Until recently (until 1969) fungi were included in the plant kingdom. In 1969, R. H. Wittaker proposed a division of the living world into five kingdoms on the basis of differences in the structure of cells and methods of food intake from the environment. In his opinion, fungi should be removed from the plant kingdom and included into a separate kingdom of fungi since they are not capable of photosynthesis and take up nutrients produced by other organisms. Wittaker’s classification continues to be used now. In the fungi kingdom that was created there are different divisions, depending on the classification of the properties of fungi. One of the divisions separates mould from fungi, as they are characterised by different qualities from other types of fungi, which are important to biological processes; however, from the point of view of their effects on the human environment, they can be treated as fungi.
Fungi differ from plants by the structure of their cell walls, body organisation and methods of reproduction. The fact that fungi take in nutrients produced by other organisms does not mean that these substances are absorbed directly. These compounds are far too complicated from the point of view of fungi's demands and thus are broken down by enzymes secreted by the fungi to substances that they can absorb.
Therefore, they play an important role in maintaining the ecological balance of our planet. Most of them, like bacteria, derive their nutrients from organic debris and dead organisms. Without the continuous decomposition of huge deposits of branches, leaves, manure, dead animals, and the release of these organic compounds, which can be re-incorporated into the various biochemical cycles, life on our planet would gradually disappear. The enzymes secreted by fungi are called mycotoxins and are extremely harmful to humans, especially those that inhabit houses which are produced by fungi called dry rot fungi (Serpula lacrymans).
Most fungi are propagated by means of microscopic spores that are spread by wind, water or animals. The concentration of spores depends on the seasons. A distinction is made between concentrations of spores indoors and outdoors. For indoor spores, the cycle of propagation is regulated by weather conditions and temperature, humidity, sunlight exposure and the quantity of nutrients. As can be expect, their concentration is lowest in winter. The concentration of indoor mould spores, because of favourable conditions, is maintained throughout the year on a high level, which is much higher than outside. Particularly high levels can be achieved in winter due to the excellent conditions for reproduction and the reduced air exchange (ventilation) due to the low outside temperature.
The minimum and maximum values of ambient temperature is different for different species of dry rot fungus and even different for different parts of a single fungus (e.g. mycelium, mushrooms and spores). Most fungi can grow when the ambient temperature is higher than 3°C. The optimum temperature is about 22°C to 30°C, whereas the upper limit value is about 40°C. It can happen that dry rot fungus exists at temperatures from about 2°C to 5°C to as low as 35°C to 38°C. The mushrooms in particular can survive in an environment with much lower or higher air temperature, although the mycelium is also very resistant to high and low temperatures.
For example, the mycelium of dry rot fungus (Serpula lacrymans) withstands frost at -8°C for 3 hours, and the mycelium of Coniophora puteana withstands temperature of -30°C. In an environment with high ambient temperature the mycelium of dry rot fungus will last for 40 minutes when the air is 40°C and for the mycelium of Coniophora puteana when the air is 60°C.
The acidity of the substrate in which fungi grow expressed as a pH value ranges from 2 to 11, while the development of fungi causes a change in the acidity of the substrate in which it grows. The optimum pH value for their development is pH 4.6 for most species and this is also the pH range for timber. The basis for their propagation in a home or apartment are all organic compounds from dust, mites, natural and synthetic fibres, hair, food crumbs, food, carpets, timber, glue, wallpaper and other building materials. It should be emphasised that for the development of the fungus it is sufficient to create local conditions necessary for their development to establish a colony within few hours, which will expand despite conditions different from those in the incubation period. Some species of fungus can synthesise water from the environment and provide adequate moisture to their growth even in the absence of moisture in the room.
The attentive readers will draw their attention to the fact that conditions such as high humidity and temperature in a room do not last long enough for the fungus to develop, because these conditions are not very comfortable for humans. However, from my experience I can confirm that there are such spaces where the relative humidity exceeds 70% and the temperature 25°C. Of course, the colonies of fungi in such circumstances feel at home and reproduce perfectly. There is another mechanism for the formation of mildew. As mentioned above, fungi need proper humidity to grow, but this is the basic humidity they need. Moisture can be accumulated over time by material which is overcooled in winter: for example in insulating materials such as mineral wool, plasterboards, or under wallpaper and wood panelling. Depending on the source of water or condensation or leakage, the material can achieve locally adequate moisture to ensure the development of the colony. Proper temperatures can provide heating of the premises from the inside or heating of, for example, the roof sheathing by the sun, starting in early spring. If the area is large enough, moisture and the possibility of pairing limited, several hours of proper humidity and temperature is sufficient for the formation of colonies of fungi.
The picture below show two examples of the functioning of fungus colonies.
The video picture shows the fungus colony. Thermovision camera image shows a significant drop in temperature at this point, whose minimum value is 11.7°C. The room temperature was 20°C and the relative humidity was 39%. Under the conditions in the room, condensation occurs at a temperature of 6.1°C. For condensation to occur in this place at the ambient temperature, the humidity should reach 57%. It is therefore clear that the conditions for the development of fungus colonies occurred in the past, which then exists as an environment sufficient for the development was created in its environment.
In the case of this room, the air temperature was 24°C at the humidity of 70%. In these circumstances condensation occurs at the temperature of 18.2°C, while the minimum temperature was 16.7°C. The green area means the surface on which continuous condensation takes place in the mentioned conditions due to the temperature lower than the temperature of condensation. The period of two months was enough for the emergence and development of fungi colonies to a form that was visible to the naked eye because the colony reached the stage of producing spores – visible dark spots.
Both cases described above relate most likely to fungi of the Aspergillus nigier species, which is characterized by spots emerging in brown and black colour, which are the spores. The same colour of spots is also produced by Aspergillus terreus, Alteranaria alternata, Rhizopus nigricans, Mucor mucedo, fungi of the genus Stemphylium Curvularia lunata. They develop on the coatings of glue paints, emulsion and oil paints, plasters, wallpapers, wallpaper adhesives, carpets, wooden parts, plasterboard, plastics. Before the spores outbreak, bulging, flaking and cracking of plaster are visible on the walls and ceilings as well as loosening of paint layers or wallpapers. The possibility of colonization of the environment by fungi after creation of the appropriate conditions for their development, is demonstrated by an experiment conducted by the researchers who have proved that the colonies of fungi were formed within three weeks on sterile glass, on which organic substances from fingerprints were placed.
Fungi of the genus Aspergillus are recognized under the pathogenic and toxigenic species that constitute a significant risk to the health of humans and animals. They cause serious diseases, which treatment is difficult. Infection occurs very often via inhalation resulting in respiratory diseases of for example lungs. The fungus produces a toxic compound called aflatoxin, which is one of mutagenic compounds classified as mycotoxins, i.e. fungal metabolites (substances produced by fungi used for the decomposition of organic matter to the compounds absorbed by the fungi). At the present moment we have knowledge about 400 compounds like this. A small amount will cause severe changes in the metabolism of proteins, fats and carbohydrates which often leads to damage of the liver or kidneys or to the development of cancer. A large number of mycotoxins cause disturbances in the functioning of the nerve tissue manifesting permanent damage of central nervous system.
In case of detection of fungi colonies the microbiology laboratory should be consulted to determine the type of contamination and the method of liquidation thereof. The causes of creation of the conditions favourable to the development of fungi should be also removed. Self-removal of contamination by means of the cleaning detergents available on the market can be ineffective and even dangerous for residents.