Moulds are fungi that grow as saprophytes or parasites on organic material. They appear as a fluffy, felt-like mass that can take different colours depending on species. The colours range from black, different shades of green to even yellow or red. Microscopically this mass, which is named mycelium, consists of a network of threadlike hyphae. They produce hydrolytic exoenzymes that break down biopolymers and subsequently absorb it as nutrition. The mycelium, which is the vegetative part of the fungi, can under certain circumstances (often depletion of substrate) make spore-bearing parts that produce masses of spores. These spores are very small (2-15 µm) and may easily be dispersed in the air. If the spores are deposited on a surface with suitable growth conditions (moisture, nutrition and temperature) they may germinate and start a new mycelium. As a consequence we are daily exposed to fungal spores. Since mould growth is encouraged by warm and humid climate, the highest spore numbers are found in the summer and autumn season. 'Mould´ is not a systematic concept, but a collective term for surface-living fungi, which have representatives from all phyla of the fungi. The description of microscopic fungal genera and species are based on light microscopical (LM) observations (Image 1). The morphology of the reproductive structures is important in the classification of fungi. Scanning electron microscopy (SEM) is a very useful tool to reveal the fine structures of the spore surfaces not easily observed by LM (Image 2).
Extensive mould growth may give a musty unpleasant odour caused by microbial volatile organic compounds (MVOC´s) that can be produced by the fungi. Another topic of concern is other types of secondary metabolites called mycotoxins. Several mould species produce these compounds that can be toxic and carcinogenic to animals and human (e.g. aflatoxins produced by Aspergillus flavus and A. parasiticus). The mycotoxins are non-volatile and can be found in the spores, fragments of hyphae or in the substrate on which the moulds grow. The same is true for allergens, a third group of substances from mould growth. They can give allergic reactions in persons sensitive to moulds.
Significant associations have been found between damp, mould-contaminated buildings and health effects although spore counts in indoor air samples are generally very low. In certain occupations like wood trimming and farming, airborne spore counts may reach more than a billion per cubic meter, which gives high risk for acute illness.
NIOH has a considerable experience and knowledge on microbiological agents in the working atmosphere, both on sampling, analysis, systematics and epidemiology (publications). We have ongoing projects in this field besides frequent service analysis for the customers and industry. Further we have collaboration with Mycoteam, a company with extensive know-how on analysis of mould, especially related to investigations of mould-contaminated buildings.
Image 1: Light microscopy image showing the morphological
structure of the sporangiophore of Aspergillus versicolor.
Stained with cotton blue. This species is frequently encountered
on water-damaged building materials like gypsum and wood.
The spores are small and easily dispersed to the air.
Elevated levels of spores in indoor-air may indicate a
mould-problem in the building.
Photo: Mycoteam AS.
Image 2: Scanning electron microscopy image of conidiospores
of Aspergillus versicolor