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排序方式: 共有233条查询结果,搜索用时 15 毫秒
51.
Xiaoqing Ye Wuye Pan Chunming Li Xiaochen M Shanshan Yin Jianhong Zhou Jing Liu 《环境科学学报(英文版)》2020,32(5):1-9
Polycyclic aromatic hydrocarbons (PAHs) are a typical class of persistent organic pollutants that is ubiquitous worldwide. Previous animal studies suggested that PAHs had adverse effects on female reproduction. However, the human data regarding relationship of PAHs exposure with women reproductive health, such as ovarian dysfunction, are scarce. In this case-control study, the associations of serum levels of PAHs with the risk of premature ovarian failure (POF) and reproductive hormones in Chinese women were investigated, with recruiting 157 POF patients and 217 healthy women. The serum levels of 12 types of PAHs, as well as reproductive hormones, including follicle-stimulating hormone, luteinizing hormone and anti-mullerian hormone, were determined. In the logistic regression models, most individual PAH congeners showed significantly positive correlations with the risk of POF (p < 0.05), except for fluorine and pyrene. Benzo(a)pyrene (BaP), as the most carcinogenic PAH congener, was observed to be significantly positively associated with the risk of POF. After adjustment for age, body mass index, educational levels and household income, per one-unit increase in the log-transformed BaP concentration was significantly correlated with 2.191-fold increased risk of POF (OR = 2.191, 95%CI: 1.634–2.938, p < 0.05). To the best of our knowledge, this is the first study to report an association between internal exposure levels of PAHs and the increased risk of POF in women. 相似文献
52.
Homogeneous formation of polychlorinated dibenzothiophenes/thianthrenes(PCDT/TAs),sulfurated compounds analogous to polychlorinated dibenzo-p-dioxin/dibenzofurans(PCDD/Fs), has been well-documented to occur via radical–radical coupling reactions from chlorinated thiophenol precursors. However, the current understanding of the formation mechanism of PCDT/TAs is exclusively limited to the inherent point of view that chlorothiophenoxy radicals act as the only required intermediates for PCDT/TAs. This study investigates reaction pathways for the formation of PCDT/TAs involving two new types of radical species, i.e., substituted phenyl radicals and substituted thiophenoxyl diradicals. Taking 2-chlorothiophenol(2-CTP) as a model compound for chlorothiophenols,we found that apart from the mostly discussed chlorothiophenoxy radicals, substituted phenyl radicals and substituted thiophenoxyl diradicals could also be readily formed via the reaction of 2-CTP with H radicals. Furthermore, direct self-and cross-coupling of these radicals can result in the formation of PCDT/TAs, including 1-monochlorothianthrene(1-MCTA), 1,6-dichlorothianthrene(1,6-DCTA), 4,6-dichlorodibenzothiophene(4,6-DCDT)and 1,6-dichlorodibenzothiophene(1,6-DCDT). The pathways proposed in this work are proven to be both thermodynamically and kinetically favorable. Particularly, comparisons were made between the formation mechanisms of sulfurated and oxygenated dioxin systems from an energetic point view, showing that replacing oxygen with sulfur atoms greatly reduces the activation barriers of the rate-controlling steps involved in the PCDT/TA formation processes compared with those involved for PCDD/Fs. The calculated results in this work may improve our understanding of the formation mechanism of PCDT/TAs from chlorothiophenol precursors and should be informative to environmental scientists. 相似文献
53.
通过对历史资料的搜集、整理和分析,对鄂尔多斯高原东南部榆林地区清代(1644-1911年)蝗灾的变化规律、蝗灾等级、发生条件及其预测进行了研究。结果表明,在清代的268a里,鄂尔多斯高原东南部地区共发生蝗灾16次,平均每16.8 a发生1次。该区清代中期是蝗灾较少发生期,早期和晚期为蝗灾较多发生期。在晚期阶段1850-1879年间的30a里,平均4.3a发生1次,且蝗灾规模大而严重,为蝗灾大爆发期。该区的蝗灾主要是由当地生长的蝗虫造成的,少数规模较大的蝗灾是省外蝗虫迁移至该区造成的。研究地区夏蝗和秋蝗发生较多,并且夏蝗发生次数略高于秋蝗。该区清代发生最多的是中度蝗灾,其次为轻度蝗灾,重度蝗灾发生最少。降水量与蝗灾发生频次的相关系数较气温的大,降水偏少年易于发生蝗灾,轻度和中度旱灾是蝗虫猖獗的最佳条件,大旱和特大干旱并不利于蝗灾发生。根据鄂尔多斯高原东南部地区清代蝗灾发生的自然条件预测,在该区降水偏少年,特别是夏季出现轻度、中度旱灾的年份容易发生蝗灾,这时要加强蝗灾的预防。 相似文献
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山东省地下水资源分布不均,各地开发利用程度差别较大.本文论述了近年来该省地下水在开发利用过程中存在的问题及其对环境的影响,提出了合理开发地下水资源的对策与措施. 相似文献
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58.
Multivariate statistical characterization of water quality in Lake Lanier, Georgia, USA 总被引:1,自引:0,他引:1
Watershed monitoring programs depend on water quality characterization data collected for many parameters, at many times and places, and with limited resources. Our objective is to present a strategy that reduces the measured parameters, locations, and frequency without compromising the quality of the monitoring program. One year of twice-monthly (growing season) and monthly (dormant season) water quality data collected from 17 lake and 10 tributary sites are used in conjunction with multivariate statistical techniques to improve the utility of collected data by identifying key parameters and monitoring locations. Factor analysis shows that tributary water quality data consists of three components-stormwater runoff, municipal and industrial discharges, and ground water-which can be distinguished using total suspended solids, total dissolved solids, and alkalinity plus soluble reactive P, respectively. Lake water quality characterization is more ambiguous than tributary water quality characterization, but factor analysis indicates that anoxia associated with lake stratification is the largest source of lake water quality variation, followed by nutrient abundance, and finally by biomass abundance. Cluster analysis suggests that tributary and lake monitoring stations can be consolidated. Reducing the number of parameters and stations frees up resources for increased monitoring elsewhere. 相似文献
59.
不同演替阶段中黧蒴栲种群的大小结构与分布格局 总被引:16,自引:0,他引:16
在中亚热带常绿阔叶林,有代表性地选择三个黧蒴栲群落类型,即黧蒴栲纯林(常绿阔叶林皆伐地自然演替而成的黧蒴栲纯林,用生长锥对优势木进行随机抽查得其最大年龄为13a)、以黧蒴栲为优势种的混交林(经优势木随机抽测其最大年龄为24a)和黧蒴栲已不成为优势种的混交林(实为天然次生林,优势木随机抽测最大年龄为53a)。测定分析结果表明,黧蒴栲群落在自然演替的前期即幼林阶段的种群大小级结构呈典型的三角状增长型; 相似文献
60.