Microbial Growth in Insulation, Plasters and Wallpaper in the Built Environment

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Microbial growth in the built environment has been extensive studied- with in vitro studies and inventories of used materials from active office building environments. Studying microbial growth has gained momentum under the sick building syndrome agenda. Sick building syndrome acknowledge that individuals are influenced by their heating and air conditioning system. But what about the walls themselves? Can fungi and bacteria grow in our office walls? Can we be getting sick just from going to work or class every day even out of flu season when no one has a virus they are trying to generously share by coughing and sneezing? The answer is maybe. (Note here that this excludes the airborne/ dust-borne bacteria that readily affect your health).

Factors Affecting Microbial Growth

Several factors can help you predict what kind of microbes you may have living in you wall. The microbial life is influenced by insulation material or composition of plaster, climate, season and moisture levels. The composition of the insulation materials has been studied; Ingredients such as polyvinylacetate coatings of gypsum lime plaster (produced from calcium sulfate dehydrate), and the substrates in natural gypsum, desulfurization gypsum, glass wool, polystyrene foam and granulated cork, and antimony trioxide (a fire retardant coating used on some building materials). The availability of accessible nutrients from these sources dictates microbial growth; for many of these materials carbon compounds or cellulose are the primary nutrients substrates for resident microbiota. Researchers have analyzed the effects of temperature - even in subartic climates we can see fungal growth. Humidity (moisture specifically) has a positive correlation with most fungal growth; the exception to this would be xerophilic species (species that can flourish in relatively dry environments).

(Trichothecenes)

Chemical structure of (Trichothecenes) mycotoxin. By User:Fk.[1]

Byproducts of Microbial Growth and their Effects on our Health

Fungal growth byproducts have been largely documented. These mycotoxins are a culprit of health risks. Mycotoxins include compounds such as aflatoxins, trichothecenes and ochratoxins. The maladies they cause- known collectively as mycotoxicoses- are associated with warm, wet climate and as such can be prevalent in certain seasons. Symptoms of myctoxicoses can blend in with symptoms associated with other seasonal disease, too; these symptoms include coughing and sneezing, and headaches, but can deviate from these familiar symptoms to include burning in the throat and lung, eventually cancer, nosebleeds, nausea, and diarrhea among other even more frightening symptoms [10]. Secondary metabolism of microbiota in insulation can produce (1-3)β-D-glucan and a subgroup of toxins known as volative fungal metabolites/volatile organic compounds [3]. (1-3)β-D-glucan causes activation of the innate and complement components of the immune system and potentially produces asthmatic symptoms. The volatile organic compounds can cause hay fever-like symptoms.

DublinMold File:http://[2]

Studies

In vitro studies are pretty standardized. They involve treatment of various surface types with water and exposure to mediated ventilation and environments and analysis of growth after allotted period of time. Researcher Friman used recycled paper samples as her substrate coated in biocides and exposed the paper to allergens (namely grass) to see what would grow (the allergens serve as a realistic example of what can incite mold growth in the walls- as some microbiota are airborne and others require surface to surface transmission. Despite the biocides, growth of Aspergillus spp.,Cladosporium spp., and Pencillinium spp. was found. Other studies used direct inoculation of the substrates by swabbing fungal solution on the insulation materials. The common theme among these studies was that less dense material were more easily sporulated and affected. The in vivo studies were helpful in concluding what microbiota most commonly grew over time- data was analyzed by DNA sequencing so that even if there was no sporulation yet- due to lack of moisture or insufficient heat or insufficient aeration of the growth substrate- the offending microbiota could be found. Studies conclude what you might expect to find in your office (granted you know what your office building is built of); common plaster fungi include Coprinus spp, Peziza spp, and Pyronema Domesticum (note spp tells us that multiple species in this fungal genus grow on plaster)[11].

Prevention and Proactive Considerations

Several solutions have been posited in research to this health threat. Germicidal irradiation is a possibility for exposed surface (wouldn’t work for inaccessible layers inside the wall). Retailers such as Ronseal offer anti-mould paints which advertises prevention of mould growth for around 5 years. Proper sealant and water stripping through buildings will help control aw (“the partial vapor pressure of water divided by the standard state partial vapor pressure of water”[13]).

UV light has multidisciplinary uses including bacterial elimination./UV light decontaminates the laminar flow bench when not used.3 March 2006.[3]

References

1. Flannigan, Brian, Robert A. Samson, and David Miller. "Microorganisms in Home and Indoor Work Environments." Google Books. CRC Press: Taylor and Francis Group, 12 Oct. 2011. Web. 25 Mar. 2015.[4]
2. Friman, Julia. "Comparative Study on Mould Growth on Plaster Boards Treated with Biocides." Goteborg University. Web. 23 Mar. 2015.[5]
3. Haleem Khan, A. A., and S. M. Kurappayil. "Fungal Pollution of Indoor Environments and Its Management." Science Direct. King Saud University, Oct. 2012. Web. 23 Mar. 2015.[6]
4. Salonen, Heidi. "Fungi and Bacteria in Mould-damaged and Non-damaged Office Environments in a Subarctic Climate." Science Direct. Elsevier, Oct. 2007. Web. 25 Mar. 2015.[7]
5. Klamer, Morten, Elisabeth Morsing, and Thor Husemoen. "Fungal Growth on Different Insulation Materials Exposed to Different Moisture Regimes."International Biodeterioration and Biodegradation. Elsevier, Dec. 2004. Web. 23 Mar. 2014.[8]
6. Krause, John D., "Generation of carbon dioxide and mobilization of antimony trioxide by fungal decomposition of building materials" (2005). Graduate Theses and Dissertations. [9]
7.Menetrez, M. Y., K. K. Foarde, T. D. Webber, D. Betancourt, and T. Dean. "Growth Response of Stachybotrys Chartarum to Moisture Variation on Common Building Materials." Sage Journals. International Society of the Built Enviroment, 15 Jan. 2004. Web. 23 Mar. 2015.[10]
8.Murtoniemi, Timo. "Microbial Growth on Plasterboard and Spore-induced Cytotoxicity and Inflammatory Responses in Vitro." Cytotoxicity and Inflammatory Responses in Vitro A 13 (n.d.): n. pag. Publications of the National Public Health Institute. Kansanterveyslaitos Folkhalsoinstitutet, 2003. Web. 23 Mar. 2015.[11]
9.Nielsen, Kristian F. "Mould Growth of Building Materials: Secondary Metabolites, Mycotoxins, and Biomarkers."Biocentrum-DTU: Technical University of Denmark. Lyngby, 2002. Web. 23 Mar. 2015.
10.Roberts, Susan L. "Symptoms of Fungal Exposure: Mycotoxicosis."Symptoms. Mold Help, 2003. Web. 25 Mar. 2015.[12].
11.Singh, Dr. Jagjit. "Building Mycology." Google Books. Taylor and Francis, 16 Jan. 2006. Web. 25 Mar. 2015.[13]
12.Verdier, Thomas, Marie Coutand, Alexandra Bertron, and Christine Roques. "A Review of Indoor Microbial Growth across Building Materials and Sampling and Analysis Methods."Research Gate. Elsevier Inc., 25 Apr. 2014. Web. 23 Mar. 2014.[14]
13."Water Activity." Wikipedia. Wikimedia Foundation, 22 Feb. 2015. Web. 24 Mar. 2015.[15]

Edited by Jocelyn Wensel, a student of Nora Sullivan in BIOL168L (Microbiology) in The Keck Science Department of the Claremont Colleges Spring 2015.