World Health Organization (WHO) 1999 Guideline Values for Cyanobacteria in Freshwater
The World Health Organization (WHO) developed guidance values for the relative probability of acute health effects to account for the possible exposures through recreational activities (contact, ingestion and inhalation) during recreational exposure to cyanobacteria based on cyanobacterial cells and chlorophyll-a levels.
| Guidance level or situation | How guidance level derived | Health risks | Typical actions |
|---|---|---|---|
Relatively low probability of adverse health effects 20 000 cyanobacterial cells/ml | From human bathing epidemiological study | Short-term adverse health outcomes, e.g., skin irritations, gastrointestinal illness | Post on-site risk advisory signs Inform relevant authorities |
Moderate probability of adverse health effects 100 000 cyanobacterial cells/ml | From provisional drinking water guideline value for microcystin-LR and data concerning other cyanotoxins | Potential for long-term illness with some cyanobacterial species health outcomes, e.g., skin irritations, gastrointestinal illness | Watch for scums or conditions conducive to scums and further investigate hazard Post on-site risk advisory signs Inform relevant authorities |
High probability of adverse health effects Cyanobacterial scum formation in areas where whole-body contact and/or risk of ingestion/aspiration occur. | Inference from oral animal lethal poisoning. Actual human illness case histories | Potential for acute poisoning Potential for long-term illness with cyanobacterial species Short-term adverse activities health outcomes, e.g., skin irritations, gastrointestinal illness | Immediate action to control contact with scums; possible prohibition of swimming and other water contact activities Public health follow-up investigation Inform public and relevant authorities |