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排序方式: 共有199条查询结果,搜索用时 15 毫秒
81.
Zhong Q Veeneman RA Steinecker WH Jia C Batterman SA Zellers ET 《Journal of environmental monitoring : JEM》2007,9(5):440-448
The adaptation of a portable gas chromatograph (GC) prototype with several unique design features to the determination of vapor-phase markers of environmental tobacco smoke (ETS) is described. This instrument employs a dual-stage adsorbent preconcentrator, two series-coupled separation columns that can be independently temperature programmed, and a detector consisting of an array of nanoparticle-coated chemiresistors, whose response patterns are used together with retention times for vapor recognition. An adsorbent pre-trap was developed to remove semi-volatile organics from the sample stream. Conditions were established to quantitatively capture two ETS markers, 2,5-dimethylfuran (2,5-DMF) and 4-ethenylpyridine (4-EP, as a surrogate for 3-EP), and to separate them from the 34 most prominent co-contaminants present in ETS using ambient air as the carrier gas. A complete analysis can be performed every 15 min. Projected detection limits are 0.58 and 0.08 ppb for 2,5-DMF and 4-EP, respectively, assuming a 1 L sample volume, which are sufficiently low to determine these markers in typical smoking-permitted environments. 相似文献
82.
Continuous, intermittent and passive sampling of airborne VOCs 总被引:1,自引:0,他引:1
Long sampling periods are often advantageous or required for measuring air quality and characterizing exposures. However, sampling periods exceeding 8 to 24 h using thermally desorbable adsorbent tube (TDT) samplers for the measurement of airborne volatile organic compounds (VOCs) face several challenges, including maintaining stable and low flow rates, and avoiding breakthrough of the adsorbent. These problems may be avoided using intermittent sampling; however, the literature contains few if any reports that have evaluated this technique in environmental, occupational or other applications. The purpose of this study is to evaluate continuous, intermittent and passive sampling methods using both laboratory and real-world tests. Laboratory tests compared continuous and intermittent (active) samplers in a controlled dynamic test gas generation system. Field tests used side-by-side active and passive samplers in an office, home workshop and four smokers' homes. All samples were analyzed for a wide range of VOCs by GC-MS. In most instances, intermittent sampling yielded better reproducibility (duplicate precision of 10 +/- 6%) than continuous low-flow sampling (18 +/- 5%), in part due to difficulty maintaining low flows. Concentrations obtained using intermittent sampling agreed with those for continuous sampling, with downward biases resulting primarily from errors in flow rate measurements. In the field, more VOC species were detected using active rather than passive sampling. Passive measurements were 12% lower than continuous measurements, a difference attributed to declining uptake rates at higher concentrations over the 3 to 4 d sampling period. Overall, most measurements obtained using the three sampling methods agreed within 20% for a wide range of concentrations (0.1 to 230 microg m(-3)). Both passive and intermittent sampling approaches are suitable for long sampling periods, but intermittent sampling provides greater flexibility with respect to sampling period, and permits the use of multi-bed adsorbents that can capture a wider range of VOCs. 相似文献
83.
Batterman S Chernyak S Gwynn E Cantonwine D Jia C Begnoche L Hickey JP 《Chemosphere》2007,69(3):444-457
While few environmental measurements of brominated diphenyl ethers (BDEs) were completed prior to the mid-1990s, analysis of appropriately archived samples might enable the determination of contaminant trends back to the introduction of these chemicals. In this paper, we first investigate the stability of BDEs in archived frozen and extracted fish samples, and then characterize trends of these chemicals in rainbow smelt (Osmerus mordax) and lake trout (Salvelinus namaycush) in each of the Great Lakes between 1979 and 2005. We focus on the four most common congeners (BDE-47, 100, 99 and 153) and use a change-point analysis to detect shifts in trends. Analyses of archived fish samples yielded precise BDE concentration measurements with only small losses (0.8% per year in frozen fish tissues, 2.2% per year in refrigerated extracts). Trends in fish from all Great Lakes showed large increases in BDE concentrations that started in the early to mid-1980s with fairly consistent doubling times (generally 2-4 years except in Lake Erie smelt where levels increased very slowly), though concentrations and trends show differences by congener, fish species and lake. The most recent data show that accumulation rates are slowing, and concentrations of penta- and hexa-congeners in trout from Lakes Ontario and Michigan and smelt from Lake Ontario started to decrease in the mid-1990s. Trends in smelt and trout are evolving somewhat differently, and trout concentrations in the five lakes are now ranked as Michigan>Superior=Ontario>Huron=Erie, and smelt concentrations as Michigan>Ontario>Huron>Superior>Erie. The analysis of properly archived samples permits the reconstruction of historical trends, congener distributions, biomagnification and other information that can aid the understanding and management of these contaminants. 相似文献
84.
土壤-水稻体系中污染重金属的迁移及其对水稻的影响 总被引:62,自引:1,他引:62
在温室条件下通过水稻盆栽试验,研究了植物对添加Pb、Cd、Cu、Zn等重金属的吸收.结果表明,供试元素的迁移受本身的性质、交互作用、添加量以及土壤吸持强度所影响.植物对Pb、Cd、Cu、Zn的吸收系数与用等温吸附方程所表示的土壤吸附强度和金属元素的第一级水解常数值有关.离子冲量与稻谷产量的关系表明,它有可能作为一种污染总量控制指标,反映了总量控制中“有效态”的重要性. 相似文献
85.
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88.
Information regarding the distribution of volatile organic compound (VOC) concentrations and exposures is scarce, and there have been few, if any, studies using population-based samples from which representative estimates can be derived. This study characterizes distributions of personal exposures to ten different VOCs in the U.S. measured in the 1999-2000 National Health and Nutrition Examination Survey (NHANES). Personal VOC exposures were collected for 669 individuals over 2-3 days, and measurements were weighted to derive national-level statistics. Four common exposure sources were identified using factor analyses: gasoline vapor and vehicle exhaust, methyl tert-butyl ether (MBTE) as a gasoline additive, tap water disinfection products, and household cleaning products. Benzene, toluene, ethyl benzene, xylenes chloroform, and tetrachloroethene were fit to log-normal distributions with reasonably good agreement to observations. 1,4-Dichlorobenzene and trichloroethene were fit to Pareto distributions, and MTBE to Weibull distribution, but agreement was poor. However, distributions that attempt to match all of the VOC exposure data can lead to incorrect conclusions regarding the level and frequency of the higher exposures. Maximum Gumbel distributions gave generally good fits to extrema, however, they could not fully represent the highest exposures of the NHANES measurements. The analysis suggests that complete models for the distribution of VOC exposures require an approach that combines standard and extreme value distributions, and that carefully identifies outliers. This is the first study to provide national-level and representative statistics regarding the VOC exposures, and its results have important implications for risk assessment and probabilistic analyses. 相似文献
89.
满江红花青素在镉胁迫下的抗氧化作用 总被引:2,自引:1,他引:1
为了研究镉胁迫诱导满江红体内花青素合成的生理功能,采用镉诱导和体外实验的方法评价了满江红体内花青素的抗氧化作用.测试指标包括还原力、清除超氧阴离子(O-2)、过氧化氢(H2O2)、羟自由基(·OH)的能力.结果表明,花青素的还原力和对氧自由基的清除作用随花青素提取物浓度的增加而增加.因此,镉胁迫下合成的花青素是一种清除活性氧自由基的良好抗氧化剂.镉胁迫对满江红活性氧代谢影响的试验结果表明,在0.5mg·L-1Cd胁迫下,满江红体内O-2和H2O2大量积累,造成活性氧胁迫,说明花青素只能在一定程度上保护满江红免受过氧化伤害.本实验初步证实,花青素含量的增加是满江红抗性机理之一,可缓解镉的毒害. 相似文献
90.