## 4 Conclusions  
This study proposed the possibility of soil contamination by gas cloud when a chemical fire accident occurs. Moreover, the biomarker such as soil microbiological and plant metabolites were excavated in contaminated soil, using metabolomics. Firstly, it was proposed that toluene derivatives such as naphthalene, 2-methylindene, ethylbenzene, etc. were identified as combustion products in the gas cloud; then, it was studied that a specific atmospheric condition such as conversion layer can trigger contacts between gas cloud and ground soil. This research also assessed the impacts of toluene combustion on microbial community and metabolites of contaminated soil in South Korea using 16S rRNA sequencing and metabolomics. The obtained results show remarkably increased metabolites such as 1,4-dichlorobenzene, 5-chloro-1,2,4-trihydroxybenzene, hydroxyhydroquinone, naphthyl-2-methyl-succinic acid, oxaloacetate, and streptomycin 6-phosphate. Moreover, the metabolites in plants surviving in contaminated soil were also identified as 3-nitroacrylate, related to the detoxification process in plant metabolism by its self-protection function against chemical stress. In addition, the downregulated biomarker were also identified as selagine, 3 beta-(1-pyrrolidin)-5 alpha-pregnant-11,20-dione, and phytoreamide. Toluene exposure led to the shift in bacterial composition and structure. _Artthoracter globiformis, Streptomyces scabici, Sphingomas lutea, Splinguomas sedimiticola, Nocardioides mesophilus, and Lysobacter niabensis groups were significantly decreased, while _Bradynhizobium japonicum_ and _Mycobacteriumarcinogenes_ groups were increased, but there was only a weak effect on the bacterial diversity. A close connection between bacterial communities and metabolic profile in soil was also observed, suggesting their consistent response to environmental stress. Further studies are needed to identify the bacterial community producing secondary metabolites that respond to toluene stress of soil microbiology and plant. In this research, few links with bacteria and its metabolites were found. Accordingly, whole-genome sequencing of bacteria will provide better information to find out the causal relationship between soil bacteria and upregulated metabolites in the next study. As a result, it is remarkable that soil contamination, not by chemical leakage but by chemical fire accidents, can strongly impact the soil ecology, considering that the alteration of bacteria community and metabolites are clearly identified, even in soil that has been contaminated for a long term, e.g., three years. Additionally, hydroxyhydroquinone discovered in field soil is a representative breakdown material of aromatic compounds. Soil contamination by gas cloud has been considered a low concentration's contamination, but the discovery of hydroxyhydroquinone in field soil implies biodegradation of toluene, and its combustion products degraded slowly, depending on the soil environment, and \begin{table}
\begin{tabular}{c c c} \hline \hline
**Phylum** & **Control** & **Field** \\ \hline Proteobacteria & 34 & 33 \\ Actinobacteria & 29 & 26 \\ Chloroflexi & 8 & 9 \\ Acidobacteria & 7 & 14 \\ Cyanobacteria & 5 & \textless{}1 \\ \hline
**Species** & **Control** & **Field** \\ \hline Arthobacter globiformis group & 3825 & 933 \\ Streptomyces scabieiei group & 2424 & 722 \\ Sphingomonas lutea group & 1644 & 714 \\ Sphingomonas sediminicola group & 1967 & 266 \\ Nocardioides mesophilus group & 1292 & 116 \\ Lysobacter niabensis group & 814 & 6 \\ Bradylrhizobium japonicum group & 319 & 1112 \\ Mycobacterium keratinocytes group & 54 & 238 \\ Hamadaea flava & 56 & 140 \\ Sphingomonas pruni group & 47 & 118 \\ Unit: DNA Counts (16s rRNA). & & \\ \end{tabular}
\end{table} 
Table 5: Fate of phylum and species of bacteria in control and field soils (contaminated soil). affect the soil microbiology even after three years of the toluene fire accident. The identified breakdown materials and metabolites in filling soil can point to traces of soil contamination.