Abstract
Heavy metal pollution that results from electronic waste (e-waste) recycling activities has severe ecological environmental toxicity impacts on recycling areas. The distribution of heavy metals and the impact on the bacteria in these areas have received much attention. However, the diversity and composition of the microbial communities and the characteristics of heavy metal resistance genes (HMRGs) in the river sediments after long-term e-waste contamination still remain unclear. In this study, eight river sediment samples along a river in a recycling area were studied for the heavy metal concentration and the microbial community composition. The microbial community consisted of 13 phyla including Firmicutes (ranging from 10.45 to 36.63%), Proteobacteria (11.76 to 32.59%), Actinobacteria (14.81 to 27.45%), and unclassified bacteria. The abundance of Firmicutes increased along with the level of contaminants, while Actinobacteria decreased. A canonical correspondence analysis (CCA) showed that the concentration of mercury was significantly correlated with the microbial community and species distribution, which agreed with an analysis of the potential ecological risk index. Moreover, manually curated HMRGs were established, and the HMRG analysis results according to Illumina high-throughput sequencing showed that the abundance of HMRGs was positively related to the level of contamination, demonstrating a variety of resistance mechanisms to adapt, accommodate, and live under heavy metal-contaminated conditions. These findings increase the understanding of the changes in microbial communities in e-waste recycling areas and extend our knowledge of the HMRGs involved in the recovery of the ecological environment.
Highlights
Electronic waste (e-waste) recycling has been a global issue for more than 10 years
This study is an effort to focus on heavy metal resistance genes (HMRGs) using a metagenomic approach, which might be technologically helpful for comprehensive characterization of microbial heavy metal resistance in an environment and the relationship between HMRGs and heavy metal contaminants
The concentrations of the various heavy metals in the different sediment samples are presented in Supplementary Table 3
Summary
Electronic waste (e-waste) recycling has been a global issue for more than 10 years. many related countries have strict restrictions on movements of e-waste and their disposal, illegal small e-waste recycling workshops have still developed and are densely distributed in some towns of developed countries due to the economic profits and the less stringent environmental. These e-waste recycling activities have inevitably resulted in severe environmental pollution (Robinson, 2009; Song and Li, 2014), such as in the towns of Longtang and Guiyu in southern China, two of the most famous e-waste recycling sites in the world (Zhang W. et al, 2012; Liu et al, 2018; Wu et al, 2019) In these areas, the typical pollutants, including polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins, polybrominated diphenyl ethers (PBDEs), and especially heavy metals, are released into local aquatic and terrestrial ecosystems, inducing the overexpression of resistance genes through the change of microbial communities in soils or sediments (Luo et al, 2011; Chen S.J. et al, 2014). This study is an effort to focus on HMRGs using a metagenomic approach, which might be technologically helpful for comprehensive characterization of microbial heavy metal resistance in an environment and the relationship between HMRGs and heavy metal contaminants
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