Nitrilotriacetic acid (NTA)
(endorsed 1996)
Guideline
Based on health considerations, the concentration of nitrilotriacetic acid in drinking water should not exceed 0.2 mg/L.
General description
NTA may be present in drinking water that has been contaminated with sewage, for example by sewage discharge into a river or stream that is then used for drinking water. It is likely to be present in the form of metal complexes rather than the free acid. NTA has been detected in water supplies of municipalities in Canada and the United States at a mean concentration of less than 0.004 mg/L, with a small number of supplies exceeding 0.01 mg/L.
NTA is a chelating agent and forms soluble metal complexes with a number of metal ions including calcium and magnesium. It is used in laundry detergents as a replacement for phosphate, particularly in countries where legislation restricts the use of phosphate-based detergents. It is also used in the treatment of boiler water to prevent scale formation, and in the photographic, metal plating, textile manufacturing, and paper and cellulose industries. It is not widely used in Australia.
Typical values in Australian drinking water
NTA has not been found in Australian drinking waters. It is included here to provide guidance in the unlikely event of contamination, and because it has been detected occasionally in drinking water supplies overseas.
Treatment of drinking water
No published reports are available on water treatment procedures to remove NTA from drinking water.
Measurement
Analysis can be undertaken using gas chromatography with a nitrogen-specific detector after converting NTA to the tri-n-butyl ester (Aue et al. 1972, Malaiyandi et al. 1979). The limit of determination is 0.0002 mg/L.
Health considerations
NTA is poorly absorbed by humans compared to experimental animals. It is rapidly excreted unchanged, but may be briefly retained in bone, probably due to the formation of complexes with calcium ions.
Data on the health effects in humans are scarce.
A number of long-term toxicity studies with animals have all shown similar results. No adverse effects are observed with low doses, but higher doses (30 mg/kg body weight per day) can cause some adverse effects to the kidney and urinary tract. The formation of kidney, urinary tract and bladder tumours has been reported in rats after prolonged exposure to high doses, but the tumours are believed to be the result of chelation of metal ions in the urinary tract.
Tests for mutagenic activity using bacteria have been negative; however, the NTA–iron complex is mutagenic in mammalian cells in vitro.
The International Agency for Research on Cancer has concluded that NTA is possibly carcinogenic to humans (Group 2B, no data in humans but sufficient evidence in animals) (IARC 1990).
Derivation of guideline
The assessment of the toxicological data for NTA by the World Health Organization (WHO) has been used without review. The guideline value was determined as follows:
where:
10 mg/kg body weight per day is the no-effect level from a 2-year feeding study using rats (Nixon et al. 1972).
70 kg is the average weight of an adult.
0.5 is the proportion of total daily intake attributable to the consumption of water, based on a WHO assessment of distribution.
2 L/day is the average amount of water consumed by an adult.
1000 is the safety factor in using the results of an animal study as a basis for human exposure (10 for interspecies variations, 10 for intraspecies variations and 10 for potential carcinogenic effects).
References
Aue WA, Hastings CR, Gerhardt KO, Pierce JO, Hill HH, Mosman RF (1972). The determination of part-per-billion levels of citric and nitrilotriacetic acids in tap water and sewage effluents. Journal of Chromatography, 72:259–267.
IARC (International Agency for Research on Cancer) (1990). IARC Monographs on the Evaluation of Carcinogenic Risks to Humans: Some flame retardants and textile chemicals, and exposures in the textile manufacturing industry. World Health Organization, IARC, 48.
Malaiyandi M, Williams DT, O’Grady R (1979). A national survey of nitrilotriacetic acid in Canadian drinking water. Environmental Science and Technology, 13:59–62.
Nixon GA, Buehler EV, Niewenhuis RJ (1972). Two-year rat feeding study with trisodium nitrilotriacetate and its calcium chelate. Toxicology and Applied Pharmacology, 21:244–252.
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