6 Wood Discoloration

6.1 Molding 123
Molded wood is, however, unmarketable. For decorative purpose, e.g., wall
paneling (Fig. 6.2b), molded wood is unsuitable, as the color spots are not mechanically
removable, but can be only masked by colored paints. Infected wood
is not suitable for various hygienic requirements, e.g., packaging material. In
addition, technological characteristics, for example the gluing of plywood, can
be affected by molds (Wolf and Liese 1977).
Mold growth in buildings is increasingly becoming a problem. Molding
in indoor environments (Thörnqvist et al. 1987) is favored by high substrate
moisture (water activity 0.9–1.0), high air humidity around 95%, warmth and
insufficient ventilation (Viitanen and Ritschkoff 1991b), like in cellars and
bathrooms. According to the German standard DIN 4108 part 2, the relative air
humidity on the indoor surfaces shall not amount to over 80% (Borsch-Laaks
2005). Moisture with following mold contamination can arise from condensation,
flood, and various types of leaks. Excessive insulation after the petroleum
crisis has markedly favored condensation areas (cold bridges), from cellars
to attics, which rapidly become sites of mold growth. Accompanying lifestyle
changes (frequent showers, new cooking methods, inadequate airing of bedrooms)
have led increasingly to the production and accumulation of moisture
in the home. A study in Belgium of isolated molds in homes of patients with
allergic problems showed that more than 90% of those houses were contaminated
by molds of the genera Cladosporium, Penicillium and Aspergillus (Nolard
2004). Cladosporium sphaerospermum infiltrated 60% of the homes and
was responsible for high contaminations, particularly in bedrooms and bathrooms.
Aspergillus versicolor, Penicillium chrysogenum, P. aurantiogriseum,
P. spinulosum, P. brevicompactum, Chaetomium globosum, Stachybotrys chartarum,
andAlternaria alternata are often found on the walls of bedrooms,
living rooms, and kitchens. While Cladosporium herbarum, a phytopathogen,
does not grow in houses, large numbers of spores enter through windows and
doors mainly during the summer months.
Molds may cause health problems. About 200 fungal species produce various
mycotoxins (about 100), of which some are highly toxic to humans and
animals (mycotoxicoses) (Müller and Loeffler 1992; Schwantes 1996; Reiß 1997;
Kiffer and Morelet 2000; Samson et al. 2004). The cancerogenic aflatoxins from
Aspergillus fumigatus and A. flavus in food (agricultural crops, cereals etc,
Meister and Springer 2004) are well known. Human health damage can further
develop by mycoallergies through direct contact with a fungus or inhaled
spores (molds in the living space). Five to 15% of the population suffering
from respiratory allergy has been sensitized to one or several molds. Exposure
of young children to molds and their metabolites may have a “stimulating”
effect on the onset of later allergies (Nolard 2004). Mold allergies also occur
in work environments. Woodworkers inhale spores of Cryptostroma corticale
and Alternaria species (woodworker’s lung). “Bagassosis” may develop during
bagasse processing. “Suberosis” is due to Penicillium glabrum growing on cork
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