SURVEY OF THE CONCENTRATIONS OF ALGAL TOXINS IN WATER SUPPLIES Final Report to the Department of the Environment
Report No DWI0355

Nov 1994

SUMMARY

A survey of the levels of the blue-green algal toxins, microcystin-LR and anatoxin-a, in drinking waters has been undertaken. Six water treatment works, where the raw waters were expected to contain significant numbers of blue-green algae, were selected for the survey and samples obtained on five occasions between early August and early September 1994.

Raw water samples taken at the treatment works were analysed to identify the predominant algal species present and to determine algal cell numbers. Treated water samples were obtained at the works and from supply zone sampling points and analysed for microcystin-LR and anatoxin-a.

No toxins were detected in any of the treated water samples analysed, although a response for microcystin-LR was obtained in a single supply zone sample. This is considered to be a false positive as no blue-green algae were detected (either by WRc or by the water company concerned) in the relevant raw water during the period of the survey.

The highest level of blue-green algal cells encountered in a raw water was 18 x 10^3 cells /ml, but at two water treatment works no blue-green algal cells were detected in any of the raw water samples. Given that the choice of sampling sites was based on the expectation that significant numbers of blue-green algal cells would be present during the survey, this demonstrates the unpredictable nature of the occurrence and abundance of these algae.

The data obtained in this survey suggest that it is unlikely that significant levels of blue-green algal toxins are present in UK drinking waters, although their occasional presence cannot be ruled out at times when levels of blue-green algae in raw waters are very high, or if the treatment processes utilised are minimal.

Copies of this report may be available as an Acrobat pdf download under the 'Pre 2000 Reports' heading on the DWI website.