In this study, three soil extracts and seven species of microalgae were prepared and the growth enhancing/inhibiting effects of the addition of the soil extract on microalgae were investigated. The microplate technique was applied for incubation under various conditions, and the specific growth rate of the microalgae was compared between the control medium (the incubated microalgae without the addition of the soil extract) and the soil-added media. In addition, we focused on the characteristics of dissolved organic matter as major factors affecting the microalgal growth effect, and examined which organic characteristics affect the microalgal growth. It was suggested that the soil extract conventionally used in the National Institute for Environmental Studies (SE-N) showed the most marked growth-enhancing effect on microalgae at 25 °C. In addition, the soil extract made from the soil from the Rajamusa Forest Reserve, Malaysia, showed the most marked growth-enhancing effect on microalgae at 30 °C. The characteristics of SE-N on the excitation emission matrix (EEM) of fluorescence analysis were very different from the others because the soil extract had a clear tryptophan-like peak not observed in the others. SE-N also had organic matter of larger molecular size than the others. These characteristics might affect the microalgal growth.

To expand the liquid chromatography–tandem mass spectrometry (LC/MS/MS) analysis method for the simultaneous determination of 140 agricultural chemicals, which was developed in the previous study as an official analytical method of analyzing drinking water in Japan, we have conducted verification tests along with 11 organizations other than the National Institute of Health Sciences to confirm the validity of the analytical method using different apparatus. The validity of the analytical method was evaluated based on 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 117 agricultural chemicals, the quantification limits were lower than 1/100 of the desired values of each chemical, and the accuracy (recovery rates) and repeatability of analysis by the majority of the testing organizations satisfied the criteria in the guideline for the validation of the testing method for drinking water provided by the Ministry of Health, Labour and Welfare, Japan. Therefore, we judged that the simultaneous analytical method that we developed in the present study is applicable to the analysis of the 117 agricultural chemicals in drinking water.

Total organic carbon (TOC) is one of the indicators of organic pollution in aquatic environments. In this study, the pretreatment and measurement procedures employed when using a TOC analyzer with combustion catalytic oxidation are investigated to improve the accuracy of the analysis for samples containing suspended particles. Our results show that ultrasonically disrupting the particles promotes the homogenization of the suspension, which improves the accuracy of the TOC measurement. The TOC analyzer, which was designed to reduce the loss of samples in the injection syringe and the pathway of the equipment, obtained good recovery rates for samples taken from the north basin of Lake Biwa. However, low recovery rates were obtained for samples with high concentrations of suspended solids or dissolved organic matter. The low recovery rates reduced the accuracy of particulate organic carbon (POC) concentrations calculated as the difference between TOC and dissolved organic carbon (DOC) concentrations. It was found that the accuracy can be improved by using different methods (NPOC and TC-IC methods) for TOC combustion oxidation, depending on the sample concentration.

In the present study, we investigated the relationship between 11 properties of digested sludge and the optimal dosage ratio of polymer flocculant, assuming a conditioning process for sludge fed into a dewatering centrifuge. Furthermore, the study was focused on the supernatant phase (mixed phase of colloidal matter and dissolved matter) obtained by centrifugal separation of sludge, and a list of the properties of the supernatant phase was created. We then attempted to identify the properties that govern the optimal dosage. As a result, no correlation between total solids and the optimal injection ratio was observed. Therefore, the dosage was defined as the absolute quantity of polymer flocculant per 100 grams of sludge (g/100 g sludge = % per sludge weight) . As a result of examining its relationship with various properties, the strongest correlation was observed between the anion concentration of the supernatant phase and the optimal quantity of polymer flocculant, with r=0.73. A correlation was also found between the optimal quantity of polymer flocculant and the turbidity of the supernatant phase (r=0.68) . We thus found that the optimal quantity of polymer flocculant can be predicted simply by centrifuging the raw sludge and measuring the turbidity of the supernatant phase.

Concentrations of neonicotinoids and fipronil in river water were investigated in rural areas, the lower reach of the sewage disposal plant and principal rivers in Osaka Prefecture. As a result, pesticides other than nitenpyram and thiacloprid were detected at all sampling sites. Concentrations of imidacloprid increased drastically in June and concentrations of dinotefuran increased drastically from August to September. These periods were contemporaneous with spraying periods of these pesticides in rice fields. It was determined that none of the pesticide concentrations exceeded the water quality standards in Japan or Predicted Environmental Concentrations (PEC) , which were calculated by the Ministry of the Environment, in all survey spots. On the other hand, more than 5% of the aquatic organisms are expected to be affected by neonicotinoids in rural area rivers from late May to June according to the calculation from species sensitivity distribution (SSD) of multiple influence of aquatic arthropods.