Improving microcystin monitoring relevance in recreative waters: A regional case-study (Brittany, Western France, Europe)

- Toxic cyanobacteria data were collected from an 8-years regional public health survey.
- Microcystin exposure was estimated in the raw waters from 26 lakes.
- Subacute toxin concentrations more frequently encountered than acute concentrations.
- Alert levels based on cell densities and cell biovolumes are compared in view of a better exposure representativity.

Cyanobacteria and their toxins are known as a health hazard in recreative and distributed waters. Monitoring data from 2004 to 2011 were collected at regional scale to characterize exposition parameters to microcystins in Brittany (Western France). The data show that cyanobacteria populations are experiencing a composition shift leading to a longer duration of cell densities higher than WHO alert levels 2 and 3. Microcystins however appear to be more frequently detected with subacute concentrations in low cell density samples than in high cell density samples or during bloom episodes. Positive relations are described between microcystin concentrations, detection frequencies and cyanobacteria biovolumes, allowing for a novel definition of alert levels and decision framework following WHO recommendations.