Examining the Potential of Enzyme-Based Detergents to Remove Biofouling from Limestone Heritage

Laurenz Schröer,Tim De Kock,Maxim Deprez,Géraldine Fiers,Nico Boon,Lander Soens,Veerle Cnudde

doi:10.3390/coatings12030375

Laurenz Schröer, Tim De Kock + Show 5 more

Open Access

https://doi.org/10.3390/coatings12030375

Copy DOI

Abstract

Commonwealth war cemeteries commemorate the fallen of both world wars. Every casualty is remembered with a memorial or on a headstone. However, the headstones need to be maintained extensively, as microorganisms easily colonise them, affecting legibility and the stone substrate in the longer term. In the past, pesticides and other chemicals were popular to clean headstones, but due to raised environmental concerns, new treatment strategies are necessary. Within conservation science, enzymes have emerged as a popular tool for restoration. However, studies related to the use of enzymes for stone conservation are limited. Within this preliminary study, we applied commercially available enzyme-based treatments on biofouled natural building stones in the laboratory and in situ. Photography and spectrophotometry were used to monitor the effect of the treatment. The application of enzymes resulted in rapid disintegration of biological pigments, whereas visual improvement occurred more gradually. The successful application of enzymes suggests their potential to replace pesticides as the principal cleaning agent for headstones and natural building stones in a more general fashion.

Highlights

To remember the casualties of World War I and II, the Commonwealth War Grave Commission has built war grave cemeteries and memorials
To describe biological discolouration by chlorophyll during the experiment, we propose the following factor: Chlorophyll discolouration (CD) =
Preliminary laboratory and in situ experiments confirmed the effectiveness of enzymebased treatment to clean natural building stones

Summary

Introduction

To remember the casualties of World War I and II, the Commonwealth War Grave Commission has built war grave cemeteries and memorials. All the cemeteries are characterised by uniform white headstones and monuments, often built with Portland limestone [1]. Headstones and any rock surface are exposed to extreme conditions of desiccation, oligotrophy, ultraviolet radiation, etc., microorganisms extensively colonise them. The colonisers include lichens, algae, fungi, bacteria and archaea [3]. The environmental conditions, together with the bioreceptivity of the material, determine the colonisation potential [4]. Microorganisms attach to the rock surface and form biofilms or aggregates held together by a matrix of mainly extracellular polymeric substances (EPS) [5–8]. Colonisation usually starts with autotrophs, such as cyanobacteria and algae [9]. Heterotrophs could be the first colonisers and could dominate without the presence of autotrophs [7,10,11]

Objectives

Methods

Results

Conclusion