The algal growth potential (AGP) test is a useful tool for assessing the eutrophication of rivers and lakes. Nevertheless, the AGP test is relatively expensive because of its large scale. In this study, a microplate technique was used in the AGP test to develop a microscale version. The algal growth in the microplate wells was monitored by examining the relationship between the absorbance (450 nm) measured using a microplate reader and cell concentration. A high correlation was observed between absorbance and cell concentration. There were few differences between the microplate wells with respect to well position, suggesting that the effect of well position on algal growth is negligible. The microscale AGP test using a microplate was compared with the conventional flask-size AGP test. A high similarity between the two methods was observed. Therefore, the microscale AGP test is a simple and useful method for conducting AGP tests on many water samples. The change in AGP level in the Tama River was investigated. AGP level increased considerably after inflow of water discharged from sewage treatment plants (STPs). This study has demonstrated that STP discharge has a considerable effect on river water quality.

View full abstract

A novel sewage treatment system consisting of an anaerobic Upflow Anaerobic Sludge Blanket (UASB) reactor and an aerobic biofilter reactor was operated continuously for over 400 days with raw domestic sewage as a feed. Sulfate-reducing bacteria plays an important role in Biochemical Oxygen Demand (BOD) degradation in the UASB reactor especially during winter when the operational temperature is low. In this study, the diversity of adenosine-5'-phosphosulfate reductase (apsA) genes, which produce a key enzyme for sulfate respiration and are present in all sulfate-respiring prokaryotes (SRPs), in UASB sludge was analyzed by cloning and sequencing techniques. The apsA amino acid sequence-based phylogenetic tree showed that the identified clones belonged to four groups: the sulfate-reducing bacterial group, Syntrophobacteraceae, Thiobacillus and the clone cluster group, distantly related to any previously described apsA clone. The amino acid sequence of the unknown apsA clones has a high homology to those of SRPs. Real-time PCR quantification which used the primer sets specific for each of the four apsA gene sequences revealed that Desulfobulbaceae and Desulfovibrionales were the predominant species all of the sulfate-reducing bacteria in the UASB sludge throughout the experimental period. An excellent correlation of apsA gene abundance and behavior was found between the sulfate-reducing bacteria and Thiobacillus, as well as between Syntrophobacteraceae and the unknown apsA clone group. However, cells having the unknown apsA gene in the UASB sludge could not be identified.

View full abstract

The hydroxyl radial, which is one of the most reactive free radicals in the environment, plays an important role in the photochemical degradation of natural organic matter and organic pollutants. The photochemical formation rates of hydroxyl radicals in 41 water samples collected from 6 rivers in Hiroshima Prefecture were determined and the sources of hydroxyl radicals were discussed. The hydroxyl radical photochemical formation rates in the Kurose and Seno rivers were much higher than those in the Ohta and Oze rivers. River water samples containing high nitrite concentrations were found to show high hydroxyl radical formation rates. In the samples which had the higher hydroxyl radical formation rates, nitrite was found to be the most important source of hydroxyl radicals. On the other hand, with decreasing photochemical formation rate of hydroxyl radicals, the percent contribution of unknown sources other than nitrate, nitrite and hydrogen peroxide increased.

View full abstract

The concentrations of norovirus (NV) genes in water samples from rivers A, B and C flowing into oyster farms in Miyagi Prefecture, Japan were determined from October 2002 to March 2004. Norovirus genes in 35 specimens collected over 17 months were measured using genogroup 1 (G1) and genogroup 2 (G2) specific real-time quantitative reverse transcription PCR techniques. The respective positive rates of NV genes in rivers A, B and C were 51% (18 of 35), 97% (34 of 35) and 26% (9 of 35). The respective concentrations of the NV G1 gene ranged from 85 - 5.3 × 10³ copies, 80 - 9.6 × 10⁴ copies and 85 - 1.7 × 10³ copies in 100 ml of water samples from rivers A, B and C. The respective concentrations of the NV G2 gene ranged from 93 - 2.0 × 10³ copies, 65 - 1.5 × 10⁵ copies and 72 - 1.2 × 10³ copies in 100 ml of the same water sample. These values were high during winter, and low but detectable during summer.

View full abstract

Nitrogen and phosphorus concentrations were measured in rivers (15 sites) and domestic wells (10 sites) in the Red River Delta, north of Vietnam in two dry and two rainy seasons between 2002 and 2004. The average concentrations of total nitrogen (TN) including particulate forms in the water samples from the rivers were 2.1 mg N·l^-1 in the urban areas and 1.3 mg N·l^-1 in the rural areas, with little differences between the dry and rainy seasons. The stable nitrogen isotope ratios (δ¹⁵N) of nitrate were from 1.4 to 11.7 ‰ (5.9 ‰ on average) in the river water samples. Markedly high concentrations of TN (4.7 mg N·l^-1 in the dry season and 6.7 mg N·l^-1 in the rainy season) were observed in water samples from wells in the rural areas. In those water samples, considerably high ammonium N concentrations and high δ¹⁵N values (upto 31.6 ‰) were often observed. Particulate forms of P predominated in the river and well water samples. The average concentration of total phosphorus (TP) in the rainy season (0.24 mg P·l^-1 ) was twofold higher than that in the dry season (0.12 mg P·l^-1) in the river water samples. The average concentrations of TP and dissolved total phosphorus (DTP) in the well water samples were 0.09 and 0.02 mg P·l^-1, respectively, with little seasonal and areal differences. The relatively low nitrogen concentrations and intermediate δ¹⁵N values of the river water samples suggest that nitrogen pollution is not yet serious in rivers in the Red River Delta, despite the rapid increase in the use of chemical fertilizers and population there. On the other hand, contamination by wastes from human or livestock is suggested in domestic wells in the rural areas.

View full abstract

The Government of Kumamoto Prefecture declared, on July 29, 1997, that the fish and shellfish of Minamata Bay, which had been polluted by mercury discharged from the Chisso plant, had returned to a safe edible state. Simultaneously, the net which had been installed to prevent expansion of mercury pollution was removed from Minamata Bay. In the present paper, the results of the total mercury concentrations in fish caught in Minamata Bay between 1978 and the present are reported. In particular-ly, given the abundance of 3 fish species (smelt-whiting, rock fish, wrasses) captured during sampling, these species were used as indicators to evaluate the state of mercury pollution in Minamata Bay. Moreover, in order to understand the characteristics, the analytical data obtained on total mercury concentrations were distinguished into 3 periods using key events in the history of mercury pollution in Minamata Bay. The first period is the time until the completion of dredgeing in the bay. The second period is from the completion of dredging (March, 1990) until the removal of the net in the bay. The third period is from the removal of the net in Minamata Bay to the present. As a result, in the present report, the total mercury concentration in fish is thought to have gradually decreased. However, fish with total mercury concentration exceeding the safety threshold ware found after the completion of dredging of Minamata Bay. The total mercury concentrations in wrasses, rock fish and smelt whiting respectively ware as follows: the first period (dredging and landfill term: 1978-1989): 0.46. 0.71 and 0.79μg·g^-1 (avg); the second period (net-closure term: 1990-1997): 0.55, 0.59 and 0.95μg·g^-1 (avg); the third period (after net removal: 1998-2004): 0.17, 0.37 and 0.42μg·g^-1 (avg). This trend is predicted to continue in the future.

View full abstract