In order to confirm the validity of a solid-phase extraction (SPE) - liquid chromatography/tandem mass spectrometry (LC/MS/MS) analytical method for the simultaneous determination of iminoctadine, diquat, and paraquat in drinking water, a validation test was conducted by 12 organizations. Recovery tests of these agricultural chemicals in drinking water obtained by each organization were performed in two set points (0.5 and 0.05 μg/L), which are 1/10 and 1/100 of target values of diquat and paraquat. Linearity of calibration curves, selectivity, accuracy (recovery), repeatability, and intermediate precision of each agricultural chemical were calculated by the data of the recovery tests. Linearity of calibration curves and selectivity were satisfactory in these 3 agricultural chemicals. Accuracy, repeatability, and intermediate precision for diquat and paraquat obtained by the recovery tests were satisfied with the criteria in the guideline for validation of testing method in drinking water, which has been notified by the Ministry of Health, Labour and Welfare, Japan. Therefore, we concluded that the analytical method is valid for the analysis of diquat and paraquat in drinking water. In contrast, accuracy and repeatability, and intermediate precision for iminoctadine were not satisfied with the criteria in the guideline in some organizations due to the highest adsorbability among 3 chemicals. Therefore, analysis of iminoctadine by the analytical method requires especial care in pretreatment.

One of the species extinct in the wild, Kunimasu, lived only in Tazawa Lake in Senboku, Akita Prefecture, Japan, and became extinct. Recently, effort for improving water quality in Tazawa Lake has been made for Kunimasu to be able to live. This study estimates the benefits of improving the water quality in Tazawa Lake with contingent valuation method (CVM) and input-output analysis (IO). A questionnaire for CVM was executed through monitor investigation, using the dichotomous choice CVM in a double-bound formulation. In analyzing data that considered protest responses, the benefit was estimated as JPY 12,100,074,340 on average and JPY 8,399,811,102 on median. On the other hand, the amount of production induced by the improvement of the water quality in Tazawa Lake is JPY 754,692,751, and the amount of employment income induced by the improvement is JPY 232,334,230.
Furthermore, full model analysis of the determinants of willingness to pay (WTP) was conducted, and WTP was found to be related positively to scenario comprehension and income.