Evansford Reservoir (Victoria) – Anabaena sp.
12 April 2011 – Anabaena sp. (coiled) – 1.67mm3/L biovolume. Reservoir already isolated from supply due to pipeline renewal work. Increased monitoring regime in accordance with BGA Management Plan. ‘Supply by Agreement’ customers notified. Assessed impact on downstream reservoir
Due to the lack of adequate data, no guideline value is set for concentrations of saxitoxins.
However given the known toxicity, the relevant health authority should be notified
immediately if blooms of Anabaena circinalis (Dolichospermum circinalis)1 or other producers
of saxitoxins are detected in sources of drinking water.
There are three types of cyanobacterial neurotoxins: anatoxin a, anatoxin a-s and the saxitoxins. The saxitoxins include saxitoxin, neosaxitoxin, C-toxins and gonyautoxins (Chorus and Bartram 1999 Chapter 3). The anatoxins seem unique to cyanobacteria, while saxitoxins are also produced by various dinoflagellates under the name of paralytic shellfish poisons (PSPs). A number of cyanobacterial genera can produce neurotoxins, including Anabaena (Dolichospermum), Oscillatoria, Cylindrospermopsis, Cylindrospermum, Lyngbya and Aphanizomenon, but to date in Australia, neurotoxin production has only been detected from Anabaena circinalis (Dolichospermum circinalis), and the Australian isolates appear to
produce only saxitoxins (Velzeboer et al. 1998). As with most toxic cyanobacteria, A. circinalis (D. circinalis) tends to proliferate in calm, stable waters, particularly in summer when thermal stratification reduces mixing. The toxicity of individual populations of A. circinalis (D. circinalis) is variable, and one extensive survey of the toxicity across the Murray-Darling Basin indicated that 54% of field samples tested were neurotoxic (Baker and Humpage, 1994). A natural population may consist of a mixture of toxic and non-toxic strains and this is believed to explain why population toxicity may vary over time and between samples (Chorus and Bartram 1999 Chapter 3). The saxitoxins are a group of carbamoyl and decarbamoyl alkaloids that are either non-sulfated (saxitoxins), singly-sulfated (gonyautoxins), or doubly-sulfated (C-toxins). The various types of toxins vary in potency, with saxitoxin having the highest toxicity. The prevalent toxins in Australian blooms of A. circinalis are the C-toxins. These can convert in the environment or by acidification or boiling to more potent toxins (Negri et al. 1997, Ravn et al. 1995). The half-lives for breakdown of a range of different saxitoxins in natural water have been shown to vary from 9 to 28 days, and gonyautoxins may persist in the environment for more than three months (Jones and Negri, 1997).
Blooms of A. circinalis (D. circinalis) have been recorded in many rivers, lakes, reservoirs and dams throughout Australia, and A. circinalis (D. circinalis) is the most common organism in riverine blooms in the Murray-Darling Basin (Baker and Humpage 1994). In temperate parts of Australia blooms typically occur from late spring to early autumn. The first reported neurotoxic bloom of A. circinalis (D. circinalis) in Australia occurred in 1972 (May and McBarron 1973). The most publicised blooms occurred in the Murray-Darling System in 1991, 2009 and 2010 (NSWBGATF 1992, NSW Office of Water 2009, MDBA 2010). The first bloom extended over 1,000 kilometres of the Darling-Barwon River system in New South Wales (NSWBGATF 1992). A state of emergency was declared, with a focus on providing safe drinking water to towns, communities and landholders. Stock deaths were associated with the occurrence of the bloom but there was little evidence of human health impacts. The blooms in 2009 and 2010
affected several hundred kilometres of the River Murray on the border between NSW and Victoria and included Anabaena, Microcystis and Cylindrospermopsin. Alerts were issued about risks to recreational use, primary contact by domestic users, livestock and domestic animals. A bloom of A. circinalis (D. circinalis) in a dam in New South Wales was shown to have caused sheep deaths (Negri et al. 1995). Relatively low numbers of A. circinalis (D. circinalis) (below 2,000 cells/mL) can produce offensive tastes and odours in drinking water due to the production of odorous compounds such as geosmin… ADWG 2011