## 1 Introduction  
Chemical accidents have occurred in South Korea consequent to the huge amount of chemicals used in various industries [1]. Even though fire and explosion accounted for 71.9% of total chemical accidents during 2008-2018 in Korea, most of the research has focused on chemical leakage accidents [2]. This might be due to a preconception that most fire or explosion gases tend to diffuse out and disappear into the atmosphere or photo-decomposed by ultra-violet of the sun [3, 4, 5], while chemical leakage can lead to contamination of the soil with a high concentration. It is questionable whether the chemical and its combustion by-product in the gas cloud, generated from a fire and explosion, affect the soil bacterial community and its metabolites for a long term since the chemical accident had occurred. Long-term risk assessment on contaminated sites by gas cloud has been poorly understood until now. On the other hand, there is another report that toxic substances in combustion gas cloud affect the soil ecology system. According to [6], chlorobenzene's combustion gases generated after fire and explosion can reach the soil even far from the accident site using the ADORA (Atmospheric Dispersion Of Reactive Agents) model (prediction model of gas diffusion in the atmosphere). Accordingly, the ecological impact of gas-affected soil where chemical fire accidents actually occur needs to be investigated using microbial-metabolic profiling and associated bacterial communities. This study focused on the toluene fire accident and its influence on contaminated soil. Toluene accidents have occurred most frequently out of using organic chemicals in the industry field, and it is one of the dangerous toxic substances [2; 7]. Toluene is a representative hydrophobic organic pollutant and is a long-term source of soil and aquifer contamination [8]. Contaminants might penetrate the ground soil, adsorb on natural soil, and act as a potential pollution source and it could result in toxicity to soil organisms [9]. Herein, a batch experiment was performed, which reproduces the fire accident of toluene, and then transportation and adsorption of combustion products onto the soil were proposed in this study. This lab-scale batch experiment was conducted to identify the name of combustion products that remained in the gas cloud in imitation of an actual chemical accident happening. There have been theoretical and computational calculations to expect the expected combustion products of toluene [10], but this study performed the batch experiment to increase the reproducibility of actual fire accidents. Gas chromatography coupled with mass spectrometry (GC-MS) was also utilized to identify combustion products in the gas cloud and remained chemicals in soil affected by toluene combustion in this study. Then, non-target metabolomics on soil located near chemical accident site was also performed based on LC-MS to identify metabolites in contaminated soil affected gas cloud generated from fire accident and further explored the metabolic response mechanisms in that soil. Moreover, analysis of bacterial community was performed using 16s ribosomal RNA (rRNA) sequencing surviving in contaminated soil near an actual chemical accident site. The specific objectives in this study are (1) identify combustion compounds in gas cloud generated from chemical combustion and study the transportation and adsorption of combustion products on ground soil, (2) propose a relationship between the chemical combustion by-products and excavate the secondary metabolites indicating trace of contamination in field soil (contaminated soil), and (3) to monitor the alteration of the microbial community of soil before and after exposure of a chemical accident. Further, this study will make it possible to determine which ground soils around the chemical accident site were contaminated by gas cloud using excavating biomarkers such as secondary metabolites in field soil (contaminated soil).