Tumor promotion and liver injury caused by oral consumption of cyanobacteria

Water supply reservoirs in many countries are now affected by intermittent water blooms of cyanobacteria. During 1989 a significant number of domestic supply reservoirs in the United Kingdom developed copious blankets of Microcystis , and pet and sheep deaths were reported due to swimming in or drinking the water. In Australia there are annual blooms of Anabaena and Microcystis in natural lakes and supply reservoirs, many of which are toxic. Studies of epidemics and individual cases of gastroenteritis and hepatitis due to cyanobacterial blooms have been reported from North America, Africa, and Australia. Our studies of the effect of low‐concentration oral consumption of Microcystis on mice have shown progressive liver injury with leucocyte invasion and hepatocyte death. Measurements of liver injury in a human population exposed to Microcystis in the domestic water supply indicate similar damage. Recent research has concentrated on the possible tumor‐promoting activity of oral consumption of cyanobacterial extracts. A group of mice given dilute Microcystis for one year showed more spontaneous tumors at the highest concentration of cyanobacterial extract. Mice stimulated to grow skin tumors by topical application of dimethylbenzanthracene showed a significantly greater weight of tumors in one group given a Microcystis extract to drink. A comparable group given an Anabaena extract in their drinking water showed no stimulation of tumor growth.