A lack of association between increases in gastrointestinal, liver, and urologic cancers and cyanobacterial contamination of fresh water lakes in Manitoba.

Cyanobacteria or blue-green algae are becoming increasingly abundant in North American fresh water lakes. Toxins produced by cyanobacteria have been associated with gastrointestinal injury, liver failure, and nephrotoxicity. They have also been implicated in the pathogenesis of gastrointestinal and liver cancers. The purpose of the present study was to determine whether the incidence rates of gastrointestinal, liver, and urologic cancers are increasing in the province of Manitoba and, if so, whether these increases spatially and/or temporally correlate with areas where cyanobacterial contamination of fresh water lakes have been identified. Cancer incidence data were obtained from the Manitoba Cancer Registry. Cyanobacterial contamination data, as reflected by microcystin toxin concentrations, were available from the Manitoba Water Stewardship. ArcGIS mapping was employed to document spatial and temporal relationships between cancer incidence and cyanobacterial data. The results revealed that although the incidence rates for all three cancers have increased over the past 20-25 years, these increases were not disproportionally higher in zones with high microcystin toxin determinations. The results of this study argue against increased exposure to cyanotoxins as an explanation for the increase in gastrointestinal, liver and urologic cancers in Manitoba.

The Geographic Distribution of Liver Cancer in Canada Does Not Associate with Cyanobacterial Toxin Exposure.

BACKGROUND: The incidence of liver cancer has been increasing in Canada over the past decade, as has cyanobacterial contamination of Canadian freshwater lakes and drinking water sources. Cyanotoxins released by cyanobacteria have been implicated in the pathogenesis of liver cancer. OBJECTIVE: To determine whether a geographic association exists between liver cancer and surrogate markers of cyanobacterial contamination of freshwater lakes in Canada. METHODS: A negative binomial regression model was employed based on previously identified risk factors for liver cancer. RESULTS: No association existed between the geographic distribution of liver cancer and surrogate markers of cyanobacterial contamination. As predicted, significant associations existed in areas with a high prevalence of hepatitis B virus infection, large immigrant populations and urban residences. DISCUSSION AND CONCLUSIONS: The results of this study suggest that cyanobacterial contamination of freshwater lakes does not play an important role in the increasing incidence of liver cancer in Canada.