Biological Risk Assessment

Given that many of the indoor air problems (whether on remediation sites or elsewhere) are caused by biological contaminants and their decomposition products, Chapter 6 provides real-world examples of biological monitoring protocols.

All sampling for biologicals must take into account surrounding environmental factors and building usage. Drawing a complete history and in some cases additional types of air sampling for other contaminants are required. In discussing sampling for biologicals we will also discuss the reasons for concern and control mechanisms that can be used.

You must always remember that biologicals, unlike chemical contaminants, have the potential to reproduce and thus grow in numbers. Care must be taken to sample in a con­sistent fashion in as short a period as possible.

Reproduction of biologicals also calls into question the relative viability of spores and bacterial colonies that are encysted. In cases where amplification is primarily bacterial, these colonies may inhibit spores from developing into vegetative structures. Conse­quently comparative levels for bacterial counts and mold colony forming units (CFUs) may be required, especially since spores in and of themselves can be problematic. Thus, the absence of visible mold growth may not be indicative of a clean environment.

When molds are amplified to the extent that the building is increasingly hospitable to further mold growth, we may begin to see pathogenic colonies (that would not otherwise be present) taking hold in a building's interior. All of us exhibit great concern when con­fronted with possible Stachybotrys atra (Stachy). Airstream movement does not readily spread Stachy, as the spores become less viable in dry airstream environments. However, in moisture-laden airstreams or within homes with other amplified mold colonies, Stachy may begin to flourish.

In areas where bird or other animal droppings are prevalent, we begin to be concerned about histoplasmosis and coccidiomycosis. Histoplasma (Histo) is the more likely disease vector where other molds are flourishing, given that Histo is better able to survive in wet­ter environments.

Keep in mind that the term wet is a relative one. Some of these molds do not need "wet" environments in the traditional sense to grow well; any condensation will do, even that caused by very slight temperature differences.

The old way of thinking that fiberglass will not grow biologicals is also not correct. The fiberglass itself may not be a good food source; however, the fiberglass forms a nice nest and traps other food sources. Fiberglass filters, lined fiberglass ducts, and fiberglass panels

inserted for insulation all become less densely packed with age and use. Particulates, espe­cially those associated with any greasy, vapor-laden airstream, stick to the fiberglass and provide a nutrient bed for biological contamination.

Because of the problems with grease or oil in airstreams and biological amplification, care must be taken in using these products. Whenever refrigerant lines bearing mineral oil and freon are serviced, any breakage should be viewed as potentially providing a nutrient "fly paper" for biological contaminants.

So—how much is bad? This is determined in part by aesthetic concerns and in part by health concerns. If you do not want visible mold growth, even small colonies may be too much. Larger colonies, even if no health effects are forthcoming, are certainly unacceptable and over time may even do structural damage. Aspergillus can thrive on cellulose, paint, and dry wall, leaving unpleasant looking stains as the colonies die. The health questions have many answers depending in part on how sampling is accomplished. With current sampling protocols we become concerned if any part of a building is showing amplified mold growth. We often compare to exterior background levels or to levels in a part of the building shown to be relatively free of mold contamination. In the sense that these biolog­ical contaminants may be ever changing in numbers as conditions change, there is no such thing as a static background level. The lack of "hard numbers" is one other reason that the sampling team and microbiologist oversight must include senior level scientists.

For sensitized individuals, the elderly or very young and immune-compromised people, even very sparse mold colonies may cause health problems. Certainly anyone hos­pitalized for surgery or other invasive medical procedures would also be considered immune compromised during that interval of time. For individuals without these types of concerns, we want to see nonpathogenic mold counts less than 200 CFU/m³ over estab­lished background levels. Higher levels may be acceptable for certain mixes of mold species, and lower levels are required for single species and pathogenic contaminant confidence.

Contact samples should always be less than 200 CFU/strip for areas to be judged "clean." A combination of contact and air-sampling information is required to assess most buildings (Figure 6.1), and these acceptable numbers vary given different biological con­taminant mixes and building usage. For example, in a hospital setting, 20 CFU/strip would be too much in the operating room and perfectly acceptable in the visitor's waiting room.

Once the level of contamination is assessed, we can begin to decide how to remedy any negative situations. Steam cleaning without the use of biocides is sometimes the wrong thing to do. Remember that even steam cools, and cool water is just what most molds need

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