[H-CG24] Nuclear Energy and Geoscience

[HCG24-P06] Evaluation of Microbial Communities Contributing to the Decrease in Concentration of Fluorescent Dye Solutions: Dependence on Oxygen and Temperature Conditions

*Ayumi Sugiyama¹, Kotaro Nakata¹, Takuma Hasegawa¹ (1.Central Research Institute of Electric Power Industry)

Keywords:fluorescent dyes, sodium fluorescein, groundwater tracers, microbial community

Fluorescent dyes have been widely used as conservative tracers for investigations and experiments using boreholes such as tracer experiments. In recent years, however, significant decrease in concentration of fluorescent dye during storage of solution has been observed. In Japan, it has been reported color of sodium fluorescein (SF) changed and concentration of it decreased significantly after SF contacted with groundwater obtained in Horonobe area that is the northernmost part of Japan (Horonobe GW) (Nakata et al., 2017). The decrease in concentration can cause the underestimation of the influence of drilling fluid in drilling and the recovery rate of the tracer in tracer experiments. Thus, clarification of the mechanism of the decrease in concentration and proposal of effective countermeasures are needed. Previous study has revealed that another groundwaters also can decrease the concentration of SF and the activity of microbes causes the decrease in concentration (Sugiyama et al., 2021). However, the mechanism has not yet been well investigated. The information such as type of microbes and reactions involved with the decrease in concentration of fluorescent dye is important to clarify the mechanism of it. We evaluated the optimal condition for microbes to decrease the concentration of fluorescent dye and analyzed the microbial community in the targeted groundwater. These results may be useful to narrow down the microbial communities involved with the decrease of the fluorescent dye. SF solution was used for the experiments because the concentration was most significantly decreased when it was contacted with Horonobe GW. SF was contacted with Horonobe GW at various temperatures and oxygen concentration in solution was also controlled. The optimal condition for microbes to decrease the concentration of fluorescent dye was discussed based on the results. In addition, the microbial community in Horonobe GW was analyzed before and after the experiments. The type of microbes involved to the change in the concentration of the SF was also discussed.
This study was carried out under a contract with the Ministry of Economy, Trade and Industry (METI) as part of its R&D supporting program titled "Research and development on groundwater flow evaluation technology in bedrock (2021 Fy) Grant Number JPJ007597.