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821.
Liang T Zhang S Wang L Kung HT Wang Y Hu A Ding S 《Environmental geochemistry and health》2005,27(4):301-311
With the continual increase in the utilization of rare earth elements (REEs) for industrial and agricultural purposes in China,
the research into the environmental biogeochemical behavior of REEs has become a pressing issue. The REEs’ content in soil
and various parts of wheat under different conditions in soil–plant systems were measured by INAA and ICP-MS. The results
showed four aspects. (1) The mean value of total REEs in soil of China was 176.8 mg kg−1. The mean ratio of ΣLREE/ΣHREE in soils was 8.0 and cerium accounts for 42% of the total REEs. The content of REEs in wheat
seed ranged between 10−11 and 10−8 g g−1, 3–4 orders of magnitude lower than that in soil. (2) The REEs contents in ryegrass, especially in roots, were significantly
related to that of soil. The bioavailability of REEs in soil mainly depended on the exchangeable fraction of REEs, which was
strongly affected by the physico–chemical properties of the soil. (3) Long-term foliage-dressing with Changle microfertilizer
of REEs did not affect the contents and distribution patterns of REEs in soil. At the maturing stage of spring wheat, the
REEs content was in the order of root > leaf >stem and crust. Compared with the control, foliage-dressing has a higher accumulation
of REEs in root and leaf. However, no significant difference was found in stem and crust between the two treatments. (4) There
was no significant accumulation with the soil-dressing method. When comparing controls in both foliage- and soil-dressing
methods, no distinct residue of REEs in grains was found. 相似文献
822.
针对传统Pasveer氧化沟内缺氧段碳源难以被反硝化菌充分利用的问题,采用内置缺氧区的改良型Pasveer氧化沟工艺,并进行中试规模实验研究,考察了不同内回流比条件下系统的脱氮除磷效果。研究结果表明,在内回流比为200%的情况下,系统的脱氮除磷效果最好,出水TN和TP的浓度分别降至12.7 mg/L和0.34 mg/L,去除率分别达到61.9%和89.2%。内置缺氧区的设置一方面能使有限的碳源充分用于反硝化,另一方面,促使了反硝化吸磷现象的发生,这使得系统在进水碳源较低的情况下仍能够获得上佳的脱氮除磷效果。但是,过高的内回流比会导致好氧区亚硝酸盐的积累,这对生物除磷是不利的。 相似文献
823.
本文介绍了投加粉未活性炭的活住污泥法的一般流程和作用机理。该法具有改善出水水质、提高抗冲击负荷能力、加强硝化作用、改善污泥况降性、能较好地脱色、脱臭、消除泡沫等优点。对活性炭的生物再生可能性进行了探讨。简单介绍了有关PACT法的模型的发展和应用性。 相似文献
824.
Level and distribution of DDT in surface soils from Tianjin, China 总被引:28,自引:0,他引:28
Gong ZM Tao S Xu FL Dawson R Liu WX Cui YH Cao J Wang XJ Shen WR Zhang WJ Qing BP Sun R 《Chemosphere》2004,54(8):1247-1253
One hundred and eighty eight surface soil samples were collected from the Tianjin area to study the contamination of DDT and its metabolites. Measurements were taken for p,p'-DDE, p,p'-DDD, p,p'-DDT, o,p'-DDE, o,p'-DDD and o,p'-DDT for all samples. The results indicated that p,p'-DDT and p,p'-DDE were the predominant contaminant compounds in the surface soil samples, with mean concentrations of 27.5 and 18.8 ng g(-1) respectively. No significant differences in DDT concentrations were found between the soils from wastewater treated irrigated areas and other areas, suggesting that wastewater irrigation is not an important source of DDT in the area. However, the spatial distribution of soil DDTs levels in the area did correlate well with early direct application rates of pesticides. In addition, both pH level and organic carbon content are also known factors affecting the level of DDT and its metabolites. Although it was assumed that the use of these chemicals was banned in the early 1980s, the current concentration levels appear to be too high to be mere residuals after 20 years degradation. 相似文献
825.
Taihu Lake is the third largest freshwater lake in China. Taihu Basin is one of the most densely populated and urbanized areas in this country. This area provides 15% of the GDP. Meiliang Bay is located in the north part of the Lake. It provides the municipal water source for Wuxi City. Some parts of the lake have been found to be highly polluted due to eutrophication for over a decade. Surface water (0-0.5 m) samples were collected from the Meiliang Bay by the aid of Global Position System (GPS) for positioning. Water samples were concentrated 5000 times with XAD-2 resin columns. A reverse mutation test using histidine-dependent Salmonella typhimurium strains was employed to assay the genotoxicity of the samples. The results showed that the sample from position 6 had the highest genotoxicity either in the case of activating with eucaryotic S9 system or without S9. The genotoxic effect included, at least, two different molecular mechanisms: nucleotide point substitution on DNA molecules and reading frame shifting caused by nucleotide insertion or deletion. The genotoxicity of the water body in Meiliang Bay, Taihu Lake should be kept in close monitoring. 相似文献
826.
Actions and interactions of heavy metals (cadmium, zinc and plumbum) and polycyclic aromatic hydrocarbons (PAHs) [phenanthrene, fluoranthene, benzo(a)pyrene] on the soil urease and dehydrogenase activity were studied after 49 days exposure. The experimental approach was based on the uniform design which can cut the experiment time and improve the efficiency of experiments. Data treatment was essentially based on the multiple regression technique. The results showed that the action and interaction between heavy metals and PAHs were strongly dependent on the time of pollution. The dehydrogenase exhibits more sensitive to the combined pollution than urease. The negative interaction between Zn and Cd to hydrogenase activity and the combined stimulatory activity of Phenanthrene and Benzo(a)pyrene (or fluoranthene) to soil enzyme were observed. The interactions between Zn (Cd) and phenanthrene towards urease (dehydrogenase) were positive, and the interaction between Zn and benzo(a)pyrene to urease activity was negative. This study corresponds to exploratory phase in order to reveal interaction effects of heavy metals and PAHs on the soil enzyme and then to set up more in-depth analysis to increase progressively the understanding of the ecotoxicological mechanisms involved. 相似文献
827.
828.
829.
环境质量评价中若干评价方法的比较 总被引:10,自引:2,他引:10
探讨了目前用于环境质量评价的若干方法--模糊综合评判法,灰色聚类法,灰关联分析方法及改进形式,物元分析方法及改进形式的共点与异点,指出要推求一种适合环境质量评价实际的方法尚有大量工作要做。 相似文献
830.