By Dr. Harriet Burge

EMLab P&K Chief Aerobiologist and Director of Scientific Advisory Board

A question that commonly arises is, “When should I use biocides during fungal remediation in buildings?” Biocides, as the word indicates, are designed to kill living organisms. The simplest answer to the question, is to use biocides when you want to kill something. Answers are never so simplistic, however. Before using a biocide, you should consider the following questions:

1. Is killing the organism going to make a difference in the remediation outcome?

2. Is the biocide effective against the organisms of concern in this case?

3. Is exposure to the biocide more or less dangerous than exposure to the living agent(s) of concern?

The answer to the first question, at least with respect to fungal growth in buildings, is usually “no”. Most illnesses and symptoms related to fungal exposure will occur whether or not the fungus is alive or dead. Also, the use of biocides will only marginally change the speed with which re-growth occurs if suitable moisture conditions recur. Cases where biocides may affect outcomes are in hospitals where infection of immunocompromised patients is of concern, in cleaning up bird droppings infested with Cryptococcus neoformans, or as a delay tactic in areas prone to repeated wetting. Fixing the water problem, or using materials that do not support fungal growth, are better long-term solutions.

The second question is equally important, especially for fungi. Most biocides were designed to kill infectious bacteria in hospitals and other high-risk environments. Many biocides that work well against bacteria are essentially useless for the control of fungi. Thus, fungi are highly resistant to ozone, ultraviolet radiation, quarternary ammonium compounds, and many other commonly used biocides. Some of these biocides (e.g., ozone) will inactivate some spores in a population and enhance germination for those remaining. For this reason, reliance on biocides is not recommended for the control of most fungi. Examples of biocides that are effective against fungi are: ethylene oxide (useful as a fumigant for wet, moldy books), formaldehyde in high concentrations, and glutaraldehyde in high concentrations. None of these are recommended for use except under exceptional circumstances due to their potential toxicity.

For any biocide, it is important to weigh the risks of human exposure to the biocide against the potential benefit of reducing human exposure to the fungal species targeted. For many infectious disease agents for which most biocides were designed, the disease is far worse than exposure to the biocide. So the answer is, for nonspecific building-related symptoms, the risk tradeoff is not so clear-cut.

Conclusion: If possible, biocide use should be avoided. If there is a logical reason to use biocides in a specific case, then care must be taken to insure that the biocide will be effective and that human exposure to the biocide will be minimized.