Temporal atmospheric concentration change (TAC) of sulfur hexafluoride (SF₆ ) is essential to estimate groundwater residence time using SF₆. This study examined a method to reconstruct a regional TAC of SF₆. Groundwater samples were collected in the Kyoto Basin to measure concentrations of tritium and SF₆. Groundwater flow and mass transport analyses were conducted using a calibrated hydrogeological model. In the mass transport analysis of SF₆, three corrected TAC models were assumed, and the calculated SF₆ concentrations in groundwater were compared with the measured SF₆ concentrations. The error between the calculated and measured SF₆ concentrations was the smallest when the TAC was corrected in accordance with the number of business establishments in Kyoto Prefecture. The difference in apparent residence time estimated from the uncorrected and corrected TAC models ranges from 7 to 10 years. This method contributes to increasing the accuracy of groundwater dating by SF₆.

As petroleum-based fuels such as gasoline are themselves mixtures of many types of petroleum hydrocarbons, evaluating soil pollution with gasoline using luminous bacteria, is almost synonymous with evaluating combined toxicity of different types of petroleum hydrocarbons (such as n-alkanes). Acute toxicity test using luminous bacteria was performed on mixtures of two-component and three-component alkanes in which n-alkanes having 5 to 12 carbon atoms were arbitrarily combined. The obtained test results were evaluated for the combined toxicity effects using the acute toxicity data of alkane single component obtained in the previous study. From the comparison of the measured combined toxicity value and the combined toxicity value calculated using the single toxicity value of individual alkanes at the reaction time of 60 minutes, applying a square root sum of squares formula was clarified to be more reproducible than doing a simple additive formula. Additionally, a good correlation was found between the logarithmic value of the combined toxicity value based on the 50％ effect concentration and the measured combined toxicity value obtained at the reaction time of 60 minutes.