Since the Ministry of Health, Labor and Welfare of Japan announced hygiene management guidelines for public baths in 2019, many local governments have revised their regulations on organic substances in bath water from potassium permanganate (KMnO₄) consumption of 25 mg L^-1 or less to the total organic carbon (TOC) of 8 mg L^-1 or less, in principle. The change in these values was 0.32 times. In Osaka City, the number of facilities that exceed the TOC standard has tended to increase after the revision of the regulations, so the relationship between KMnO₄ consumption and TOC was examined. As a result, the relation of TOC = 0.456 KMnO₄ in 38 facilities where inorganic disinfectant was used for bath water was determined in a survey of 47 facilities, and the coefficient of KMnO₄ was significantly larger than 0.32. This study in Osaka City showed that the new TOC standard for bath water is stricter than the former KMnO₄ standard.

Recently, it has become possible to select the test concentration range in the fish acute toxicity test using the trend analysis (TA) estimate by a categorical approach, but few studies have been conducted on comparing the TA estimate with the measured toxicity. In this study, we compared the TA estimate［48-h median lethal concentration (LC₅₀) ］and the measured toxicity (96-h LC₅₀) of sodium n-decyl sulfate using medaka (Oryzias latipes) . Our results indicated that the estimated and experimental values were 310 and 420 mg L^-1, respectively, and the difference was within 1.5 times. Since the alkyl carbon chain length of sodium n-decyl sulfate is outside the range of alkyl carbon chain lengths in existing data, the TA estimate obtained in this study was considered an unreliable extrapolated value. Therefore, there was a concern that the basis for the determination of the concentration range in the definitive test was weak. However, it is considered possible to determine the test concentration in the definitive test with higher accuracy by considering relevant available information (e.g., 96-h LC₅₀ of other fish species) in addition to the TA estimate.

Because of the reduction of nutrients in marine areas nationwide, the rates of achieving total nitrogen (TN) and total phosphorus (TP) water quality standards have reached 96% and 95%, respectively. Nevertheless, the achievement rate of the chemical oxygen demand (COD) standard has remained almost unchanged over the last 30 years. The cause of this discrepancy was investigated in Osaka Bay and the following was found. Eutrophication measures such as “TN reduction to suppress the occurrence of high-concentration phytoplankton blooms (red tide) ” are working effectively. This was seen in the water quality indicators associated with particulate organic matter. In contrast, the amount of dissolved organic matter has not decreased. The reduction of nutrients has resulted in a rise in the C: N ratio of organic matter, caused by the constancy of the organic carbon concentration and the decrease in organic nitrogen concentration. A discrepancy between COD and TOC trends has also occurred. It was common to Tokyo Bay and Ise Bay that COD has not decreased because nutrient reduction induces a change in the quality of organic matter.