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Ecological effects of combined pollution associated with e-waste recycling on the composition and diversity of soil microbial communities Jun Liu, Xiao-Xin He, Xue-Rui Lin, Wen-Ce Chen, Qi-Xing Zhou, Wensheng Shu, and Li-Nan Huang Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/es5049804 • Publication Date (Web): 28 Apr 2015 Downloaded from http://pubs.acs.org on May 3, 2015
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Environmental Science & Technology
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Ecological effects of combined pollution associated with e-waste recycling on the
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composition and diversity of soil microbial communities
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Jun Liu,†,# Xiao-xin He,†,# Xue-rui Lin,‡ Wen-ce Chen,† Qi-xing Zhou,§ Wen-sheng Shu,†
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Li-nan Huang*,†
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†
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Conservation of Guangdong Higher Education Institutes, College of Ecology and Evolution,
State Key Laboratory of Biocontrol, Key Laboratory of Biodiversity Dynamics and
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Sun Yat-sen University, Guangzhou 510275, PR China
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‡
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Guangzhou 510655, PR China
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§
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Tianjin Key Laboratory of Environmental Remediation and Pollution Control, College of
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Environmental Science and Engineering, Nankai University, Tianjin 300071, PR China
South China Institute of Environmental Sciences, Ministry of Environmental Protection,
Key Laboratory of Pollution Processes and Environmental Criteria (Ministry of Education),
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#
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*Corresponding author
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College of Ecology and Evolution, Sun Yat-sen University, Guangzhou 510275, PR China
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Tel.: +86 20 39332933
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Fax: +86 20 39332944
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E-mail:
[email protected] These authors contributed equally to this work
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ABSTRACT: The crude processing of electronic waste (e-waste) has led to serious
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contamination in soils. While microorganisms may play a key role in remediation of the
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contaminated soils, the ecological effects of combined pollution (heavy metals,
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polychlorinated biphenyls and polybrominated diphenyl ethers) on the composition and
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diversity of microbial communities remain unknown. In this study, a suite of e-waste
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contaminated soils were collected from Guiyu, China, and the indigenous microbial
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assemblages were profiled by 16S rRNA high-throughput sequencing and clone library
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analysis. Our data revealed significant differences in microbial taxonomic composition
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between the contaminated and the reference soils, with Proteobacteria, Acidobacteria,
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Bacteroidetes and Firmicutes dominating the e-waste-affected communities. Genera
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previously identified as organic pollutants-degrading bacteria, such as Acinetobacter,
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Pseudomonas and Alcanivorax, were frequently detected. Canonical correspondence analysis
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revealed that approximately 70% of the observed variation in microbial assemblages in the
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contaminated soils was explained by eight environmental variables (including soil
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physiochemical parameters and organic pollutants) together, among which moisture content,
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decabromodiphenyl ether (BDE-209) and copper were the major factors. These results
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provide the first detailed phylogenetic look at the microbial communities in e-waste
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contaminated soils, demonstrating that the complex combined pollution resulting from
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improper e-waste recycling may significantly alter soil microbiota.
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Environmental Science & Technology
INTRODUCTION
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Discarded or unused electrical and electronic devices, generally referred to as electronic
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waste (e-waste), are an increasingly important environmental problem worldwide. It has been
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estimated that globally about 40 million tons of e-waste are generated each year,(1) with an
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increasing rate of 4% per year.(2) The United States Environmental Protection Agency
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estimates that only 15-20% of e-waste can be recycled while the remaining parts are often
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disposed of in landfills.(3) However, e-waste typically contains high levels of toxic substances
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such as organic pollutants (e.g. polychlorinated biphenyls (PCBs) and polybrominated
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diphenyl ethers (PBDEs)) and heavy metals (e.g. lead, zinc, copper and cadmium);(2) if
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disposed of improperly, these hazardous substances pose a serious threat to the environment
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and human health.(2) Notably, most e-waste has been transported to developing countries, in
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particular China, where these waste materials are processed extensively (e.g. burning and
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scouring) for recovery of precious metals and the residues are improperly discarded.(4) These
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practices have caused serious pollution problems for air, terrestrial and aquatic
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environments.(4)
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Microbes drive the bulk of Earth’s biogeochemical cycles and are crucial to the functioning
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of virtually all ecosystems. However, microbes and especially their metabolic activities are
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sensitive to environmental change. Numerous studies have demonstrated that environmental
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pollution may cause drastic changes in microbial community composition and activity,(5, 6)
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or have found significant correlations between microbial diversity and contamination
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gradients.(7, 8) Typically, pollution could result in a decrease of microbial diversity and
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enrichment of tolerant species via the process of environmental filtering; this in turn may
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affect their overall ecosystem function.(5) On the other hand, microorganisms may be actively
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involved in the degradation and transformation of various pollutants and play a crucial role in
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the remediation of polluted environments.(9)
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In the past two decades, the influence of heavy metal contamination on soil microbial
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communities has attracted much attention,(5, 7, 10, 11) and many species (e.g. Pseudomonas
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spp., Acinetobacter spp. and Sphingomonas spp.) resistant and tolerant to heavy metals (e.g.
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copper, zinc and cadmium) have been isolated.(5, 12) Meanwhile, recent research has focused
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on investigating bacterial community composition in soils polluted by toxic organic
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pollutants(13-15) and obtaining in pure culture functional bacteria (e.g. Acinetobacter spp.,
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Pseudomonas spp. and Alcanivorax spp.) capable of degrading PBDEs, PCBs and polycyclic
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aromatic hydrocarbons.(16-18) Subsequently, the mechanisms of microbial degradation in
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these bacteria have been studied, which will help improve degradative capabilities for the
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bioremediation of polluted environments.(19-21) Furthermore, some laboratory studies have
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examined both single and combined influences of individual metals or individual organic
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compounds on soil microbial assemblages.(22-24) However, field studies with a specific
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focus on the effects of combined pollution (e.g. PBDEs and heavy metals, and PCBs and
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heavy metals) on the indigenous microorganisms have been very limited.(13, 15, 25)
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Improper e-waste processing could result in heavy metal and toxic organic compound
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contamination in soil.(2) However, the responses of soil microbiota as a whole community to
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the combined pollution (including PCBs, PBDEs and heavy metals) and its ecological
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consequences have not been explored. Here, we report an in-depth and comprehensive survey
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of the microbial assemblages from a suite of soils contaminated by uncontrolled e-waste
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recycling activities. Microbial populations were profiled by both Illumina high-throughput
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sequencing and clone library analysis targeting the 16S rRNA genes that were then
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taxonomically analyzed. Specifically, we aimed to elucidate the composition and diversity of
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microbes in the e-waste affected soils and examine how microbial assemblages are shaped by
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the environmental conditions.
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MATERIALS AND METHODS
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Site Description and Sample Collection. Guiyu, a town with a total area of 52 km2 and a
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population of 400,000 in Guangdong Province, China, has been a booming e-waste
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processing center since 1995.(26) Due to crude e-waste recycling activities in a large number
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of simple household e-waste recycling workshops, the air, water and soil have been heavily
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contaminated by toxic organic compounds and heavy metals.(2, 26) In November 2011,
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representative contaminated soil samples were collected in triplicate at a depth of 0-10 cm
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from two e-waste dumping sites (Dump-1 and Dump-2), two e-waste burning sites (Burn-1
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and Burn-2), one acid stripping site (Acid-strip), one contaminated farmland site (Farmland)
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and one contaminated mudflat site near the Lianjiang river (Mudflat) (Figure 1). For
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comparison, triplicate samples were also collected from each of the five corresponding
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reference soil types (Dump_ck, Burn_ck, Acid-strip_ck, Farmland_ck and Mudflat_ck) that
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were well apart in the upstream direction from the contaminated sites and thus unlikely
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affected by e-waste. All samples were kept in cooler boxes during sampling and then
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transported to the laboratory where they were stored at 4 °C prior to processing (within 48 hrs)
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for subsequent analyses (see below).
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Physicochemical Analyses. Moisture content was determined by weighing subsamples
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before and after oven-drying at 105 °C for 24 h. Samples were air-dried and sieved to
