Influence of heavy metals and PCBs pollution on the enzyme activity and microbial community of paddy soils around an e-waste recycling workshop

Spatial distribution and health risks assessment of heavy metals in e-waste dumping sites from Pakistan

The present study focused on to determine the concentration and health risk of heavy metals (Cu, Pb, Zn, Cd, Hg, Cr) in e-waste contaminated soils collected from different provinces of Pakistan. Further, the impact of heavy metals on soil enzyme activities and microbial community was also investigated. The concentration (mg/kg) of Hg, Zn, Fe, Cu, Pb, Cd, and Cr ranged between 0-0.258, 2.284-6.587, 3.005-40.72, 8.67-36.88, 12.05-35.03, 1.03-2.43, and 33.13-60.05, respectively. The results revealed that Lahore site of Punjab province indicated more concentration of heavy metals as compared to other sites. The level of Cr at all sites whereas Hg at only two sites exceeds the World Health Organization standards (WHO) for soil. Soil enzyme activity exhibited dynamic trend among the sites. Maximum enzyme activity was observed for urease followed by phosphatase and catalase. Contamination factor (Cf), Pollution load index (PLI), and geo-accumulation index (Igeo) results showed that all the sites are highly contaminated with Cu, Cd, and Pb. Hazard index (HI) was less than 1 for children and adults suggesting non-carcinogenic health risk. Principle component analysis results depicted relation among Cr, Fr, catalase, and actinomycetes; Cd, OM, urease, and bacteria, and Pb, Cu, Zn, Hg, and phosphatase, suggesting soil enzymes and microbial community profiles were influenced by e-waste pollution. Therefore, there is a dire need to introduce sustainable e-waste recycling techniques as well as to make stringent e-waste management policies to reduce further environmental contamination.

Pot experimental trial for assessing the role of different composts on decontamination and reclamation of a polluted soil from an illegal dump site in Southern Italy using Brassica juncea and Sorghum bicolor

A pot experiment was carried out to evaluate the remediation potential of Brassica juncea and Sorghum bicolor in the decontamination of soil polluted with heavy metals such as copper, lead, tin, and zinc along with polychlorinated biphenyls, polycyclic aromatic hydrocarbons, and heavy hydrocarbons. Two composts obtained from different composting processes were tested as biostimulating agents. At the end of the trial, the effect of plant/compost combinations on soil microbial composition, contaminant removal, biochemical indicators, and plant biomass production was determined. The results highlighted that compost addition improved plant biomass despite slowing down plants' removal of organic and inorganic contaminants. In addition, compost partially enhanced the soil biochemical indicators and modified the relative abundance of the rhizosphere microorganisms. Sorghum showed better mitigation performance than Brassica due to its higher growth. The soil fertility level, the choice of plant species, and microbial richness were found fundamental to perform soil remediation. In contrast, compost was relevant for a higher crop biomass yield.

Ecological and human health risk assessment of heavy metals based on their source apportionment in cropland soils around an e-waste dismantling site, Southeast China

An accurate understanding of soil heavy metal (HM) pollution characteristics and source apportionment, and a recognition of the major factors influencing ecological and human health risks (HHRs) are essential for soil HM pollution control and remediation. In this study, 212 surface soils (0-20 cm) and 15 profile soils (0-100 cm) were collected from cropland soils around an e-waste dismantling site in Taizhou city, Zhejiang Province, China. Spatial analysis was used to evaluate the pollution characteristics of HMs (Cd, Cu, Pb, Zn, Cr and Ni). Principal component analysis (PCA) and positive matrix factorization (PMF) were also conducted to quantify their source contributions. A modified source-oriented HHR assessment integrated source-oriented ecological risk and source-oriented HHR assessment was developed to describe the major factors that influenced HHR. Results showed that 94.81 %, 88.21 %, 36.79 % and 47.17 % of Cd, Cu, Pb and Zn, respectively, in surface soils exceeded their screening values in the soil environmental quality standard for agricultural soils (GB 15618-2018). Spatial analysis indicated that high values of Cd, Cu, Pb and Zn were distributed near the e-waste dismantling site. The results of PCA and PMF showed that the primary sources of HMs in the study area are e-waste dismantling activities, natural sources and atmospheric deposition, which contribute 27 %, 46 % and 27 % of HM pollutants, respectively. The results of source-oriented ecological risk and HHR assessment indicated that e-waste dismantling activities and natural sources were primary sources for ecological risk and HHR. However, source-oriented HHR assessment may underestimate the contribution of e-waste dismantling activities by ignoring HM pollution levels. The modified source-oriented HHR assessment highlights that e-waste dismantling activities were major factor that affect noncarcinogenic risk. This study could provide important data support for subsequent environmental remediation of soil HM pollution in cropland soils around e-waste dismantling sites.

Spatial variation of heavy metals and their ecological risk and health risks to local residents in a typical e-waste dismantling area of southeastern China

There is an increasing concern that soils in e-waste recycling regions are severely contaminated by unregulated e-waste dismantling activities. Hence, it is urgent to reveal the spatial variation of hazardous elements in arable lands close to e-waste stacking and dismantling areas and their potential risks to human beings. We collected 349 topsoil samples based on an intensive grid of 100 m × 100 m in southeastern China. The average concentrations of heavy metals were 1.25 (Cd), 35.44 (Ni), 77.68 (Cr), 77.38 (Pb), 122.14 (Cu), 203.39 (Zn), 0.21 (Hg), and 4.74 (As) mg kg^-1, respectively. Compared to the risk screening values of hazardous elements in Chinese agricultural land, Cd and Cu were severely accumulated in the soils. The results of ecological risk analysis revealed that Cd posed the crucial risk among the studied elements. However, the levels of non-carcinogenic and carcinogenic risk were still within the acceptable quantity for adults. Spatial distribution by kriging interpolation displayed that the heavy metals were mainly distributed close to e-waste dismantling sites.

Chemical remediation and advanced oxidation process of polychlorinated biphenyls in contaminated soils: a review

Polychlorinated biphenyls (PCBs) are synthetic organic compounds ubiquitously distributed worldwide due to their persistence, long-range atmospheric transport, and bioaccumulation. Owing to teratogenic properties, PCBs are a global environmental problem. Different physical, biological, and chemical techniques are utilized for the remediation of PCBs. This review paper discusses the recent development in photocatalytic and chemical techniques for the remediation of PCBs in contaminated soils. In particular, the photocatalytic degradation of PCBs combined with soil washing, Fe-based reductive dichlorination, and advanced oxidation process (Fenton advance oxidation and persulfate oxidation) is discussed and reviewed in detail. The review suggested that advanced oxidation is an efficient remediation technique with 77-99% of removal efficiency of PCBs. Persulfate oxidation is the most suitable technique which could work at normal environmental conditions (such as pH, temperature, soil organic matter (SOM), etc.). Different environmental factors such as pH, temperature, and SOM affect the Fe-based reductive dechlorination and Fenton advance oxidation techniques. The surfactants and organic solvents used in soil washing combined with photocatalytic degradation affect the degradation capability of these techniques. This review will contribute to PCBs degradation by the detailed discussion of development in chemical technique future perspective and research needs.

Forty years studies on polychlorinated biphenyls pollution, food safety, health risk, and human health in an e-waste recycling area from Taizhou city, China: a review

E-waste generation has become a serious environmental challenge worldwide. Taizhou of Zhejiang Province, situated on the southeast coastline of China, has been one of the major e-waste dismantling areas in China for the last 40 years. In this review, we focused on the polychlorinated biphenyl (PCB) trends in environmental compartments, burden and impact to humans, food safety, and health risk assessment from Taizhou, China. The review suggested that PCBs showed dynamic trends in air, soil, water, biodiversity, and sediments. Soils and fish samples indicated higher levels of PCBs than sediments, air, water, and food items. PCB levels decreased in soils with the passage of time. Agriculture soils near the e-waste recycling sites showed more levels of total PCBs than industrial soils and urban soils. Dioxin-like PCB levels were higher in humans near Taizhou, suggesting that e-waste pollution could influence humans. Compared with large-scale plants, simple household workshops contributed more pollution of PCBs to the environment. Pollution index, hazard quotient, and daily intake were higher for PCBs, suggesting Taizhou should be given priority to manage the e-waste pollution. The elevated body burden may have health implications for the next generation. The areas with stricter control measures, strengthened laws and regulations, and more environmentally friendly techniques indicated reduced levels of PCBs. For environment protection and health safety, proper e-waste dismantling techniques, environmentally sound management, awareness, and regular monitoring are very important.

Biotreatment potential of co-contaminants hexavalent chromium and polychlorinated biphenyls in industrial wastewater: Individual and simultaneous prospects

Co-existence of polychlorinated biphenyls (PCBs) and hexavalent chromium (Cr(VI)) in the environment due to effluent from industries has aggravated the pollution problem. Both contaminants can alter chemical interactions, processes and impair enzymatic activities in the ecosystem that results in negative impacts on aquatic and terrestrial life. Previously, research has been performed for the fate and transfer of these contaminants individually, but simultaneous removal approaches have not received much attention. Cr(VI) exists in a highly toxic form in the environment once released, whereas location of chlorine atoms in the ring determines PCBs toxicity. Lower chlorinated compounds are easily degradable whereas as high chlorinated compounds require sequential strategy for transformation. Microorganisms can develop different mechanism to detoxify both pollutants. However, occurrence of multiple contaminants in single system can alter the bioremediation efficiency of bacteria. Use of metal resistance bacterial for the degradation of organic compounds has been widely used bioaugmentation strategy. Along with that use of sorbents/bio sorbents, biosurfactants and phytoremediation approaches have already been well reported. Bioremediation strategy with dual potential to detoxify the Cr(VI) and PCBs would be a probable option for simultaneous biotreatment. Application of bioreactors and biofilms covered organic particles can be utilized as efficient bioaugmentation approach. In this review, biotreatment systems and bacterial oxidative and reductive enzymes/processes are explained and possible biotransformation pathway has been purposed for bioremediation of co-contaminated waters.

Expatiating the impact of anthropogenic aspects and climatic factors on long-term soil monitoring and management

This article is an extensive collection of scientific literature related to the impact of fertilizers on soil microbial and enzymatic activity. Due to the significance of technology in quantitative and qualitative evaluation of agricultural production, this is a basic problem for the present and future of mankind, where the scientific data being of utmost importance related to the topic. The comparison, including pedo-enzymological evaluation of minerals along with organic fertilization, highlights significant differences between mineral and organic fertilizers, confirming the superiority of complex mineral-organic fertilization. Enzymatic indicators that describe and define the soil quality resulted from enzymatic activities value and provide valuable information regarding the soil fertility status. Moreover, soil enzyme responds to soil management as well as to environmental pollutants. Changes of environmental conditions and pollutants like heavy metals and other toxic substances result in a shift in the biological activity of the soil. These changes can destabilize the soil system and cause a decrease in the nutrient pools. To ensure the improvement of fertilization techniques, the properties of nanoparticles are exploited that can efficiently release nutrients to plant cells. Numerous researches were performed in order to follow the long-term effects of incorporating nanofertilizers into the soil, obtaining an exhaustive overview of this new technology over the development of sustainable agriculture.

Global occurrence, chemical properties, and ecological impacts of e-wastes (IUPAC Technical Report)

The waste stream of obsolete electronic equipment grows exponentially, creating a worldwide pollution and resource problem. Electrical and electronic waste (e-waste) comprises a heterogeneous mix of glass, plastics (including flame retardants and other additives), metals (including rare Earth elements), and metalloids. The e-waste issue is complex and multi-faceted. In examining the different aspects of e-waste, informal recycling in developing countries has been identified as a primary concern, due to widespread illegal shipments; weak environmental, as well as health and safety, regulations; lack of technology; and inadequate waste treatment structure. For example, Nigeria, Ghana, India, Pakistan, and China have all been identified as hotspots for the disposal of e-waste. This article presents a critical examination on the chemical nature of e-waste and the resulting environmental impacts on, for example, microbial biodiversity, flora, and fauna in e-waste recycling sites around the world. It highlights the different types of risk assessment approaches required when evaluating the ecological impact of e-waste. Additionally, it presents examples of chemistry playing a role in potential solutions. The information presented here will be informative to relevant stakeholders seeking to devise integrated management strategies to tackle this global environmental concern.

Cadmium influences the litter decomposition of Solidago canadensis L. and soil N-fixing bacterial communities

It is important to illuminate the effects of litter decomposition of invasive alien species on soil N-fixing bacterial communities (SoNiBa), especially under heavy metal pollution to better outline the mechanisms for invasion success of invasive alien species. This study attempts to identify the effects of litter decomposition of Solidago canadensis L. on SoNiBa under cadmium (Cd) pollution with different concentrations (i.e., low concentration, 7.5 mg/kg soil; high concentration, 15 mg/kg soil) via a polyethylene litterbags-experiment. Electrical conductivity and total N of soil were the most important environmental factors for determining the variations of SoNiBa composition. S. canadensis did not significantly affect the alpha diversity of SoNiBa but significantly affect the beta diversity of SoNiBa and SoNiBa composition. Thus, SoNiBa composition, rather than alpha diversity of SoNiBa, was the most important determinant of the invasion success of S. canadensis. Cd with 15 mg/kg soil did not address distinct effects on alpha diversity of SoNiBa, but Cd with 7.5 mg/kg soil noticeably raised the number of species and species richness of SoNiBa mainly due to the hormonal effects. The combined S. canadensis and Cd with 15 mg/kg soil obviously decreased cumulative mass losses and the rate of litter decomposition (k) of S. canadensis, but the combined S. canadensis and Cd with 7.5 mg/kg soil evidently accelerated cumulative mass losses and k of S. canadensis. Thus, Cd with 7.5 mg/kg soil can accelerate litter decomposition of S. canadensis, but Cd with 15 mg/kg soil can decline litter decomposition of S. canadensis.

Associations between metal exposure and global DNA methylation in potentially affected people in E-Waste recycling sites in Taizhou City, China

Electronic waste (e-waste) has been an emerging environmental health issue, and it has already provoked all aspects of attention. Taizhou is one of the three largest e-waste recycling locations in China. Atpresent, to prevent the environmental problems stem from e-waste dismantling, the local government has shut down all the industries in 2015. In this study, we collected blood samples of residents living near e-waste dismantling factories, and in matched reference areas in Taizhou, in December 2017, after the factories have been shut down for two years. Twenty-five metals were quantified in all blood samples. Among them, the concentrations of As, Ni, Ag, La, and Ce were statistically significant higher in individuals in e-waste recycling locations than those in reference location. Global DNA methylation was measured in blood as a marker of human health. Pearson correlation and multiple linear regression analysis between the changed metals and global DNA methylation in blood were performed. The result showed that only blood Ce was negatively correlated with global DNA methylation level significantly in pre-workers exposed e-waste workers (r = -0.51, p = 0.01). Our findings indicated that high concentrations of exposure to Ce in e-waste dismantling site could have sustained effects on the DNA methylation in blood although the e-waste industry had been closed for 2 years.

Endophyte: Understanding the Microbes and its Applications

The ability of endophytes to colonize every plant tissue has led to the opportunity of using the microorganism in a lot of biological applications. Endophytes are beneficial to their host cells as such its application is observed in every aspects of life. This study therefore endeavored to give an analysis of endophytes, what they were and what they had been used for till the present time. Sampling of several literature studies in endophytes was done in this study to enable a complete understanding of the mechanism of application of the actions of endophytes, so as to be able to do a thorough assessment of the current state in the knowledge of the microbes. From the complete analysis of the literature on the application and use of endophytes, in nutrient asquition and increase the stress tolerance in plants. This study provided a platform for further research gaps through the presentation of what endophytes were, what they had been used for till date, the mechanism of operation of the micro-organism and the type of interaction between them and their hosts. There are still ways to improve on the methods of application of endophytes as a type of biological organism. This will be done by adjusting to the current trends in biological studies using molecular mechanization, following an intensive further study on endophyte mechanisms.

The correlation study between PCBs and δ15N values or FAs in fish collected from Dongting Lake

The toxicity of polychlorinated biphenyls (PCBs) and their transformation have been intensively investigated in recent years. However, the potential mechanisms of biotransformation in a lake food web remain unclear. To explore the correlation between the PCBs and δ¹⁵N values or FAs, six fish species were collected from Dongting Lake, and various tissues were dissected to analyze the δ¹⁵N values, FAs and PCBs. Based on the wet weight (ww), the concentration of ∑PCBs₁₁₅ ranged from 0.04 to 9.77 ng g^-1, and the highest level was found in the gonad of Cyprinus carpio. The toxicity equivalent (TEQ) of PCBs ranged from 0.003 to 2.39 pg g^-1, and the highest level was found in the fat of Silurus asotusy. The PCB levels in fish collected from Dongting Lake were at the low end of the global range. PCB28, 52, 95, 99, 101, 105 110, 118, 138, 153, 155 and 209 were found in all tissues. PCBs were distributed in a tissue-specific and species-specific manner in fish. PCB153 and 138 had a positive correlation with the TEQ in liver, gill, intestine and skin of fish on the basis of lipid weight (lw). Docosahexaenoic acid/eicosapentaenoic acid (DHA/EPA) and polyunsaturated fatty acid/saturated fatty acid (PUFA/SFA) had a positive correlation with some PCB congeners in the intestine. PCB52, ∑tetra-PCBs and Ind-PCBs had a positive correlation with the δ¹⁵N values in liver of fish on the basis of ww. PUFA/SFA and DHA/EPA might be indicators for the transfer of PCB congeners.

Effects of soil properties, heavy metals, and PBDEs on microbial community of e-waste contaminated soil

Heavy metals and polybrominated diphenyl ethers (PBDEs) are ubiquitous pollutants at electronic waste (e-waste) contaminated sites, their individual impacts on soil microbial community has attracted wide attention, however, limited research is available on the combined effects of heavy metals and PBDEs on microbial community of e-waste contaminated. Therefore, combined effects of heavy metals and PBDEs on the microbial community in the e-waste contaminated soil were investigated in this study. Samples were collected from Ziya e-waste recycling area in Tianjin, northern China, and the soil microbial communities were then analyzed by the high-throughput MiSeq 16S rRNA sequencing to assess the effects of soil properties, heavy metals, and PBDEs on the soil microbial community. Candidatus Nitrososphaera, Steroidobacter and Kaistobacter were the dominant microbial species in the soils. Similar microbial metabolic functions, including amino acid metabolism, carbohydrate metabolism and membrane transport, were found in all soil samples. Redundancy analysis and variation partition analysis revealed that the microbial community was mainly influenced by PBDEs (including BDE 183, BDE 99, BDE 100 and BDE 154) in horizontal soil samples. However, TN, biomass, BDE 100, BDE 99 and BDE 66 were the major drivers shaping the microbial community in vertical soil samples.

Vertical profile of soil/sediment pollution and microbial community change by e-waste recycling operation

The present study aims to assess the effect of electronic waste (e-waste) recycling on microbial community and the underlying modulation mechanism. Core soil/sediment samples were collected from an abandoned e-waste burning site and neighboring farmland/stream sites in Guiyu, China. High concentrations and health risks of toxic heavy metals, particularly, Sb and Sn, and halogenated flame retardants (HFRs), including decabromodiphenyl ether (BDE 209) and decabromodiphenyl ethane (DBDPE) were mostly retained at the top surface layers of soils/sediments (0-30cm) after more than one year of natural vertical diffusion and microbe-facilitated biodegradation. Heavy metals, such as Ag, Cd, Cu, Pb, Sb, and Sn, played a critical role for the reduction of microbial diversity. This is the first study reporting the open burning of e-waste caused an obvious heat effect and enriched thermophilic/mesophilic microbes in local area. The acid washing during e-waste recycling process may result in the enrichment of acidophilic microbes. This investigation showed that e-waste processing operation resulted in not only severe pollution of the soils/sediments by various pollutants, but also reduction of microbial diversity that was difficult to self-store by the local ecosystem.

Effects of Pretreatment Methods of Wheat Straw on Adsorption of Cd(II) from Waterlogged Paddy Soil

Two types of pretreatment categories, namely microwave-assisted alkalization and microwave-assisted acid oxidation, were used to synthesize novel wheat straw adsorbents for the effective removal of Cd(II) in simulated waterlogged paddy soil. A systematic adsorption behavior study, including adsorption kinetics and adsorption isotherms was conducted. Results showed that wheat straw pretreated by microwave-assisted soaking of NaOH and ethanol solution obtained the highest Cd(II) removal efficiency of 96.4% at a reaction temperature of 25 ℃, pH of 7.0, initial Cd(II) concentration of 50 mg/L, and adsorbent/adsorbate ratio of 10 g/L. Sequential extraction experiment was carried out to analyze the changes of different of Cd(II) in soil, the aim of which was to study the mobility of Cd(II) and then evaluate the toxicity that Cd(II) might bring to plants. A 60-day incubation was performed to investigate the dynamic variations of soil pH and dissolved organic carbon content over incubation time. Characterization analyses revealed the morphological changes of wheat straw adsorbents, which suggested that those pretreatment methods were of significance. This study provided an environmentally friendly way to reuse agricultural wastes and remedy Cd(II) contaminated soil.

Ecological and health risks assessment and spatial distribution of residual heavy metals in the soil of an e-waste circular economy park in Tianjin, China

Ziya Circular Economy Park is the biggest e-waste recycle park in North China before 2011, its function was then transformed in response to regulations and rules. In this paper, investigation was conducted to research the residual concentrations of 14 analytes (12 heavy metals and 2 non-metals) in the surface soil of Ziya Circular Economy Park and surrounding area. Both ecological and health assessments were evaluated using GI (geo-accumulation index) and NPI (Nemerow pollution index), and associated health risk was assessed by using USEPA model. According to the ecological risk assessment, Cu, Sb, Cd, Zn and Co were seriously enriched in the soil of the studied area. The health risk assessment proposed by USEPA indicated no significant health risks to the population. Soil properties, such as pH and organic matter, were found to correlate with the enrichment of heavy metals. Arsenic concentrations in the soil were found positively correlated to dead bacteria concentrations. Spatial distribution of heavy metals revealed that Ziya Circular Economy Park was the dominant pollution source in the studied area. Findings in this study suggest that enough attention should be payed to the heavy metal pollution in Ziya Circular Economy Park.

Rhizospheric effects on the microbial community of e-waste-contaminated soils using phospholipid fatty acid and isoprenoid glycerol dialkyl glycerol tetraether analyses

We performed the study of rhizospheric effects on soil microbial community structure, including bacteria, fungi, actinomycete, and archaea, at an electronic waste (e-waste) recycling site by analyzing the phospholipid fatty acid (PLFA) and isoprenoid glycerol dialkyl glycerol tetraether (GDGT) contents. By comparing PLFA and isoprenoid GDGT profiles of rhizospheric and surrounding bulk soils of 11 crop species, we observed distinct microbial community structures. The total PLFA concentration was significantly higher in rhizospheric soils than in non-rhizospheric soils, whereas no obvious difference was found in the total isoprenoid GDGT concentrations. The microbial community structure was also different, with higher ratios of fungal-to-bacterial PLFAs (F/B) and lower relative abundance of Gram-positive bacteria in rhizospheric soils. The extent of rhizospheric effects varied among plant species, and Colocasia esculenta L. had the greatest positive effects on the total microbial biomass. Dissolved organic carbon and pH were the main environmental factors affecting the microbial community represented by PLFAs, while the archaeal community was influenced by copper and zinc in all soils. These results offer a comprehensive view of rhizospheric effects on microbes in heavy metal and persistent organic pollutant co-contaminated soil, and provide fundamental knowledge regarding microbial ecology in e-waste-contaminated soils.

Assessment on cadmium and lead in soil based on a rhizosphere microbial community

The soil ecosystem is easily polluted by heavy metals. Cadmium (Cd) and lead (Pb), as the main pollutants of heavy metals, cause much harm to the soil ecosystem. However, the impact of the two chemicals on rhizosphere microorganisms remains almost unknown. The change of catalase (CAT) activity was consistent with the microbial biomass. 16S rRNA gene sequencing was performed on soil samples to study the toxic effect of heavy metals. On performing sequence analysis at the phylum and family taxonomic levels, 32 identified phyla and 303 families were observed. The dominant phylum was Proteobacteria followed by Bacteroidetes, Acidobacteria, and Actinobacteria. The relative abundance of the dominant phyla was obviously changed under the stress of Cd and Pb, suggesting that the heavy metal input had affected the microbial community structure. At the Order and Family levels, there was different variation of richness and diversity in Cd and Pb group as compared to those in the control group. Furthermore, abundance and similarity analysis showed the differences between Cd and Pb, indicating different toxicology effect on rhizosphere microbial communities because of the unique properties. This study provided a novel insight into the composition of microbial communities of rhizosphere, which could be used to evaluate the soil environment.

Diversity and distribution of 16S rRNA and phenol monooxygenase genes in the rhizosphere and endophytic bacteria isolated from PAH-contaminated sites

This is the first investigation of the diversity and distribution of 16S rRNA and phenol monooxygenase (PHE) genes in endophytic and rhizosphere bacteria of plants at sites contaminated with different levels of PAHs. Ten PAHs at concentrations from 34.22 to 55.29 and 45.79 to 97.81 mg·kg⁻¹ were measured in rhizosphere soils of Alopecurus aequalis Sobol and Oxalis corniculata L., respectively. The diversity of 16S rRNA and PHE genes in rhizosphere soils or plants changed with varying PAH pollution levels, as shown based on PCR-DGGE data. Generally, higher Shannon-Weiner indexes were found in mild or moderate contaminated areas. A total of 82 different bacterial 16S rRNA gene sequences belonging to five phyla; namely, Acfinobacteria, Proteobacteria, Chloroflexi, Cyanophyta, and Bacteroidetes, were obtained from rhizosphere soils. For the 57 identified PHE gene sequences, 18 were excised from rhizosphere bacteria and 39 from endophytic bacteria. The copy numbers of 16S rRNA and PHE genes in rhizosphere and endophytic bacteria varied from 3.83 × 10³ to 2.28 × 10⁶ and 4.17 × 10² to 1.99 × 10⁵, respectively. The copy numbers of PHE genes in rhizosphere bacteria were significantly higher than in endophytic bacteria. Results increase our understanding of the diversity of rhizosphere and endophytic bacteria from plants grown in PAH-contaminated sites.

Ecological effects of combined pollution associated with e-waste recycling on the composition and diversity of soil microbial communities

The crude processing of electronic waste (e-waste) has led to serious contamination in soils. While microorganisms may play a key role in remediation of the contaminated soils, the ecological effects of combined pollution (heavy metals, polychlorinated biphenyls, and polybrominated diphenyl ethers) on the composition and diversity of microbial communities remain unknown. In this study, a suite of e-waste contaminated soils were collected from Guiyu, China, and the indigenous microbial assemblages were profiled by 16S rRNA high-throughput sequencing and clone library analysis. Our data revealed significant differences in microbial taxonomic composition between the contaminated and the reference soils, with Proteobacteria, Acidobacteria, Bacteroidetes, and Firmicutes dominating the e-waste-affected communities. Genera previously identified as organic pollutants-degrading bacteria, such as Acinetobacter, Pseudomonas, and Alcanivorax, were frequently detected. Canonical correspondence analysis revealed that approximately 70% of the observed variation in microbial assemblages in the contaminated soils was explained by eight environmental variables (including soil physiochemical parameters and organic pollutants) together, among which moisture content, decabromodiphenyl ether (BDE-209), and copper were the major factors. These results provide the first detailed phylogenetic look at the microbial communities in e-waste contaminated soils, demonstrating that the complex combined pollution resulting from improper e-waste recycling may significantly alter soil microbiota.