北京市蔬菜硝酸盐和亚硝酸盐污染状况评价

为了解北京市蔬菜中硝酸盐和亚硝酸盐的污染情况 ,于 2 0 0 3年 4月～ 8月从北京 15个菜市场采集应季蔬菜样品 ,共 4 0个品种 4 44份样品 ,用国标法 (GB T 5 0 0 9 33— 2 0 0 3)分析蔬菜中的硝酸盐和亚硝酸盐的含量。结果显示 :检测样品中 ,污染程度严重的占 33 1% ;中、重度污染的占2 3 6 % ;轻度的占 4 3 2 % ;硝酸盐的含量依次为绿叶菜类 >白菜类 >根茎类 >瓜茄类 >葱蒜类 >豆类 >果类 >水生植物类 ,但同一类蔬菜不同品种的硝酸盐的含量差别较大 ,从几倍到几十倍 ;同一品种的蔬菜中硝酸盐含量差别也很大 ,可能与产地、生长条件不同有关。蔬菜中亚硝酸盐含量相对较低 ,其含量与蔬菜的新鲜程度有关。研究结果提示需要制定限量标准 ,加强监督管理     

Ozone/electron beam process for water treatment: Design,limitations and economic considerations

Electron beam irradiation of water is technically the easiest way to generate OH free radicals but the efficiency of the irradiation process as an advanced oxidation process (AOP) is deteriorated by reducing species formed simultaneously with the OH free radicals. Addition of ozone to the water before or during irradiation improves the efficiency by converting the reducing species into OH free radicals and turning the irradiation process into a full AOP. The main reaction pathways of the primary species formed by the action of ionizing radiation on water in a natural groundwater with and without the presence of ozone are reviewed. Based on these data an explanation of both the dose rate effect and the ozone effect is attempted. New data are presented which illustrate the effect of alkalinity on the way in which ozone is introduced into the water, and the impact of both water matrix and chemical structure of the pollutants to the efficacy of the ozone/electron beam process.     

Role of alkaline nitrites in the corrosion performance of steel in composite cements

The influence of alkaline nitrites on the inhibition of corrosion of steel in binary and ternary cement environments was tested. pH measurements carried out for binary and ternary cement extracts showed that the alkalinity of the cement was not affected by making use of binary and ternary cements. Gravimetric measurements showed that the decrease in the corrosion rate of steel in different systems follows the order: Ternary > (OPC + PSC) > (OPC + PPC) > (PPC + PSC). Potential–time studies indicated that the ability to maintain the passivity of steel in different systems also follows the order as above. Potentiodynamic polarisation studies for steel in binary and ternary cement environments showed the favourable influence of the presence of higher amounts of chlorides. Nitrites of sodium, potassium and calcium act as anodic inhibitors and they compete with chloride ions for the ferrous ions at the steel to form a film of ferric oxide. An efficiency as high as 91% is obtained for the ternary system containing 1% chloride and 0.5% nitrite. The degree of surface coverage showed a maximum value for the ternary system (>0.9) even in the presence of a higher amount of chloride thereby indicating the better performance of the system.     

Field Evaluation of Marine Structures Containing Calcium Nitrite

A field study of corrosion of reinforcing bars in existing concrete pier structures is presented in this paper. The objective of the research was to evaluate the effectiveness of calcium nitrite for combating corrosion in marine structures. Five sites were selected for field evaluation of reinforcement corrosion in cooperation with the Harbors Division of the Hawaii Department of Transportation. The concrete for each of these sites included a calcium nitrite-based admixture as a corrosion inhibitor. Each site was tested for permeability, chloride ion concentration, half-cell potential, polarization resistance, and pH. Corrosion activity identified by half-cell potential measurements, polarization resistance measurements, and visual inspection of bars taken from cores indicated that high dosages of calcium nitrite, 19.8 to 22.3?L/m3, provided the steel with significantly greater protection than lower dosages, 12.4?L/m3. This occurred despite the fact that the sites with higher dosages were older and usually more permeable than the structures with lower dosages.     

Simultaneous Determination of Nitrite and Nitrate in Milk Samples by Ion Chromatography Method and Estimation of Dietary Intake

The presence of nitrate and nitrite in foods may be considered hazardous after ingestion in the gastrointestinal tract due to their reaction with naturally occurred secondary amines to form potentially carcinogenic nitrosamines. Due to this fact, a new method was developed in this study for the simultaneous determination of nitrite and nitrate in milk samples using by ion chromatography. Proposed mobile phase composed of sodium hydrogen carbonate and sodium carbonate (1.0 and 3.2 mmol/L) with a flow rate of 0.7 ml/min. The average recoveries for nitrate and nitrite were higher than 86 and 88%, respectively. The limit of detection for nitrate and nitrite were 0.24 and 0.09 mg/L, respectively. The results of 102 real milk samples showed nitrate was found in all of the samples (100%) with a mean of 34 ± 11 mg/L, while nitrite was found in none of the samples. The mean intake of nitrate in all age groups was lower than World Health Organization guideline. The present assessment concludes that the maximum contaminant level was equal to 82.8 mg/L nitrate. This method was fast, sensitive and accurate and is capable of being an alternative method in food control laboratories for investigation of nitrite and nitrate content. This is the first study of the determination and survey of nitrite and nitrate and exposure assessment of the Iranian population to nitrite and nitrate level in milk, which was widely used in infants and adolescents as one of the basic food components.     

In situ FT-infrared investigation of CO or/and NO interaction with CuO/Ce0.67Zr0.33O2 catalysts

In situ FT-IR was employed to investigate CO or/and NO interaction with CuO supported on Ce_0.67Zr_0.33O₂ (hereafter denoted as CZ) catalysts. The physicochemical properties of CuO–CZ were also studied by combination of XRD, TPR and NO + CO activity tests. The results indicated that the dispersed CuO species were the main active components for this reaction. The catalysts showed different activities and selectivities at low and high temperatures, which should be resulted from the reduction of dispersed copper oxide species. This reaction went through different mechanisms at low and high temperatures due to the change of active species. FT-IR results suggested: (1) CO was activated by oxygen originating from CZ support, which led to surface carbonates formation, and partial dispersed CuO was reduced to Cu⁺ species above 150 °C; (2) NO interacted with the dispersed CuO and formed several types of nitrite/nitrate species, whereas crystalline CuO made little contribution to the formation of new NO adsorbates; (3) NO was preferentially adsorbed on CuO–CZ catalysts compared with CO in the reactants mixture. These adsorbed nitrite/nitrate species exhibited different thermal stability and reacted with CO at 250 °C. As a result, a possible mechanism was tentatively proposed to approach NO reduction by CO over CuO–CZ catalyst.     

晋南野菜和蔬菜硝酸盐、亚硝酸盐和维生素C含量分析

目的对山西南部的10种野菜和4种常食用蔬菜的硝酸盐、亚硝酸盐和维生素C含量进行测定。方法硝酸盐含量测定采用镉柱法;亚硝酸盐含量测定采用盐酸萘基乙二胺法;维生素C含量测定采用2,6-二氯酚靛酚滴定法。结果苜蓿、黄瓜和西红柿的硝酸盐含量低于轻度污染水平,亚硝酸盐含量低于亚硝酸盐含量的限量标准,维生素C的含量较低,属于一级蔬菜,可以安全生食;马齿苋、荠菜、蒲公英的硝酸盐含量低于中度污染水平,亚硝酸盐含量低于或相当于亚硝酸盐含量的限量标准,维生素C的含量高或较高,属于二级蔬菜,不宜生食,可盐渍和熟食;苣荬菜、车前草、苦菜、胡萝卜的硝酸盐含量过高,低于重度污染水平,不宜生食和盐渍,可以熟食;藜菜、菠菜、白蒿、地肤的硝酸盐含量高于1234mg/kg,属于高度污染水平,亚硝酸盐含量超过或相当于亚硝酸盐含量限量标准,维生素C的含量高或极高,不宜食用或限量食用。结论大多数供试野菜的各个指标含量均高于栽培蔬菜。     

Effect of freeze-dried leek powder (FDLP) and nitrite level on processing and quality characteristics of fermented sausages

Fermented sausages were produced with 0.84% and 1.68% freeze-dried leek powder (FDLP), providing 75 and 150 mg/kg NaNO₃, respectively, and three levels of added nitrite (0, 75, and 150 mg/kg NaNO₂). A control treatment was also produced with 150 mg/kg NaNO₂. Sausages with FDLP were darker and yellower (p < 0.05) than the control. Higher FDLP levels produced less red, yellower and darker sausages (p < 0.05). Lower FDLP levels resulted in higher (p < 0.05) sensory scores for external appearance, flavour and overall acceptability. No differences were found among the treatments with FDLP plus 75 or 150 ppm NaNO₂ in TBA value, lightness, redness (cross section), redness stability, yellowness, texture parameters and sensory firmness, flavour and overall acceptability. The use of 0.84% FDLP and 75 ppm NaNO₂ is considered more appropriate for the production of fermented sausages, as it results in a 50% reduction in added nitrite.     

Application of the Nitritation and Anammox Process into Inorganic Nitrogenous Wastewater from Semiconductor Factory

The first full-scale nitritation and anaerobic ammonium oxidation (Anammox) processes for an inorganic wastewater of semiconductor factory were installed and performances were evaluated. Existing facilities of conventional nitrification and denitrification were retrofitted to a combination of the nitritation and Anammox process. Novel nitritation method, selective acceleration of ammonia oxidation by high concentration of inorganic carbon, was evaluated in full-scale aeration tank with carrier material. The ammonia conversion rate of the nitritation reactor was in the range of 0.27–0.48?kg?NO2-N/m3?day after start-up period, and stable nitritation was achieved for over 10 months. In an Anammox reactor, on-site cultivation of anammox bacteria was performed, and the most plausible reason for slower nitrogen conversion at the beginning was oxygen contamination into the reactor. After minimizing influence of oxygen contamination, design loading was achieved within 3 months of operation. After start-up period, stable Anammox reactions are maintained for over 10 months. The nitrogen removal rate after start-up period was in the range of 1.04–3.29?kg?N/m3?day. In combination with conventional denitrification process, soluble nitrogen in the final effluent was reduced below 8 mg/L.     

Electrochemically Assisted Photocatalytic Oxidation of Nitrite over Cr‐Doped TiO2 under Visible Light

To investigate the photocatalytic oxidation (PCO) of nitrite ions under visible light, Cr‐doped TiO₂ supported on a titanium plate was used as a photoelectrode operated under anodic bias potential. The results showed that applying bias potential (E_appl) played an important role in the PCO of NO₂^–. Without bias potential the PCO reaction could not be initiated due to the rapid recombination rate of the photogenerated carriers, but when the potential was larger than 1.2 V (vs. saturated calomel electrode, SCE) the removal efficiency of NO₂^– increased up to 90 % within 3 h for an initial concentration of 8 mg L^–1. Zero‐order kinetics were observed at E_appl = 0.4 V (vs. SCE), while pseudo first order kinetics were found at E_appl ≥ 0.8 V (vs. SCE). The effects of the initial concentration of NO₂^–, initial solution pH, the gas atmosphere, and cathodic reaction on the PCO of NO₂^– were studied as well. Furthermore, the PCO mechanism of NO₂^– was investigated by using tert‐butyl alcohol or benzoic acid as a diagnostic probe. It showed that the PCO of NO₂^– under visible light most probably proceeded indirectly via OH radicals, not directly via the valence‐band holes.