13 research outputs found
Bromide Ion Effect on <i>N</i>-Nitrosodimethylamine Formation by Monochloramine
<i>N</i>-Nitrosodimethylamine (NDMA) formation
experiments
conducted in phosphate buffer demonstrated that in waters containing
monochloramine, the presence of bromide ion enhanced NDMA formation
at the relatively high pH values of 8 and 9 after 24 h of reaction
time, which was consistent with literature results. However, at relatively
low to neutral pH (6 to 7), the presence of bromide resulted in lower
NDMA formation as compared to results obtained in the absence of bromide.
The hypothesis that bromamines were the species directly responsible
for enhanced NDMA formation at high pH was tested and was shown not
to be valid. Additional active bromine species were also tested, including
hypobromous acid, hypobromite ion, and tribromide ion, with no species
showing an ability to directly enhance NDMA formation. Analysis of
the UV spectral data corresponding to the NDMA experiments suggest
that the mechanism by which bromide enhances NDMA formation lies in
the formation of a haloamine compound, possibly the mixed dihaloamine
bromochloramine
Kinetics of Bromochloramine Formation and Decomposition
Batch experiments were performed
to study the kinetics of bromochloramine
formation and decomposition from the reaction of monochloramine and
bromide ion. The effects of pH, initial monochloramine and bromide
ion concentrations, phosphate buffer concentration, and excess ammonia
were evaluated. Results showed that the monochloramine decay rate
increased with decreasing pH and increasing bromide ion concentration,
and the concentration of bromochloramine increased to a maximum before
decreasing gradually. The maximum bromochloramine concentration reached
was found to decrease with increasing phosphate and ammonia concentrations.
Previous models in the literature were not able to capture the decay
of bromochloramine, and therefore we proposed an extended model consisting
of reactions for monochloramine autodecomposition, the decay of bromamines
in the presence of bromide, bromochloramine formation, and bromochloramine
decomposition. Reaction rate constants were obtained through least-squares
fitting to 11 data sets representing the effect of pH, bromide, monochloramine,
phosphate, and excess ammonia. The reaction rate constants were then
used to predict monochloramine and bromochloramine concentration profiles
for all experimental conditions tested. In general, the modeled lines
were found to provide good agreement with the experimental data under
most conditions tested, with deviations occurring at low pH and high
bromide concentrations
Toxicity of Drinking Water Disinfection Byproducts: Cell Cycle Alterations Induced by the Monohaloacetonitriles
Haloacetonitriles
(HANs) are a chemical class of drinking water
disinfection byproducts (DBPs) that form from reactions between disinfectants
and nitrogen-containing precursors, the latter more prevalent in water
sources impacted by algae bloom and municipal wastewater effluent
discharge. HANs, previously demonstrated to be genotoxic, were investigated
for their effects on the mammalian cell cycle. Treating Chinese hamster
ovary (CHO) cells with monoHANs followed by the release from the chemical
treatment resulted in the accumulation of abnormally high DNA content
in cells over time (hyperploid). The potency for the cell cycle alteration
followed the order: iodoacetonitrile (IAN) > bromoacetonitrile
(BAN)
âŦ chloroacetonitrile (CAN). Exposure to 6 ΞM IAN, 12
ΞM BAN and 900 ΞM CAN after 26 h post-treatment incubation
resulted in DNA repair; however, subsequent cell cycle alteration
effects were observed. Cell proliferation of HAN-treated cells was
suppressed for as long as 43 to 52 h. Enlarged cell size was observed
after 52 h post-treatment incubation without the induction of cytotoxicity.
The HAN-mediated cell cycle alteration was mitosis- and proliferation-dependent,
which suggests that HAN treatment induced mitosis override, and that
HAN-treated cells proceeded into S phase and directly into the next
cell cycle. Cells with multiples genomes would result in aneuploidy
(state of abnormal chromosome number and DNA content) at the next
mitosis since extra centrosomes could compromise the assembly of bipolar
spindles. There is accumulating evidence of a transient tetraploid
state proceeding to aneuploidy in cancer progression. Biological self-defense
systems to ensure genomic stability and to eliminate tetraploid cells
exist in eukaryotic cells. A key tumor suppressor gene, p53, is oftentimes
mutated in various types of human cancer. It is possible that HAN
disruption of the normal cell cycle and the generation of aberrant
cells with an abnormal number of chromosomes may contribute to cancer
induction and perhaps be involved in the induction of adverse pregnancy
outcomes associated with long-term consumption of disinfected water.
Here we present the first observation of the induction of hyperploidy
by a class of DBPs
Characterizing Bacteriophage PR772 as a Potential Surrogate for Adenovirus in Water Disinfection: A Comparative Analysis of Inactivation Kinetics and Replication Cycle Inhibition by Free Chlorine
Elucidating
mechanisms by which pathogenic waterborne viruses become
inactivated by drinking water disinfectants would facilitate the development
of sensors to detect infectious viruses and novel disinfection strategies
to provide safe water. Using bacteriophages as surrogates for human
pathogenic viruses could assist in elucidating these mechanisms; however,
an appropriate viral surrogate for human adenovirus (HAdV), a medium-sized
virus with a double-stranded DNA genome, needs to be identified. Here,
we characterized the inactivation kinetics of bacteriophage PR772,
a member of the <i>Tectiviridae</i> family with many similarities
in structure and replication to HAdV. The inactivation of PR772 and
HAdV by free chlorine had similar kinetics that could be represented
with a model previously developed for HAdV type 2 (HAdV-2). We developed
and tested a quantitative assay to analyze several steps in the PR772
replication cycle to determine if both viruses being inactivated at
similar rates resulted from similar replication cycle events being
inhibited. Like HAdV-2, we observed that PR772 inactivated by free
chlorine still attached to host cells, and viral DNA synthesis and
early and late gene transcription were inhibited. Consequently, free
chlorine exposure inhibited a replication cycle event that was post-binding
but took place prior to early gene synthesis for both PR772 and HAdV-2
Analysis of the Viral Replication Cycle of Adenovirus Serotype 2 after Inactivation by Free Chlorine
Free
chlorine is effective at inactivating a wide range of waterborne
viral pathogens including human adenovirus (HAdV), but the mechanisms
by which free chlorine inactivates HAdV and other human viruses remain
to be elucidated. Such advances in fundamental knowledge are key for
development of new disinfection technologies and novel sensors to
detect infectious viruses in drinking water. We developed and tested
a quantitative assay to analyze several steps in the HAdV replication
cycle upon increasing free chlorine exposure. We used quantitative
polymerase chain reaction (qPCR) to detect HAdV genomic DNA as a means
to quantify attachment and genome replication of untreated and treated
virions. Also, we used quantitative reverse-transcription PCR (RT-qPCR)
to quantify the transcription of E1A (first early protein) and hexon
mRNA. We compared these replication cycle events to virus inactivation
kinetics to determine what stage of the virus replication cycle was
inhibited as a function of free chlorine exposure. We observed that
adenovirus inactivated at levels up to 99.99% by free chlorine still
attached to host cells; however, viral DNA synthesis and early E1A
and late hexon gene transcription were inhibited. We conclude that
free chlorine exposure interferes with a replication cycle event occurring
postbinding but prior to early viral protein synthesis
Modeling the Effect of Charge Density in the Active Layers of Reverse Osmosis and Nanofiltration Membranes on the Rejection of Arsenic(III) and Potassium Iodide
We used an extended solution-diffusion model that incorporates
Donnan electrostatic exclusion of ions and unhindered advection due
to imperfections, and measurements of charge density in the polyamide
active layers of reverse osmosis (RO) and nanofiltration (NF) membranes,
to predict the rejection of a strong electrolyte (i.e., potassium
iodide) and a weak acid (i.e., arsenious acid) as a function of the
pH of the feed aqueous solution. Predictions of solute rejection were
in agreement with experimental data indicating that (i) the extended
solution-diffusion model taking into account Donnan exclusion and
unhindered advection due to imperfections satisfactorily describes
the effect of pH on solute rejection by RO/NF membranes and (ii) measurement
of charge density in active layers provides a valuable characterization
of RO/NF membranes. Our results and analysis also indicate that independent
ions, and not ion pairs, dominate the permeation of salts
Development and Performance Characterization of a Polyimine Covalent Organic Framework Thin-Film Composite Nanofiltration Membrane
Two-dimensional covalent organic
frameworks (COFs) were used to
create the first asymmetric, thin-film composite (TFC) nanofiltration
(NF) membrane with a COF active layer. NF membrane active layers of
polyimine COF were synthesized via the interfacial polymerization
(IP) of terephthalaldehyde and trisÂ(4-aminophenyl)Âbenzene monomers
on top of a polyÂ(ether sulfone) (PES) ultrafiltration membrane support.
Rutherford backscattering spectrometry and Fourier transform infrared
spectroscopy analyses confirmed the presence of an imine-linked film
with a thickness of âž10 nm that was formed reproducibly. The
rejection efficiencies of the COF NF membrane for a model organic
compound, Rhodamine-WT, and a background electrolyte, NaCl, were higher
than those of the PES support without the COF film. This enhanced
solute rejection is the first successful demonstration of a TFC membrane
with a thin COF active layer. However, this work also demonstrates
the need for COF NF membranes with smaller active layer pores and
alternative support materials. The former should result in greater
solute rejection, and the latter is key because the PES used for support
in the COF membranes is incompatible with the organic solvents used
for the COF IP process
Adenovirus Replication Cycle Disruption from Exposure to Polychromatic Ultraviolet Irradiation
Polychromatic ultraviolet (UV) light
with bandwidth of 20 nm and
peak emission centered at 224, 254, or 280 nm (UV<sub>224</sub>, UV<sub>254</sub>, and UV<sub>280</sub>, respectively) were used to inactivate
human adenovirus type 2 (HAdV-2). Quantitative polymerase chain reaction
(qPCR) and reverse transcriptase qPCR assays were used to elucidate
the step in the HAdV-2 replication cycle that was disrupted after
UV exposure. UV treatment at any of the wavelengths analyzed did not
inhibit association of HAdV-2 to the host cells even after exposure
to a fluence (UV dose) that would produce a virus inactivation efficiency,
measured by plaque assay, greater than 99.99%. In contrast, UV irradiation
at all three peak emissions disrupted early E1A gene transcription
and viral DNA replication, but different mechanisms appeared to be
dominating such disruptions. UV<sub>224</sub> seemed to have little
effect on the integrity of the viral genome but produced a structural
transformation of the viral capsid that may inhibit the delivery of
viral genome into the host cell nucleus. On the other hand, UV<sub>254</sub> and UV<sub>280</sub> did not affect the integrity of the
viral capsid, but the mutations they produced on the viral genome
might cause the inhibition of the early gene transcription and DNA
replication after the viral genome successfully translocated into
the host cell nucleus
Chloroacetonitrile and <i>N</i>,2-Dichloroacetamide Formation from the Reaction of Chloroacetaldehyde and Monochloramine in Water
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 <i>K</i><sub>1</sub> = 1.87 Ã 10<sup>3</sup> M<sup>â1</sup>)
with the carbinolamine 2-chloro-1-(chloroamino)Âethanol. 2-Chloro-1-(chloroamino)Âethanol
undergoes slow dehydration to form the imine 1-chloro-2-(chloroimino)Âethane
that decomposes at a faster rate to chloroacetonitrile. 2-Chloro-1-(chloroamino)Âethanol
is also oxidized by monochloramine to produce the previously unreported
DBP <i>N</i>,2-dichloroacetamide. The carbinolamine dehydration
step was found to be acid/base catalyzed (<i>k</i><sub>2</sub><sup>0</sup> = 3.30 Ã 10<sup>â6</sup> s<sup>â1</sup>, <i>k</i><sub>2</sub><sup>H</sup> = 2.43 M<sup>â1</sup> s<sup>â1</sup>, <i>k</i><sub>2</sub><sup>OH</sup> = 3.90 M<sup>â1</sup> s<sup>â1</sup>). In contrast, <i>N</i>,2-dichloroacetamide formation was observed to be only
base catalyzed (<i>k</i><sub>3</sub><sup>OH</sup> = 3.03
à 10<sup>4</sup> M<sup>â2</sup> s<sup>â1</sup>). <i>N</i>,2-dichloroacetamide cytotoxicity (LC<sub>50</sub> = 2.56
à 10<sup>â4</sup> M) was found to be slightly lower compared
to that reported for chloroacetamide but higher than those of di-
and trichloroacetamide
Changes in Physicochemical and Transport Properties of a Reverse Osmosis Membrane Exposed to Chloraminated Seawater
This
study contributed to improving our understanding of how disinfectants,
applied to control biofouling of reverse osmosis (RO) membranes, result
in membrane performance degradation. We investigated changes in physicochemical
properties and permeation performance of a RO membrane with fully
aromatic polyamide (PA) active layer. Membrane samples were exposed
to varying concentrations of monochloramine, bromide, and iodide in
both synthetic and natural seawater. Elemental analysis of the membrane
active layer by Rutherford backscattering spectrometry (RBS) revealed
the incorporation of bromine and iodine into the polyamide. The kinetics
of polyamide bromination were first order with respect to the concentration
of the secondary oxidizing agent Br<sub>2</sub> for the conditions
investigated. Halogenated membranes were characterized after treatment
with a reducing agent and heavy ion probes to reveal the occurrence
of irreversible ring halogenation and an increase in carboxylic groups,
the latter produced as a result of amide bond cleavage. Finally, permeation
experiments revealed increases in both water permeability and salt
passage as a result of oxidative damage