Effect of cooking on the formation of N-nitrosodimethylamine in Korean dried seafood products

Only N-nitrosodimethylamine (NDMA) was detected when N-nitrosamines (NA) were analysed in seven dried seafood products, either uncooked or cooked. The cooking methods used were a briquet fire, a gas range, an electric oven, a microwave oven, a steam cooker and an electric coil cooker. The contents of NDMA ranged from 1.0 to 46.9 μg kg^-1 in uncooked products. When these samples were cooked, regardless of the cooking method, the content of NDMA tended to increase, ranging from 1.1 to 630.5 μg kg^-1. In general, indirect heating such as a steam cooker and a microwave oven, as compared with direct heating such as a gas range and a briquet fire, caused less increase in NDMA during cooking.     

Fate of N-nitrosodimethylamine in recycled water after recharge into anaerobic aquifer

Laboratory and field experiments were undertaken to assess the fate of N-nitrosodimethylamine (NDMA) in aerobic recycled water that was recharged into a deep anaerobic pyritic aquifer, as part of a managed aquifer recharge (MAR) strategy. Laboratory studies demonstrated a high mobility of NDMA in the Leederville aquifer system with a retardation coefficient of 1.1. Anaerobic degradation column and ¹⁴C-NDMA microcosm studies showed that anaerobic conditions of the aquifer provided a suitable environment for the biodegradation of NDMA with first-order kinetics. At microgram per litre concentrations, inhibition of biodegradation was observed with degradation half-lives (260 ± 20 days) up to an order of magnitude greater than at nanogram per litre concentrations (25-150 days), which are more typical of environmental concentrations. No threshold effects were observed at the lower ng L⁻¹ concentrations with NDMA concentrations reduced from 560 ng L⁻¹ to <6 ng L⁻¹ over a 42 day ¹⁴C-NDMA aerobic microcosm experiment.Aerobic ¹⁴C-NDMA microcosm studies were also undertaken to assess potential aerobic degradation, likely to occur close to the recharge bore. These microcosm experiments showed a faster degradation rate than anaerobic microcosms, with a degradation half-life of 8 ± 2 days, after a lag period of approximately 10 days.Results from a MAR field trial recharging the Leederville aquifer with aerobic recycled water showed that NDMA concentrations reduced from 2.5 ± 1.0 ng L⁻¹ to 1.3 ± 0.4 ng L⁻¹ between the recharge bore and a monitoring location 20 m down gradient (an estimated aquifer residence time of 10 days), consistent with data from the aerobic microcosm experiment. Further down gradient, in the anaerobic zone of the aquifer, NDMA degradation could not be assessed, as NDMA concentrations were too close to their analytical detection limit (<1 ng L⁻¹).     

砂滤前置或后置对消毒副产物生成潜能的影响

采用常规一深度处理工艺处理东太湖原水,对比砂滤前置与后置对各工艺流程出水消毒副产物生成潜能去除效果的影响。研究发现,无论砂滤前置还是后置,生物活性炭工艺对有机物都有着良好的去除效果,整套工艺出水COD和uV。的去除率分别稳定在74．2％～87．1％和75．0％～80．2％。两套工艺对二甲基亚硝胺生成潜能（NDMAFP）的去除效果没有明显差别,出水NDMAFP降低35％～41％。砂滤前置工艺对三卤甲烷生成潜能（THMFP）和卤乙酸生成潜能（HAAFP）的控制效果优于砂滤后置工艺,砂滤前置工艺活性炭单元出水和砂滤后置工艺砂滤单元出水的THMFP分别降低31．0％～37．4％和28．2％～35．3％,HAAFP分别降低20．0％～24．6％和16．3％～23．2％。     

Glutamate receptor-mediated restoration of experience-dependent place field expansion plasticity in aged rats.

Place fields of hippocampal pyramidal cells expand asymmetrically when adult rats repeatedly follow the same route. This behaviorally induced expression of neuronal plasticity uses an NMDAR-dependent, LTP-like mechanism and could be used by hippocampal networks to store information. Aged spatial memory-impaired rats exhibit defective experience-dependent place field expansion plasticity. One possible explanation for this aged-associated deficit is alterations in glutamatergic function. In fact, both NMDAR- and AMPAR-mediated field excitatory postsynaptic potentials in CA1 decrease with aging. The current study investigated whether modulation of either AMPA or NDMA receptor activity could restore this experience-dependent plasticity by prolonging AMPAR activity with the ampakine CX516 and modulating the NMDAR with the noncompetitive antagonist memantine. The spatial firing characteristics of multiple CA1 pyramidal cells were monitored under both treatment conditions as aged rats repeatedly traversed a circular track. Compared to the saline baseline condition, acute administration of memantine, but not CX516, reinstated experience-dependent place field expansion. Taken together, these data suggest that pharmacological manipulation of the NMDAR can improve the function of hippocampal networks critical to optimal cognition in aging. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

偏二甲肼大气氧化生成亚硝基二甲胺(NDMA)的机理

为确定大气中偏二甲肼(UDMH)转化为亚硝基二甲胺(NDMA)的反应路径,采用量子化学方法对UDMH在大气中氧化生成NDMA的反应机理进行了研究,在B3LYP/6-311+G(d,p)和M06-2X/6-311+G(d,p)水平上对反应体系的反应物、中间体、过渡态及产物进行了几何构型优化和频率计算,在CCSD(T)/aug-cc-pVTZ水平下进行单点能校正,构筑了反应的势能剖面。结果表明,UDMH氧化反应引发的过程是一个脱氢或加氧过程;考虑到大气中氧化剂(HO·/O_3/O_2)的浓度,不同氧化剂引发UDMH反应速率的比例关系为v(O_3)≈10~4×v(HO·)≈10~8×v(O_2)。因此UDMH在大气氧化的引发过程中最主要是被O_3氧化,UDMH摘除氢原子后生成中间体(CH_3)_2NN(H)·(IM1)。IM1在大气环境中HO·、HO_2·及O_3作用下都可以转化为NDMA,臭氧参与过程将降低反应活化能,促进NDMA在大气中生成。     

NDMA在水处理过程中产生与去除的研究进展

N-亚硝基二甲胺是近年来新发现的强致癌性消毒副产物,已引起水处理界的广泛关注。本文综述了NDMA的基本特性、在水处理过程中的产生机制以及去除的研究进展,并在此基础上对今后的研究方向进行了展望,提出研发经济高效地去除NDMA的工艺是亟待解决的问题。     

N-nitrosodimethylamine (NDMA) as a product of potassium permanganate reaction with aqueous solutions of dimethylamine (DMA)

The reactivity of permanganate with dimethylamine, as possible path of NDMA formation, has been investigated.The results have shown that potassium permanganate reaction with aqueous solutions of dimethylamine (DMA) leads to the formation of N-nitrosodimethylamine (NDMA). The contact time, the molar ratio of permanganate and DMA, pH and presence of nitrite are the key factors influencing the efficiency of NDMA formation. Significant conversion rates of DMA to NDMA were observed only for the high doses of permanganate, which were many times higher than those typically used in water treatment. This reaction however is of importance for water treatment technology, since it shows the possibility of NDMA formation as a result of oxidation of DMA.It is likely that nitrosation is the main path of the reaction. An important role of MnO₂ suspension, formed as a result of permanganate reduction in NDMA formation is emphasized. Significant influence of MnO₂ suspension on NDMA formation should draw our attention to the potential impact of MnO₂ activated filtration beds on NDMA formation.     

固相微萃取法检测啤酒中的N-亚硝基二甲胺

N-亚硝基二甲胺（NDMA）是一种高致癌物质,它在啤酒中以痕量水平存在。本文利用顶空取样及气相色谱质谱检测联用技术,建立了一种检测啤酒中NDMA的固相微萃取方法。文中选用聚二甲基硅氧烷／二乙烯基苯（PDMS—DVB）萃取纤维,借助因子实验设计,对平衡时间、离子强度、萃取时间和萃取温度进行了评价。此方法的线性、重现性、检测限和定量限良好。通过标准添加法和内标法相结合的方法对啤酒中的NDMA进行定量分析。     

Solid-phase microextraction of N-nitrosodimethylamine in beer

N-nitrosodimethylamine (NDMA) is a highly active carcinogen that has been detected in trace levels in beers. Solid-phase microextraction (SPME) was used to develop a method for the extraction of NDMA from beer using headspace sampling and gas chromatography with mass spectrometry detection. Polydimethylsiloxane/divinylbenzene (PDMS–DVB) fibres were used to evaluate the influence of equilibrium time, ionic strength, extraction time and temperature by means of a factorial design. The method was validated calculating the linearity, reproducibility, limit of detection and limit of quantification. The method was applied to the quantitative analysis of NDMA combining the standard addition method with an internal standard method.     

在钴/氧化铝(Co/Al_2O_3)上臭氧催化降解水体中痕量N-亚硝基二甲胺(NDMA)

在实验室的间歇反应器中研究了在Al_2O_2和Co/Al_2O_3催化剂上臭氧催化降解水体中N-亚硝基二甲胺(NDMA)的效果,结果表明两种催化剂的添加显著地提高了NDMA的降解效率。主要试验参数的研究表明:Co/Al_2O_3的投加量、臭氧的投加量、温度等试验参数对于降解率有很大影响;当单位体积溶液中催化剂Co/Al_2O_3的投加量为167 mg/L、臭氧的投加量为3 mg/L时可以获得最佳的降解效果。随着温度的升高,NDMA降解去除率逐渐升高,当反应温度由283 K升高到323 K时,在Al_2O_3和Co/Al_2O_3上NDMA的降解效率分别由17.4%、55.4%提高到69.4%、82.5%。另外,在催化剂上添加K元素可明显提高Co/Al_2O_3臭氧催化降解NDMA的效率。