Determination of PbO2 formation kinetics from the chlorination of Pb(II) carbonate solids via direct PbO2 measurement

Lead dioxide (PbO(2)), a new form of lead corrosion product discovered in the distribution system, is formed via the chlorination of Pb(II) solids and plays an important role in regulating lead concentration in drinking water. The kinetics of its formation, however, has not been quantitatively determined primarily because of the difficulties in accurately measuring PbO(2) concentration. In this study, we apply an iodometric method for direct PbO(2) measurement to determine its formation kinetics from the chlorination of cerussite (PbCO(3)) and hydrocerussite (Pb(3)(CO(3))(2)(OH)(2)). The obtained rate equations suggest that for both Pb(II) carbonate solids, the formation of PbO(2) is first-order with respect to the available Pb(II) solid surface area, free chlorine concentration, and OH(-) concentration. Dissolved inorganic carbon concentration (DIC) was found to inhibit PbO(2) formation because of the formation of carbonate-lead surface complexes that protect the surface Pb(II) sites from oxidation. The rate of PbO(2) formation from the chlorination of hydrocerussite was faster than that of cerussite under the same Pb(II) solid loading. However, after normalization of the surface area, the rate constants obtained for both Pb(II) solids are similar. The kinetics of PbO(2) formation is elucidated for the first time in this study.     

Stability of cyanogen chloride in the presence of free chlorine and monochloramine

Cyanogen chloride (CNCl) is a disinfection byproduct found in chlorinated and chloraminated drinking water. Although there is an apparent greater association of CNCI with chloraminated water relative to chlorination systems, it was not clear whether these phenomenological observations are explained by differences in the stability or formation potentials of CNCI between the two disinfectants. In this study, the stability of CNCl was examined in the presence of free chlorine and monochloramine using membrane introduction mass spectrometry. CNCI decomposes relatively rapidly when free chlorine is present but is stable in the presence of monochloramine. The decomposition kinetics and observed reaction products are consistent with a hypochlorite-catalyzed hydrolysis mechanism, and the rate law is described by (d[CNCl]/dt) = - kOCl[CNCl][OCl-]. At 25 degrees C, pH 7, and a free chlorine residual of 0.5 mg/L as Cl2, the half-life of CNCl is approximately 60 min, suggesting significant decomposition is expected over disinfection time scales. Under some winter season temperature conditions, however, the decay half-life of CNCl can be longer than typical disinfection contact times. The results of this study demonstrate that the observed association of CNCl with chloramination systems can in part be explained by the differences in its stability with chlorine and chloramines.     

Aqueous chlorination kinetics of some endocrine disruptors

The aqueous chlorination kinetics of six endocrine disruptors (EDs: 4-n-nonylphenol, beta-estradiol, estrone, estriol, 17alpha-ethinylestradiol, progesterone) were studied in the 3.50-12.00 pH range, at 20+/-2 degrees C, in the presence of an excess of total chlorine. Under these conditions, all molecules with a phenolic group in their structure were rapidly oxidized by chlorine, whereas progesterone remained unchanged. In the first step, apparent kinetic rate constants were determined at various pH levels. Then each elementary reaction kinetic rate constant, i.e., the reaction of hypochlorous acid (HOCl) with ionized EDs and neutral EDs and an acid-catalyzed reaction of HOCl with neutral EDs, was calculated in the second step. The results showed that chlorination exhibits a second-order reaction rate. The rate constants for the acid-catalyzed reaction ranged from 3.02 x 10(4) M(-1) s(-1) (for 4-n-nonylphenol) to 1.82-2.62 x 10(5) M(-1) s(-1) (for hormones). The rate constants of HOCI reactions with ionized EDs were found to be equal to 7.5 x 10(4) M(-1) s(-1) (for 4-n-nonylphenol) and between 3.52 and 4.15 x 10(5) M(-1) s(-1) (for hormones), while the rate contants of HOCI with neutral EDs were much lower, i.e., between 1.31 M(-1) s(-1) (for 4-n-nonylphenol) and 3.74-4.82 M(-1) s(-1) (for hormones). At pH 7, the apparent-second-order rate constants were calculated to range from 12.6 to 131.1 M(-1) s(-1). For a total chlorine concentration of 1 mg/L, the corresponding half-life times at pH 7 were about 65 min for 4-n-nonylphenol and 6-8 min for hormones.     

Haloacetic acid and trihalomethane formation from the chlorination and bromination of aliphatic beta-dicarbonyl acid model compounds

While it is known that resorcinol- and phenol-type aromatic structures within natural organic matter (NOM) react during drinking water chlorination to form trihalomethanes (THMs), limited studies have examined aliphatic-type structures as THM and haloacetic acid (HAA) precursors. A suite of aliphatic acid model compounds were chlorinated and brominated separately in controlled laboratory-scale batch experiments. Four and two beta-dicarbonyl acid compounds were found to be important precursors for the formation of THMs (chloroform and bromoform (71-91% mol/mol)), and dihaloacetic acids (DXAAs) (dichloroacetic acid and dibromoacetic acid (5-68% mol/mol)), respectively, after 24 h at pH 8. Based upon adsorbable organic halide formation, THMs and DXAAs, and to a lesser extent mono and trihaloacetic acids, were the majority (> 80%) of the byproducts produced for most of the aliphatic beta-dicarbonyl acid compounds. Aliphatic beta-diketone-acid-type and beta-keto-acid-type structures could be possible fast- and slow-reacting THM precursors, respectively, and aliphatic beta-keto-acid-type structures are possible slow-reacting DXAA precursors. Aliphatic beta-dicarbonyl acid moieties in natural organic matter, particularly in the hydrophilic fraction, could contribute to the significant formation of THMs and DXAAs observed after chlorination of natural waters.     

Volatile disinfection byproduct formation resulting from chlorination of organic-nitrogen precursors in swimming pools

Clinical studies have documented the promotion of respiratory ailments (e.g., asthma) among swimmers, especially in indoor swimming pools. Most studies of this behavior have identified trichloramine (NCl3) as the causative agent for these respiratory ailments; however, the analytical methods employed in these studies were not suited for identification or quantification of other volatile disinfection byproducts (DPBs) that could also contribute to this process. To address this issue, volatile DBP formation resulting from the chlorination of four model compounds (creatinine, urea, L-histidine, and L-arginine) was investigated over a range of chlorine/precursor (Cl/P) molar ratios. Trichloramine was observed to result from chlorination of all four model organic-nitrogen compounds. In addition to trichloramine, dichloromethylamine (CH3NCl2) was detected in the chlorination of creatinine, while cyanogen chloride (CNCl) and dichoroacetonitrile (CNCHCl2) were identified in the chlorination of L-histidine. Roughly 0.1 mg/L (as Cl2) NCl3, 0.01 mg/L CNCHCl2, and 0.01 mg/L CH3NCl2 were also observed in actual swimming pool water samples. DPD/FAS titration and MIMS (membrane introduction mass spectrometry) were both employed to measure residual chlorine and DBPs. The combined application of these methods allowed for identification of sources of interference in the conventional method (DPD/FAS), as well as structural information about the volatile DBPs that formed. The analysis by MIMS clearly indicates that volatile DBP formation in swimming pools is not limited to inorganic chloramines and haloforms. Additional experimentation allowed for the identification of possible reaction pathways to describe the formation of these DBPs from the precursor compounds used in this study.     

Mechanism of cyanogen reduction in cassava roots during cooking

The cyanogen elimination profile during cooking of cassava roots was investigated and correlated with the changes in cyanogenic β-glucosidase (GLase) activity monitored at close intervals in the cook water and root. Cyanogenic β-glucosidase (GLase) activity was detected in the cook water within 5 min of starting cooking. Whilst significant decrease in the GLase activity was noticed in cook water and root within 15 and 10 min, respectively, for varieties M4 and H165, H1687 GLase activity decreased tremendously only at 20 and 15 min in the cook water and root, respectively. There was no GLase activity in cook water after the 30 min pre-boiling phase while GLase activity was present in the roots even after 60 min of cooking. The decrease in GLase activity at 15–20 min pre-boiling phase led to accumulation of cyanogens in cook water. The cyanogen fractions (glucosidic and non-glucosidic) increased significantly with cooking in the cook water in the case of varieties M4 and H165 while their levels were almost static throughout the post-boiling phase for H1687. The amount of HCN escaping through steam did not bear a direct relationship with the initial cyanogen content in cassava roots. Although free cyanogen is highly volatile, all of it does not escape through steam and a certain quantity appears to be stabilised in the cook water. ©1997 SCI     

Phenol chlorination and photochlorination in the presence of chloride ions in homogeneous aqueous solution

Phenol chlorination was studied in the presence of dissolved Fe(III) and chloride under irradiation and of hydrogen peroxide and chloride in dark acidic solutions. In the former case phenol photochlorination is most likely due to the formation of Cl2*- as a consequence of Fe(III) irradiation in the presence of chloride. The most efficient pathway is the photolysis of FeOH2+ producing hydroxyl, which oxidizes chloride to Cl*. The latter finally yields Cl2*- upon further reaction with chloride. The importance of the pathway involving FeOH2+ is higher at higher pH and moderately low chloride concentration. At pH 2.0 and [Cl-] > 0.03 M chlorophenol generation rate decreases with increasing [Cl-], due to the formation of the much less photoactive species FeCl2+/FeCl2+. The photolysis of FeCl2+/ FeCl2+ yielding Cl* is likely to play an important role at pH 0.5 and high chloride, but under such conditions chlorophenol formation rates are about an order of magnitude lower than at pH 2.0. Due to pH and kinetic constraints, under most environmental conditions the photochemistry of FeCl2+/FeCl2+ can be expected to play a minor role toward chlorination when compared with the one of FeOH2+, which leads to hydroxyl-mediated chloride oxidation. Hydrogen peroxide and chloride react in dark acidic solutions to yield HClO, involved in electrophilic chlorination processes. Chlorophenol formation rates under such conditions are directly proportional to [H+]. The described chlorination and photochlorination processes can take place in acidic aerosols of marine origin, naturally rich in chloride and Fe(III). Antarctic aerosol is also rich of hydrogen peroxide and often strongly acidic due to the presence of sulfuric acid of biogenic origin.     

NDMA formation during chlorination and chloramination of aqueous diuron solutions

Formation of the potent carcinogen N-nitrosodimethylamine (NDMA) during chlorine disinfection of water containing secondary amines is now generally acknowledged. The phenylurea herbicide diuron is one of the most widely used herbicides in California, has been frequently detected in California's water sources with a transient nature of appearance, and has a structure that suggests it might be an NDMA precursor. This study sought to quantify the potential for NDMA formation from aqueous diuron solutions under varied chlorine and chloramine conditions. NDMA formation was consistently observed even in the absence of added ammonia, which has usually been the source of the nitroso-nitrogen during chloramination of other precursors. It appears that both nitrogen atoms in NDMA are donated by diuron during chlorination in the absence of added ammonia. For a given chlorine and diuron dose, NDMA formation increased in the order OCl- < NH2Cl < NHCl2, a result consistentwith previous NDMAformation studies. Significant quantities of NDMA (170 ng/L) were produced during dichloramination of diuron using a low dichloramine concentration and a diuron concentration at the upper end of typically detected concentrations in California (20 microg/L), suggesting a need for further investigation to accurately assess the human health risks posed by diuron with respect to NDMA formation potential. A reaction pathway is proposed to provide a possible explanation for NDMA formation from diuron during chlorination or chloramination. The findings in this study identify a specific potential precursor of NDMA formation, one that arises from nonpoint sources. This further highlights the difficulties associated with determining the environmental safety of chemicals and their associated byproducts.     

Equilibrium and kinetics of bromine chloride hydrolysis

Aqueous-phase halogen reactions play an important role in tropospheric ozone depletion that is observed during Arctic sunrise where bromine chloride is a key intermediate. The temperature dependencies of BrCl(aq) equilibration with BrCl2-, HOBr(aq), Br2(aq), Cl2(aq), HOCl(aq), Br-, and other species (Br3-, Br2Cl-, Cl3-, OBr-, and OCI-) are determined as a function of Cl- concentration from pH 0 to pH 7. Values for K1 (=[BrCl2-]/([BrCl(aq)][Cl-])) at mu = 1.0 M are 3.8 M(-1) at 25.0 degrees C, 4.7 M(-1) at 10.0 degrees C, and 5.5 M(-1) at 0.0 degrees C, with deltaH1 degrees = -9.9 kJ mol(-1) and deltaS1 degrees = -22 J K(-1) mol(-1). BrCl(aq) hydrolysis equilibria have little or no temperature dependence with Kh1 (=[HOBr(aq)][Cl-][H+]/[BrCl(aq)]) = 1.3 x 10(-4) M2 from 25.0 to 5.0 degrees C, mu = 1.0 M. When conditions are adjusted to give a rapid partial hydrolysis of BrCl in equilibrium with HOBr and Cl- at p[H+] 4.31, a relatively slow reaction (kobsd = 2.4 s(-1)) to form HOCl and Br- is observed. This takes place via BrCl reaction with Cl- to form Cl2, which hydrolyzes in the rate-determining step to give HOCl. On the other hand, the rate of complete BrCl hydrolysis to form HOBr and Cl- at p[H+] 6.4 is extremely rapid with a first-order rate constant of 3.0 x 10(6) s(-1) at 25.0 degrees C. The reverse reaction between HOBr, Cl-, and H+ has a rate constant of 2.3 x 10(10) M(-2) s(-1), so that in seawater, where [Cl-]/[Br-] = 700, the formation of BrCl is much faster than the formation of Br2 from HOBr, Br-, and H+. Rapid formation of BrCl(aq) and its subsequent reaction with Br- is a viable pathway to give Br2(aq). Photolysis of Br2(g) is believed to initiate the reactions associated with ozone depletion.     

Texture and colour characteristics,and optimisation of sodium chloride,potassium chloride and glycine of reduced-sodium frankfurter

The three-components mixture design was applied to optimise a ratio of NaCl (0%–65%), KCl (35%–100%) and glycine (0%–20%) in reduced-sodium frankfurters. Fourteen frankfurters were analysed for texture and colour, and consumer (n = 100) acceptability. Results indicated that NaCl levels affected consumer acceptability of reduced-sodium frankfurters. Increasing NaCl generally increased texture hardness. Optimisation of a salt mixture was performed by superimposing contour plots of predicted acceptability scores (≥5.5 on a 9-points hedonic scale) of all sensory attributes and revealed the optimal salt mixture: 40.03%–63.66% NaCl, 35.00%–55.90% KCl and 0.00%–20.00% glycine. The optimal salt mixture contained 220–340 mg Na/100g frankfurter compared with 540 mg Na/100 g of the control formulation (100% NaCl). The mean overall liking score (5.9 vs. 5.9) of the optimal reduced-sodium frankfurter was not different from the control (100% NaCl). This optimal formulation had >25% sodium reduction and could be claimed as ‘reduced-sodium’ according to US Food and Drugs Administration regulation.     

Effect of bromide and iodide ions on the formation and speciation of disinfection byproducts during chlorination

Two natural waters were fortified with various levels of bromide or iodide ions (0-30 microM) and chlorinated in the laboratory to study the impact of bromide and iodide ions on the formation and speciation of disinfection byproducts. Trihalomethanes (THMs), haloacetic acids (HAAs), total organic halogen (TOX), and its halogen-specific fractions total organic chlorine (TOCl), bromine (TOBr), and iodine (TOI), were measured in this work. The molar yields of THMs and HAAs increased as the initial bromide concentration increased. No significant change in TOX concentration was found for varying bromide concentrations. However, TOX concentrations decreased substantially with increasing initial iodide concentrations. At higher levels of bromide, there was a decreasing level of unknown TOX and unknown TOCl but an increasing level of unknown TOBr. The extent of iodine substitution was much lower than that of bromine substitution when comparing identical initial concentrations because a substantial amount of iodide was oxidized to iodate by chlorine. The tendency toward iodate formation resulted in the unusual situation where higher chlorine doses actually caused reduced levels of iodinated organic byproducts. Quantitative assessment of the results of this study showed a good agreement with kinetic data in the literature.     

Iodate and iodo-trihalomethane formation during chlorination of iodide-containing waters: role of bromide

The kinetics of iodate formation is a critical factor in mitigation of the formation of potentially toxic and off flavor causing iodoorganic compounds during chlorination. This study demonstrates that the formation of bromine through the oxidation of bromide by chlorine significantly enhances the oxidation of iodide to iodate in a bromide-catalyzed process. The pH-dependent kinetics revealed species specific rate constants of k(HOBr + IO(-)) = 1.9 × 10(6) M(-1) s(-1), k(BrO(-) + IO(-)) = 1.8 × 10(3) M(-1) s(-1), and k(HOBr + HOI) < 1 M(-1) s(-1). The kinetics and the yield of iodate formation in natural waters depend mainly on the naturally occurring bromide and the type and concentration of dissolved organic matter (DOM). The process of free chlorine exposure followed by ammonia addition revealed that the formation of iodo-trihalomethanes (I-THMs), especially iodoform, was greatly reduced by an increase of free chlorine exposure and an increase of the Br(-)/I(-) ratio. In water from the Great Southern River (with a bromide concentration of 200 μg/L), the relative I-incorporation in I-THMs decreased from 18 to 2% when the free chlorine contact time was increased from 2 to 20 min (chlorine dose of 1 mg Cl(2)/L). This observation is inversely correlated with the conversion of iodide to iodate, which increased from 10 to nearly 90%. Increasing bromide concentration also increased the conversion of iodide to iodate: from 45 to nearly 90% with a bromide concentration of 40 and 200 μg/L, respectively, and a prechlorination time of 20 min, while the I-incorporation in I-THMs decreased from 10 to 2%.     

Mechanism of glycine transport in mouse mammary tissue

The mechanism of glycine transport in lactating mouse mammary gland was investigated. Three Na+-dependent systems of glycine transport, distinguished on the basis of their ionic requirement and sensitivity to 2-(methylamino)isobutyric acid (MeAIB), were A (Na+-dependent, MeAIB-sensitive); (Na++Cl-)-dependent, MeAIB-insensitive; and Na+-dependent, Cl--independent, MeAIB-insensitive. These systems were further distinguished on the basis of inhibition analysis and sensitivity to pH of the extracellular medium and preloading mammary tissue with amino acids. The uptake of glycine via the A system (Km 0.53 mM) was inhibited by preloading mammary tissue with alanine, while glycine uptake mediated by the (Na++Cl-)-dependent, MeAIB-insensitive system (Km 0.47 mM) was downregulated by preloading mammary tissue with all amino acids (alanine, sarcosine and histidine) tested. Treatment of mammary tissue with N-ethylmaleimide inhibited the uptake of glycine via both these systems. Decreasing the pH of the extracellular medium inhibited the uptake of glycine via the A system but not the (Na++Cl-)-dependent, MeAIB-insensitive system. On the basis of ionic requirement, system A appears to comprise two components, one dependent on Na+ plus Cl- and the other on Na+ alone. Insulin upregulated the A system-mediated uptake of glycine in pregnant mouse mammary tissue cultured in vitro, while the (Na++Cl-)-dependent, MeAIB-insensitive system remained unaffected.     

Potassium chloride, potassium lactate and glycine as sodium chloride substitutes in fermented sausages and in dry-cured pork loin

Salt is essential in the elaboration of dry meat products, contributing to their texture and flavour development. The effect brought about by substituting NaCl with KCl (0-60%), potassium lactate (0-100%) and glycine (0-100%) on the texture, flavour and colour characteristics of fermented sausages and dry-cured pork loins was evaluated. Texture profile analysis and a sensory analysis were performed. Important flavour defects were detected with substitutions above 40% for the three substituents in both products, and with substitutions above 30% for glycine in dry-cured loin. A loss of cohesiveness was detected by the sensory analysis in fermented sausages at substitution levels higher than 30% with potassium lactate (K-lactate) and higher than 50% with glycine. Although the instrumental analysis detected texture changes in dry-cured loin, the sensory analysis did not detect any substitution effect on texture.     

Mechanism and direct kinetics study on the homogeneous gas-phase formation of PBDD/Fs from 2-BP, 2,4-DBP, and 2,4,6-TBP as precursors

This study investigated the homogeneous gas-phase formation of polybrominated dibenzo-p-dioxin/dibenzofurans (PBDD/Fs) from 2-BP, 2,4-DBP, and 2,4,6-TBP as precursors. First, density functional theory (DFT) calculations were carried out for the formation mechanism. The geometries and frequencies of the stationary points were calculated at the MPWB1K/6-31+G(d,p) level, and the energetic parameters were further refined by the MPWB1K/6-311+G(3df,2p) method. Then, the formation mechanism of PBDD/Fs was compared and contrasted with the PCDD/F formation mechanism from 2-CP, 2,4-DCP, and 2,4,6-TCP as precursors. Finally, the rate constants of the crucial elementary reactions were evaluated by the canonical variational transition-state (CVT) theory with the small curvature tunneling (SCT) correction over a wide temperature range of 600-1200 K. Present results indicate that only BPs with bromine at the ortho position are capable of forming PBDDs. The study, together with works already published from our group, clearly shows an increased propensity for the dioxin formations from BPs over the analogous CPs. Multibromine substitutions suppress the PBDD/F formations.