AWWA ACE59931

Cyanobacteria, also called blue-green algae, are photosynthetic bacteria found primarily in surface waters. Eutrophic surface waters are at highest risk for cyanobacterial blooms; these include ponds, lakes, and water treatment plant reservoirs under the influence of extraneous nutrients from agricultural runoff or sewage. Cyanobacteria are of interest to the water treatment community because they produce compounds which are toxic to humans and animals. This work reviews the current state of water treatment for cyanotoxins and presents the results of a summer 2003 survey of microcystin levels in 33 North American raw water supplies operated by American Water. Recommendations to water treatment plants are made in view of the treatment options and extent of toxin contamination. A commercially available immunoassay kit detected microcystins in 87% of 40- fold concentrated raw samples and 30% of concentrated effluent samples. The remainder in each case was below the enhanced assay detection limit of 0.031 ppb for raw samples and 0.080 ppb for effluent samples. Raw water microcystin levels, expressed as the mean of six measurements, can be considered background when compared to the 1 ppb World Health Organization (WHO) guideline. However, two raw water sources consistently showed high microcystin concentrations. One of these was inactive, and the other was removed from service during testing due to odor problems. Plant effluent levels, expressed as the mean of two measurements, were only detectable at five of 28 sampling sites. All detectable plant effluent levels were below the WHO guideline. Because raw water microcystin levels are generally low across the American Water system, source water protection measures should be adequate to control the development of algae problems. Existing water treatment regimens are sufficient to control microcystins. In a context of increased source water eutrophication, the effect of water treatment processes on higher levels of toxins will require additional study. In the few instances where raw water contamination was a concern, the World Health Organization method of microscopic cell enumeration is the recommended monitoring method for the months of July through September. In response to high cell numbers, toxin levels may be conveniently quantified using methanol extraction of water samples, evaporation under nitrogen at 45^oC, and reconstitution in 10% methanol for immunological assay. Includes 32 references, tables, figures.