Triclosan reactivity in chloraminated waters

Triclosan, widely employed as an antimicrobial additive in many household personal care products, has recently been detected in wastewater treatment plant effluents and in source waters used for drinking water supplies. Chloramines used either as alternative disinfectants in drinking water treatment or formed during chlorination of nonnitrified wastewater effluents have the potential to react with triclosan. This study examined triclosan reactivity in chloraminated waters over the pH range of 6.5-10.5. Experimental and modeling results show that monochloramine directly reacts with the phenolate form of triclosan; however, the reaction is relatively slow as evinced by the second-order rate constant k(ArO)-NH2Cl = 0.025 M(-1) s(-1). Kinetic modeling indicates that for pH values less than 9.5, reactions between triclosan and two monochloramine autodecomposition intermediates, hypochlorous acid (k(ArO)-HOC = 5.4 x 10(3) M(-1) s(-1)) and dichloramine (k(ArO)-NHCl2 = 60 M(-1) s(-1)), are responsible for a significant percentage of the observed triclosan decay. The products of these reactions include three chlorinated triclosan byproducts as well as 2,4-dichlorophenol and 2,4,6-trichlorophenol. Low levels of chloroform were detected after 1 week at pH values of 6.5 and 7.5. The slow reactivity of triclosan in the presence of chloramines explains the recalcitrance of this species in nonnitrified wastewater effluents.     

Hydroxyl radical formation upon oxidation of reduced humic acids by oxygen in the dark

Humic acids (HAs) accept and donate electrons in many biogeochemical redox reactions at oxic/anoxic interfaces. The products of oxidation of reduced HAs by O(2) are unknown but are expected to yield reactive oxygen species, potentially including hydroxyl radical (·OH). To quantify the formation of ·OH upon oxidation of reduced HAs by O(2), three HAs were reduced electrochemically to well-defined redox states and were subsequently oxidized by O(2) in the presence of the ·OH probe terephthalate. The formation of ·OH upon oxidation increased with increasing extent of HA reduction. The yield of ·OH ranged from 42 to 160 mmol per mole of electrons donated by the reduced HA. The intermediacy of hydrogen peroxide (H(2)O(2)) in the formation of ·OH was supported by enhancement of ·OH formation upon addition of exogenous H(2)O(2) sources and by the suppression of ·OH formation upon addition of catalase as a quencher of endogenous H(2)O(2). The formation of ·OH in the dark during oxidation of reduced HA represents a previously unknown source of ·OH formation at oxic/anoxic interfaces and may affect the biogeochemical and pollutant redox dynamics at these interfaces.     

Factors influencing the formation and relative distribution of haloacetic acids and trihalomethanes in drinking water

Various water quality and treatment characteristics were evaluated under controlled chlorination conditions to determine their influences on the formation and distribution of nine haloacetic acids and four trihalomethanes in drinking water. Raw waters were sampled from five water utilities and were coagulated with alum and fractionated with XAD-8 resin. The resulting four fractions--raw and coagulated water and the hydrophobic and hydrophilic extracts--were then chlorinated at pH 6 and 8 and held at 20 degrees C for various contact times. The results show that increasing pH from 6 to 8 increased trihalomethane formation but decreased trihaloacetic acid formation, with little effect on dihaloacetic acid formation. More trihalomethanes were formed than haloacetic acids at pH 8, while the reverse was true at pH 6. Hydrophobic fractions always gave higher haloacetic acid and trihalomethane formation potentials than their corresponding hydrophilic fractions, but hydrophilic carbon also played an important role in disinfection byproduct formation for waters with low humic content. The bromine-containing species comprised a higher molar proportion of the trihalomethanes than of the haloacetic acids. The hydrophilic fractions were more reactive with bromine than their corresponding hydrophobic fractions. Coagulation generally removed more haloacetic acid precursors than trihalomethane precursors. Waters with higher specific ultraviolet absorbance values were more amenable to removal of organic material by coagulation than waters with low specific ultraviolet absorbance values. Experimental evidence suggests that haloacetic acid precursors have a higher aromatic content than trihalomethane precursors.     

Bromide ion effect on N-nitrosodimethylamine formation by monochloramine

N-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.     

Fatty acids and cholesterol oxidation in salted and dried shrimp

The aim of this work was to evaluate the occurrence of cholesterol oxidation products and to analyze the lipidic profile in salted–dried shrimp. Fifty samples of salted–dried shrimp were evaluated, and the cholesterol oxides (7β-OH, 7α-OH, 7-Keto and 25-OH) were quantified by high-performance liquid chromatography. The cholesterol oxides: 7β-OH (34.63–72.56 μg/g), 7α-OH (5.02–12.12μg/g), 7-Keto (7.44–32.68 μg/g) and 25-OH (2.37–22.88 μg/g) were determined in all samples analyzed. Regarding to the total cholesterol content and the average thiobarbituric acid reactive substances (TBARS) content, the results ranged from 73.88 to 247.69 mg/100 g, and 0.02 to 1.30 mgMA/kg, respectively. The fatty acids profile was: 27.48% saturated, 43.90% monounsaturated and 28.61% polyunsaturated. The presence of cholesterol oxidation products and the values of TBARS indicate the degree of oxidation of this product, which was probably initiated by inadequate conditions of processing and storage.     

Fenton oxidation products derived from hydroxycinnamic acids increases phenolic‐based compounds and organic acid formation in sugar processing

The hydroxycinnamic acids (HCAs), caffeic acid (CaA), p‐coumaric acid (pCoA) and ferulic acid (FeA) are the main phenolic acid colour precursors present in sugar cane juice. The Fenton oxidative degradation products of these HCAs and mixture using Fe²⁺/H₂O₂ at pH 4.72 at 25 °C were identified using chromatography and mass spectrometry techniques. Oxalic (≤14 wt%), isobutyric (≤13.5 wt%) and formic acids (≤1.3 wt%) were the main organic acids formed. CaA produced the highest proportion of oxalic and isobutyric acids, while FeA produced the highest proportion of formic acid. The presence of increased proportion of oxalic acid in juice will increase the proportion of calcium oxalate scale in sugar mill heat exchangers. The phenolic‐based products identified include protocatechuic aldehyde and 4‐hydroxybenzoic acid and the basic phenols, p‐allyphenol, p‐vinylguaiacol, trans‐isoeugenol, which when present in juice may react with juice constituents to increase juice colour in subsequent processing.     

Supercritical water oxidation of sulfide

Supercritical water oxidation (SCWO) of sulfide wastewater with oxygen as the oxidant was investigated using ammonium sulfide solution as the model waste. The experiments, which were conducted in a bench-scale continuous SCWO installation, indicated that S2- could be completely oxidized to SO4(2-) within the residence time of less than 10 s under the supercritical water conditions at 698.2-773.2 K and 22.0 MPa-30.0 MPa. The reaction pathway of S2- in SCWO was determined to be S2- --> S2O3(2-) --> SO3(2-) --> SO4(2-). The effects of temperature, pressure, and oxygen content on SCWO of S2- were also studied. The kinetic model based on this pathway was established with the reaction rate constants and orders found by fitting the experimental data. The dependence of the rate constants on the temperature can be described with Arrhenius' law. The rate constants are dependent on the density of SCW, and the dependence is logarithmically linear.     

溴离子与硫氰酸根共存时溴含量的测定

主要介绍了Br-与SCN-共存时对溴离子含量的检测方法,利用紫外-可见分光光度计对SCN-的浓度进行检测,通过Br-与SCN-总量的测定,从而完成对Br-的含量的测定.     

Effects of different levels of trans fatty acids and oxidised lipids in diet on cholesterol and cholesterol oxidation products formation in rabbit

The objective was to assess the effects of trans fatty acids and oxidised lipids, present in dietary fat by-products used in feeds, on cholesterol and oxycholesterols in meat, liver and plasma of rabbits. A palm fatty acid distillate, before and after hydrogenation (trans fatty acid trial), and a sunflower–olive oil blend (70/30, v/v), before and after use in a commercial frying process (oxidised lipid trial), were used in experimental feeds (at 3%, w/w). High trans fatty acid and oxidised lipid diets caused significantly higher cholesterol and oxycholesterol levels in all tissues of rabbit (0.01 < p ? 0.05). The content of oxycholesterols in rabbit meat, liver and plasma obtained from trans fatty acid experiments varied from 9 to 34 μg/100 g, 24 to 61 μg/100 g and 60 to 138 μg/dl, respectively, from low to high levels. In the oxidised lipid experiments, content of oxycholesterols varied from 16 to 52 μg/100 g, 14 to 108 μg/100 g and 52 to 269 μg/dl in meat, liver and plasma, respectively. As a consequence, meat products from rabbits fed a diet containing higher levels of trans fatty acids or oxidised lipids may result in higher intakes of cholesterol and oxycholesterols by humans.     

Lipid oxidation and metmyoglobin formation in sausages containing chickpea flour

Rapid lipid oxidation and metmyoglobin formation in sausages containing up to 30% chickpea flour is due to the presence of lipoxidase in chickpea flour. This enzyme oxidises the unsaturated fats present to peroxides (or related compounds) which then catalyse myoglobin oxidation. Heat treatment of chickpea flour at 80° C for 1 h in water prior to its addition to the batter will prevent both accelerated lipid and myoglobin oxidation in these sausages. An antioxidant containing α-tocopherol and ascorbyl palmitate inhibited the lipid oxidation in these products but had no effect on myoglobin oxidation in sausage batter containing unheated chickpea flour. The relevance of these results to the interdependence of lipid and myoglobin oxidation in meat and meat products is discussed.     

Competitive oxidation of fatty acids. Effect of the carboxylic group and of saturated fatty acids

The kinetics of the oxidation of mixtures of methyl linoleate-linoleic acid and of mixtures of pelargonic acid-linoleic acid have been studied at 30°C by the oxygen absorption method. During the oxidation of methyl linoleate-linoleic acid mixtures, a linear relationship was found between the overall monomolecular rate constant, Km, and the composition of the sample. When the reaction entered the bimolecular period, a strong prooxidant effect was found when the molar fraction of methyl linoleate was above 0.50. With mixtures of pelargonic acid-linoleic acid, it was found that the saturated fatty acid behaved as an inert diluent throughout all the levels of oxidation studied and for all the range of molar fractions.     

Effect of cooking and storage on lipid oxidation and development of cholesterol oxidation products in water buffalo meat

Buffalo meat was subjected to two cooking methods viz. broiling and pressure cooking and two storage procedures viz. refrigerated (4 °C) storage for six days and frozen (-10 °C) storage for 90 days. Changes in lipid oxidation and development of cholesterol oxidation products were studied in raw as well as cooked meat samples. Total lipid, phospholipid, cholesterol, free fatty acid, glycolipid and glyceride contents increased significantly on cooking of meat but did not show any significant changes during either refrigerated or frozen storage except for free fatty acid content which showed an increase. The TBA values also increased during storage but not to the extent of indicating rancidity. Cholesterol oxidation products separated by thin layer chromatography were: cholestanetriol, 7-α-hydroxycholesterol, 19-hydroxycholesterol, 7-ketocholesterol, cholesterol-α-epoxide, cholesterol-β-epoxide and an unidentified fraction. All these fractions, except for the unidentified fraction, increased on cooking and storage. The cholesterol-β-epoxide fraction was resistant to changes. Changes in broiled meat were more pronounced compared to pressure cooked meat. Frozen storage did not prevent the development of cholesterol oxidation products in buffalo meat.     

Effect of hydroxycinnamic acids on lipid oxidation and protein changes as well as water holding capacity in frozen minced horse mackerel white muscle

The antioxidant effectiveness of different hydroxycinnamic acids for inhibiting the formation of off-flavours associated to rancidity in minced frozen horse mackerel white muscle stored at −10 and −18 °C was studied. The influence of lipid oxidation on protein aggregation, protein denaturation and water holding capacity was also determined. Caffeic acid, o-coumaric acid and ferulic acid were the antioxidants tested. The order of antioxidant effectiveness was caffeic acid > ferulic acid > o-coumaric acid accordingly with previous results obtained in chilled horse mackerel. A strong dependence of antioxidant effectiveness to the ratio lipid/antioxidant concentration was observed. There was no evidence to suggest that antioxidants reduce protein aggregation or water holding capacity changes. Protein aggregation was not accompanied by gross protein denaturation, as monitored by differential scanning calorimetry. No evidence was found for a link between extent of lipid oxidation and degree of protein aggregation or water holding capacity changes.     

Impact of peroxydisulfate in the presence of zero valent iron on the oxidation of cyclohexanoic Acid and naphthenic acids from oil sands process-affected water

Large volumes of oil sands process-affected water (OSPW) are produced during the extraction of bitumen from oil sands in Alberta, Canada. The degradation of a model naphthenic acid, cyclohexanoic acid (CHA), and real naphthenic acids (NAs) from OSPW were investigated in the presence of peroxydisulfate (S(2)O(8)(2-)) and zerovalent iron (ZVI). For the model compound CHA (50 mg/L), in the presence of ZVI and 500 mg/L S(2)O(8)(2-), the concentration decreased by 45% after 6 days of treatment at 20 °C, whereas at 40, 60, and 80 °C the concentration decreased by 20, 45 and 90%, respectively, after 2 h of treatment. The formation of chloro-CHA was observed during ZVI/S(2)O(8)(2-) treatment of CHA in the presence of chloride. For OSPW NAs, in the presence of ZVI alone, a 50% removal of NAs was observed after 6 days of exposure at 20 °C. The addition of 100 mg/L S(2)O(8)(2-) to the solution increased the removal of OSPW NAs from 50 to 90%. In absence of ZVI, a complete NAs removal from OSPW was observed in presence of 2000 mg/L S(2)O(8)(2-) at 80 °C. The addition of ZVI increased the efficiency of NAs oxidation by S(2)O(8)(2-) near room temperature. Thus, ZVI/S(2)O(8)(2-) process was found to be a viable option for accelerating the degradation of NAs present in OSPW.     

聚乙烯醇在超临界水氧化体系中的降解

用超临界水氧化法对聚乙烯醇(PVA)废水进行降解研究,分别考察了反应温度、反应压力、氧化剂过氧倍数以及反应时间对PVA废水降解效率的影响,并用GC/MS对液相降解产物进行表征,推测其可能降解途径.结果表明:超临界水氧化法能有效降解PVA废水,随反应温度的升高、压力的增大、反应时间的延长,COD去除率也随之提高.PVA在超临界水氧化体系中降解为烯烃、烯酮、醇和羧酸类中间产物,最终降解为小分子的饱和直链烷烃类液相产物.     

Relationship between N-nitrosodiethylamine formation and protein oxidation in pork protein extracts

The relationship between protein oxidation and N-nitrosodiethylamine (NDEA) formation was assessed. Packaged fresh minced pork was stored at 2 ± 1 °C for 0, 4, 7, and 10 days. Myofibrillar protein (MP), sarcoplasmic protein (SP), and muscle homogenate were obtained from the stored minced pork and allowed to react with sodium nitrite at 80 °C for 1 h. The relationship between NDEA formation and indexes of protein oxidation was assessed by principal component analysis. The formation of NDEA in meat was correlated with protein and lipid oxidation. Lipid oxidation promoted the formation of NDEA and was positively correlated with protein oxidation. Carbonyl compounds from oxidized MP and free amines from dissociated SP promoted NDEA formation. Therefore, the effect of protein oxidation on NDEA formation depends on the type of protein and its oxidation products.     

Copper-catalyzed ascorbate oxidation results in glyoxal/AGE formation and cytotoxicity

Previously we showed that 10 muM glyoxal compromised hepatocyte resistance to hydrogen peroxide (H(2)O(2)) by increasing glutathione (GSH) and NADPH oxidation and decreasing mitochondrial membrane potential (MMP) before cytotoxicity ensued. Since transition metal-catalyzed oxidation of ascorbate (Asc) has been shown to result in the generation of both glyoxal and H(2)O(2), we hypothesized that glyoxal formation during this process compromises hepatocyte resistance to H(2)O(2). We used isolated rat hepatocytes and incubated them with Asc/copper and measured cytotoxicity, glyoxal levels, H(2)O(2), GSH levels, and MMP. To investigate the role of Asc/copper on glyoxal-BSA adducts, we measured the appearance of advanced glycation end-products (AGE) in the presence and absence of catalase or aminoguanidine (AG). Asc/copper increased glyoxal and H(2)O(2) formation. Hepatocyte GSH levels were decreased and cytotoxicity ensued after a collapse of the hepatocyte MMP. Glyoxal traps protected hepatocytes against Asc/copper-induced cytotoxicity. In cell-free studies with BSA, incubation with Asc and copper resulted in glyoxal-hydroimidazolone formation, which was decreased by both AG and catalase. To the best of our knowledge, this is the first study that illustrates the importance of glyoxal production by transition metal-catalyzed Asc autoxidation. Understanding this mechanism of toxicity could lead to the development of novel copper chelating drug therapies to treat diabetic complications.     

Lipid oxidation promotes acrylamide formation in fat-rich model systems

Lipid oxidation is one of the major chemical reactions occurring during food processing or storage and may have a strong impact on the final quality of foods. A significant role of carbonyl compounds derived from lipid oxidation in acrylamide formation has been recently proposed. In this work, the effect of lipid oxidation level on acrylamide formation was investigated by thermal treatment of differently formulated fat-rich model systems. Results showed that lipid oxidation positively influenced the formation of acrylamide. The effect was more evident in sugar-free system where lipid become the main sources of carbonyls. Catechins reduced acrylamide formation presumably by trapping carbohydrates and/or preventing lipid oxidation. More acrylamide was formed in model systems composed with sunflower oil than in those containing palm oil which is less susceptible to oxidation.In systems containing higher amount of water, acrylamide formation was delayed due to evaporative cooling. In these systems, the effect of catechin was more pronounced and the effect of lipid oxidation became detectable only after a prolonged reaction time.These findings suggested that lipid oxidation could become a relevant factor for acrylamide formation, particularly for dry foods with low carbohydrate content.