# Biological Risk for Hypogea: Shared Data from
## 1 Introduction  
Subterranean sites such as caves and catacombs are generally characterised by limited air circulation, a limited variation in temperatures throughout the year, a high level of humidity, and at times, pronounced gradients of light [1]. Hypogea show similarities but also differences with caves due to their more limited size which leads to greater fragility also on the basis of the variability of materials used by human activities [2, 3]. In fact, they were often embellished by wall paintings, stuccos, ceramics, bricks, and mosaics for decorative and augural purposes, as well as by statues, scarophagi, and funerary objects which need to be preserved as testimony of their cultural heritage [4, 5]. Moreover, the tombs which often maintained an environment cut off from the exterior world for hundreds of years, undergo substantial environment changes after excavations and consequent weathering [6, 7]. Literature on biological colonisation in caves is becoming highly relevant, with hundreds of papers describing the microbial diversity and the relationship with environmental conditions, whereas muchless is available for tombs. The most common inhabitants of subterranean sites are oligotrophs (bacteria, represented mainly by _Actinobacteria_, and fungi), accustomed to long periods of starvation and, at times, phototrophs (cyanobacteria, green algae, diatoms, mosses, ferns) that have adapted to scarce light [4; 5; 6; 8; 9; 10; 11; 12; 13]. The current knowledge of the ecological succession of microbial communities in hypogea in relation to environmental factors, such as the efficiency or risks of different control methods seems insufficiently addressed. The peculiarities of hypogea, which vary according to different cultures also deserve special attention, as they give rise to distinct biodeterioration phenomena. There are relatively few studies on the biodeterioration of tombs. The first tombs were in Egypt [14; 15] and Japan [16; 17; 18; 19], then in Italy and other European countries, and more recently in Korea and China [6; 7; 13; 20; 21; 22]. Environmental conditions of subterranean tombs give rise to physic-chemical weathering especially when water evaporation occurs which leads to efflorescence (carbonation, nitrification, sulfatation) or when it reaches condensation, causing a loss of pigment and lithic effects of materials [2; 23; 24]. They also greatly increase the biological risk since the levels of humidity, temperature, input of nutrients, light, and the nature of the substratum, have long been considered facilitating factors for microbial colonisation [16; 18; 25; 26; 27; 28]. Knowledge of microbial biodiversity and their metabolic and ecological profile, such as the environmental conditions which favor the various taxonomic groups, are important in defining the risk for artefacts and in creating both indirect (preventive) and direct (biocide treatments) control methods [4; 29]. Knowledge of the tolerance range of each limiting factor for the various species has a great practical relevance in stopping or reducing undesirable growth [4; 30]. Such information is also relevant when biocide treatment is taken into consideration, due to the need to choose the most efficient one against specific microorganisms [31]. Within an international cooperation project between Italy and Korea, we selected Etruscan tombs (mainly in Tarquinia but also at other sites of ancient Eturia), along with the ancient tombs in Songsan-ri (Gongju) and in Neungsan-ri (Buyeo), respectively. They are of interest also because most of them constitute relevant UNESCO World Heritage Sites. The aim of this paper is to analyse and provide a critical review and comparison of recurrent biodeterioration phenomena observed in the Etruscan tombs in Italy and the ancient tombs in Republic of Korea, as well as the respective conservative treatments carried out at these sites, with a special focus on preventive intervention and biocides.