Health Stream Literature Summary - Issue 56 - December 2009

Drinking water quality: An in vitro approach for the assessment of cytotoxic and genotoxic load in water sampled along distribution system.
Maffei, F., Carbone, F., Forti, G.C., Buschini, A., Poli, P., Rossi, C., Marabini, L., Radice, S., Chiesara, E. and Hrelia, P. (2009) Environment International, 35(7); 1053-1061.

Chemical disinfection of water has been a major public health benefit and has led to dramatic decreases in both morbidity and mortality of waterborne diseases. However chemical disinfection also leads to low-level chronic exposure to a very large number of disinfection by-products (DBPs), some of which are known to be genotoxic. The potential toxicity of tap water can increase along the distribution system via additional disinfection by-product formation, production of toxic substances by biofilm microorganisms, and leaching from tank and pipeline materials. Monitoring for all potential toxicants is not feasible or practical, and interest is growing in new approaches which assess global toxicity in addition to testing concentrations of specific chemicals. In this study, an integrated approach was applied to evaluate the presence of different mixtures of cytotoxic and/or genotoxic compounds in water samples collected from two drinking water plants supplied by the River Po in Italy.

Drinking water samples were collected from Plant #1ocated near the source and Plant #2 near the mouth of the River Po. At both plants raw water was treated by sedimentation, flocculation, rapid sand filtration, ozone pre-disinfection, granular activated carbon, filtration and chlorine dioxide post-disinfection. Water was sampled before (R) and after (A) the disinfection process and from two points (T1 and T2) in different branches of the respective distribution systems. The water was taken weekly for 5 weeks at each sampling point. Water sample were analysed for total organic carbon (TOC), total trihalomethanes (TTHM) and haloacetic acid (HAA) concentrations. The main chlorine dioxide by-products, chlorite and chlorate were also analysed. THM formation potential was also determined as this parameter estimates the expected concentration of THM in water samples treated with an excess of free chlorine.

Lymphocytes and leukocytes were obtained from blood samples from healthy non-smoking males provided by the AVIS (Italian Association of Voluntary Blood Donors). The cytotoxicity and genotoxicity of concentrated water samples was evaluated in human leukocytes and human liver-derived Hep-G2 cells using a Comet assay and the micronucleus (MN) assay. Short term exposure (1h, 37 degrees C) and long-term exposure (24h, 37 degrees C) were evaluated with extracts of water collected from each sampling point of the two networks.

The raw water at the two plants had different chemical characteristics. The UV absorbance at 240 nm for Plant #2 was about double of that of Plant #1. Concentrations of organic halogens and nitrate were about twice as high at Plant #1 than Plant #2. The concentrated raw water (R) from both plants was found to be cytotoxic but not genotoxic in human lymphocytes and the Hep-G2 cell line (24 h treatment). However, genotoxic effects (DNA damage) were detected by Comet assay in the raw water of Plant #2 in leukocytes at a concentration of greater than or equal to 0.25 Leq/mL. The results indicate pollution of the River Po, suggesting the presence of different mixtures of cytotoxic/genotoxic compounds at different locations. This river receives pollutants including industrial solvents, pesticides and persistent organic chemicals from several tributaries.

Samples of treated water from both plants and distribution systems complied with limits for conventional physical-chemical parameters. Drinking water samples from both plants did not induce cytotoxic effects and/or increase MN frequency in Hep-G2 cells or in human lymphocytes. This suggests the disinfection treatment reduced the concentration of toxic chemicals in the drinking water relative to raw water and did not generate products which could induce structural or numerical chromosomal damage. However for Plant #1 the comet assay in human leukocytes showed a significant increase of DNA migration (indicating DNA damage) when treated water was compared to raw water. This increase was also seen for water in one branch of the distribution system but not in the other, suggesting that the responsible compound(s) may be degraded or diluted as water moves through the system, or possibly that they are generated locally in the pipeline. For Plant#2 there was little difference in the comet assay results for raw water and treated water from the plant, and genotoxic effects were lower in both branches of the distribution system.

This study shows that using an integrated approach is a useful and practical tool to understanding the full toxicological effects of complex mixtures of compounds present in drinking water. If this approach is used with normal chemical analysis then these in vitro toxicological tests will contribute to improve the monitoring of drinking water.

Comment This paper refers to water being sampled before the 'disinfection process'but then refers to the 'before'samples as 'raw water'. This suggests the samples were untreated river water and the term 'disinfection process' actually refers to the entire water treatment and disinfection process.

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