A web-based computational system to support the analysis of post-calibration-type mass spectrometric target screening test results was developed. The developed system is equipped with two types of databases: a database of chemical names, regulatory classifications, etc., of 36,436 chemicals, a database of mass spectra of 7,086 chemicals ionized by the electron ionization method and the experimental retention index (RI) values of 3,377 chemicals. The NIST/EPA/NIH Mass Spectral Library (NIST2020) , from which the mass spectra and the RI values were collected, is rich in ecotoxicants, but poor in some categories important for Japanese legislation, such as the priority assessment chemical substances in the act on the evaluation of chemical substances and the regulation of their manufacture, etc. The developed system demonstrated its capability to hit the correct name of the detected chemical. Target screening test results of spilled chemicals in a simulated river water sample prepared by adding 30 kinds of chemicals to an actual river water sample were obtained using a gas chromatograph-mass spectrometer to conduct the demonstration. The demonstration test results showed that the developed system could hit the correct name of the detected chemical.

The contributions of oxygen consumption by bottom-layer water and sediment were compared by investigating the oxygen consumption rates of bottom-layer water and sediment in Lake Kitaura and using in situ data on thermal stratification and hypoxic water. The oxygen consumption rate of bottom-layer water in Lake Kitaura was 2,550–2,910 mg m^-3 d^-1 and that of sediment was 652–1,080 mg m^-2 d^-1. These rates suggest that the contribution of oxygen consumption by sediment becomes greater when the height of the bottom-layer water column is less than 0.16 m. On the other hand, the contribution of oxygen consumption by bottom water becomes greater when the height of the bottom-layer water column exceeds 0.60 m. In addition, the in situ contribution of oxygen consumption was assessed using the vertical time-series data of thermal stratification and hypoxic water from July 28 to August 3, 2019, at Kamaya Observatory in Lake Kitaura. As a result, it was found that the contribution of oxygen consumption of by bottom-layer water was larger than that by sediment. However, it was considered that the effect of oxygen consumption by sediment could not be ignored, because hypoxic water formed gradually from the bottom of the lake.

Natural gas brine pumped up from below the ground surface contains not only natural gas and iodine, but also high concentrations of ammonia. To sustain healthy water environments, it is important to understand the status of NH₄–N in waste brine drained into a public water area after the collection of natural gas and iodine from the brine. In this study, the status of ammonia has been evaluated through field surveys, laboratory experiments, and simulation models of the flow and advection/diffusion of nitrogen in the Ichinomiya River, the tidal river into which the waste brine is drained. As a result of field survey and numerical simulation, the waste brine flows downriver along the top of seawater which inflows through the river bottom. It was calculated that the average residence time of the waste brine was about 1–3 days. Using the nitrification rate obtained from laboratory experiments, the concentration of NH₄–N nitrified to NO_x–N was estimated to range from 0.06 to 0.22 mg-N L^-1 during this residence time. The ammonia nitrogen was not nitrified in the field survey and the maximum NO_x–N concentration in the sampled water was about 2.5 mg-N L^-1. These simulation model and field survey results suggested that the concentration of NO_x–N produced by the oxidation of ammonia nitrogen in the Ichinomiya River would not exceed environmental standards.