All kinds of microbes, including Aspergillus, contribute actively to geological phenomena. Biodeterioration refers to the branch of science that explores the microbial transformation of compounds; particularly, the undesirable transformation of man-made materials via processes that include mineral formation, dissolution and deterioration. Aspergillus spp. can colonise and damage many different types of material, including: woods, metals, polymers, stone and fuels. The fungus has been associated with a reduction in both the stability and durability of man-made structures and materials. Important examples of the materials that can be affected include: The concrete housing of nuclear waste departments, structural components of bridges, building materials, glass, paper and fuels.

Perhaps most worryingly, research by Fomina et al (2007) has demonstrated that prolonged fungal biochemical activity promotes adverse environmental effects through the consequential damage of nuclear waste disposal units. This occurs despite high radioactivity, as fungi are able to successfully colonise concrete and induce deterioration both biochemically and biomechanically under these conditions (Zhdanova et al. 2000, Fomina et al. 2007). Fungal hyphae may directly induce damage by physical perforation and tunnelling through decaying rock formations (Fomina et al. 2007). In a process referred to as (bio)chemical dissimilatory biodeterioration, fungi can also excrete organic compounds which degrade materials (Allsopp et al. 2004). A primary concern is that without the adequate maintenance or treatment of waste disposal units, environmental leakage of highly radioactive substances may result. A recent study of the inner concrete of the Chernobyl reactor found Aspergillus to be one of the most prevalent fungal species (Zhadanova et al. 2016). Turick and Berry (2016) have explained that:

“the microbial contribution to degradation of the concrete structures containing radioactive waste is a constant possibility. The rate and degree of concrete biodegradation is dependent on numerous physical, chemical and biological parameters”.

Furthermore, Zlobenko (2013) found that Aspergillus niger had the greatest capacity for the biodeterioration of concrete nuclear waste containment units. The colonisation and biodegradation of concrete is also seen on many modern building materials, bridges, buildings and monuments (Lugauskas and Jaskelevicus. 2007, Geweely. 2010, Piotrowska et al. 2014, Farooq et al. 2015); this has similar potential for disastrous consequences, as well as the loss of heritage.

Aspergillus and other fungi have also been identified on the orbiting International Space Station (ISS). With over thirty seven strains of fungi isolated, one of the most prevalent was Aspergillus (Satoh et al. 2016). These fungi are strongly associated with the degradation of polymers (Lugauskas et al. 2004) and other materials on which the structure of the ISS depends. Biodeterioration may therefore be a real danger, potentially resulting in system failure.

Biocorrosion is defined as the enhanced degradation of substances through microbial interactions. Aspergillus has been shown to mediate biocorrosion in metal, wood, oil and clay-containing structures (Gadd. 2010). One of the primary enabling mechanisms through which biodeterioration occurs is fungal biofilm formation. This is defined by the clustering of surface-bound microbial cells that are encapsulated in an extra-cellular macromolecular matrix (Donlan. 2002). Biofilm formation involves the production of acidic substances and pigments, which can directly damage the integrity of structures and are associated with the degradation of hydrocarbon-containing compounds (Morton and Surman, 1994). The extent to which this happens is varied and may be unclear for given sites. Unique environmental conditions, as well as the varying diversity and concentrations of organisms on structures, makes it increasingly difficult to determine the extent to which deterioration occurs on untested sites (Saiz-Jimenez, 2001).

Prevention of biodeterioration

Numerous protective compounds have been developed to aid in both the prevention and the treatment of biodeterioration. Rajkowska et al (2016) indicated that quaternary ammonium biocides (QACs) may be highly beneficial in protecting both wood and brick from six different moulds, including Aspergillus. Other preventative measures include the use of antifungals in cement mortars, ozone application on concrete, and ZnO-based nanocomposites specifically designed to mitigate fungal-induced corrosion (Do. 2005; Ditaranto. 2015). Thus, the use of these compounds may negate or slow biodegradation by inhibiting biofilm formation on structural materials.

Bioremediation

Bioremediation is the deliberate application of microorganisms for the reclamation, immobilisation or detoxification of metallic and radionuclide pollutants. Santos et al (2014) have demonstrated the bioremediatory effects of Aspergillus awamori and its ability to degrade the toxic components of cyanide-containing wastewater. The innate capacity of Aspergillus terreus to degrade contaminants such as Endosulfan ⁠— a known insecticide ⁠— has also been identified (Mukherjee et al. 2005). Furthermore, the bioremediatory potential of A. niger has been established in the removal of cadmium ⁠— a toxic heavy metal ⁠— from soil (Srivastava and Thakur, 2006).

Biocides

Biocides are chemical agents with the capability of destroying living organisms ⁠— pathogenic and non-pathogenic (Block. 2001). Thus, they have numerous applications: steriliser, tuberculicide, disinfectant, fungicide, virucide and sanitiser (Rossmore. 2012). Tortarano et al (2005) have demonstrated that Aspergillus fumigatus is susceptible to the activity of the biocides commonly used in hospital settings. However, it has also been indicated that biocides may enhance the growth of some toxigenic species (eg. Aspergillus westerdijkiae) and can be a threat to human health when used in buildings (Mikkola. 2015). Their application in certain settings has had a limited impact on the reduction of Aspergillus and other fungal growth. The pesticide action network (PAN) estimate at least 10% of all biocides are known endocrine disruptors and potentially carcinogenic (PAN, 2016).

Silver nanoparticles (AgNPs) have been developed as an alternate antifungal to biocides and are effective in reducing common indoor mould loads (Ogar et al. 2015). However, the neurotoxic capacity of AgNPs has been under scrutiny in recent years. Xu et al (2013) have published data that “clearly demonstrates the potential detrimental effects of AgNPs on neuronal development and physiological functions”. They warn against their prolific usage within homes and public buildings.

Reducing indoor fungal loads

Fungal spores and other hyphal debris are known to cause respiratory health problems when inhaled. The growth of Aspergillus and other fungi on building materials in the home and offices is often noted as a source of airborne spores – see Air Quality for more details. Preventing the growth of fungi within our homes, places of work & recreation areas may be highly beneficial in reducing these respiratory health effects (Benndorf et al. 2008).

Moulds present within buildings pose a clear health risk to those with asthma and respiratory allergies: Aspergillus is one of the most prevalent fungi (Twaroch et al, 2015). Thus, it is clear that precautionary measures should to be adhered to in order to mitigate the potential health risks caused by Aspergillus. This entails preventing the biodeterioration of future constructions. A study evaluating several common antifungals demonstrated that tea tree oil had the greatest growth inhibitory capacity against A. fumigatus and P. chrysogenum (Rogawansamy et al. 2015). Furthermore, Inouye et al (2000) observed the promising antifungal potential of several essential oils, indicating a possible non-toxic alternative to conventional antifungal solutions for use in enclosed environments.

Biodeterioration sources

Reviews

Reviews (external sources)

Diercks, M., Sand, W. and Bock, E. (1991) ‘Microbial corrosion of concrete’, Experientia, 47(6), pp. 514–516. doi:10.1007/bf01949869. Springer

Bibliography

Bibliography (external sources)

Allsopp, D., Seal, K.J. and Gaylarde, C.C. (2004) Introduction to Biodeterioration. United Kingdom: Cambridge University Press. Available at Amazon

Block, S.S. (2001) Disinfection, sterilization, and preservation. Available at Amazon  (Accessed: 10 August 2016).

PAN Germany – Pesticide Action Network Germany, The draft biocide regulation is not enough to adequately protect human and the environment, Flyer, 2010, pp.1-2 Available here (Accessed: 10 August 2016).

Rossmoore, H.W. (2012) Handbook of Biocide and preservative use. Available here (Accessed: 10 August 2016).

Slideshow

Zlobenko, B.P. (2013). ‘Assessment of the Biodegradability of Containers for Low and Intermediate Level Nuclear Waste’ (IAEA-TECDOC- CD– 1701(Companion CD)). International Atomic Energy Agency (IAEA)

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