Development of health alerts for cyanobacteria and related toxins in drinking water in South Australia

Cyanobacterial blooms occur intermittently in various reservoirs, rivers, and lakes in South Australia. Well-documented human and animal health effects related to blooms and the associated cyanotoxins have led health and water authorities in this state to recognize the need for establishing health alert (acute exposure) values for these cyanobacteria and their toxins. Distinct from lifetime drinking-water guideline values, these health alerts take into account known and possible acute health effects. Operationally, water authorities involved in monitoring the quality of water resources are required to contact the health authorities immediately if a health alert condition is detected. This then triggers a rapid assessment of potential health consequences of continued water use and sets in motion an appropriate management response. This article outlines the development of proposed health alerts for microcystin-LR-eq toxicity (10 μg/L), nodularin (10 μg/L), and saxitoxins (3 μg STX-eq/L). Corresponding cell densities for Microcystis aeruginosa (50,000 cells/mL), Nodularia spumigena (50,000 cells/mL), and Anabaena circinalis (20,000 cells/mL) are also provided for use as health alert indicators prior to determination of toxin concentration. In practice, it is likely that cell densities well below these values render drinking water unpalatable.