Dissolved organic matter (DOM) significantly relates to the speciation of heavy-metal ions in aquatic environments. To evaluate the toxicity changes of heavy-metal ions induced by the existence of DOM or dissolved humic substances (DHS), a microscaled algal growth inhibition (μAGI) test was conducted using a commercially available 96-well micro-plate. The μAGI test was compared with a regular AGI test using an Erlenmeyer flask. A regular AGI test is not very beneficial for accessing the toxicity of chemicals in an aqueous solution containing DOM or DHS because it absorbs visible light, which is required for algal growth. However, in this study, we clarified that the amount of algal growth in the μAGI test is hardly affected even at a high DHS concentration. The changes in the toxicity of copper to Chlamydomonas reinhardtii were evaluated under two conditions of the μAGI test, that is, with and without DOM/DHS. DOM and DHS samples were extracted from freshwater samples from Sakata in Niigata prefecture, Japan. The toxicity mitigation coefficients (TMCs) at 10 mgC · l^-1 DOM and DHS were estimated to be 1.4-2.7 and 4.8, respectively. Evidence found in this study shows that DHS strongly reduces the toxicity of copper (II) to algae, as compared with nonhumic components in DOM.

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The occurrence of pathogenic viruses and indicator microorganisms in water samples from a wastewater treatment plant in Japan was investigated monthly from July 2003 to June 2004. Forty-eight samples of raw sewage, treated sewage before chlorination, effluent after chlorination, and reclaimed water after advanced wastewater treatment using sand filtration and ozonation were subjected to a virus concentration method using an HA electronegative membrane, followed by virus detection using a TaqMan PCR method. Noroviruses of genogroups I and II were detected in all 12 raw sewage samples, showing much higher concentrations in winter, an epidemic season. Corresponding to the occurrence in raw sewage, the concentrations of noroviruses in treated sewage and effluent also increased in winter. The concentrations of enteroviruses and adenoviruses in the tested samples were relatively constant compared with those of noroviruses. Noroviruses and adenoviruses were still detected even after advanced wastewater treatment, but the concentrations of these viruses were much lower than those in the effluent samples. Viruses were removed by wastewater treatment as effectively as indicator microorganisms (total coliforms, Escherichia coli, and F-specific phages), suggesting that sewerage systems can contribute to reducing the load of pathogenic viruses discharged into aquatic environments.

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To establish a new method of detecting Cryptosporidium and Giardia in source and drinking water, we designed and evaluated a loop-mediated isothermal amplification (LAMP) assay, using a set of primers targeting of the 18S rRNA genes of Cryptosporidium and Giardia. The method showed a rapid and specific amplification of all the strains of Cryptosporidium and Giardia tested within 1 hour at 63°C. The detection limit of either protozoon was 0.8 (oo)cysts/test. The LAMP assay was considered to be used for testing the presence of Cryptosporidium and/or Giardia in drinking water having diagnostic high sensitivity and specificity.

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We compared macroinvertebrate assemblages between two sites in the Otani River, namely, upstream and downstream from the treated wastewater outlet of the Ikuno silver mine. The concentrations of heavy metals (i.e., copper, zinc, cadmium and lead) at the upstream site were remarkably high, based on the water quality criteria of the US Environmental Protection Agency for the protection of aquatic organisms. At the downstream site, the concentrations of heavy metals were lower by 60-80%. The water hardness was approximately 6 times higher at the downstream site than at the upstream site. Thus, it appeared that the toxicity of heavy metals to macroinvertebrates was reduced after the discharge of treated water. However, we observed no significant changes in most variables, indicating species richness and the abundance of macroinvertebrates. At the downstream site, heavy-metal concentrations were not reduced and/or there could have been some adverse effects of physicochemical changes, so that assemblage diversity and abundance cannot increase. We observed thick slime deposition on the riverbed at the downstream site, which is likely to have significant adverse effects on macroinvertebrates. Because such slime deposition is often observed in several rivers that received mine treated wastewater effluent, we should clarify its effects on aquatic organisms for the conservation of the river ecosystem around abandoned mines.

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