2022/23 Nyah (Victoria) – Trihalomethanes
2022/23 – Nyah (Victoria) – Trihalomethanes 0.25ug/L (max), 0.13mg/L (av.)
Australian Drinking Water Guideline THM’s 0.25ug/L
Why and how are THMs formed?
“When chlorine is added to water with organic material, such as algae, river weeds, and decaying leaves, THMs are formed. Residual chlorine molecules react with this harmless organic material to form a group of chlorinated chemical compounds, THMs. They are tasteless and odourless, but harmful and potentially toxic. The quantity of by-products formed is determined by several factors, such as the amount and type of organic material present in water, temperature, pH, chlorine dosage, contact time available for chlorine, and bromide concentration in the water. The organic matter in water mainly consists of a) humic substance, which is the organic portion of soil that remains after prolonged microbial decomposition formed by the decay of leaves, wood, and other vegetable matter; and b) fulvic acid, which is a water soluble substance of low molecular weight that is derived from humus”. Source: https://water.epa.gov/drink/contaminant
Nyah – Victoria – Cyanide
2022/23: Nyah (Victoria) 0.041mg/L (highest level) (51.25% of Australian Guideline)
Based on health considerations, the concentration of cyanide in drinking water should not
exceed 0.08 mg/L.
GENERAL DESCRIPTION
Cyanide can be present in drinking water through the contamination of source water, or through the natural decomposition of some plants that synthesise cyanoglycosides. Some microorganisms, such as the cyanobacterium Anacystis nidulans and the bacterium Chromobacterium violaceum, produce free cyanide. In uncontaminated water sources, free cyanide concentrations are usually less than 0.01 mg/L. Sodium cyanide is used in the extraction of gold and silver from low-grade ores. It is also used in the electroplating, steel and chemical industries. Some foods can contain quite high concentrations of cyanide. Green almonds and improperly treated cassava are of particular concern.
TYPICAL VALUES IN AUSTRALIAN DRINKING WATER
In major Australian reticulated supplies cyanide concentrations range up to 0.05 mg/L, with typical concentrations usually less than 0.02 mg/L.
TREATMENT OF DRINKING WATER
There are no published reports on methods for the removal of cyanide from drinking water. Chlorine gas or hypochlorite will react with cyanide to form cyanate. Ozone is also an effective oxidant.
HEALTH CONSIDERATIONS
Cyanide is highly toxic. It is rapidly absorbed by the gastrointestinal tract and metabolised to thiocyanate. In humans, long-term consumption of improperly prepared cassava in the tropics has been linked with effects on the thyroid gland and particularly the nervous system. Cyanide may deplete vitamin B12 and result in a deficiency that can cause goitre and cretinism. People most at risk are those with a nutritionally inadequate diet…. ADWG 2011