Complexation of arsenite with humic acid in the presence of ferric iron

In the presence of iron (Fe), dissolved organic matter (DOM) may bind considerable amounts of arsenic (As), through formation of Fe-bridged As-Fe-DOM complexes and surface complexation of As on DOM-stabilized Fe-colloids (collectively referred to as As-Fe-DOM complexation). However, direct (e.g., chromatographic and spectroscopic) evidence and fundamental kinetic and stability constants have been rarely reported for this As-Fe-DOM complexation. Using a size exclusion chromatography (SEC)-UV-inductively coupled plasma mass spectrometry (ICP-MS) technique, arsenite (As(III))-Fe-DOM complexation was investigated after adding As(III) into the priorly prepared Fe-DOM. A series of evidence, including coelution of As, Fe, and DOM from the SEC column and coretention of As, Fe, and DOM by 3 kDa MWCO centrifugal filtration membrane, demonstrated the occurrence of As(III)-Fe-DOM complexation. The kinetic data of As(III)-Fe-DOM complexation were well described by a pseudofirst order rate equation (R(2) = 0.95), with the rate constant (k') being 0.17 ± 0.04 1/h. Stability of As(III)-Fe-DOM complexation was characterized by apparent stability constant (K(s)) derived from two-site ligand binding model, with log K(s) ranging from 4.4 ± 0.2 to 5.6 ± 0.4. Considering the kinetics (within hours) and stability (similar to typical metal-humates) of As(III)-Fe-DOM complexation, this complexation needs to be included when evaluating As mobility in Fe and DOM rich environments.     

Photoinduced oxidation of antimony(III) in the presence of humic acid

Interactions of antimony with natural organic matter (NOM) are important for the fate of Sb in aquatic systems. The kinetics of the photosensitized oxidation of Sb(III) to Sb(V) in the presence of Suwannee River Humic Acid (SRHA) was investigated using UV-A and visible light (medium-pressure mercury lamp). At a concentration of 5 mg L(-1) dissolved organic carbon (DOC) the light-induced reaction was 9000 times faster (rate coefficient k(exp) = 7.0 +/- 0.05 x 10(-4) s(-1)) than the dark reaction and followed pseudo-first-order kinetics. Rates increased linearly with the concentration of DOC. Between pH 4 and 8 rates increased by a factor of 5. Further results and kinetic considerations indicate that singlet oxygen, hydroxyl radicals, hydrogen peroxide, and hydroperoxyl radicals/superoxide are not important photooxidants in this system, while other NOM-derived reactive species, in particular excited triplet states and/or phenoxyl radicals, seem to be relevant. The dependence of rate coefficients on Sb(III)/DOC ratio was consistent with a two binding site model including (i) a strong binding site at low concentration inducing fast oxidation, (ii) a weak binding site at high concentration inducing slower oxidation, and (iii) the even slower oxidation of Sb(OH)3. Photoirradiation of natural water samples spiked with Sb(III) showed that the oxidation rates could be well predicted based on DOC.     

Cadmium bioavailability and accumulation in the presence of humic acid to the zebra mussel, Dreissena polymorpha

Metal speciation in aquatic systems is mainly determined by the type and concentration of ligands present in solution. A very important group of complexing agents is dissolved organic matter (DOM), e.g., humic and fulvic acids. According to the free-ion activity model, only the free metal ion is available to biota. Nevertheless, DOM has been reported to decrease or increase metal uptake, leading to uncertainty concerning the bioavailability of metal-DOM complexes. In this work the effect of Aldrich humic acid on cadmium accumulation by the zebra mussel, Dreissena polymorpha, was studied under laboratory conditions. Mussels, collected in a drinking water reservoir, were exposed to varying environmentally relevant concentrations of cadmium in the presence and absence of humic acid. Cadmium concentrations in the mussel tissues were analyzed, and measurements with a cadmium-ion-selective electrode were made to determine the free cadmium ion activity in the exposure waters. The uptake of humic acid by the zebra mussels was measured by the decrease of the total organic carbon (TOC) concentration in the water over time. The free cadmium ion activity in the water decreased from 51.6% to 19.9% of the total cadmium concentration in the presence of humic acid. This decrease by a factor of 2.6 resulted in a decrease in the cadmium uptake rate in the soft tissue of zebra mussels from 12.9 to 7.9 nmol/g dry wt/day, which corresponds to a decrease by a factor of 1.6. This implies that cadmium uptake rates were higher than predicted by the free-ion activity model and indicates that cadmium-humic acid complexes are partly available to zebra mussels.     

以偏钛酸为原料制备纳米二氧化钛

介绍了以工业偏钛酸为原料制备纳米二氧化钛的方法,分析讨论了均匀沉淀法制备中各环节的影响因素,如酸钛比、硫酸浓度、硫酸氧钛TiOSO4溶液质量浓度、尿素用量、煅烧温度等.结果表明:(1)偏钛酸的酸解条件是酸钛比为3,硫酸浓度为8.2 mol/L,反应温度为100℃,溶解时间为1 h;(2)在90℃下加入理论量3倍的尿素可以得到同等条件下粒径最小的纳米TiO2;(3)所得样品为锐钛型纳米TiO2,在850℃下煅烧时开始出现金红石型,当温度达到900℃时出现大量的金红石型,即锐钛型向金红石型转化的起始温度为850℃.     

Factors influencing the production of acetoin and diacetyl by lactic acid bacteria in skim milk

Nine strains of starter cultures belonging to the genera Streptococcus, Leuconostoc and Lactobacillus were studied for the effect of pyruvate concentration, incubation period and the associative growth on the production of acetoin and diacetyl in skim milk. The absolute amount of acetoin and diacetyl and the amount pro μmol pyruvate increased with increasing the concentration of pyruvate. At the low concentration of pyruvate the maximum amount of these neutral carbonyl compounds was first reached after 34 days, whereas at the high concentration it was readily achieved after 6 days and then decreased. Production of acetoin and diacetyl by mixed-species cultures from added citrate was either increased or markedly decreased compared to the single-species culture.     

Factors influencing the production of volatile phenols by wine lactic acid bacteria

This work aimed to evaluate the effect of certain factors on the production of volatile phenols from the metabolism of p-coumaric acid by lactic acid bacteria (LAB) (Lactobacillus plantarum, L. collinoides and Pediococcus pentosaceus). The studied factors were: pH, L-malic acid concentration, glucose and fructose concentrations and aerobic/anaerobic conditions. It was found that, in the pH range of 3.5 to 4.5, the higher the pH the greater the production of volatile phenols. This behaviour is correlated with the effect of pH on bacterial growth. Increasing levels of L-malic acid in the medium diminished the production of 4-vinylphenol (4VP) and stimulated the production of 4-ethylphenol (4EP) by L. plantarum NCFB 1752 and L. collinoides ESB 99. The conversion of 4VP into 4EP by the activity of the vinylphenol reductase may be advantageous to the cells in the presence of L-malic acid, presumably due to the generation of NAD+, a cofactor required by the malolactic enzyme. Relatively high levels of glucose (20 g/L) led to an almost exclusive production of 4VP by L. plantarum NCFB 1752, while at low concentrations (≤ 5 g/L), 4EP is mainly or solely produced. Part of the glucose may be diverted to the production of mannitol as an alternative pathway to regenerate NAD+. This is corroborated by the experiments done with fructose, a compound that can be used as an electron acceptor by some bacteria becoming reduced to mannitol. In anaerobiosis, the reduction of 4VP into 4EP is clearly favoured, which is consistent with the need to increase the availability of NAD+ in these conditions. This study shows that the amount and the ratio 4VP/4EP produced by LAB are greatly affected by certain environmental and medium composition factors. The behaviour of the bacteria seems to be driven by the intracellular NAD+/NADH balance.     

Impedance measurement of growth of lactic acid bacteria in the presence of nisin and lysozyme

Effect of nisin (0.500 g/l), lysozyme (0.035 g/l) and the mix of nisin (0.500 g/l) and lysozyme (0.035 g/l) against two nisin-producing lactococci strains, three non-nisin-producing lactococci strains and four lactobacilli strains with antimicrobial activity was determined by the impedimetric method. None of the tested lactococci and lactobacilli strains were inhibited by lysozyme at concentration of 0.035 g/l. Only the nisin-producing lactococci strains were resistant to nisin at 0.500 g/l, the other lactococci and lactobacilli were inhibited by nisin at 0.500 g/l intensively. The mix of lysozyme and nisin displayed a comparable effect to the nisin addition against the used lactococci strains and was very variable depending on the strain of tested lactobacilli. The impedimetric method was shown to be convenient for screening the growth abilities of lactococci and lactobacilli in the presence of antimicrobial components.     

Estimation of factors influencing fatty acid profiles in light lambs

Fatty acid composition of intramuscular, intermuscular, subcutaneous, omental and kidney knob fat depots of eighty male light lambs (±21 kg live weight) from five Spanish sheep breeds was analysed. Fat depot, anatomical depot location (internal, external and intramuscular), breed (Spanish Merino, Grazalema Merino, Churra Lebrijana, Segureña and Montesina), weaning type (weaning at 45 days after birth or no weaning) and subcutaneous fat thickness factors were analyzed using a statistical model to quantify their contribution to the variation of each fatty acid. Production system was the main factor to explain variations in overall fatty acid profiles (34.68%). However, for several fatty acids and indices (arachidonic, linoleic, PUFA, n − 3/n − 6) anatomical depot location was the most significant factor. Feeding system explained 65.49% of CLA variance, indicating a strong influence of suckling period length on CLA deposition in lambs’ fat. Moreover, due to the lack of interaction between anatomical depot location or depot and breed type or weaning system for total CLA, for future research only one depot would be enough to study the effect of those factors on CLA levels.     

酸乳中益生细菌活性影响因素的研究概况

阐述了发酵型酸乳中益生菌的种类，特性和活性条件。重点讨论了益生菌的（特别是酸乳中常用的乳酸细菌）保健功能，探讨了酸乳中益生菌活性抑制因素和提高益生菌活性的方法，目的在于探求和开发生产高质量，高活性益生菌酸乳途径。     

U(VI)-kaolinite surface complexation in absence and presence of humic acid studied by TRLFS

Time-resolved laser-induced fluorescence spectroscopy (TRLFS) was applied to study the U(VI) surface complexes on kaolinite in the presence and absence of humic acid (HA). Two uranyl surface species with fluorescence lifetimes of 5.9 +/- 1.4 and 42.5 +/- 3.4 micros and 4.4 +/- 1.2 and 30.9 +/- 7.2 micros were identified in the binary (U(VI)-kaolinite) and ternary system (U(VI)-HA-kaolinite), respectively. The fluorescence spectra of adsorbed uranyl surface species are described with six and five fluorescence emission bands in the binary and ternary system, respectively. The positions of peak maxima are shifted significantly to higher wavelengths compared to the free uranyl ion in perchlorate medium. HA has no influence on positions of the fluorescence emission bands. In the binary system, both surface species can be attributed to adsorbed bidentate mononuclear surface complexes, which differ in the number of water molecules in their coordination environment. In the ternary system, U(VI) prefers direct binding on kaolinite rather than via HA, but it is sorbed as a uranyl-humate complex. Consequently, the hydration shell of the U(VI) surface complexes is displaced with complexed HA, which is simultaneously distributed between kaolinite particles. Aluminol binding sites are assumed to control the sorption of U(VI) onto kaolinite.     

Chlorination byproduct formation in the presence of humic acid, model nitrogenous organic compounds, ammonia, and bromide

The formation of trihalomethanes (THMs), haloacetic acids (HAAs), and cyanogen halides (CNXs) after chlorination of synthetic solutions containing humic acid, nitrogenous organic (N-organic) compounds, ammonia, and bromide ions was studied. Humic acid (from Aldrich) was used to provide the source of the precursors. Glycine was chosen as the primary model N-organic compound and other four model N-organic compounds (including glutamic acid, glycylglycine, diethylamine, and methylamine) were also evaluated for comparison. The formation of THMs and HAAs was found to decrease with increasing glycine and ammonia concentrations but to increase with increasing bromide ion concentration. CNX formation was found to be highly sensitive to free chlorine to glycine ratios, and its formation trends were significantly affected bythe presence/absence of ammonia. The incorporation of bromine changed the byproducts speciation toward brominated species and enhanced the yields of total THMs, HAAs, and CNXs. Different model N-organic compounds exerted different effects on the formation of THMs, HAAs, and CNXs. Their effects on the formation of THMs and HAAs were likely dependent on their reactivity to chlorine in competing with the humic acid chlorination reactions. The difference in the CNCI yields was attributable to the variations in the compound structures.     

制备冷冻干燥乳酸菌的相关影响因素的研究进展

从技术和经济角度出发,让乳酸菌在干燥及其后续的贮藏过程中,尽可能多的存活是非常重要的。这篇文章主要综述与冷冻干燥乳酸菌制备的几个相关因素。     

影响浓缩苹果汁中富马酸因素的研究

采用高效液相色谱法测定不同质量的苹果原料中富马酸含量，获得了不同加工工艺条件下富马酸变化趋势，提出了控制富马酸超标的方法。     

纳米TiO2处理的聚丙烯酸盐及其混合浆液的研究

研究了纳米TiO2加入到聚丙烯酸盐浆液后浆液黏度的变化。测试结果表明,加入纳米材料后,聚丙烯酸盐浆液及混合浆液的黏度降低,稳定性增强;改性后的浆液对纯棉纱的黏附力有所提高,混合浆液的综合性能得到改善。     

Degradation pathways of pentachlorophenol by photo-Fenton systems in the presence of iron(III), humic acid, and hydrogen peroxide

The degradation characteristics and pathways of pentachlorophenol (PCP) by the photo-Fenton systems were studied in H2O2 aqueous solutions, which contained Fe(III) only [H2O2/Fe(III) system] and Fe(III) + humic acid (HA) [H2O2/Fe(III)/HA system] at pH 5.0. Although 40% of the PCP was degraded after 5 h of irradiation in the H2O2/Fe(III) system, more than 90% was degraded in the H2O2/Fe(III)/HA system. This shows that at pH 5.0 the degradation of PCP is clearly enhanced by the presence of HA in the photo-Fenton system. In the H2O2/Fe(III) system, the production of octachlorodibenzo-p-dioxin (OCDD) was detected, and 2-hydroxy nonachlorodiphenyl ether was also identified as a precursor of OCDD. However, no OCDD production was observed in the H2O2/Fe(III)/HA system. This indicates that the presence of HA represses the production of OCDD during the degradation of PCP by the photo-Fenton system. Such an effect by HA can be attributed to a reaction sequence wherein reaction intermediates derived from PCP, such as PCP., are incorporated into HA. This was verified by 13C NMR and pyrolysis-GC/MS studies.     

On the acid-base properties of humic acid in soil

Humic acid was isolated from three contrasting organic-rich soils and acid-base titrations performed over a range of ionic strengths. Results obtained were unlike most humic acid data sets; they showed a greater ionic strength dependency at low pH than at high pH. Forward- and back-titrations with the base and acid revealed hysteresis, particularly at low pH. Previous authors attributed this type of hysteresis to humic acid aggregates-created during the isolation procedure-being redissolved during titration as the pH increased and regarded the results as artificial. However, forward- and back-titrations with organic-rich soils also demonstrated a similar hysteretic behavior. These observations indicate (i) that titrations of humic acid in aggregated form (as opposed to the more usual dissolved form) are more representative of the acid-base properties of humic acid in soil and (ii) that the ionic strength dependency of proton binding in humic acid is related to its degree of aggregation. Thus, the current use of models based on data from dissolved humic substances to predictthe acid-base properties of humic acid in soil under environmental conditions may be flawed and could substantially overestimate their acid buffering capacity.     

13C NMR analysis of biologically produced pyrene residues by Mycobacterium sp. KMS in the presence of humic acid

Cultures of the pyrene degrading Mycobacterium sp. KMS were incubated with [4-13C]pyrene or [4,5,9,10-14C]pyrene with and without a soil humic acid standard to characterize the chemical nature of the produced residues and evaluate the potential for bonding reactions with humic acid. Cultures were subjected to a "humic acid/ humin" separation at acidic pH, a duplicate separation followed by solvent extraction of the humic acid/humin fraction, and a high pH separation. 13C NMR analysis was conducted on the resulting solid extracts. Results indicated that the activity associated with solid extracts did not depend on pH and that approximately 10% of the added activity was not removed from the solid humic acid/humin fraction by solvent extraction. 13C NMR analysis supported the conclusion that the majority of pyrene metabolites were incorporated into cellular material. Some evidence wasfound for metabolite reaction with the added humic material, but this did not appear to be a primary fate mechanism.     

Effects of humic substances on precipitation and aggregation of zinc sulfide nanoparticles

Nanoparticulate metal sulfides such as ZnS can influence the transport and bioavailability of pollutant metals in anaerobic environments. The aim of this work was to investigate how the composition of dissolved natural organic matter (NOM) influences the stability of zinc sulfide nanoparticles as they nucleate and aggregate in water with dissolved NOM. We compared NOM fractions that were isolated from several surface waters and represented a range of characteristics including molecular weight, type of carbon, and ligand density. Dynamic light scattering was employed to monitor the growth and aggregation of Zn-S-NOM nanoparticles in supersaturated solutions containing dissolved aquatic humic substances. The NOM was observed to reduce particle growth rates, depending on solution variables such as type and concentration of NOM, monovalent electrolyte concentration, and pH. The rates of growth increased with increasing ionic strength, indicating that observed growth rates primarily represented aggregation of charged Zn-S-NOM particles. Furthermore, the observed rates decreased with increasing molecular weight and aromatic content of the NOM fractions, while carboxylate and reduced sulfur content had little effect. Differences between NOM were likely due to properties that increased electrosteric hindrances for aggregation. Overall, results of this study suggest that the composition and source of NOM are key factors that contribute to the stabilization and persistence of zinc sulfide nanoparticles in the aquatic environment.