2013/2017: Gunn Point (Northern Territory) – Naegleria fowleri, E.coli, Chlorine

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Gunn Point (Northern Territory) – Naegleria fowleri

2015/16: All distribution systems and sources monitored during the 2012-16 were free of N. fowleri, with the exception of Gunn Point and Tennant Creek distribution systems.

“GUIDELINE No guideline value is set for Naegleria fowleri in drinking water, but an ‘action level’ is recommended for water supplies likely to be contaminated. If the organism is detected, advice should be sought from the relevant health authority.

Naegleria fowleri is a free-living, thermophilic amoeboflagellate which causes the waterborne disease primary amoebic meningoencephalitis (PAM). This rare but fatal condition has followed use of water for swimming, or domestic bathing. The organism occurs naturally in freshwater of suitable temperature, feeding on bacteria. Its occurrence is only indirectly related to human activity, inasmuch as such activity may modify temperatures or promote bacterial production. PAM has been reported from many countries, usually associated with thermally polluted environments, geothermal water or heated swimming pools. N. fowleri is almost exclusively aquatic, and water is the only known source of infection. Numerous nonvirulent Naegleria species are known in Australia.

PAM cases have been recorded from South Australia, Western Australia, Queensland and New South Wales; Naegleria fowleri has been detected in water in each of these states and in the Northern Territory. Australia is the only country where N. fowleri has been detected in public water supplies (Dorsch et al. 1983). Most of the available data on the density of N. fowleri in water relates to water supplies in South Australia (including the highest reported densities). In temperate Australia, significant seasonal cycles of density occur, from below one organism per litre to hundreds or thousands per litre in poorly disinfected water (Robinson and Christy 1984). N. fowleri detected at water temperatures below 18°C is likely to be present as cysts, which are not infectious, but which may seed a suitable environment.” Australian Drinking Water Guidelines 2011.

Gunn Point (Northern Territory) – E.coli
The Gunn Point incident was likely due to low level faecal contamination from small animals…
Power and Water Corporation Water Quality Report 2016
Gunn Point 24 September 2013: Samples with E.coli detections (1). Number of E.coli detected in sample (MPN/100ml) (1)
Gunn Point 20 September 2016: Samples with E.coli detections (1). Number of E.coli detected in sample (MPN/100ml) (1)

2016/17 – Gunn Point (Northern Territory) – Chlorine

2016/17: Gunn Point Chlorine 9mg/L

GENERAL DESCRIPTION
Chlorine dissociates in water to form free chlorine, which consists of aqueous molecular chlorine, hypochlorous acid and hypochlorite ion. Chlorine and hypochlorites are toxic to microorganisms and are used extensively as disinfectants for drinking water supplies. Chlorine is also used to disinfect sewage and wastewater, swimming pool water, in-plant supplies, and industrial cooling water.

Chlorine has an odour threshold in drinking water of about 0.6 mg/L, but some people are particularly sensitive and can detect amounts as low as 0.2 mg/L. Water authorities may need to exceed the odour threshold value of 0.6 mg/L in order to maintain an effective disinfectant residual.

In the food industry, chlorine and hypochlorites are used for general sanitation and for odour control. Large amounts of chlorine are used in the production of industrial and domestic disinfectants and bleaches, and it is used in the synthesis of a large range of chemical compounds.

Free chlorine reacts with ammonia and certain nitrogen compounds to form combined chlorine. With ammonia, chlorine forms chloramines (monochloramine, dichloramine and nitrogen trichloride or trichloramine) (APHA 2012). Chloramines are used for disinfection but are weaker oxidising agents than free chlorine.

Free chlorine and combined chlorine may be present simultaneously (APHA 2012). The term totalchlorine refers to the sum of free chlorine and combined chlorine present in a sample.

Chlorine (Free) ADWG Guideline: 5mg/L (Chlorine in chloraminated supplies 4.1mg/L). Chlorine dissociates in water to form free chlorine, which consists of aqueous molecular chlorine, hypochlorous acid and hypochlorite ion.

Chlorine (Total) ADWG Guideline 5mg/L (chloraminated supplies 4.1mg/L): The term total chlorine refers to the sum of free chlorine and combined chlorine present in a sample