Calcium oxalates in biofilms on limestone walls of Maya buildings in Chichen Itza, Mexico

Microbial biofilms frequently cause the esthetic and biological deterioration of stone monuments. Chichen Itza, designated as a UNESCO World Heritage Site and as one of the seven new wonders of the world, is one Maya archeological site affected by biofilms. In the present study, we analyzed the biofilms at three different building complexes of Chichen Itza: the Lower Temple of the Jaguars, the Temple of the Warriors, and Tzompantli. Samples of biofilms and detached rocks were taken from walls with abundant white-, green-, black-, and orange-colored biofilms. The morphology of rock fragments and dust was analyzed by electron and optical microscopy and was structurally characterized by X-ray diffraction. An HCl treatment (5% v/v) was subsequently applied to eliminate carbonates. The morphological analysis evidenced the presence of cyanobacteria, algae, and lichens. Some algae formed small nodules on orange-or black-colored rocks. Lichens were associated with a distinct mineral content on the inner surface of rocks versus on the outer surface. The presence of calcium oxalates such as weddellite (C2CaO4 center dot 2H(2)O) and whewellite (C2CaO4 center dot H2O) and other minerals, including quartz and feldspars, was confirmed by X-ray diffraction. The lichens collected from the Lower Temple of the Jaguars and Tzompantli were therefore confirmed to disintegrate rock surfaces through biomineralization and the formation of oxalate crystals. At sites with greater solar radiation, a higher quantity of weddellite and a lower quantity of whewellite were observed. In conclusion, the establishment of microorganisms on the stone surfaces of Chichen Itza causes esthetic damage and also leads to the biomineralization of these rock surfaces.