Assessment On Genotoxicity And Health Risk Of Microcystin In Drinking Water Sources

Eutrophocation has become the most important problem of water environment. Cyanobacterial blooms in lakes and reservoirs are known to occur throughout the world. These blue green alge blooms not only result in water quality deterioration, but also releases some toxins which bring severe threats to drinking water safety. Since first reported that wild animals died of drinking cyanobacterial contaminated water in 1878, lots of aquatic organism, birds and domestic animals were affected by microcystin. The most shocking human accident occurred at Caruaru hemodialysis center in Brazil in 1996, when 52 renal dialyzed patients died from liver failure resulting from cyanobacterial contamination of the water used for renal dialysis.Microcysin (MC) is one of the most common and potent cyanobacterial toxins. Research has indicated that microcystin which was evaluated as being Group 2B has tumor-promoting activity. Epidemiological studies have suggested that microcystin is a risk factor for the high incidence of primary liver cancer and high mortality of male stomach cancer in certain area where people have consumed water contaminated blue-green algae. It is reported that microcystin, hepatitis B virus and aflatoxin have become three main risk factors for liver cancer in environment.The tumor-promoting mechanism of microcystin is still not clear. It is known that the change of genetic materials in cells could induce carcinogenesis, teratogenesis and mutagenesis. Most cancer occurs because of genetic material change. It is well known that tumor development has close relationship with the damage of genetic materials.Zhejiang Province is situated on China's southeastern coast, on the southern part of the Yangzi River Delta. In this province, the total amount of water resources are relatively rich, but the average water resource per capita is below the mean level of the country because of the high population density. Based on the analysis data of organic pollutant in drinking water sources provided by Zhejiang Province Environment Monitoring Center, microcystin has become the main typical pollutant in drinking water sources, especially in Taihu Lake. It is the first health risk assessment of organic pollutants in drinking water sources in Zhejiang province. The genotoxicity study of microcystins in drinking water sources has profound theoretical and practical significance.Objective1. To evaluate the health risk caused by organic pollutants in drinking water sources via drinking water.2. To discuss the genotoxicity of MCLR and MCRR in drinking water source, measure DNA breakages by single cell gel electrophoresis (SCGE), investigate the mutagenicity by Ames test, and detect the chromosome damage by micronucleus test.Methods1. Health risk assessment of organic pollutants in drinking water sourceBased on the analysis data of organic pollutant in drinking water sources provided by Zhejiang province, a professional assessment model of water pollution was applied to evaluate the health risk caused by organic pollutants detected in drinking water sources.2. The genotoxicity of MC extracts and MC-containing water samplesSurface water of 2 typical drinking water source A and B were sampled, which were relatively seriously polluted by MC. The diluted microcystins of MCLR and MCRR were added to the water samples respectively, while MC-containing purified water was prepared. The HLB resin was used to absorb and concentrate the microcystin in source water samples. The bacteria, human peripheral blood lymphocytes and ornamental carp erythrocyte were treated by purified water, drinking water source A and B, concentrated water samples, and MC-containing purified water, respectively. The mutation of bacterial DNA was assessed by Ames test. The DNA damage of human peripheral blood lymphocytes was tested by comet assay. Micronucleus of ornamental carp erythrocyte was measured by micronucleus test.Results1. Glyphosate, MCLR, MCRR, DEHP, DBP and carbazole are the main organic pollutants, and Glyphosate, MCLR, MCRR are typical organic pollutants in drinking water source in this study. The health risks caused by organic pollutant is relatively slight, the drinking source water is relatively safe.2. MC extracts and MC-containing purified water could result in DNA damage of human peripheral blood lymphocytes. Compared with pure MC, the level of DNA damage caused by MC-containing purified water has significant differences.3. Ames test showed that DNA mutation induced by MC extracts, pure MC and MC-containing purified water were not observed.4. MC-containing water samples were able to induce higher frequency of micronucleus in carp erythrocyte, while the chromosome damage induced by MC extracts were not observed.Conclusions1. The organic pollution degree in drinking water sources was relatively slightly, the health risk caused by organic pollutants in drinking water source was much lower than the maximum allowance levels recommended by ICRP.2. MC extracts and MC-containing water samples were able to induce DNA damage of human peripheral blood lymphocytes, increase frequency of micronucleus in carp erythrocyte, but DNA mutation in Ames test were not observed.