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Manganese micro-nodules on ancient brick walls
P López-Arce1, J García-Guinea, J L G Fierro
1Centro Tecnológico de Toledo (AITEMIN), C/Río Valdemarías, s/n E-45007, Toledo, Spain. paulal.arce@aitemin.es
The Science of the Total Environment
|January 16, 2003
Summary
Manganese micro-nodules on ancient Toledo bricks indicate pollution. These nodules form from anthropogenic manganese in water, exacerbated by algae, signaling environmental contamination.
Area of Science:
- Geochemistry
- Environmental Science
- Materials Science
Background:
- Ancient bricks in Toledo, Spain, built by diverse cultures, are the primary construction material.
- These historical bricks are increasingly degraded by modern anthropogenic activities, including industrial emissions and traffic pollution.
- Manganese micro-nodules, approximately 2 micrometers in diameter, have been observed growing beneath the biofilm on the bricks' external surfaces.
Purpose of the Study:
- To investigate the composition and origin of manganese micro-nodules found on ancient Toledo bricks.
- To determine the role of anthropogenic activities and natural processes in the formation of these micro-nodules.
- To assess the potential of manganese micro-nodules as indicators of manganese pollution in urban environments.
Main Methods:
- Energy-dispersive X-ray microanalysis (XPS) was used to determine the elemental composition of the micro-nodules.
- Scanning electron microscopy (SEM-EDS) and X-ray diffraction (XRD) were employed to analyze the ancient wall surfaces.
- Chemical and biological analyses of local water bodies (River Tagus, Torcón and Guajaraz reservoirs) were conducted to identify manganese sources.
Main Results:
- XPS analysis revealed the presence of Al, Si, Ca, K, Fe, and Mn in the micro-nodules, with manganese exclusively as Mn(4+) and iron as Fe(3+).
- The study suggests micro-nodule formation occurs either through the reduction of anthropogenic MnO(4)K in water or oxidation of dissolved Mn(2+) facilitated by algae biofilms.
- High concentrations of algal biomass in surrounding waters correlate with manganese micro-nodule development.
Conclusions:
- Manganese micro-nodules on ancient brick walls serve as reliable indicators of manganese pollution.
- Anthropogenic sources, particularly industrial and traffic emissions, contribute significantly to manganese pollution in the Toledo region.
- The interaction between pollutants, water chemistry, and biological activity (algae) drives the formation of these mineral deposits on historical structures.