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<sup>o</sup>C, and reconstitution in 10% methanol for
immunological assay. Includes 32 references, tables, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 810 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 18 |
| Published : | 06/17/2004 |
