Moulds “The Good, The Bad and The Ugly”
An Introduction to Fungi, Moulds and Yeasts
Moulds are part of a larger family of organisms known as fungi. Some fungi are multi-cellular, and some are uni-cellular, the single cellular varieties are known as yeasts. By contrast, due to their size and method of reproduction, moulds are classified as microbes, despite the fact that they are in fact multicellular filamentous organisms. These filaments known as ‘hyphae’ and grow into a colony which is a network of branching filaments called a ‘mycelium’ and when such a colony grows large enough, it becomes visible to the human eye.
Like all fungi, moulds require sufficient moisture to grow and, they do not derive their energy and sustenance for life by photosynthesis but instead by digesting the organic materials upon which they live. They accomplish this by secreting enzymes which can dissolve organic materials into simpler substances that can then be readily absorbed into the mycelium for digestion. Therefore, fungi, moulds and yeasts play a pivotal role in the decomposition and the recycling of organic nutrients throughout our ecosystem.
All moulds reproduce by creating large numbers of spores which can easily be transmitted by air currents or from the surface to surface by cross-contamination. Once a spore lands on a surface that has sufficient moisture and organic material for its needs, it will germinate and grow prolifically and rapidly reaching maturity and creating millions of more spores to spread further.
The Good Mould
Not all fungi, moulds and yeasts are bad or harmful to human life, indeed they play a significant role in the biotechnology industry in the manufacture of pharmaceuticals, antibiotics, foods and beverages. Some moulds such as the Penicillium spp. produce mycotoxins as they grow which inhibit the growth of competing microorganisms and have played an important role in the pharmaceutical and antibiotics industry. Others, such as Aspergillus oryzae, and Aspergillus sojae have been utilised in Asia for centuries to ferment soya beans and wheat to make soybean paste and soy sauce. Moulds and yeasts that are used in food production include:
- Fusarium venenatum – Quorn
- Geotrichum candidum – Cheese
- Neurospora sitophila – Oncom
- Penicillium spp. – Various cheeses including Brie and blue cheeses
- Rhizomucor miehei – Microbial rennet for making vegetarian and vegan cheeses
- Rhizopus oligosporus – Tempeh
- Rhizopus oryzae – Chinese Rice Wine
The Bad Mould
Of course, neither are all fungi, moulds and yeasts beneficial, in fact, many can be extremely hazardous to human health. Moulds and their spores are found ubiquitously in our environment and a normal fraction of workplace and household dust.
However, when elevated levels of mould spores become present in the air or deposited on surfaces, it can become hazardous to human health. Some diseases can be caused by allergic sensitivity to mould spores. Symptoms of mould allergies may include inflammation of the eyes and nasal passages, breathing difficulties with blocked sinuses, frequent coughing and sneezing, asthma, headaches, migraine and in some cases dermatological reactions such as urticaria. Some people also suffer from the presence of pathogenic moulds within their bodies or disease conditions caused by the ingestion or inhalation of toxic compounds (mycotoxins) synthesised by the moulds as they proliferate.
Additionally, food spoilage moulds can proliferate on products intended for animal and human consumption and can be a significant cause of food spoilage and illness making the food unsuitable, unpalatable or even toxic when consumed. Many well-known food preservation methods such as dehydrating, freezing, chilling, pickling or preserving with vinegar, salt or sugar are intended to prevent mould spoilage.
The Ugly Mould
Excessive and unsightly mould growth will become visible in buildings when temperatures and humidity levels become conducive to their growth. Then the ubiquitous spores present in the air will land and germinate allowing the moulds colonise and grow. Moulds will proliferate on surfaces either contaminated with organic residues or on building products that actually contain organic components such as paper, wood products or natural fibres and fabrics. Apart from being visibly unsightly, causing musty smells or foul odours, moulds will also cause biodegradation of the natural materials they are digesting to nourish their growth.
Analysis and Diagnosis of Mould
The determination of mould species and airborne spore concentration is best achieved by qualitative and quantitative air sampling. A special pump with a predetermined flow rate is used for a predefined period of time. Therefore, the volume of air passing through the pump can be accurately quantified.
To provide statistically significant samples with normalised background levels, air samples will be taken from the affected test area, a control area and from fresh air outside. The air pump draws in a known quantity of air and separates any microscopic airborne particles before depositing them on nutrient-rich culture medium. This medium is then incubated in a laboratory at an optimal temperature and moisture level to encourage any mould spores present to germinate.
The laboratory results can quantify fungal mould densities by comparing spore counts between the samples and other well empirical norms. Although a very small quantity of air is actually sampled, the spore count data is extrapolated to estimate the number of spores that would be present within a cubic meter of air. Following germination, the mould species is also determined by optical recognition using a microscope.
Physical Control and Mitigation of Molds
Serious mould issues in buildings can be controlled and then mitigated in the future by a few simple good housekeeping practices. The most crucial action is to reduce Relative Humidity levels below those that facilitate mould growth. Efficiently functioning air conditioning systems are a prerequisite to controlling the Relative Humidity and indoor ambient temperatures. The USA Environmental Protection Agency (EPA) recommends that Relative Humidity should be maintained below 60% and ideally between 30% to 50%, to preclude the germination and proliferation of fungal spores.
Eliminating any other sources of excess moisture such as persistent leaks is also one the most important steps that can be taken to control mould growth. The use of High-Efficiency Particulate Air (HEPA) filters can also reduce the airborne density of the mould spores available for germination. Finally, it may also be necessary to remove any affected materials and replace them with inorganic or antimicrobial alternatives.
Chemical Treatment and Cleaning of Molds
The chemical treatment regime recommended for serious mould colonisations is a three-step process:
The first step is to thoroughly clean and sanitise the affected area and proximate surrounding areas using hot water and a detergent based sanitising formulation. This is intended to remove the mould and its mycelium along with any organic residues upon which the mould might be using as a substrate for growth and proliferation.
Once the affected areas (and the adjacent surrounding areas that might be subject to contamination by spores) have been cleaned and sanitised, all the areas need to be thoroughly disinfected using a hot solution of sodium hypochlorite (a chlorine based bleaching agent) which will effectively kill any remaining moulds and spores. Additionally, the oxidising properties of the chlorine solution can, in most circumstances, also remove any staining and residual odours caused by the mould.
Finally, once the surfaces have been cleaned, sanitised and treated with a bleach solution, there is a need to prevent any re-colonisation of the mould. Assuming all the physical control and mitigation actions have also been successfully implemented, then this final step is best achieved by the widespread application of an organo-silane based antimicrobial surface coating. This provides long-term protection against all known microbes, including moulds, yeasts, bacteria and viruses on a 24/7 basis for up to six months.
Post Remediation Evaluation and Assessment
Following all the treatment protocols described above, it is also necessary to monitor the situation closely to ensure that the potential for any mould re-colonisation is precluded. This is undertaken with a regular integrated sampling approach including the measurement of ambient temperatures, relative humidity and air-sampling for spore density in the air.