Chapter 12
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Carbonaceous and Nitrogenous Disinfecion By-Product Formation Potentials of Amino Acids Meric Selbes,1 Junhong Shan,2 S. Sule Kaplan Bekaroglu,3 and Tanju Karanfil*,4 1Hazen
and Sawyer, Environmental Engineers and Scientists, Fairfax, Virginia 22030, USA 2Public Utilities Board, Singapore 608576, Singapore 3Water Institute, Suleyman Demirel University, Isparta 32260, Turkey 4Department of Environmental Engineering and Earth Sciences, Clemson University, Anderson, South Carolina 29625, U.S.A. *E-mail:
[email protected].
Nine amino acids (AAs) were examined under different oxidation conditions to determine their formation potential for regulated carbonaceous DBPs (trihalomethanes (THMs) and haloacetic acids (HAAs)) and selected emerging nitrogenous DBPs (haloacetonitriles (HANs), halonitromethanes (HNMs) and nitrosamines). Aspartic acid and histidine exhibited very high dihalogenated-HANs and HAAs formation during chlorination, but their reactivity significantly decreased after ozonation. Glycine followed by lysine yieled the highest level of HNMs and THMs formation during ozonation-chlorination, but they did not have measurable yields for either classes of DBPs during chlorination. All other AAs showed very low carbonaceous and nitrogenous DBP yields. The nitrosamine yields of all nine AAs were very low or below the minimum reporting levels during chloramination, ozonation, and ozonation-chloramination. These results indicated that the presence of AAs in natural waters can result in some contributions to certain halogenated DBPs depending on the oxidation conditions. However, they do not appear to be an important contributor to nitrosamines formation.
© 2015 American Chemical Society Karanfil et al.; Recent Advances in Disinfection By-Products ACS Symposium Series; American Chemical Society: Washington, DC, 2015.
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Introduction Recent research has shown that emerging nitrogenous disinfection by-products (N-DBPs) exhibit orders of magnitude higher cyto- and geno-toxicity than the regulated carbonaceous DBPs (C-DBPs) (1). Therefore, it should not be surprising to see N-DBP regulated in the near future. Recent research has shown that nitrogen-rich organic materials in natural waters play an important role in the formation of N-DBPs (2–4). However, the important precursors and the formation mechanisms of N-DPBs still remain largely unknown. Amino acids (AAs) have been found in fresh waters in a wide range of concentrations from 5 to 2000 µg/L, in either free or combined peptides, nucleic acids, purines, pyrimidines, and proteins (5, 6). Thurman (7) reported that the total AAs, which were the sum of the free and combined AAs, accounted for 2.6% of the dissolved organic carbon (DOC) and 35% of the dissolved organic nitrogen (DON) in some lakes. Hagedorn and colleagues (8) observed in their studies of catchment runoff a 20% to greater than 75% of the DON of the total AAs observed. Elevated amino acid levels were also found in the presence of algae blooms, the degradation of which is a major cause of increased AA levels in natural waters (7, 9–11). In a recent survey of sixteen water treatment plants in the United States, the total AA concentrations, identified as glycine, glutamic acid, alanine, aspartic acid, leucine, proline and serine, constituted an average 15% of the DON in the source waters (2, 7, 12–14). The presence of AAs in raw and treated waters requires substantial amounts of chlorine for treatment (15, 16). The relative chlorine reactivity of the AAs depends on the side chain groups attached to the α-carbon. Studies conducted for purposes of reacting AAs with chlorine clearly indicated the formation of various classes of DBPs including haloacetaldehydes, haloacetonitriles (HANs), cyanogen chloride, trihalomethanes (THMs) and haloacetic acids (HAAs) (15, 17, 18). A recent study showed that AAs with activated aromatic structures (e.g. tryptophan, tyrosine) were potent precursors of THMs and HAAs (17). Additionally, absent the reactive ring structure, aspartic acid and asparagines produced high levels of HAAs. Investigations conducted on the reaction(s) of ozone with AAs determined that the side chains of AAs were responsible for the high ozone reactivity in polypeptide structures (19). Structures that possess side groups such as amino nitrogen or activated aromatic ring were identified as the most reactive AAs. This AA ozonation leads to the formation of aldehydes such as formaldehyde, acetaldehyde, glyoxal and glyoxal derivatives. Unlike the carbonaceous DBPs (C-DBPs), very little is known regarding how N-DBPs form from amino acids, especially for halonitromethanes (HNMs) and N-nitrosamines. HNM constitutes one group of N-DBPs that exhibits high degrees of cyto- and geno-toxicity (1, 21). Drinking waters and wastewater effluents under chloramination conditions are a particularly relevant medium in which nitrosamine, especially N-nitrosodimethylamine (NDMA), can form (20). Nitrosamines, which have been classified as a probable human carcinogen by the United States Environmental Protection Agency, can pose important health risks even at ng/L concentrations. As a result, the Canada Ontario Ministry of 216 Karanfil et al.; Recent Advances in Disinfection By-Products ACS Symposium Series; American Chemical Society: Washington, DC, 2015.
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the Environmental and Energy established a maximum allowable concentration of 9 ng/L for NDMA, and the California Department of Health Service set an interim action level of 10 ng/L. Although nitrosamines are not currently regulated in the United States, NDMA and four other nitrosamines [N-nitrosodiethylamine (NDEA), N-nitroso-di-n-propylamine (NDPA), N-nitrosodiphenylamine (NDPhA), N-nitrosopyrrolidine (NPYR)] are on the USEPA’s Contaminant Candidate List-3, and are monitored under the Unregulated Contaminant Monitoring Rule 2. Recent studies on the formation potentials of HNMs in natural waters found that HNM yields increased with decreasing DOC/DON ratios (i.e., increasing organic nitrogen content per organic carbon in water) during ozonation followed by chlorination (3). The hydrophilic components of dissolved NOM, especially nitrogenous organic compounds, are important precursors of HNMs in the NOM pool (2, 3). Only a limited number of studies, however, have been conducted to elucidate trichloronitromethane (TCNM) formation by AAs during chlorination, using glycine (4, 22), tyrosine (4), tryptophan and aspartic acid (23). Similarly, very little is known about of the formation of NDMAs caused by AAs, aside from that undertaken by Mitch et al. (4). Specifically, they observed nitrosamine formation (NDMA, NMEA and NDEA) in aspartic acid, proline and histidine after chloramination (24); and NDMA formation of
