1.8: Other disinfectants

This information sheet provides information on a number of other chemicals that have been used, or are proposed for use, as disinfectants of drinking water. Currently, these chemicals are not recommended for use as disinfectants in municipal water systems, but may be of use in specific, small scale applications, where the use of more traditional disinfectants may not be practical. Prior to use, expert advice should be sought regarding the appropriateness of using these chemicals as disinfectants.

Bromine

Definition and uses

Bromine has been widely used to disinfect swimming pools through the addition of solid bromine-releasing agents such as N-bromo-N-chloro-5,5-dimethylhydantoin or dibromocyanuric acid. Bromine chloride (BrCl) is under investigation for large-scale use, such as the control of biofouling in cooling towers or wastewater disinfection, as it is much less corrosive than liquid bromine and has sufficient vapour pressure to enable it to be metered in equipment similar to that used for chlorine.

Relative to chlorine, bromine is costly to use on a municipal-scale water supply system.

Health effects

Bromine is corrosive to human tissue in a liquid state and its vapours irritate the eyes and the throat. Bromine vapours are very toxic if they are inhaled. Bromine concentrations of around 0.5 mg/L in swimming pools cause eye and mucous membrane irritation and can lead to odour nuisance. Bromine aggressively reacts with metals and it is a corrosive material. Security measures should be taken when bromine is transported, stored or used.

Iodine

Definition and uses

Iodine has been used as a disinfectant for small drinking water supplies; however, like bromine, it is costly to use on a municipal scale. It is not recommended for regular use as a disinfectant due to possible health effects associated with long-term consumption. It can, however, be used for emergency water disinfection.

Health effects

Iodine is an essential trace element for humans and is used in the synthesis of thyroid hormones. The recommended dietary intake for adults ranges from 0.03 mg/day to 0.15 mg/day. Iodine is efficiently absorbed by the gastrointestinal tract and deposited in the thyroid gland, the eye, and muscle tissue. More than 70% is found in the thyroid gland. High oral doses (more than 30 mg/kg body weight) of iodine can be lethal. Lower doses (3.3 mg/kg body weight) have been used to treat asthmatic patients without adverse effects.

Chronic exposure to high amounts of iodide in the diet (over 2 mg/day) can result in a condition known as iodism. Symptoms resemble those of a sinus cold. Long-term consumption of iodinated drinking water has not been associated with adverse health effects in humans. Experiments with humans who drank water containing up to 1 mg/L iodine for five years showed no signs of iodism or hypothyroidism, but some changes in uptake of iodine by the thyroid gland were observed.

Animal studies using chickens susceptible to autoimmune thyroiditis reported an increase in the incidence of the disease when they were given high doses of iodide in their drinking water (200 mg/L). Excessive iodide consumption may increase the incidence of this disease in humans.

Iodide has not been shown to increase the incidence of cancer of the thyroid in laboratory animals.

No data are available on the mutagenic activity of iodine.

For further information refer to the Iodine Fact Sheet contained in Part V of these guidelines.

Silver

Definition and uses

Silver is a weak biocide/bacteriostat that has been used occasionally for disinfection, particularly in point-of-use devices. However, there is no reliable evidence that these products worked effectively to kill micro-organisms. A long exposure time of several hours to days is required for any biocidal effect to be observed (Bosch et al, 1993). This is generally not practical in the supply of potable water. In addition, for protozoan pathogenic microorganisms, antiprotozoan activity does not appear to be significant for metal ions acting alone (Cassels et al. 1995). The Australian Pesticides and Veterinary Medicines Authority provide a comprehensive review on the effectiveness of silver as a disinfectant (https://apvma.gov.au/node/1039).

For the reasons outlined above silver is not recommended for use as a disinfectant for municipal drinking water supplies.

Health effects

Although silver can be found in many biological substances, it is not considered an essential trace element for mammals. It has been estimated that less than 10% of dietary silver is absorbed by the gastrointestinal tract.

Silver is stored mainly in the liver and skin and is capable of binding to amino acids and proteins. The best-known clinical condition of silver intoxication is argyria, which results in a bluish-grey metallic discolouration of the skin, hair, mucous membranes, mouth and eye. Most cases have been associated with self-administration of silver preparations, or occupational exposure to silver and silver compounds.

Experiments with laboratory rats and mice have reported similar results. Very high concentrations of silver in drinking water (over 600 mg/L) for a lifetime caused discolouration in the thyroid and adrenal glands, the choroids of the eyes, the choroid plexus of the brain, and the liver and kidney. Some hypoactive behaviour was also reported.

No data are available on the carcinogenicity of silver. Silver salts are not mutagenic in tests with bacteria, but can induce damage in mammalian DNA.

For further information refer to the Silver Fact Sheet contained in Part V of these guidelines.

References

Bosch, A., Diez, J.M.and Abad, F.X. (1993). Disinfection of human enteric viruses in water by copper:silver and reduced levels of chlorine. Water Science and Technology, 27, 3-4: 351-356.

Cassells, J.M., Yahya, M.T., Gerba, C.P. and Rose, J.B. (1995). Efficacy of a combined system of copper and silver and free chlorine for inactivation of Naegleria fowleri amoebas in water. Water Science and Technology,31: 119-122.