The objective of biological testing is to evaluate the affected components to determine the presence of amplified biological activity. The determination of biological sources is usually accomplished with bulk samples of materials such as carpet and fiberglass, or surface samples of materials such as drywall, wood and masonry. Source testing is important because it identifies the actual taxa that have colonized a material. This analysis is usually done by culturing the organisms, and is the most reliable way to accurately identify the types of organisms present.
Air samples have more limited utility. Air samples are not a good survey tool, since there are numerous variables that determine whether the organisms are airborne. The temporal variability (changes over time) is enormous. False negatives are common, and even when a positive result is reported, air testing alone does not inform about the nature, extent or location of the source. Air samples are used to help confirm surface samples, and sometimes to provide a comparison of pre-mitigation and post mitigation conditions.
There are also several non-culturing methods that can be used as a screening tool in the survey. Tape lift samples can determine whether there is biological activity on a surface, but the identification is weak and the numbers are not quantitative. Spore counts in air samples can provide useful information on general air quality, but have the same weaknesses as the viable samples described above. Air testing is sometimes conducted inside wall cavities, and may identify the presence of mold without destroying the wall. Or not.
With the limited testing tools at our disposal, we are nonetheless expected to draw conclusions based at least partially on the testing results. While we rely heavily on the visual and moisture clues, professionals use testing to supplement and confirm their suspicions.
Evaluation:
There are currently no widely established numerical standards for acceptable concentrations of microorganisms, and there are several reasons for this. Fungi occur commonly in nature, since microbes provide the final decomposition of many organic waste materials. It is common to find substantial fungi populations in normal buildings, and it can be difficult to distinguish unusual fungi populations from typical ones. In addition, individual response to microbial levels is a function of sensitivity, which can range from no effect to significant allergic discomfort in the typical building population. As a result, it is virtually impossible to predict whether exposure to a given concentration of microbial species will elicit a response in a given individual.
The evaluation of hazard in the indoor environment is a process of comparing concentrations in an area of concern to ambient levels found in non-problem areas or outdoors. In general, the airborne levels of fungi inside a building should be similar to those on the outside, and should not cause irritation or discomfort in most people. Levels that are significantly higher than the normal outdoor range, which can seasonally range from <100 to >1,000 cfu/m3, indicate that a local source of contamination may be present. In addition, microbial populations that include the presence of a dominant genus that is not dominant in natural settings suggest that local contamination may be present. If a species dominates an air sample, it suggests that it has found a place to live.
Surface concentrations are evaluated on an order-of-magnitude basis. Fungi occur naturally, and their presence up to several thousand colonies per square inch of surface is unremarkable in a normal building. Surface levels substantially higher, or that exhibit as visible growth, indicate that contamination is present. The distribution of organisms in the population is also important, especially if one or two genera have become dominant. This indicates that they have found a favored environment in which to grow at the expense of other species.
Of special interest are the presence of the moisture indicator fungi, such as Stachybotrys chartarum, Aspergillus flavus, Aspergillus fumigatus and Fusarium moniliforme. The confirmed presence of these taxa may require urgent risk management measures to be considered. The confirmed presence means a lot of spores or colonies, not just a couple.
As described by EPA and ACGIH, and supported by publications by the American Industrial Hygiene Association and the National Institute of Occupational Safety and Health, the amplification of biological populations should not be tolerated in occupied buildings. The presence of amplification requires mitigation measures to remove the biological growth.
