Occurrence of microcystins in raw water sources and treated drinking waterof Finnish waterworks

Problems caused by cyanobacteria are common around the world and also in ra w water sources of drinking water treatment plants. Strains belonging to ge nera Microcystis, Anabaena and Planktothrix produce potent hepatotoxins, th e microcystins. Laboratory and pilot scale studies have shown that microcys tins dissolved in water may pass the conventional surface water treatment p rocesses. In 1998 the World Health Organization proposed a guide value of 1 mug/L for microcystin-LR (MC-LR) in drinking water. The purpose of this re search was to study the occurrence of microcystins in raw water sources of surface waterworks and in bank filtration plants and to evaluate the remova l of microcystins in operating waterworks. Four bank filtration plants and nine surface waterworks using different processes for water treatment were monitored. Phytoplankton was identified and quantified, and microcystins an alysed with sensitive immunoassay. Microcystin occurrence in selected water samples was verified with HPLC and a protein phosphatase inhibition method . Microcystins were detected sporadically in raw water sources of most of t he waterworks. In two raw water supplies toxins were detected for several m onths. The highest microcystin concentrations in incoming raw water were ap proximately 10 mug/L MC-LR equivalents. In treated drinking water microcyst ins were detected occasionally but the concentrations were always below the guide value proposed by WHO.