Biodeterioration of sandstone under the influence of different humidity levels in laboratory conditions Alka Jain a, * , Seema Bhadauria a , Virendra Kumar b , Ramvir Singh Chauhan c a Department of Botany, R.B.S. College, Khandari, Agra- 282002, Uttar Pradesh, India b Department of Electron Microscopy, National JALMA Institute of Leprosy and Other Mycobacterial Diseases (ICMR), Agra, India c Department of Physics, R.B.S. College, Agra, India article info Article history: Received 25 June 2008 Received in revised form 17 September 2008 Accepted 21 September 2008 Keywords: Fungi Relative humidity Sandstone Biodegradation XRD SEM abstract Excessive moisture in building materials supports microbial growth. It has been referred that relative humidity more than 55% promotes the microbial growth. To test the effect of different relative humidity tropical chamber test was set up at 52%, 76%, 85% and 96% RH and maximum diversity of fungi was found at 85% and 96% RH. Two fungi Aspergillus sydowi and Aspergillus flavipes were present throughout the course of study from moderate to highly abundant form. It was observed that Fusarium moniliforme, Cephalosporium acremonium, Papulospora sp. proliferated at higher relative humidity (i.e. at 85% and 96.6% RH) and Fusarium roseum, Fusarium oxysporum only at 96% RH level. The relative humidity level lower than 62%, i.e. at 52% level exhibited no fungal growth on sandstone surface during two-year observations. During the study pattern it was noticed that diversity decreased gradually and dominance of particular species increased with the time factor. Analysis of sandstone after fungal colonization by X-ray diffraction and SEM showed the formation of newly formed biomineral. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction The role of micro-organisms in deterioration of stone is related to climatic conditions and to the physical and chemical properties of construction materials. Micro-organisms through their biological action cause physical alteration to pore size, cracking, changes in water circulation, in the chemical composition of the surfaces and finally acidolithic and oxido-reductive deterioration, leading to weakening of the mineral structures [12]. Using different tech- niques diverse filamentous fungi (fungi that show thread like structure) have been isolated from deteriorating stone samples. The isolated fungi are primarily terrestric xerophilic and xerotolerant (the fungi growing on land and loving and tolerable to dry condi- tions) species and also because of the melanin (black pigment) in cell wall they have the quality of oligotrophy (low nutrition condition) and UV protection [20]. The fungi and other microbes probably brought coincidently on sandstone surface where active weathering process and prime colonisators took place and allowed them to grow and contributed to sandstone degradation. The most typical structures of fungi – hyphae (synonym of filaments) enable the fungi to penetrate and their colonization into stone, that is reflected in the form of disruption of stone structure and increasing porosity. Another mode of biodegradation is evident due to the production of numerous extracellular metabolites like organic acids that reflected in the form of biopitting (pit formation by microbes) and lamellar dissolution of minerals. Although the inorganic composition of the stones was not favorable for the growth of these heterotrophic micro-organisms, yet it was likely that organic residues from different sources on the stone surface were utilized as nutrients [6]. Light and sufficient warm temperature combined with rich nutrients of organic resi- dues present on stone surface create suitable conditions for reproduction of quiescent (dormant) fungal spores [11]. Those sensitive to humidity and heat emit hyphae that penetrate the substrate, with mechanically destructive effects [3]. The high moisture content of atmosphere in building material supports microbial growth. The perusal of literature referred that relative humidity more than 55% suitable for their growth. The present study was aimed to investigate the mycoflora (species content of fungi in an area) acting on sandstone at different relative humidity and their effect on substrate. The surface water near the stone surface combined with carbon dioxide from microbial respiration and produced carbonic acid that could dissolve the calcium and magnesium carbonates of limestone and the silicate and nitrates, the constituents of stones [6]. The dissolution of constituents of stones caused alternation of stone composition and material loss. In another form the bioweathering of mineral substrate results in the formation of secondary biominerals on the attacked substrates. * Corresponding author. Tel.: þ91 09412255279. E-mail address: alka.jain@rediffmail.com (A. Jain). Contents lists available at ScienceDirect Building and Environment journal homepage: www.elsevier.com/locate/buildenv 0360-1323/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.buildenv.2008.09.019 Building and Environment 44 (2009) 1276–1284