Proceedings e report - Firenze University Press

MOULD ON ORGANS AND CULTURAL HERITAGE OBJECTS. INVESTIGATIONS IN EIGHT CHURCHES IN SAXONY
2. Characteristics of Mould fungi
Within the kingdom of fungi, mould fungi are a large group which belong to the classes of
Zygomycetes (genus e.g. Mucor, Absidia), Ascomycetes (genus e.g. Chaetomium, Eurotium) or
Deuteromycetes (Fungi imperfecti; genus e.g. Aspergillus, Penicillium, Trichoderma, Aureobasidium,
Cladosporium) [5].
In the beginning of growth, hyphae originate from germination of spores. These occur in the
surrounding air more or less constantly and are – as well as the colourless hyphae – not visible to the
naked eyes. Under suitable conditions, the hyphae grow on and branch to a hyphae netting, the so
called mycelium.
The reproduction is possible both sexual and asexual. The spores play the key role for the
dissemination of mould fungi, since they may be produced in large amounts. Due to the coloured
spores, mould may be observed macroscopically as white, green, yellow, brown or black colonies. In
case of wood as substrate, mould is accounted to the wood discolouring fungi (together with blue stain
fungi).
Moulds usually grow on the surface of a substrate, but the hyphae may grow into porous materials.
They may effect discolourations, but also materials damages (e.g. coatings, glues, leather, paper or
linen). If hyphae grow between a substrate and its coating, e.g. a paint (polychrome) or a varnish, the
coating may leave its adhesion to the substrate and get loose. Additionally, mould may increase the
moisture content of a substrate and thus prepare the attack by e.g. wood destroying fungi
(basidiomycetes, soft rot).
Independent of materials damages, moulds shall not be tolerated indoor from hygienic aspects, since
spores, mycelia fragments, metabolites and mycotoxines as well as microbial volatile organic
compounds (MVOC) generally have an allergic potential or may effect diseases. Old infections are to
be considered as critically like new ones.
The living conditions are well-known so far. Sufficient moisture is needed, i.e. a relative air humidity
above 70 %. An important value for the mould growth is the so called water activity aw. It is defined as
the quotient of the relative humidity above the substrates surface and those above water at same
temperature (usually, aw value may be calculated by dividing relative humidity by 100). This value
describes the amount of free water of a substrate which is available for micro-organisms at the surface.
Most mould fungi need an aW value between 0.80 and 0.85. Some species, e.g. representatives of the
Aspergillus-glaucus group, may germinate already at values from 0.70. Moulds prefer slightly acid
substrates with a pH value of 4.5 up to 6.5; values up to 10.5 at most are tolerated. Some species
tolerate extreme acid conditions, e.g. Aspergillus niger grows even at pH 2.0.
Moulds have a wide temperature range of tolerance: mycelia of some species may grow at minimum
temperatures from –2 C up to +5 C (e.g. Alternaria alternata, Cladosporium herbarum); the
temperature optimum is approximately at 25°C, and the maximum temperatures are at 30°C up to
40 °C. In particular, the durable forms of moulds, the spores, may survive at their inactive status very
high temperatures, but also other extreme conditions like dryness and lack of nutrients.
From the described living conditions follows that moulds are very modest. They live on easy usable
matters like sugars, proteins and fats. As a source of nutrients, deposits on surfaces, like dust, soap,
soot or pollen, may be used. Thus, even almost inert materials may be grown on, as Fig. 2 shows. Also
thermoplastics, which often contain plasticisers or additives, may be infected or damaged.
3. Investigations
At first, eight churches with mould damages from different regions of Saxony were investigated. The
extend of mould attack, the conditions of location, outdoor and indoor climate, specialties of the
building, including heating, ventilation and use, and last but not least the microbial load of the indoor
air were taken into consideration.
Two of those eight churches, the Peter and Paul Church in Reichenbach/Vogtland and the St. Mary
Cathedral of Zwickau were selected for more detailed investigations. These two were chosen as
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