Exposure to artificial daylight or UV irradiation (A, B or C) prior to chemical cleaning: an effective combination for removing phototrophs from granite

Abstract

This study evaluated whether exposing samples of granite colonized by a natural biofilm to artificial daylight or UV-A/B/C irradiation for 48 h enhanced removal of the biofilm with a chemical product previously approved for conservation of monuments by the European Biocide Directive. Rodas granite, which is commonly found in stone-built heritage monuments in Galicia (NW Spain), was naturally colonized by a sub-aerial biofilm. The efficacy of the cleaning method was evaluated relative to uncolonized surfaces and colonized control samples without previous irradiation, treated by dry-brushing or with benzalkonium chloride. The effect of UV irradiation in the combined treatment was evident, as comparable cleaning levels were not reached in the controls. Although the biofilm was not totally removed by any of the treatments, UV-B irradiation followed by benzalkonium chloride was potentially useful for cleaning stone, with results comparable to those achieved by UV-C irradiation, which is known to have germicidal effects.

Keywords:

• Ultraviolet light
• chemical cleaning
• biofilm
• cultural heritage
• biofilm treatment
• benzalkonium chloride

Acknowledgements

The authors thank Rafael Carballeira for taxonomic identification of the biofilm and Justo Arines for assistance with spectral measurements.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was partly financed by grant [GRC2014/028] (Xunta de Galicia). J.S. Pozo-Antonio was supported by a postdoctoral contract awarded by the University of Vigo within the framework of the 2011–2015 Galician Plan for Research, Innovation and Growth [Plan I2C] for 2014. P. Sanmartín is financially supported by a postdoctoral contract [POS-B/2016/030] (Xunta de Galicia).