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Microbial Ecology of Contaminated Farmland Around E-Waste Recycling Sites

Author: ChenLiTao
Tutor: ChenYingXu
School: Zhejiang University
Course: Microbiology
Keywords: Electrical and electronic waste Dismantling PCBs Soil Microbial Ecology Microbial community structure
CLC: X705
Type: Master's thesis
Year: 2007
Downloads: 218
Quote: 2
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Abstract

The rapid increase of the number of electrical and electronic products led to the generation of a large number of electrical and electronic waste, also gave birth to the recycling of electrical and electronic waste dismantling industry, without specification of electrical and electronic waste dismantling caused serious pollution to the surrounding environment . Contamination of heavy metals and PCBs (polychlorinated biphenyls, PCBs) and other persistent organic pollutants is one of the more prominent issues, the presence of these pollutants pose a serious threat to environmental safety and public health. In-depth understanding of the interaction between pollutants and soil microbial communities, help to understand the potential risks of these pollutants and their migration and transformation in the soil, but also to provide valuable information for the contaminated soil biological repair . The project from two PCBs spill had occurred typical electrical and electronic waste dismantling point (dryland areas D and paddy field area P) around contaminated farmland soil samples were collected and analysis including heavy metals, PCBs and organochlorine pollutants content and distribution, and the integrated use of traditional research methods of microbial ecology and PCR-DGGE, molecular cloning techniques to study the pollution caused due to the dismantling of farmland soil microbial ecology, the main conclusions are as follows: (1) D zone and P zone are subject to a certain degree of heavy metal contamination. D regional Cd content exceeded the national soil environmental quality three standard doubled, Cu, Pb, Zn concentration exceeds the national soil environmental quality standards. From the dismantling of the center point of the nearest point D1 has been a very serious Pb, Zn pollution were more than three national standard 2-fold and 5-fold. P regional Cd content is also more than doubled three national standards, the Cu content exceeds the national secondary standard, also slight Zn, Pb pollution. (2) D dismantling point near the soil PCBs pollutants average concentration of 1.31mg · kg ^{-1 , highest concentration of 1.67mg · kg ^{-1 . Than prescribed by the Committee of Environment Canada has the potential threats to the concentration of 6 times, the ecological risk is very high. With the increase from the dismantling of the distance from the center, the downward trend of the concentration of PCBs in the soil. The average concentration of the the P sample area of ??PCBs 9.70μg · kg ^{-1 , low ecological risk. D dryland sampling area PCBs mainly to three, four, five, six chlorinated PCBs P sample area of ??rice fields by four, five, six chlorinated PCBs based. Speculated D region may have been dismantling made with the low chlorine PCBs and imports capacitors containing high chlorine PCBs, the P region mainly main dismantling imports capacitor. Two sampling areas organochlorine pesticide residues, but its concentration is low, the average concentration of the D region of BHC and DDT were 22.4μg · kg ^{-1 and 0.5μg · kg < sup> -1 P region, the average concentration of BHC and DDT for 16.3μg kg ^{-1 and 6.6 μg · kg ^{-1 organochlorine pesticide residues in the soil has undergone a remarkable transformation. (3) Correlation analysis showed that the levels of pollutants between D regional upland soil PCBs and Cu, Cd content has a significant correlation between the content of Zn and Pb. PCBs and Cu, Cd, is likely to have the same origin, Zn and Pb contaminants from another kind dismantling matter. P zone paddy significant correlation, Cu and Zn, the main heavy metal pollutants Cd and Pb might have the same source has a significant correlation, Pb and Cd, Cu and Zn may be derived from another type of dismantling thereof. (4) soil respiration and enzyme activity analysis showed that dryland sample area, as close to the center point to the dismantling of the soil microbial activity has been enhanced, possible causes of PCBs on microbial metabolic stimulation. Dryland urease activity and the content of Cu, Cd has a significant negative correlation between the activity of the decline may be of Cu, result of Cd heavy metal. Urease is more sensitive to heavy metal pollutants, may be more suitable for the evaluation of the impact of the heavy metal contaminated soil. In the sample area of ??rice fields, the intensity of soil respiration and activity of the three enzymes was fluctuated major pollutants Cd, Cu, of OCPs and PCBs there is no significant correlation between this may be because of the lower concentration of various pollutants , had no significant effect on soil microbial activity. (5) Tablet separation count With a growing trend towards the the dismantling center point near the number of upland soil bacteria and actinomycetes, DGGE spectra Shannon for index analysis shows that the upward trend of soil bacterial diversity diversity of actinomycetes downward trend; principal component analysis of DGGE map display, with close to dismantling the center point, the greater the difference of soil bacteria and actinomycetes community structure characteristics of the control points, which may be caused by gradient distribution of pollutants such as PCBs and Cu. Each sampling point the number of bacteria and actinomycetes homogeneous area of ??rice fields, the fluctuations in the number of fungi, bacteria and actinomycetes Shannon index is more consistent, some differences in community structure, but no significant change in trend. (6) The specific dryland areas soil DGGE profiles with cloning and sequencing, and phylogenetic analysis. Clone sequence obtained for analysis found that most of the clones are all Proteobacteria door (Proteobacteria) and Bacteroides door (Bacteroidetes), and clones of the two taxa found in a large number of possible PCBs, polycyclic aromatic hydrocarbons degradation of organic pollutants, benzene analogues closely related microbial groups, but did not find microbial groups associated with heavy metal pollutants. This shows that these two microbial groups may play an important role in the microbial ecosystem contaminated by PCBs, and may have an important role in the conversion of PCBs pollutants in soil and metabolic. PCBs have a more significant impact of pollutants on soil microbial community structure.}}}}}}

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