This report describes an investigation of genotoxic effects in medicinal leech (Hirudo verbana) exposed to water and sediment of Lake Njivice (Krk Island, Croatia) contaminated by aluminium compounds. The levels of primary DNA damage in leech haemocytes and loss of DNA integrity caused by acute and chronic exposure to contaminated water and sediment were investigated using the alkaline comet assay. Genotoxic effects induced by acute exposure to contaminants were evaluated on leech haemocytes and blood cells of fish and mouse treated ex vivo. The effects of chronic exposure were assessed on haemocytes sampled from an animal kept under laboratory conditions on contaminated water and sediment for 180 days. The results indicate the DNA damaging potential of aluminium compounds present in an excess amount in tested samples.