Interpreting Airborne Data
To: Laura Alexander, HarrisMartin Publishers
Reference: COLUMNS:MOLD; Jan, Feb, March, 2004
Author: Joe Spurgeon, Ph.D, CIH
Part 1: Methods for Comparing Data
Part 2: Using Databases of Sample Results
Part 3: The Use of Multiple Sample Media
INTERPRETING AIRBORNE FUNGAL SPORE SAMPLES
This is the first in a series of articles discussing the interpretation of airborne fungal spore samples. The article discusses four general methods for interpreting airborne data. Other articles in the series will discuss the use of databases, the use of multiple sample media, one or more case studies, how fungal spore concentrations can vary with time, and the effect of sampling time on the utility of the collected data. One of the objectives of this series of articles is to add to the reader's knowledge about interpreting sample results, allowing them to assume a more active role in assessing airborne data.
The topic of this article is a discussion of the various methods for assessing airborne fungal spore data when only a limited number of samples have been collected. The assumption is that a statistical analysis of the data can not be performed, which is often true for residential investigations, and even many smaller commercial investigations. When only a small number of samples are available, interpreting the sample results for airborne fungal spores becomes more of an art than a science.
Therefore, the consultant has to rely heavily on their training, experience and professional judgment. There are only a limited number of methods the consultant can use in that environment. The methods I'm familiar with are: (1) reference samples, (2) control samples, (3) "expected values", and (4) statistical databases.
The first article in this series briefly discussed referencing an airborne concentration of fungal spores to a statistical database. This article discusses the use of databases in more detail. In addition, summary data for two typical databases are included in the article as examples.
When a single airborne concentration is measured, it is just one small part of a distribution of possible concentrations that could have been measured. An important difference is that the measured concentration can change significantly between samples, but the distribution from which the sample was drawn can be rather stable. If the distribution is stable, it provides a reference for evaluating site-specific sample results. For example, the site-specific concentration can be characterized as low, moderate, high, or extreme relative to the expected distribution of concentrations.
Note: The 50th percentile concentration means that 50 % of all sample results are expected to be less than that concentration - a typical concentration. The 95th percentile concentration means that only 5 % of all sample results are expected to exceed that concentration - an unusually high concentration.
A second advantage of characterizing the distribution of concentrations is that extreme concentrations can be compared as well as average concentrations (although with less confidence). This is important because adverse health effects are typically associated with exposures to extreme concentrations, not average concentrations. The 95th percentile concentration of Aspergillus versicolor is more likely to cause an adverse health reaction than the 20th percentile concentration.
For example, what is the significance of an airborne concentration of 240 colony forming units per cubic meter (cfu/m3) of Aspergillus versicolor? It's difficult to even guess, because there isn't any point of reference. But, what if I can convince the reader that this is the 95th percentile concentration? Does that make it easier to assess that particular sample result? | 