of the samples. The samples had between one and 25 spores for each of the missed genera counted. These numbers could easily mean the difference between a zero total spore count by the 15 percent method and a significant total spore count by the 100 percent method.

In 9 percent of the samples, the 15 percent counting method failed to detect spores in concentrations less than or equal to 227 per cubic meter. Again, these concentrations are low, but the reporting of such results occurred only with the 100 percent counting method, and the counts may have included Stachybotrys or other key genera.

Selecting a laboratory for IAQ analysis may be a difficult choice, especially with the number of laboratories available. In the absence of a standard method for spore trap analysis, it is advisable to look at the benefits of using a laboratory employing the 100 percent counting method. Heterogeneous spore deposition on an indoor slide, low spore concentrations, and the difference between a 100 percent counting method and a 15 percent counting method can make all the difference in the world when accuracy is of the utmost importance.

Technical Briefs presents short but information-packed items on a variety of field-related topics in environmental health. The information this month is provided courtesy of two sister corporations that specialize in environmental health laboratory testing: Precision Analytical Laboratories, Inc., and Aerotech Laboratories, Inc., both based in Phoenix, Arizona. Readers interested in receiving additional information about Precision Analytical Laboratories and Aerotech Laboratories, including information about how to subscribe to a free "Tech Tips" listserv for environmental health professionals, can contact Aerotech Laboratories/Precision Analytical Laboratories at 2020 West Lone Cactus Drive, Phoenix, AZ 85027. Aerotech and Precision also can be reached by phone at [phone] or [phone]; by fax at [phone]; or on the Internet at http://www.aerotechlabs.com or http://www.palabs.com.