Yumiko Ohkouchi

A survey on levels and seasonal changes of assimilable organic carbon (AOC) and its precursors in drinking water

In Japan, customers’ concerns about chlorinous odour in drinking water have been increasing. One promising approach for reducing chlorinous odour is the minimization of residual chlorine in water distribution, which requires stricter control of organics to maintain biological stability in water supply systems. In this investigation, the levels and seasonal changes of assimilable organic carbon (AOC) and its precursors in drinking water were surveyed to accumulate information on organics in terms of biological stability. In tap water samples purified through rapid sand filtration processes, the average AOC concentration was 174 µgC/L in winter and 60 µgC/L in summer. This difference seemed to reflect the seasonal changes of AOC in the natural aquatic environment. On the other hand, very little or no AOC could be removed after use of an ozonation–biological activated carbon (BAC) process. Especially in winter, waterworks should pay attention to BAC operating conditions to improve AOC removal. The storage of BAC effluent with residual chlorine at 0.05–0.15 mgCl2/L increased AOC drastically. This result indicated the possibility that abundant AOC precursors remaining in the finished water could contribute to newly AOC formation during water distribution with minimized residual chlorine. Combined amino acids, which remained at roughly equivalent to AOC in finished water, were identified as major AOC precursors. Prior to minimization of residual chlorine, enhancement of the removal abilities for both AOC and its precursors would be necessary.

Inflammatory responses and potencies of various lipopolysaccharides from bacteria and cyanobacteria in aquatic environments and water supply systems

Inflammatory substances derived from indigenous bacteria in aquatic environments or water systems are of great concern. Lipopolysaccharides (LPSs), one of the major inflammatory substances in water, are usually identified using Limurus amoebocyte lysate (LAL) assay on the basis of their endotoxic activity, but endotoxin levels do not accurately represent their inflammatory potency in humans. In this investigation, the cellular endotoxin contents of pure-cultured bacteria/cyanobacteria, which are frequently detected in water sources and distribution systems, and of indigenous bacteria in a river and in biologically activated carbon (BAC) effluent, were investigated. The indigenous bacteria showed the highest endotoxin contents exceeding 10(-3)EU/cell. The LPSs were then purified from those samples, and their inflammatory potencies were examined using a human monocytic cell line. The LPSs from Acinetobacter lwoffii culture, the river water, and the BAC effluent sample revealed a unique cytokine secretion pattern; they induced both IL-8 and TNF-α more strongly than the other tested bacterial LPSs. These results suggest that natural bacterial/cyanobacterial flora in aquatic environments and water distribution systems have the potential to induce relatively strong inflammatory responses in humans; therefore, further accumulation of data on water quality from the perspective of not just endotoxins but inflammatory potency is needed.

Comparison of inflammatory responses in human cells caused by lipopolysaccharides from Escherichia coli and from indigenous bacteria in aquatic environment.

The endotoxic activities of lipopolysaccharides (LPSs) in water samples are usually determined using a Limulus amoebocyte lysate (LAL) assay, but it is known that the determined activities do not always represent their inflammatory potency in humans. In this investigation, the inflammatory responses in three different human cells stimulated with Escherichia coli LPS, keratinocyte, CD14+ monocyte, and THP-1, were compared using cytokine secretion as biomarkers to develop novel in vitro assay systems for detecting changes in inflammatory potencies of endotoxins in aquatic environment. Only THP-1 with 6-h stimulation showed dose-dependent responses in the range of normal endotoxin levels in aquatic environment. Then, the inflammatory potency of environmental LPS, which was purified from river water, was tested using THP-1. The levels and patterns of cytokine secretion after the environmental LPS stimulation were completely different from E. coli LPS. Interleukin 8 (IL-8) secretions after the environmental LPS stimulation were approximately 10-fold higher than those after E. coli LPS stimulation. The environmental LPS also induced much higher levels of TNF-α secretions in THP-1. These results suggest that a diversity of LPS structures in aquatic environment could contribute to stronger and different inflammatory responses. This investigation indicated that the proposed THP-1 assay system could be useful for detecting the changes in inflammatory potencies caused by aquatic bacteria.