On the basis of a worldwide trend of the indirect and direct potable reuse of wastewater, methodologies of risk assessment and management for chemical and microbial risk in water were discussed. First, the definition of risk was described, and the characteristics of health risk caused by consuming drinking water were summarized. Second, the methods to set drinking water quality standards and a recent implementation of the precautious principle were explained. An example of an indirect potable reuse system proposed by the authors was shown. Only 17 chemicals, including disinfection by-products, among a tremendous number of chemicals in wastewater were selected as target chemicals. A procedure for estimating the required and sufficient removal efficiencies of the water treatment process to produce potable water, which is also the procedure for avoiding overtreatment, was described. Third, the characteristics of microbial risk were explained, and the significance of disability-adjusted life years (DALYs) , by which chemical risk and microbial risk can be compared, was highlighted. A relationship between the safety level estimated using DALYs and the required treatment level was described. Furthermore, it was pointed out that the characteristics of people’s risk perception should be taken into account when discussing acceptable risk levels.

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Iron is an important trace element for the growth of phytoplankton in natural waters. Primary production in coastal water is considered to be maintained by the supply of terrigenous iron that migrates downstream via surface water and ground water flow. In this review, we summarize previous studies on iron biogeochemistry in coastal and freshwater systems with particular emphasis to the influence of dissolved organic matter and its quality on the iron transformation kinetics and the iron availability to phytoplankton in coastal waters. A number of previous studies, particularly those in the field of ocean science revealed that in air-saturated water at circumneutral pH, the solubility of inorganic ferric iron is at the subnanomolar level, whereas the presence of dissolved organic matter substantially increases the iron solubility. In addition to iron coordination by organic ligands, other reactions, including photochemical and thermal redox reactions, are also related to iron bioavailability. Given that iron bioavailability to phytoplankton is tightly associated with its speciation, studies on iron chemical speciation is necessary to properly assess the contribution of terrigenous iron in coastal primary productivity. Finally, to understand the connection between terrigenous iron and coastal primary productivity, integrated studies that cover not only the iron speciation and availability in freshwater and coastal waters but also the hydrochemical processes associated with terrigenous iron runoff are recommended.

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We have developed the liquid chromatography – ultraviolet adsorption detector (LC/UV) , mass spectrometry (LC/MS) , and tandem mass spectrometry (LC/MS/MS) analysis methods for the simultaneous determination of formaldehyde and acetaldehyde in drinking water. Furthermore, 15 organizations have conducted a validation test to confirm the validity of the analytical methods. Recovery tests of these chemicals spiked into drinking water samples distributed to each organization were performed for two set points; the standard value and 1/10 of the standard value for formaldehyde in the Japanese Waterworks Act. The linearity of the calibration curves, selectivity, accuracy (recovery) , repeatability, and intermediate precision for each chemical were calculated using the data of the recovery tests. The linearity of the calibration curves and selectivity were satisfactory for both chemicals. The accuracy, repeatability, and intermediate precision for both chemicals obtained by the recovery tests satisfied the criteria in the guideline for the validation of testing methods for drinking water, which has been specified by the Ministry of Health, Labour and Welfare, Japan. Therefore, we concluded that the analytical method developed in the present study is valid for the analysis of formaldehyde and acetaldehyde in drinking water.

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Sediment core samples with a length of about 1 m were collected at station 35, which is located at the intersection of the extended lines of the Arakawa and Tamagawa Rivers in northwest Tokyo Bay. The core samples were cut into pieces of 2.5 cm depth and ¹³⁷Cs and dioxins were analyzed. There was a clear relationship between the depth and the years of some marked ¹³⁷Cs fallout events. The sedimentation rate at 0 - 50 cm depths was estimated to be 0.78 cm y^-1. On the other hand, the dioxin concentration began to increase in 1946, reached its maximum in 1970, and then gradually decreased. The change in the dioxin concentration was well explained by governmental actions, such as the establishment of environmental laws in the estimated years. The dioxins compositions in the surface sediments of seven stations around the Arakawa and Tamagawa Rivers showed that the sediment at station 35 was derived mainly from the Arakawa River.

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Hypoxia is a serious environmental problem in most enclosed coastal seas. The duration of hypoxia must be known to evaluate the impact of hypoxia on the benthos or surrounding environment. In Osaka Bay, continuous dissolved oxygen (DO) data have been available for several observation points on the website of the Kinki Regional Development Bureau, Ministry of Land, Infrastructure, Transport and Tourism since April, 2010. Using these hourly data, we have calculated the monthly average, the standard deviation of DO, and the durations of hypoxia and anoxia. In summer, the daily variation (daily maximum - daily minimum) of bottom DO values exceeded 1 mg L^-1 at the observation points in the coastal area. The monthly standard deviation of bottom DO values is also over 1 mg L^-1. Strong wind caused intermittent DO rises in the southeastern part of Osaka Bay. As a result, hypoxia with a duration shorter than 24 hours occupied half the total period of hypoxia in one month in the southeastern part of Osaka Bay in summer, except August, when hypoxia is most severe. On the other hand, the duration of hypoxia in the northern part of Osaka Bay is longer than that in the southeastern part of Osaka Bay.

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