An algal bloom in South Australia's Yorke Peninsula has led to the discovery a new cyanobacterial toxin. The bloom in the Paskeville reservoir led to a health alert being issued for about 15,000 residents in 35 towns. Many visitors were also affected by the alert in the popular tourist area during the Easter holiday period. The incident began on Friday 14 April with a number of complaints from consumers about an unpleasant taste and odour in tap water. Tests detected the presence of MIB (2-methyl isoborneol), a cyanobacterial metabolite which although not considered toxic is often responsible for "musty" taste and odour in water supplies.

Investigations by SA Water revealed the source to be one of two shallow earthern storage reservoirs in Paskeville where filtered water was stored prior to chlorination and distribution. A cyanobacterial "mat" growing on the floor of the reservoir had broken up and become detached, resulting in algal fragments contaminating the water intake. The reservoir was removed from service and examination of algal samples showed the bloom to be a Phormidium species. This filamentous cyanobacteria commonly grows on the surface of submerged rocks in shallow clear water bodies, and has not been reported to produce toxins. It is generally not regarded as a concern in drinking water supplies. The local media were notified of the bloom and advised there were no health concerns. The South Australian Department of Human Services was also notified.

Despite the absence of reported toxin production by Phormidium, algal samples were collected by SA Water for toxicity testing by intraperitoneal injection in mice. These tests showed the material to be toxic, and a health alert was issued on Tuesday 18 April. Due to uncertainty over the identity of the toxin the South Australian Department of Human Services advised consumers not to use tap water for drinking, making cold or hot beverages, washing or cooking foods, making ice or cleaning teeth. Bottled water was distributed free through supermarkets and local fire stations. Farmers were warned not to use tap water for livestock.

A program of mains flushing was commenced to clear the affected water from the distribution system. Due to the large area affected, it was several days before the all clear was issued to the last townships on Tuesday 25 April. According to local media, no instances of human illness or stock losses have been reported. Shortly after the incident the state government announced a $9 million project to cover and line five major water storages including the Paskeville reservoirs. The project is part of a $36 million Country Water Quality Improvement Program to be carried out in South Australia over the next 5 years.

Preliminary characterisation of the toxin has been carried out by the Australian Water Quality Centre and the University of Adelaide Department of Clinical Pharmacology (both participants in the CRCWQT). The toxin appears chemically distinct from the known major toxin classes (not a microcystin, nodularin, saxitoxin or cylindrospermopsin), and is somewhat less toxic in mouse tests than the most toxin microcystins. The effects are protracted, with injected mice generally surviving more than 6 hours and sometimes more than 24 hours before succumbing. Examination of internal organs shows no gross organ damage, but liver damage is evident on histopathological examination. It has also been established that the toxin is effectively inactivated by boiling and by water chlorination.

A similar protracted toxic effect from cyanobacteria has been reported previously for Aphanizomenon flos-aquae. In this case chemical characterisation of the toxin was not performed but it was reported that no gross organ damage was seen in mice, but liver and lung damage was evident on histopathological examination (1). Histopathological data from this toxin is now being compared with observations on the South Australian isolate.

The finding of a new toxin from an algal species hitherto regarded as innocuous raises concerns for water and health authorities. Phormidium growth on the bottom of shallow reservoirs is not unusual, and this species has been regarded as a nuisance organism only on the rare occasions when algal growth becomes detached and enters the water column. Now it appears that water authorities may need to consider testing for toxicity whenever Phormidium is identified, rather than assuming there are no health concerns.

(1) Underdal B. Nordstoga K. and Skulberg OM. Protracted toxic effects caused by saline extracts of Aphanizomenon flos-aquae (Cyanophyceae /Cyanobacteria). Aquatic Toxicology. 46(3-4): 269-278, 1999.