# Biological Risk for Hypogea: Shared Data from
## 3 Results
### The Ancient Tombs of the Baekje Dynasty
#### 3.2.2 Conservation Treatments  
In Republic of Korea, indirect methods have been used to control the environment to prevent problems caused by microorganisms in ancient tombs. Since 2003, the indoor temperature and humidity in Tomb No. 6 has been maintained with an air conditioning system at 18 \({}^{\circ}\)C and 90% humidity on average. However, air flow from the system dried the air too much creating problems for the wall paintings hence the system was shut down in 2011. An analysis of the microclimatic conditions was carried out and buffer zones were set up to assist prolonged conservation of the hypogea. Research was also conducted on the biochemical characteristics and environment influences (temperature, moisture, and nutrients) of microorganisms over the seasons [58]. On the basis of previous investigations, internal microclimatic conditions, and thermal preferences of isolates, three risk periods for microorganism occurrence in ancient tombs were classified [56] as follows: (1) Safe: T \(<\) 18 \({}^{\circ}\)C, (2) Warning: T = 18-22 \({}^{\circ}\)C, (3) Risk: T \(>\) 22 \({}^{\circ}\)C [6]. In addition, the risk periods for microorganism occurrence in the two tombs were respectively: \"safe period for microorganism occurrence\" from January to July for Tomb No. 6 and from January to October for Tomb No. 1 while the \"warning period for microorganism occurrence\" was from August to December for Tomb No. 6 and from November to December for Tomb No. 1. Such differences in the risk periods for microorganism occurrence in the two ancient tombs is due to the different structures and environments.  
Further research was also conducted to select biocides to remove the blue-green algae (_Gloecapsa_ spp. and _Lyngbia_ spp. [83; 84] that occurred in Tomb No. 6 and the surroundings tombs. Reagent K101 was selected (composition: EDTA, (NH4)2 CO2, Na2 CO3, sodium hypochlorite) which was developed by differentiating the composition of AC322 [93] and B57 solutions [83]. After spraying the biocides to the walls, poultices were applied, and ultraviolet rays were subsequently irradiated for 24 h [83; 85]. The treatment did not give rise to recolonisation phenomena and secondary damage [90]. A thermo-hygrostat was installed in 2003 to maintain stable environmental conditions but unfortunately it caused the drying of murals and walls, so that its use has been stopped in the Tomb No. 6 since 2011. Then, a treatment was conducted to prevent possible damage being fungal growth started on the facing when the thermo-hygrostat was stopped. Benzalkonium chloride (C22H40 CN) 1% was used to remove the fungi, and the rayon paper that was applied was later removed using tepid distilled water [94]. After that, there have been no cases in which biocides have been used directly inside ancient tombs and on the wall paintings.  
Since heterotrophic microorganisms and algae may grow if there are suitable nutritional and environmental conditions, the development and application of efficient eco-friendly biocides that do not damage the murals is necessary [87]. Several studies have been conducted to select and field test substances from medicinal plants and tree extracts capable of managing microorganisms that occur on such sites [95; 96; 97; 98; 99; 100]. Research has also been conducted on ingredients and extracts of herbal medicine to remove biofilms from external stone cultural heritage elements [102]. Such studies have led to selecting a biocide (Stone Keeper) based on eugenol with an eco-friendly emulsifier [103]. This biocide was applied to fungi taken from ancient tombs on the basis of a study showing that the natural substances anethole and eugenol have antibacterial and antifungal properties [87]. The mixture of anethole and eugenol (1:2) significantly inhibited the growth of _Aspergillus creber_ and _Aspergillus versicolor_. A simulation also tested the effects of natural ingredients, thereby verifying their potential to inhibit and kill microorganisms that occurred on ancient tomb murals [85; 87].