Oral toxicity of a bloom of the Cyanobacterium microcystis Aeruginosa administered to mice over periods up to 1 year.

Cyanobacterial blooms in lakes have been reported causing livestock deaths and liver injury to human populations. In this study bloom material consisting of Microcystis aeruginosa was collected from a farm water storage after the death of sheep drinking from it. The cyanobacterial cells were lysed and a cell-free extract was provided to mice at a series of dilutions as their only source of drinking water. Mice of both sexes, with controls, were killed at intervals up to 1 yr of administration. Autopsies, histopathological examination, and analyses of plasma lactate dehydrogenase and alanine aminotransferase were carried out. Increased mortality was observed, particularly among males, together with chronic active liver injury and elevated alanine aminotransferase in blood. In control mice and those receiving lower concentrations of extract, hepatic amyloidosis with neutrophil infiltration, and bronchopneumonia, were seen with increasing age. The bronchopneumonia appeared earlier among mice receiving cyanobacterial extract. Four tumors were seen in 71 mice receiving a high concentration of extract for up to 1 yr, none in 150 mice receiving lower concentrations, and 2 in 73 control mice. No effects on male or female fertility, embryonic mortality, neonatal viability, or skeletal development were observed, but 7 out of 73 neonatal mice born to parents given cyanobacterial extract showed reduced brain size. No cases were seen in controls. We conclude that the major toxicity exhibited is liver injury. Further attention is needed for evaluation of carcinogenicity and embryonic damage.