An increasing number of people drink water from fresh water supply reservoirs. However, with the global change a lot of reservoirs become eutrophic, which facilitates the occurrence of toxin-producing cyanobacterial blooms.
Microcystins (powerful hepatotoxic water-soluble heptapeptides) are the most important
cyanobacterial toxins affecting humans. High doses of
microcystins produce hepatic
necrosis. Consequently, WHO Guidelines limit
microcystins to 1 ppb in drinking waters. However,
microcystins are present frequently in tap water at lower doses. Here, we hypothesized that chronic consume of tap water containing low doses of
microcystins may be a risk factor for liver and
colorectal cancer. Two kinds of evidences support this hypothesis. On one hand some epidemiological data (mainly in China). On the other hand, the molecular mechanism of
microcystins toxicity (inhibition of
protein phosphatases PP1 and PP2) is just like
okadaic acid (a potent
tumor promoter).
Cancer risk from
drinking water is certainly less than smoking, occupational exposures or some foods. But it is significant and with a rapid increase of toxic cyanobacterial blooms by eutrophycation, become more frequent.