Biodeterioration (of Stone)
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BIODETERIORATION (OF STONE)
Cross-references Bacteria Sulfur Cycle Thiomargarita Thiotrophic Bacteria
BIODETERIORATION (OF STONE) Christina Beimforde University of Göttingen, Göttingen, Germany
Definition Biodeterioration: Undesirable alteration of the properties of materials caused by vital activities of organisms. Introduction Materials are exposed to weathering processes caused by physical, chemical, and biological factors, leading to an irreversible loss of our cultural heritage. The reduction of decay by conservation strategies is of particular importance to protect historical monuments or significant cultural artifacts. Generally, the velocity of decay depends on the chemical nature and physical structure of materials as well as external factors associated to the locations where the objects are exposed. In many studies it was demonstrated that the process of weathering consists of various mechanisms acting together in coassociation with more or less intensity, making it impossible to separate individual aspects such as physical, chemical, or biological factors from each other (Koestler et al., 1994; Ehrlich, 2002). In many cases microbial activities can accelerate or trigger physicochemical processes. But the composition of microbial consortia, rather the microbial activity, is also affected by the surrounding chemical and physical factors. Solar irradiation, wind, and variations in temperature and humidity predominate the physical effects. Wind and humidity, of course, lead to the erosion of particles from stone surfaces. Variations in temperature, due to diurnal and seasonal changes, cause tensile stresses that can break up the structure of the material, resulting in a loss of persistence. Humidity, in combination with frost and salt, can intensify this effect. The crystallization of water or saline solutions is connected with an increase in volume that leads to “frost shattering” or “saline shattering” (Steiger and Dannecker, 1995). Chemical weathering may be caused by rain water which dissolves carbon dioxide originating from the ambient air or from respiration of present microorganisms. Generated carbon acid reacts with calcium carbonate, thereby producing calcium hydrogen carbonate with a higher solubility than calcium carbonate (Bell, 1993). According to Krumbein and Schönborn (1987), biological damages of building material can be divided into
different categories: (1) Anthropogenically induced damages due to atmospheric pollution as a result of the industrialization. These processes lead to an increasing level of inorganic (SO2, NOx) and organic (aliphatic and aromatic hydrocarbons) compounds in the air. This implicates acid rain that has a corrosive effect on stone buildings or other exposed materials (Pitzurra et al., 2003; Winkler, 1987). (2) Damages caused by higher plants and animals. The growth of higher plants, for example, leads to the physical destruction of materials. Moreover, excrements of birds contain ammoniac and nitrite, which can be utilized by chemolithotrophic bacteria. (3) Micr
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