Contamination of Drinking Water by Cyanotoxins in Reservoirs: An Ecological Study Approach

Objectives: In order to investigate relationship between some cancers (Total cancer cases, primary liver cancer and colorectal cancer cases) occurrence and drinking water consumption from eutrophic reservoirs an ecological study was performed in two Sardinia provinces between 2002-2011 comparing cancer incidence between an exposed area and a reference area. Cyanobacteria are a group of ubiquitous photosynthetic microorganisms existing mainly in freshwater and marine environments.

Indications on the actions to be pursued in the future to protect human health from cyanobacterial blooms exposure.

Methods: The provinces of Sassari and Olbia Tempio are the study area and the Ragusa Province (Sicily) the reference area since its water sources are just groundwaters and springs. Sardinia populations experienced continuous shortage of water resources for thousands of years. To solve this problem, during 1950-1980, the main rivers were dammed constructing 45 reservoirs which rapidly became eutrophic or hypertrophic, with toxic cyanobacterial blooms and a generally poor water quality.

An ecological study has been developed since our work is an observational study characterized by trying to relate exposure and disease at the region and population level. Cancer incidence rates were calculated for the study area and compared to those of the reference area.

Results: Among Sardinian men, for the entire study period risk excesses for cancer of esophagus (Standardized Rate Ratio SRR=3.50), colon-rectum (SRR=1.04), liver (SRR=1.21) and pancreas (SRR=1.24) are observed. Between 2002 and 2011, women showed risk excesses for cancer of esophagus (SRR=3.44) and pancreas during the first (SRR=1.44) and third (SRR=1.67) sub-periods and risk defects for stomach (SRR=0.79) and colon-rectum (SRR=0.92) cancer during the whole study period.

Conclusion: Exposure from cyanobacterial blooms can be considered a risk factor for the onset of cancers of the digestive organs. At a general level, there is the need to plan active water safety strategies on cyanotoxin presence and eutrophic. Prevention and water body remediation can be anyway suggested as preliminary measures to start as soon as possible. Further studies on individual exposure, effective daily intake and chlorination by-product presence are therefore needed to better define the role of this peculiar risk factor; as well as prevention and water body remediation measures.