Disinfection By-products in Drinking Water / Edition 1 available in Hardcover
Disinfection By-products in Drinking Water / Edition 1
- ISBN-10:
- 1782620885
- ISBN-13:
- 9781782620884
- Pub. Date:
- 10/09/2015
- Publisher:
- RSC
Disinfection By-products in Drinking Water / Edition 1
Hardcover
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$175.00Overview
Product Details
| ISBN-13: | 9781782620884 |
|---|---|
| Publisher: | RSC |
| Publication date: | 10/09/2015 |
| Series: | Special Publications , #352 |
| Pages: | 378 |
| Product dimensions: | 6.20(w) x 9.30(h) x 1.10(d) |
Read an Excerpt
Disinfection By-products in Drinking Water
By Clive Thompson, Simon Gillespie, Emma Goslan
The Royal Society of Chemistry
Copyright © 2016 The Royal Society of ChemistryAll rights reserved.
ISBN: 978-1-78262-271-0
CHAPTER 1
THE NEXT GENERATION OF DRINKING WATER DISINFECTION BY-PRODUCTS: OCCURRENCE, FORMATION, TOXICITY, AND NEW LINKS WITH HUMAN EPIDEMIOLOGY
Susan D. Richardson and Cristina Postigo
1 INTRODUCTION
Drinking water disinfection by-products (DBPs) are an unintended consequence of using disinfectants to kill harmful pathogens in drinking water. They are formed primarily by the reaction of disinfectants with natural organic matter (NOM) and bromide or iodide but can also be formed from pollutants, such as pesticides, pharmaceuticals, antibacterial agents, estrogens, textile dyes, bisphenol A, parabens, surfactants, and algal toxins Popular disinfectants for drinking water include chlorine, chloramines, ozone, chlorine dioxide, and UV.
Eleven DBPs are regulated in the United States, but more than 600 have been identified And, despite this large number of DBPs identified, more than 50% of the halogenated material formed in chlorinated drinking water is still unknown, as well as the toxicological risk that it poses to human health
Adverse health concerns include bladder cancer, miscarriage, and birth defects. While bladder cancer is the primary cancer observed in humans, none of the 11 regulated DBPs cause bladder cancer in animals; consequently, many researchers believe that the regulations are not adequately controlling for these effects in humans. As a result, there is intensive research in emerging, unregulated DBPs. These include iodo-trihalomethanes, iodo-acids, haloamides, halonitromethanes, halofuranones, haloacetonitriles, haloacetaldehydes, nitrosamines, and halobenzoquinones. Many of these unregulated DBPs are more genotoxic or cytotoxic than those currently regulated. For example, iodoacetic acid is the most genotoxic DBP identified to-date, and is 2x more genotoxic than bromoacetic acid. Iodoacetic acid was also recently shown to be tumorigenic in mice.
Nitrogen-containing DBPs (N-DBPs) have become a major focus because they are generally more toxic than DBPs that do not contain nitrogen. For example, many nitrosamines are known to be carcinogens. Nitrosamines were on the U.S. Environmental Protection Agency's (EPA's) Unregulated Contaminant Monitoring Rule and are currently being considered for regulation in the United States.
DBPs can also form in disinfected swimming pool water. Some swimming pool DBPs are the same as those found in drinking water, but some are different, due to the additional human precursors that can be present in pools (e.g., urine, sweat, hair, sunscreens, lotions, personal care products etc.) For example, trichloramine is a common DBP found in chlorinated swimming pools, and it is formed by the reaction of urea (from urine or sweat) with chlorine. While trichloramine is produced in the water, it is quickly transported to the air phase above, due to its high Henry's Law constant. Trichloramine is suspected as the causal agent in the increased asthma in epidemiologic studies of elite swimmers. One study has also shown increased incidence of bladder cancer with heavy exposure from swimming pools.
Newer potential health concerns include severe skin rashes, and respiratory and digestive issues resulting from exposure to chloraminated drinking water. However, there has not yet been a controlled scientific study to examine these issues. Chloramination has become a popular disinfectant in the U.S., due to tightened DBP regulations, and is also used in other countries, including the UK and Australia. The use of chloramines can result in ~90% reduction in the levels of regulated trihalomethanes (THMs) and haloacetic acids (HAAs) compared to chlorination, and it also allows longer residual disinfection in distribution systems.
DBP formation depends on the type of disinfectant, dose, and the type of organic matter or other precursors present in the water Formation mechanisms for several DBPs and DBP classes have been investigated, including iodo-DBPs, halonitromethanes, nitrosamines, haloamides, halopyrroles, and halobenzoquinones. A review of their formation follows.
2 IODO-DBPs
Iodo-DBPs identified to-date include iodo-THMs (dichloroiodomethane, bromochloroiodomethane, dibromoiodomethane, chlorodiiodomethane, bromodiiodomethane, and iodoform); iodo-acids (iodoacetic acid, bromoiodoacetic acid, chloroiodoacetic acid, diiodoacetic acid, (Z)-3-bromo-3-iodopropenoic acid, (E)-3-bromo-3-iodopropenoic acid, and (E)-2-iodo-3-methylbutenedioic acid) iodoamides (bromoiodoacetamide and chloroiodoacetamide); and the recently reported iodoacetaldehyde.
Iodo-THMs were the first iodo-DBPs to be discovered, back in the mid-1970s, and have been measured in drinking waters treated with chlorination or chloramination. Highest levels are consistently observed in chloraminated water.(up to 15 µg/L), and total iodo-THM levels can be as much as 81% of the regulated THMs. Point-of- use treatment with iodine, and chlorination or chloramination of hydraulic fracturing (HF) wastewater can also produce iodo-THMs.
Iodo-acids, which are the most genotoxic of the iodo-DBPs, were first identified in a U.S. Nationwide Occurrence Study, and levels up to 1.7 µg/L were reported in a 23 city survey of chloraminated and chlorinated drinking water from the U.S. and Canada Chlorine dioxide was also reported to form iodoacetic acid when reacted with source waters, and iodo-acids were also tentatively identified in simulated drinking waters treated with chlorine, monochloramine, and chlorine-chloramine. Finally, iodoacetic acid and chloroacetic acid can form when chlorinated tap water is allowed to react with iodized table salt (containing potassium iodide) or with potassium iodide itself. The rank order for genotoxicity is iodoacetic acid >> diiodoacetic acid > bromoiodoacetic acid > (E)-2-iodo-3-methylbutenedioic acid > (E)-3-bromo-3-iodopropenoic acid > (E)-3-bromo-2-iodopropenoic acid. Iodoacetic acid is also teratogenic, producing developmental effects (neural tube closures) in mouse embryos, at low nM levels similar to levels that induce DNA damage in mammalian cells. Iodoacetic acid is also tumorigenic in mice.
Iodoacetamides — bromoiodoacetamide and chloroiodoacetamide — have been identified in drinking water treated with chloramines or chlorine. Bromoiodoacetamide was originally found in chloraminated drinking water from several cities in the U.S.; later, both bromoiodoacetamide and chloroiodoacetamide were found in chloraminated and chlorinated drinking water from three provinces in China. Haloacetamides can form by hydrolysis of the corresponding haloacetonitriles, or by an independent pathway; they are preferentially formed with chloramination vs. chlorination. Both of these iodoacetamides are highly cytotoxic and genotoxic in mammalian cells. As a class, haloamides are the most cytotoxic of all DBP classes measured to-date, and they are the second-most genotoxic DBP class, close behind the halonitriles.
Chloramination increases the formation of all of these iodo-DBPs. In practice, drinking water plants can add preformed monochloramine (NH2Cl, formed by the reaction of chlorine and ammonia), but generally chlorine is added first and allowed to react for a certain amount of time (free chlorine contact time) before the ammonia is added, to enable a higher level of microbial inactivation. Most research shows that a lower free chlorine contact time (increased NH2Cl contact time) increases the formation of iodo-DBPs consistent with a mechanism proposed by Bichsel and von Gunten, which involves competing mechanisms to form iodate and organic iodo-DBPs. Reaction of aqueous chlorine (HOCl) with iodide initially forms hypoiodous acid (HOI), which then reacts quickly with HOCl to form iodite and iodate. The corresponding reactions to form organic iodo-DBPs (e.g., iodo-THMs and iodo-acids) are much slower, favoring the formation of iodate instead of organic iodo-DBPs. On the other hand, reactions of NH2Cl with HOI to form iodite and iodate are much slower, such that NH2Cl favors the formation of organic iodo-DBPs over iodate. New research indicates that ozone pretreatment at lower pH might be used to minimize iodo-DBP (and bromate) formation by selectively oxidizing iodide to iodate.
Natural iodide is believed to be the major source of iodine in the formation of iodo-DBPs, but, new research has revealed that compounds used for medical imaging (i.e., iodinated X-ray contrast media (ICM)) can also be a source of iodine ICM are excreted within ~24 h after medical imaging, are stable during wastewater treatment, and can be present up to 100 µg/L in rivers and creeks and up to 2.7 µg/L in drinking water reservoirs. These ICM structures have 3 iodines attached to a benzene ring that also contains 3 amide side chains, and can react with chlorine or chloramine to form iodo-THMs and iodo-acids. NOM and pH can significantly impact their formation, and OCl- is hypothesized as the reacting disinfectant species. Moreover, new controlled laboratory studies indicate that iodo-THMs are favored at low chlorine doses.
Iopamidol appears to be more reactive that other ICM investigated (e.g., iopromide, iohexol, iomeprol, diatrizoate, hiztodenz, and iodixanol). New mechanistic research using liquid chromatography (LC)-high resolution MS/MS and nuclear magnetic resonance (NMR) spectroscopy has revealed the initial points of reaction on the iopamidol structure, along with the initial high molecular weight DBPs formed. Proposed reaction mechanisms involve cleavage of one of side chains, substitution of chlorine for iodine on the benzene ring, amide hydrolysis, cleavage of the other side chains, and oxidation of NH2 to NO2. Structures for 19 high molecular weight DBPs were proposed.
3 NITROSAMINES
N-Nitrosodimethylamine (NDMA) was discovered to be a DBP in 2002 and created significant interest due to its potent carcinogenicity. NDMA was initially discovered in chlorinated drinking waters from Ontario, Canada, and was later found in many other locations. Other nitrosamines have also been found as DBPs, including N-nitrosopiperidine, N-nitrosodiphenylamine, N-nitrosopyrrolidine, and N-nitrosomorpholine, A new total nitrosamine (TONO) assay indicates that the nitrosamines identified so far only represent 5-10% of the total nitrosamines formed in drinking water and recreational waters. Tobacco-specific nitrosamines — 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol — were also recently discovered as chloramination DBPs.
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Excerpted from Disinfection By-products in Drinking Water by Clive Thompson, Simon Gillespie, Emma Goslan. Copyright © 2016 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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