Guidelines for Canadian Drinking Water Quality: Guideline Technical Document - Haloacetic Acids

4.0 Identity, use and sources in the environment

There are nine common HAAs: MCA, DCA, TCA, MBA, DBA, bromochloroacetic acid, bromodichloroacetic acid, chlorodibromoacetic acid and tribromoacetic acid. This document focuses on the first five HAAs on this list, referred to as either HAA5 or total HAAs.

HAAs belong to the family of halogenated aliphatic carboxylic acids. Although these chemical analogues will in most cases be referred to as "acids" in this document, it should be understood that when present in drinking water at normal pHs, they will in fact be present as salts and strictly should be called acetates (EC, 2003; U.S. EPA, 2003b). The physical-chemical properties of the HAA5 compounds shown in Table 2 apply to the acids.

Table 2: Physical-chemical properties of the HAA5 compounds^a

Property	MCA	DCA	TCA	MBA	DBA
a References are as follows: 1) Budavari et al., 1996; 2) Lide, 2003-2004; 3) Morris and Bost, 2002; 4) Daubert and Danner, 1989; 5) Weast, 1973; 6) Chemada Fine Chemicals, 2002; 7) Serjeant and Dempsey, 1979; 8) Maruthamuthu and Huie, 1995; 9) ZirChrom Separations, Inc., undated; 10) Nikolaou et al., 1999; 11) Hansch et al., 1995; 12) Schultz et al., 1999. b 1 mmHg = 133.3 Pa. c n/a: not available.
CAS No.	79-11-8	79-43-6	76-03-9	79-08-3	631-64-1
Formula	ClCH2COOH	Cl2CHCOOH	Cl3CCOOH	BrCH2COOH	Br2CHCOOH
Molecular weight	94.5	128.942	163.387	138.948	217.844
Boiling point (°C)	189.11)	193-1941)	196-1971)	2082)	1952)
Melting point (°C)	631)	13.52)	57-581)	502)	492)
Density (g/cm3)	1.40 at 25°C 3)	1.56 at 20°C 1)	1.62 at 25°C1)	1.932)	n/ac
Vapour pressure (mmHg)b	0.065 at 25°C3)	0.179 at 25°C4)	0.16 at 25°C5)	0.549 at 25°C6)	n/ac
Dissociation constant (pKa) at 25°C	2.877)	1.268)	0.662)	2.699)	n/ac
Water solubility (g/mL)	1.09 at 25°C10)	Miscible10)	1.50 at 25°C10)	1.75 at 25°C10)	2.11 at 25°C10)
Log octanol/ water partition coefficient	0.2211)	0.9211)	1.3311)	0.4111)	1.2212)

MCA is described as a colourless solution or white crystal with a vinegar-like odour (Budavari et al., 1996; CHEMINFO, 2003a, 2003b). It is used mainly as a chemical intermediate in the production of cellulose ethers (mainly carboxymethylcellulose), thioglycolic acid and herbicides (Morris and Bost, 2002). It is also used in the manufacture of glycine, phenoxyacetic acid, sarcosine, amphoteric surfactants, synthetic caffeine, various indigo dyes, pharmaceuticals, preservatives (ethylenediaminetetraacetic acid) and bacteriostats (Lewis, 2001; Koenig et al., 2002; Morris and Bost, 2002).

DCA is a colourless to slightly yellow liquid with a pungent odour (IARC, 1995; Budavari et al., 1996). It is used as a topical astringent, fungicide and medicinal disinfectant, as a test reagent for analytical measurements, to treat lactic acidosis and in the synthesis of organic materials, including pharmaceuticals (Budavari et al., 1996; Koenig et al., 2002; Morris and Bost, 2002).

TCA is a colourless to white deliquescent crystal with a sharp, pungent odour (Ashford, 1994; Budavari et al., 1996). TCA is used as an intermediate in the synthesis of organic chemicals and as a laboratory reagent, herbicide, soil sterilizer and antiseptic (Budavari et al., 1996; Lewis, 2001; Verschueren, 2001; Meister, 2002). It has been used as an etching or pickling agent, a swelling agent and a solvent in plastics and in textile finishing (Koenig et al., 2002). Clinically, TCA has been used in 10-25% aqueous solutions in the treatment of recurrent corneal disease (Grant and Schuman, 1993), for the treatment of external cervical root resorption in dentistry (Heithersay and Wilson, 1988; Lewinstein and Rotstein, 1992) and to treat various skin afflictions (Koenig et al., 2002). TCA has been used as a facial chemical peel and for other therapeutic applications, such as a cauterizing agent, in wart removal and as an astringent (NTP, 2003a).

MBA is a colourless hygroscopic crystalline solid (Ashford, 1994). It has been used in organic synthesis, abscission of citrus fruit in harvesting (Lewis, 2001), commercial letterpress printing and production of plastics, as well as in medical and surgical hospitals (NIOSH, 1990).

DBA is a hygroscopic crystal (U.S. EPA, 2005a). It has no reported industrial use (NIOSH, 1990).

HAAs are formed in drinking water when chlorine disinfectants used in water treatment react with organic matter (e.g., humic or fulvic acids) and inorganic matter (e.g., bromide ion) naturally present in the raw water (IPCS, 2000). HAAs are the second most frequently occurring DBPs, after THMs.

Various water treatment methods lead to the formation of chlorinated and brominated acetic acids, including chlorination, ozonation and chloramination. In the case of chlorination, hypochlorous acid (HOCl) and the hypochlorite ion (OCl^-) are formed, which in turn react with a bromide ion, if present, oxidizing it to hypobromous acid (HOBr^-) and hypobromite ion (OBr^-), respectively. Hypochlorous acid and hypobromous acid then react with natural organic matter (NOM) to form different DBPs, including HAAs. The chlorinated HAAs generally dominate; however, in high-bromide waters, the brominated HAAs may be more prevalent (IPCS, 2000). In the case of ozonation, brominated acetic acids (MBA, DBA) can be formed when organic matter and bromide are present in the source waters (U.S. EPA, 2005a). Chloramination also results in HAA production if chloramine is produced by chlorination followed by ammonia addition (IPCS, 2000).

HAA formation can be appreciable when drinking water is chlorinated under conditions of slightly acid pH (IPCS, 2000). Whereas THM formation increases with increasing pH, HAA formation decreases, hydrolysis likely being a significant factor (Krasner et al., 1989; Pourmoghaddas and Stevens, 1995). Despite the fact that HAAs and THMs have different pH dependencies, their formation appears to correlate strongly when treatment conditions are relatively uniform and when the water has a low bromide concentration (Singer, 1993).

Longer contact times and higher water temperatures are contributing factors in HAA formation. At higher water temperatures, reactions are faster and chlorine demand is higher (Nikolaou et al., 1999). Increased concentrations of NOM with aromatic content (humic acids) in raw water favour formation of HAAs (Reckhow et al., 1990; Nikolaou et al., 1999). Increased concentrations of NOM in raw water also increase the chlorine demand and favour the formation of chlorinated DBPs. In the presence of bromide, the chlorination process may also favour the formation of brominated DBPs, depending on the physical and chemical properties of the water. High chlorine concentrations also favour the formation of higher concentrations of TCA compared with MCA and DCA. However, if bromide levels are high in source waters, the formation of brominated and chloro-brominated HAAs is more likely to occur (Nikolaou et al., 1999). Bromide levels in surface water and groundwater may fluctuate seasonally and may occur as a result of saltwater intrusion or pollution as well as from natural sources (Richardson et al., 1999; IPCS, 2000).

The HAA5 compounds may be released into the environment through various waste streams following their production and use. MCA and TCA can be formed as combustion by-products of organic compounds (waste incineration) in the presence of chlorine (Juuti and Hoekstra, 1998). Other potential sources of atmospheric TCA are the photooxidation of tetrachloroethylene (PCE), trichloroethylene (TCE) and 1,1,1-trichloroethane (Reimann et al., 1996; Sidebottom and Franklin, 1996; Juuti and Hoekstra, 1998; Bakeas et al., 2003), as well as biomass burning and natural formation in the marine boundary layer (Hoekstra, 2003). Some atmospheric MCA may also be formed from the hydrolysis of monochloroacetanilide herbicides (Reimann et al., 1996;) and directly or indirectly from car exhaust (Bakeas et al., 2003). DCA is believed to be a minor atmospheric degradation product of TCE (Peters, 2003).

HAAs are present in raw water, possibly the result of chlorinated municipal waste effluent, drinking water inputs, precipitation, the degradation of herbicides and industrial inputs involving reactions between chlorine and organic material. Scott et al. (2002) found that HAA levels in raw surface water corresponded with the level of industrial activity in the surrounding area. Concentrations of HAAs in the Detroit River were as follows: MCA, <0.005-0.59 µg/L; DCA, 0.48-1.2 µg/L; TCA, 0.1-2.2 µg/L; MBA, <0.005-0.04 µg/L; and DBA, <0.005-0.26 µg/L. Lake Malawi (Africa), with little industry, had no detectable levels of HAAs, whereas the Laurentian Great Lakes had total concentrations of approximately 0.5 µg/L, consisting of TCA, DCA and MCA; no significant levels of bromoacetic acids were detected at either of these locations (Scott et al. 2002).

4.1 Environmental fate

Volatilization from water surfaces is not expected based upon the low vapour pressures and high water solubilities of the HAA5 compounds. Low pK_a values indicate that these compounds will exist almost entirely in the ionized form at pH values found in drinking water.

Microbial degradation of MCA in water is most likely the main aquatic degradation pathway. MCA was biodegraded in stream water with 73% conversion to carbon dioxide in 10 days at 29°C under laboratory conditions at the highest concentration used (Boethling and Alexander, 1979). In comparison, DCA was found to be more persistent in the aquatic environment. At a concentration of 10 mg/L, only 14% and 8% degradation were reported for river

water and seawater, respectively, after 3 days of incubation (Kondo et al., 1988). TCA is likely to be relatively persistent in water given its high solubility and low vapour pressure. The estimated half-lives of TCA in a model river and a model lake were 1632 and 12 000 days, respectively (HSDB, 2003). In a study to determine the stability of HAAs incubated in river water and seawater (20°C) for 30 and 9 days, respectively, TCA concentrations did not decrease significantly, whereas MCA, DCA, MBA and DBA almost completely disappeared (Hashimoto et al., 1998). The same authors indicated that approximately half the decomposition was due to microbial activity.