Tetramethylammonium hydroxide (TMAH) , which is mainly used in the manufacturing process of semiconductors and liquid-crystal panels, is not subject to effluent regulation under the Water Pollution Control Law. Therefore, the possibility is not excluded that some portion of TMAH used is released into the environment, and the effects of TMAH on aquatic organisms are of concern. In this study, we conducted reproduction tests with Ceriodaphnia dubia and short-term toxicity tests on embryonic and sac-fry stages of zebrafish to set a management target value of TMAH concentration in wastewater. As a result, the concentrations yielding no observed effect on Ceriodaphnia dubia and zebrafish were 0.0158 and 500 mg L^-1, respectively, indicating a high sensitivity of Ceriodaphnia dubia to TMAH. Therefore, given that the dilution ratio of wastewater in public water bodies is 10 times, the TMAH concentration in wastewater discharged directly from a factory site to public waters should be managed to be below 0.158 mg L^-1 in consideration of the protection of aquatic organisms.

The effect of sponge-pore size for a combined downflow hanging sponge (DHS) and upflow sludge blanket (USB) filtering system for the nitrification and denitrification, respectively, of a marine aquaculture system was evaluated. The nitrifying DHS reactor maintained the concentrations of total ammonia nitrogen and NO₂^--N of the breeding water at 0.08 mg-N L^-1 and 0.05 mg-N L^-1, respectively. The DO concentration in the breeding water was about 6.17 mg L^-1 without direct aeration of the tank. Despite the high DO of the denitrifying USB reactor influent, the nitrogen-removal performance was good and the NO₃^--N concentration in the breeding water was maintained below the theoretical value. Regarding the effect of sponge-pore size for nitrification by the DHS reactor, the sponge with the smallest pore size, named CFH-30, had the fastest nitrification rate and sludge growth rate. Microbial community analysis of sludge contained in sponge revealed that sponge with the largest pore size had the highest detection rates for ammonia-oxidizing archaea and nitrite-oxidizing bacteria.

We developed a liquid chromatography–tandem mass spectrometry (LC/MS/MS) analysis method for the simultaneous determination of 141 agricultural chemicals, the “Complimentary Items” in tap water in the Japanese Waterworks Act. Furthermore, we evaluated the validity of the analytical method on the basis of the results of the recovery tests performed with two set points, that is 1/10 of the desired value and 1/100 of the desired value of each agricultural chemical in the Japanese Waterworks Act. For 129 agricultural chemicals (when dechlorinated with sodium ascorbate) or 127 agricultural chemicals (when dechlorinated with sodium thiosulfate) , the quantification limits were lower than 1/10 of the desired values of each chemical, and the accuracy (recovery ratio) and repeatability also satisfied the criteria. For 120 agricultural chemicals, the quantification limits were lower than 1/100 of the desired values of each chemical, and the accuracy (recovery ratio) and repeatability satisfied the criteria of the Japanese guideline concerning water quality analysis. Therefore, we judged that our simultaneous analytical method developed in the present study is applicable to the analysis of 120 agricultural chemicals in drinking water. However, we should select the dichlorination treatment agent in accordance with the target chemicals.

Extensive marine environment monitoring has been performed using oxidative stress biomarkers. However, progress regarding the use of these biomarkers in river environment monitoring has been insufficient. When applying oxidative stress biomarkers in river aquatic organisms, it is important to take into consideration the natural fluctuation of these markers. In this study, we investigate the effect of body size and seasonal changes on oxidative stress biomarkers in stream caddisfly, Hydropsyche spp., which is one of the primary consumers in river ecosystems. Body sizes were classified into 4 classes in accordance with wet weight. Catalase activity, which is a type of antioxidant enzyme, tended to differ depending on the class. Catalase activity and the oxygen radical absorbance capacity had a significant correlation with wet weight. On the other hand, examining the seasonal change for the same size class, the catalase activity, oxygen radical absorbance capacity, and oxidative damage showed different responses. Furthermore, Hydropsyche spp. in August, in a survey conducted immediately after a flood, indicated low oxidative damage. Hydropsyche spp. was able to adequately remove the reactive oxygen species produced as a result of stress caused by the flood.

To clarify the origin of lead (Pb) in an irrigation reservoir with a shooting range in upstream, sediments of a small stream located in the shooting range, sediments and soil from upstream of the shooting range, sediments in the irrigation reservoir, and river water have been observed. It is well known that the Pb stable isotope ratio has an original value in each Pb mine. The Pb stable isotope ratios in soil and sediment were totally different between the samples from upstream and downstream of the shooting range. On the basis of the composition ratios of Pb and other metals (zinc and copper) used in the brass coating of bullets, the distance index (D.I.) was calculated and the results were applied for cluster analysis. Both D.I. and cluster analysis results indicated that soil and sediment samples from the upstream and downstream are clearly different. Our results indicate that our integrated approach of using the Pb isotope ratio, D.I. and cluster analysis is a good indicator of the origin of Pb contamination in soil and sediment.