Biocalcification the Context for Bioremediation

Monumental stone decay is a consequence of the interaction between the material and environmental factors, such as water, heat, atmospheric pollutants and living organisms. This interaction starts at the stone's surface and progresses inward, leading to the gradual increase of stone porosity and weakening of the cohesion in mineral structures. Conservation of monuments foresees, in most cases, the application of consolidating products in order to strengthen the weathered stones and to avoid the dwindling and scaling of the material. Numerous kinds of organic and inorganic products have been used to this aim, but almost all have shown, in time, different negative results. In recent years new approaches have been attempt and tested, based on the use of bioremediation procedures in which biocontrolled, using living bacteria and biomediated, using bacterial cell fractions or organic matrix macromolecules, methodologies have been applied in order to induce, inside the stone porosity, the formation of new calcite crystals, a product very similar to the natural composition of calcareous rocks. These treatments should overcome the negative effects related both to the chemical structure and the use of solvents observed for organic products, and the very superficial formation of calcareous film, for inorganic ones. Besides, this bioinduced calcium carbonate should last for a longer period of time. In fact, due to its nature of composite material, it is less sensitive to the chemical and physical factors which remove inorganic products or degrade synthetic resins exposed to natural weathering.