Disinfectants inactivate pathogens in source water; however, they also react with organic matter and bromide/iodide to form disinfection byproducts (DBPs). Although only a few DBP classes have been systematically analyzed for toxicity, iodinated and brominated DBPs tend to be the most toxic. The objectives of this research were (1) to determine if monochloramine (NH2Cl) disinfection generated drinking water with less toxicity than water disinfected with free chlorine (HOCl) and (2) to determine the impact of added bromide and iodide in conjunction with HOCl or NH2Cl disinfection on mammalian cell cytotoxicity and genomic DNA damage induction. Water disinfected with chlorine was less cytotoxic but more genotoxic than water disinfected with chloramine. For both disinfectants, the addition of Br(-) and I(-) increased cytotoxicity and genotoxicity with a greater response observed with NH2Cl disinfection. Both cytotoxicity and genotoxicity were highly correlated with TOBr and TOI. However, toxicity was weakly and inversely correlated with TOCl. Thus, the forcing agents for cytotoxicity and genotoxicity were the generation of brominated and iodinated DBPs rather than the formation of chlorinated DBPs. Disinfection practices need careful consideration especially when using source waters containing elevated bromide and iodide.
Granular activated carbon (GAC) adsorption
is well-established
for controlling regulated disinfection byproducts (DBPs), but its
effectiveness for unregulated DBPs and DBP-associated toxicity is
unclear. In this study, GAC treatment was evaluated at three full-scale
chlorination drinking water treatment plants over different GAC service
lives for controlling 61 unregulated DBPs, 9 regulated DBPs, and speciated
total organic halogen (total organic chlorine, bromine, and iodine).
The plants represented a range of impacts, including algal, agricultural,
and industrial wastewater. This study represents the most extensive
full-scale study of its kind and seeks to address the question of
whether GAC can make drinking water safer from a DBP perspective.
Overall, GAC was effective for removing DBP precursors and reducing
DBP formation and total organic halogen, even after >22 000
bed volumes of treated water. GAC also effectively removed preformed
DBPs at plants using prechlorination, including highly toxic iodoacetic
acids and haloacetonitriles. However, 7 DBPs (mostly brominated and
nitrogenous) increased in formation after GAC treatment. In one plant,
an increase in tribromonitromethane had significant impacts on calculated
cytotoxicity, which only had 7–17% reduction following GAC.
While these DBPs are highly toxic, the total calculated cytotoxicity
and genotoxicity for the GAC treated waters for the other two plants
was reduced 32–83% (across young–middle–old GAC).
Overall, calculated toxicity was reduced post-GAC, with preoxidation
allowing further reductions.
The introduction of drinking water disinfection greatly reduced waterborne diseases. However, the reaction between disinfectants and natural organic matter in the source water leads to an unintended consequence, the formation of drinking water disinfection byproducts (DBPs). The haloace-taldehydes (HALs) are the third largest group by weight of identified DBPs in drinking water. The primary objective of this study was to analyze the occurrence and comparative toxicity of the emerging HAL DBPs. A new HAL DBP, iodoacetaldehyde (IAL) was identified. This study provided the first systematic, quantitative comparison of HAL toxicity in Chinese hamster ovary cells. The rank order of HAL cytotoxicity is tribromoacetaldehyde (TBAL) ≈ chloroacetaldehyde (CAL) > dibromoacetaldehyde (DBAL) ≈ bromochloroacetaldehyde (BCAL) ≈ dibromochloroacetaldehyde (DBCAL) > IAL > bromoacetaldehyde (BAL) ≈ bromodichloroacetaldehyde (BDCAL) > dichloroacetaldehyde (DCAL) > trichloroacetaldehyde (TCAL). The HALs were highly cytotoxic compared to other DBP chemical classes. The rank order of HAL genotoxicity is DBAL > CAL ≈ DBCAL > TBAL ≈ BAL > BDCAL > BCAL ≈ DCAL > IAL. TCAL was not genotoxic. Because of their toxicity and abundance, further research is needed to investigate their mode of action to protect the public health and the environment.
Disinfection
byproducts (DBPs) are a ubiquitous source of chemical
exposure in drinking water and have been associated with serious health
impacts in human epidemiologic studies. While toxicology studies have
pinpointed DBPs with the greatest toxic potency, analytical methods
have been lacking for quantifying complete classes of most toxic DBPs
at sufficiently low quantification limits (ng/L). This new method
reports the parts-per-trillion quantification for 61 toxicologically
significant DBPs from 7 different chemical classes, including unregulated
iodinated haloacetic acids (HAAs) and trihalomethanes (THMs), haloacetaldehydes,
haloketones, haloacetonitriles, halonitromethanes, and haloacetamides,
in addition to regulated HAAs and THMs. The final optimized method
uses salt-assisted liquid–liquid extraction in a single extraction
method for a wide range of DBPs, producing the lowest method detection
limits to-date for many compounds, including highly toxic iodinated,
brominated, and nitrogen-containing DBPs. Extracts were divided for
the analysis of the HAAs (including iodinated HAAs) by diazomethane
derivatization and analysis using a GC-triple quadrupole mass spectrometer
with multiple reaction monitoring, resulting in higher signal-to-noise
ratios, greater selectivity, and improved detection of these compounds.
The remaining DBPs were analyzed using a GC-single quadrupole mass
spectrometer with selected ion monitoring, utilizing a multimode inlet
allowed for lower injection temperatures to allow the analysis of
thermally labile DBPs. Finally, the use of a specialty-phase GC column
(Restek Rtx-200) significantly improved peak shapes, which improved
separations and lowered detection limits. Method detection limits
for most DBPs were between 15 and 100 ng/L, and relative standard
deviations in tap water samples were mostly between 0.2 and 30%. DBP
concentrations in real samples ranged from 40 to 17 760 ng/L for this
study.
Combined chlorine is increasingly being used as an alternative disinfectant to free chlorine to maintain a residual in drinking water distribution systems mainly because it would reduce the formation of regulated disinfection byproducts (DBPs) trihalomethanes and haloacetic acids. However, the use of combined chlorine could promote the formation of currently unregulated nitrogenous DBPs (N-DBPs) such as haloacetonitriles and haloacetamides that are found to be more cyto- and genotoxic than regulated DBPs. Monochloramine quickly reacts with chloroacetaldehyde, a DBP formed during primary disinfection with free chlorine, forming and reaching pseudoequilibrium (equilibrium constant K1 = 1.87 × 10(3) M(-1)) with the carbinolamine 2-chloro-1-(chloroamino)ethanol. 2-Chloro-1-(chloroamino)ethanol undergoes slow dehydration to form the imine 1-chloro-2-(chloroimino)ethane that decomposes at a faster rate to chloroacetonitrile. 2-Chloro-1-(chloroamino)ethanol is also oxidized by monochloramine to produce the previously unreported DBP N,2-dichloroacetamide. The carbinolamine dehydration step was found to be acid/base catalyzed (k2(0) = 3.30 × 10(-6) s(-1), k2(H) = 2.43 M(-1) s(-1), k2(OH) = 3.90 M(-1) s(-1)). In contrast, N,2-dichloroacetamide formation was observed to be only base catalyzed (k3(OH) = 3.03 × 10(4) M(-2) s(-1)). N,2-dichloroacetamide cytotoxicity (LC50 = 2.56 × 10(-4) M) was found to be slightly lower compared to that reported for chloroacetamide but higher than those of di- and trichloroacetamide.
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