Monochloramine
CAS NO 10599-90-3 (endorsed 2014)
Guideline
Based on health considerations, the concentration of monochloramine in drinking water should not exceed 3 mg/L (equivalent to 5 mg Cl as in chloraminated systems).
General description
Monochloramine is used as a disinfectant for drinking water supplies. It is increasingly being used in conjunction with chlorine, or in its own right, to provide primary disinfection of drinking water entering the distribution system and/or maintain a disinfectant residual through the distribution network. Although it is not as strong an oxidant as chlorine, monochloramine can be quite useful and effective in distribution systems with long water ages as it persists for longer. Where monochloramine is used overseas, concentrations typically range from 1.5 to 2.5 mg/L (as ).
Use of monochloramine for primary disinfection at the treatment facility needs to be considered carefully in terms of the range of C.t (disinfectant concentration × contact time) values achievable prior to the first customer.
Use of monochloramine can significantly reduce the level of disinfection by-products compared to that produced by similar levels of chlorine. If not managed proactively, however, use of chloramine can lead to nitrification in the distribution system resulting in a reduction of its effectiveness.
Monochloramine is formed by the addition of ammonia and chlorine in drinking water. This reaction can also result in the formation of dichloramine and trichloramine, both of which have lower taste and odour thresholds than monochloramine, and which should be minimised. The preferential formation of monochloramine is affected by the pH and the physical arrangements of adding the two chemicals.
Monochloramine has an odour threshold of 0.5 mg/L.
For additional information refer to the Disinfection Information Sheet for Chloramines.
Typical values in Australian drinking water
Monochloramine is used as a disinfectant in some Australian reticulated supplies, and concentrations up to 4-5 mg/L (as total chlorine) have been applied at the start of long distribution systems to achieve concentrations ranging from 0.5-1.5 mg/L at the ends of distribution systems.
Treatment of drinking water
Monochloramine can be removed from drinking water by the use of granular activated carbon, or by reducing agents such as sodium sulphite or sodium bisulphite.
Measurement
The concentration of monochloramine in drinking water can be determined by the DPD ferrous titrimetric method (APHA Method 4500-Cl Part F 2012) or by amperometric titration (APHA Method 4500-Cl Part D 2012). The limit of determination is typically 0.1 mg/L for the DPD method and can be lower for amperometric titration. Water utilities should refer to Standard Methods when selecting a method (APHA 2012).
Health considerations
In studies with rats it has been shown that monochloramine is readily absorbed and does not accumulate in tissues. It is metabolised rapidly to the chloride ion and excreted in urine in mammals. No specific toxic effects have been reported for monochloramine from either short-term or long-term studies. However, monochloramine is toxic to fish.
In humans, short-term exposure to concentrations of up to 24 mg/L of monochloramine in drinking water did not produce adverse effects. Similarly, volunteers given water containing up to 5 mg/L of monochloramine for 12 weeks did not exhibit adverse effects.
Acute haemolytic anaemia has been reported in haemodialysis patients when tap water containing chloramines was used for dialysis (Eaton et al. 1973; Kjellstrand et al. 1974; Tipple et al. 1988). Chloramines present in water are harmful to people on kidney dialysis and to animal species in aquaria; therefore, it is important for water utilities using chloramination to inform consumers at risk. Water suppliers that disinfect with chloramines need to contact coordinators of home dialysis and renal dialysis clinics to advise on the presence and concentrations of chloramines in drinking water.
Carcinogenicity studies have reported a slight increase in the incidence of mononuclear cell leukaemia in female rats exposed to monochloramine for 2 years, at doses of approximately 10 mg/kg bodyweight per day. There was no evidence of carcinogenic activity in male rats, or male and female mice.
Monochloramine exhibited weak mutagenic activity in one test using bacteria but was negative in another test (Shih and Lederberg 1976; Thomas et al. 1987). It did not induce chromosome aberrations in mammalian cells.
Based on inadequate evidence in humans and experimental animals, the International Agency for Research on Cancer concluded that chloramines are not classifiable as to their carcinogenicity to humans (Group 3) (IARC 2004).
No data are available on the health effects of dichloramine or trichloramine in drinking water.
Derivation of guideline
The guideline value for monochloramine in drinking water was derived as follows:
where:
9.4 mg/kg bodyweight per day is the no-observed-adverse-effect level (NOAEL) based on 2-year drinking water study using rats (NTP 1992). A similar value was obtained from a human study but this was of a limited duration.
70 kg is taken as the average weight of an adult.
2 L/day is the estimated maximum amount of water consumed by an adult.
100 is the safety factor applied to the NOAEL derived from an animal study (10 for interspecies variations, and 10 for intraspecies variations).
Where monochloramine is measured by determining mg Cl as by standard DPD ferrous titrimetric methods the equivalent guideline value is:
It is assumed that all monochloramine intake is from drinking-water.
References
APHA Method 4500-Cl Part D (2012). Chlorine (residual): Amperometric titration method. Standard Methods for the Examination of Water and Wastewater, 22nd edition. APHA (American Public Health Association), AWWA (American Water Works Association) and WEF (Water Environment Federation), Washington, DC.
APHA Method 4500-Cl Part F (2012). Chlorine (residual): DPD Ferrous Titrimetric method. Standard Methods for the Examination of Water and Wastewater, 22nd edition. APHA (American Public Health Association), AWWA (American Water Works Association) and WEF (Water Environment Federation), Washington, DC.
Eaton JW, Kolpin CF, Swofford H, Kjellstrand CM and Jacob HS (1973). Chlorinated urban water: a cause of dialysis-induced hemolytic anaemia. Science, 181:463–464.
IARC (International Agency for Research on Cancer) (2004). Chloramine. IARC Monograph Vol 84, IARC Publications, Lyon.
Kjellstrand CM, Eaton JW, Yawata Y, Swofford H, Kolpin CF, Buselmeier TJ, von Hartitzsch B and Jacob HS (1974). Hemolysis in dialyzed patients caused by chloramines. Nephron, 13:427–433.
NTP (National Toxicology Program) (1992). Toxicology and carcinogenesis studies of chlorinated water and chloraminated water in F344/N rats and B6C3F1 mice (drinking water studies). NTP, Technical Report No. 392, Publication No. 92-2847. United States Department of Health and Human Services, National Institute of Health.
Shih KL and Lederberg J (1976). Chloramine mutagenesis in Bacillus subtilis. Science 192: 1141-1143.
Tipple MA, Bland LA, Favero MS and Jarvis WR. (1988) Investigation of hemolytic anaemia after chloramine exposure in a dialysis center. American Society for Artificial Internal Organs (ASAIO) Transactions, 34(4):1060.
Thomas EL, Jefferson MM, Bennett JJ and Learn DB (1987). Mutagenic activity of chloramines. Mutation Research 188:35-43.
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