Cyanide
(endorsed 1996)
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.
Measurement
The cyanide concentration in drinking water can be determined with a colorimetric method using chloramine-T (APHA Method 4500-CN Part E 1992). The limit of determination is 0.02 mg/L.
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.
Animal studies indicate that pigs may be more sensitive than rats to the effects of long-term exposure to cyanide. In a six-month study using pigs, exposure to cyanide was reported to increase ambivalence (sic) and result in slower response times to stimuli. Behaviour demanding high energy appeared to be more readily affected by cyanide exposure than low-energy behaviour.
No data are available on the carcinogenic properties of cyanide. Tests for mutagenicity with different strains of bacteria have been mostly negative.
Derivation of guideline
The guideline value for cyanide in drinking water was derived as follows:
where:
1.2 mg/kg body weight per day is the no-effect level from 6-month feeding studies using pigs Jackson et al. 1986, (Jackson 1988).
70 kg is the average weight of an adult.
0.2 is the proportion of total daily intake attributable to the consumption of water.
2 L/day is the average amount of water consumed by an adult.
100 is the safety factor in applying the results of animal studies to humans (10 for interspecies variations and 10 for intraspecies variations).
The World Health Organization guideline of 0.07 mg/L was based on an adult weight of 60 kg. The difference in guideline values is not significant.
References
APHA Method 4500-CN Part E (1992). Cyanide: Colorimetric method. Standard Methods for the Examination of Water and Wastewater, 18th edition. American Public Health Association, Washington.
Jackson LC, Chandler JP, Jackson RT (1986). Inhibition and adaptation of red cell glucose-6-phosphate dehydrogenase in vivo to chronic sublethal dietary cyanide in an animal model. Human Biology, 58:67–77.
Jackson LC (1988). Behavioural effects of chronic sub-lethal dietary cyanide in an animal model: Implications for humans consuming cassava (Manihot esculenta). Human Biology, 60:597–614.
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