While drinking water disinfection has effectively prevented waterborne diseases, an unintended consequence is the generation of disinfection byproducts (DBPs). Epidemiological studies have consistently observed an association between consumption of chlorinated drinking water with an increased risk of bladder cancer. Out of the >600 DBPs identified, regulations focus on a few classes, such as trihalomethanes (THMs), whose concentrations were hypothesized to correlate with the DBPs driving the toxicity of disinfected waters. However, the DBPs responsible for the bladder cancer association remain unclear. Utilities are switching away from a reliance on chlorination of pristine drinking water supplies to the application of new disinfectant combinations to waters impaired by wastewater effluents and algal blooms. In light of these changes in disinfection practice, this article discusses new approaches being taken by analytical chemists, engineers, toxicologists and epidemiologists to characterize the DBP classes driving disinfected water toxicity, and suggests that DBP exposure should be measured using other DBP classes in addition to THMs.

Drinking Water Disinfection Byproducts (DBPs) and Human Health Effects: Multidisciplinary Challenges and Opportunities

Halogenated disinfection byproducts (DBPs) are generated via reactions with natural organic matter (NOM) in chlorine disinfection of drinking water. How large NOM molecules are converted to halogenated aliphatic DBPs during chlorination remains a fascinating yet largely unresolved issue. Recently, many relatively toxic halogenated aromatic DBPs have been identified in chlorinated drinking waters, and they behave as intermediate DBPs to decompose to halogenated aliphatic DBPs. There is still one gap between NOM and halogenated aromatic DBPs. In this study, nine nonhalogenated aromatic compounds were identified as new intermediate DBPs in chlorination, including 4-hydroxybenzaldehyde, 4-hydroxybenzoic acid, 3-formyl-4-hydroxybenzoic acid, salicylic acid, 5-formyl-2-hydroxybenzoic acid, 4-hydroxyphthalic acid, 4'-hydroxyacetophenone, 4-methylbenzoic acid, and 4-hydroxy-3-methylbenzaldehyde. These nonhalogenated aromatic DBPs formed quickly and reached the maximum levels at relatively low chlorine doses within a short contact time, and their formation pathways were proposed. The formation kinetics of three nonhalogenated aromatic DBPs and their corresponding monochloro-/dichloro-substitutes during chlorination were then modeled. The nonhalogenated aromatic DBPs contributed up to 84% of the formed monochloro-substitutes and 22% of the formed dichloro-substitutes, demonstrating that they somewhat acted as intermediates between NOM and halogenated aromatic DBPs. Furthermore, the formed nonhalogenated aromatic DBPs were found to be removed by >50% by granular activated carbon adsorption.

Nonhalogenated Aromatic DBPs in Drinking Water Chlorination: A Gap between NOM and Halogenated Aromatic DBPs.

Application of (LC/)MS/MS precursor ion scan for evaluating the occurrence, formation and control of polar halogenated DBPs in disinfected waters: A review.

ConspectusFormation of iodinated disinfection byproducts (I-DBPs) in drinking water has become an emerging concern. Compared to chlorine- and bromine-containing DBPs, I-DBPs are more toxic, have different precursors and formation mechanisms, and are unregulated. In this Account, we focus on recent research in the formation of known and unknown I-DBPs in drinking water. We present the state-of-the-art understanding of known I-DBPs for the six groups reported to date, including iodinated methanes, acids, acetamides, acetonitriles, acetaldehyde, and phenols. I-DBP concentrations in drinking water generally range from ng L–1 to low-μg L–1. The toxicological effects of I-DBPs are summarized and compared with those of chlorinated and brominated DBPs. I-DBPs are almost always more cytotoxic and genotoxic than their chlorinated and brominated analogues. Iodoacetic acid is the most genotoxic of all DBPs studied to date, and diiodoacetamide and iodoacetamide are the most cytotoxic. We discuss I-DBP formation mechan...

Formation of Iodinated Disinfection Byproducts (I-DBPs) in Drinking Water: Emerging Concerns and Current Issues

Since the first regulation of disinfection by-products (DBPs) in the 1970s, >700 DBPs have been identified, and many of these are much more toxic than those regulated. Moreover, drinking water today is not the same as it was in the past, with increasing use of alternative disinfectants like chloramine, ozone, chlorine dioxide, and UV (which can form other types of DBPs), as well as new impacts on our source waters from climate change, population increases, wastewater intrusion, and energy exploration. The question today is whether we are regulating the right DBPs to protect human health, and if not, what should be done. New approaches may involve (1) the use of in vitro data and a Precautionary Principle approach, (2) using surrogate metrics of finished waters, such as total organic bromine/iodine, total nitrosamines, or total organic nitrogen rather than creating longer lists of regulated DBPs, and (3) using toxicity assays for whole drinking water extracts to pinpoint potential problems, then using chemical analyses to identify the toxic agents, and finally, (4) invoking different treatment strategies to reduce the toxicity. While the early regulations likely significantly improved the safety of drinking water, DBP exposure is a constant in modern life, and there is more that we can do.

To regulate or not to regulate? What to do with more toxic disinfection by-products?

Disinfection by-products (DBPs) are a complex mixture of compounds unintentionally formed as a result of disinfection processes used to treat drinking water. Effects of long-term exposure to DBPs are mostly unknown and were the subject of recent epidemiological studies. However, most bioanalytical methods focus on a select few DBPs. In this study, a new comprehensive bioanalytical method has been developed that can quantify mixtures of organic halogenated compounds, including DBPs, in human urine as total organic chlorine (TOCl), total organic bromine (TOBr), and total organic iodine (TOI). The optimized method consists of urine dilution, adsorption to activated carbon, pyrolysis of activated carbon, absorption of gases in an aqueous solution, and halide analysis with ion chromatography and inductively coupled plasma-mass spectrometry. Spike recoveries for TOCl, TOBr, and TOI measurements ranged between 78% and 99%. Average TOCl, TOBr, and TOI concentrations in five urine samples from volunteers who consumed tap water were 1850, 82, and 21.0μg/L as X-, respectively. Volunteers who consumed spring water (control) had TOCl, TOBr, and TOI average concentrations in urine of 1090, 88, and 10.3μg/L as X-, respectively. TOCl and TOI in the urine samples from tap water consumers were higher than the control. However, TOBr was slightly lower in tap water urine samples compared to mineral water urine samples, indicating other sources of environmental exposure other than drinking water. A larger sample population that consumes tap water from different cities and mineral water is needed to determine TOCl, TOBr, and TOI exposure from drinking water.

Weiwei Zheng

Papers

Total organic halogen (TOX) in human urine: A halogen-specific method for human exposure studies