Disinfection by-products (DBPs) are formed when disinfectants (chlorine, ozone, chlorine dioxide, or chloramines) react with naturally occurring organic matter, anthropogenic contaminants, bromide, and iodide during the production of drinking water. Here we review 30 years of research on the occurrence, genotoxicity, and carcinogenicity of 85 DBPs, 11 of which are currently regulated by the U.S., and 74 of which are considered emerging DBPs due to their moderate occurrence levels and/or toxicological properties. These 74 include halonitromethanes, iodo-acids and other unregulated halo-acids, iodo-trihalomethanes (THMs), and other unregulated halomethanes, halofuranones (MX [3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone] and brominated MX DBPs), haloamides, haloacetonitriles, tribromopyrrole, aldehydes, and N-nitrosodimethylamine (NDMA) and other nitrosamines. Alternative disinfection practices result in drinking water from which extracted organic material is less mutagenic than extracts of chlorinated water. However, the levels of many emerging DBPs are increased by alternative disinfectants (primarily ozone or chloramines) compared to chlorination, and many emerging DBPs are more genotoxic than some of the regulated DBPs. Our analysis identified three categories of DBPs of particular interest. Category 1 contains eight DBPs with some or all of the toxicologic characteristics of human carcinogens: four regulated (bromodichloromethane, dichloroacetic acid, dibromoacetic acid, and bromate) and four unregulated DBPs (formaldehyde, acetaldehyde, MX, and NDMA). Categories 2 and 3 contain 43 emerging DBPs that are present at moderate levels (sub- to low-mug/L): category 2 contains 29 of these that are genotoxic (including chloral hydrate and chloroacetaldehyde, which are also a rodent carcinogens); category 3 contains the remaining 14 for which little or no toxicological data are available. In general, the brominated DBPs are both more genotoxic and carcinogenic than are chlorinated compounds, and iodinated DBPs were the most genotoxic of all but have not been tested for carcinogenicity. There were toxicological data gaps for even some of the 11 regulated DBPs, as well as for most of the 74 emerging DBPs. A systematic assessment of DBPs for genotoxicity has been performed for approximately 60 DBPs for DNA damage in mammalian cells and 16 for mutagenicity in Salmonella. A recent epidemiologic study found that much of the risk for bladder cancer associated with drinking water was associated with three factors: THM levels, showering/bathing/swimming (i.e., dermal/inhalation exposure), and genotype (having the GSTT1-1 gene). This finding, along with mechanistic studies, highlights the emerging importance of dermal/inhalation exposure to the THMs, or possibly other DBPs, and the role of genotype for risk for drinking-water-associated bladder cancer. More than 50% of the total organic halogen (TOX) formed by chlorination and more than 50% of the assimilable organic carbon (AOC) formed by ozonation has not been identified chemically. The potential interactions among the 600 identified DBPs in the complex mixture of drinking water to which we are exposed by various routes is not reflected in any of the toxicology studies of individual DBPs. The categories of DBPs described here, the identified data gaps, and the emerging role of dermal/inhalation exposure provide guidance for drinking water and public health research.

Occurrence, genotoxicity, and carcinogenicity of regulated and emerging disinfection by-products in drinking water: a review and roadmap for research.

/pdf/water-analysis-emerging-contaminants-and-current-issues-4iaf1qar5i.pdf

Water Analysis: Emerging Contaminants and Current Issues

A survey of disinfection byproduct (DBP) occurrence in the United States was conducted at 12 drinking water treatment plants. In addition to currently regulated DBPs, more than 50 DBPs that rated a high priority for potential toxicity were studied. These priority DBPs included iodinated trihalomethanes (THMs), other halomethanes, a nonregulated haloacid, haloacetonitriles, haloketones, halonitromethanes, haloaldehydes, halogenated furanones, haloamides, and nonhalogenated carbonyls. The purpose of this study was to obtain quantitative occurrence information for new DBPs (beyond those currently regulated and/or studied) for prioritizing future health effects studies. An effort was made to select plants treating water that was high in total organic carbon and/or bromide to enable the detection of priority DBPs that contained bromine and/or iodine. THMs and haloacetic acids (HAAs) represented the two major classes of halogenated DBPs formed on a weight basis. Haloacetaldehydes represented the third major cla...

Occurrence of a New Generation of Disinfection Byproducts

Advanced oxidation processes (AOPs) generating nonselective hydroxyl radicals (HO*) provide a broad-spectrum contaminant destruction option for the decontamination of waters. Halide ions are scavengers of HO* during AOP treatment, such that treatment of saline waters would be anticipated to be ineffective. However, HO* scavenging by halides converts HO* to radical reactive halogen species (RHS) that participate in contaminant destruction but react more selectively with electron-rich organic compounds. The effects of Cl-, Br-, and carbonates (H2CO3+HCO3-+CO3(2-)) on the UV/H2O2 treatment of model compounds in saline waters were evaluated. For single target organic contaminants, the impact of these constituents on contaminant destruction rate suppression at circumneutral pH followed the order Br->carbonates>Cl-. Traces of Br- in the NaCl stock had a greater effect than Cl- itself. Kinetic modeling of phenol destruction demonstrated that RHS contributed significantly to phenol destruction, mitigating the impact of HO* scavenging. The extent of treatment efficiency reduction in the presence of halides varied dramatically among different target organic compounds. Destruction of contaminants containing electron-poor reaction centers in seawater was nearly halted, while 17beta-estradiol removal declined by only 3%. Treatment of mixtures of contaminants with each other and with natural organic matter (NOM) was evaluated. Although NOM served as an oxidant scavenger, conversion of nonselective HO* to selective radicals due to the presence of anions enhanced the efficiency of electron-rich contaminant removal in saline waters by focusing the oxidizing power of the system away from the NOM toward the target contaminant. Despite the importance of contaminant oxidation by halogen radicals, the formation of halogenated byproducts was minimal.

Effect of halide ions and carbonates on organic contaminant degradation by hydroxyl radical-based advanced oxidation processes in saline waters.

Haloacetonitriles (HANs) are toxic nitrogenous drinking water disinfection byproducts (N-DBPs) and are observed with chlorine, chloramine, or chlorine dioxide disinfection. Using microplate-based Chinese hamster ovary (CHO) cell assays for chronic cytotoxicity and acute genotoxicity, we analyzed 7 HANs:  iodoacetonitrile (IAN), bromoacetonitrile (BAN), dibromoacetonitrile (DBAN), bromochloroacetonitrile (BCAN), chloroacetonitrile (CAN), dichloroacetonitrile (DCAN), and trichloroacetonitrile (TCAN). The cytotoxic potency (%C1/2 values) ranged from 2.8 μM (DBAN) to 0.16 mM (TCAN), with a descending rank order of DBAN > IAN ≈ BAN > BCAN > DCAN > CAN > TCAN. HANs induced acute genomic DNA damage; the single cell gel electrophoresis (SCGE) genotoxicity potency ranged from 37 μM (IAN) to 2.7 mM (DCAN). The rank order of declining genotoxicity was IAN > BAN ≈ DBAN > BCAN > CAN > TCAN > DCAN. The accompanying structure−activity analysis of these HANs was in general agreement with the genotoxicity rank order. Thes...

Haloacetonitriles vs. Regulated Haloacetic Acids: Are Nitrogen-Containing DBPs More Toxic?

Halonitromethanes are drinking water disinfection byproducts that have recently received a high priority for health effects research from the U.S. Environmental Protection Agency (EPA). Our purpose was to identify and synthesize where necessary the mixed halonitromethanes and to determine the chronic cytotoxicity and the acute genotoxicity of these agents in mammalian cells. The halonitromethanes included bromonitromethane (BNM), dibromonitromethane (DBNM), tribromonitromethane (TBNM), bromochloronitromethane (BCNM), dibromochloronitromethane (DBCNM), bromodichloronitromethane (BDCNM), chloronitromethane (CNM), dichloronitromethane (DCNM), and trichloronitromethane (TCNM). Low- and high-resolution gas chromatography/mass spectrometry (GC/MS) was used to identify the mixed chloro-bromonitromethanes in finished drinking waters, and analytical standards that were not commercially available were synthesized (BDCNM, DBCNM, TBNM, CNM, DCNM, BCNM). The rank order of their chronic cytotoxicity (72 h exposure) to Chinese hamster ovary (CHO) cells was DBNM > DBCNM > BNM > TBNM > BDCNM > BCNM > DCNM > CNM > TCNM. The rank order to induce genomic DNA damage in CHO cells was DBNM > BDCNM > TBNM > TCNM > BNM > DBCNM > BCNM > DCNM > CNM. The brominated nitromethanes were more cytotoxic and genotoxic than their chlorinated analogues. This research demonstrated the integration of the procedures for the analytical chemistry and analytical biology when working with limited amounts of sample. The halonitromethanes are potent mammalian cell cytotoxins and genotoxins and may pose a hazard to the public health and the environment.

Paulina Jazwierska

Papers

Halonitromethane drinking water disinfection byproducts: chemical characterization and mammalian cell cytotoxicity and genotoxicity.