E-waste is discarded and shipped mostly to developing countries located in Asian continent for disposal from other developed countries. Especially 70% of the world's e-waste ends up in Guiyu, a small ...town located in Guangdong Province of China. As little as 25% is recycled in formal recycling centers with adequate protection for workers and the other e-waste arrived in those areas is not handled in organized manner. As per reports only roughly 12.5% of e-waste is actually recycled, and the recycling efforts in those regions are primitive and result in toxic substances being leached into the surrounding ecosystems. In addition to persistent organic pollutants, there are many heavy metals found in the ground and river sediments in Guiyu, exceeding the threshold set to protect human health. Those areas are no longer suitable for growing food, and water is unsafe for drinking, due to the amount of toxins leached into the groundwater and land. Hazardous threats to environment and human health due to hazardous substances of e-waste all around China, as well as the current e-waste management were documented in this review. The article concludes with controlled contamination sources, and eco-friendly and efficient remediation technologies to solve e-waste problem in China.
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•E-waste represents a major health and environmental threat, especially in Asian countries.•Only 25% of e-waste is recycled in formal recycling centers with adequate protection for workers.•Most of e-waste pollutants leached into the land and water, and release toxic substances.•Effective e-waste management and its eco-remediation technologies are important.
Microbial carbonate precipitation is known as an efficient process for the remediation of heavy metals from contaminated soils. In the present study, a urease positive bacterial isolate, identified ...as Bacillus cereus NS4 through 16S rDNA sequencing, was utilized on a large scale to remove nickel from industrial soil contaminated by the battery industry. The soil was highly contaminated with an initial total nickel concentration of approximately 900 mg kg−1. The soluble-exchangeable fraction was reduced to 38 mg kg−1 after treatment. The primary objective of metal stabilization was achieved by reducing the bioavailability through immobilizing the nickel in the urease-driven carbonate precipitation. The nickel removal in the soils contributed to the transformation of nickel from mobile species into stable biominerals identified as calcite, vaterite, aragonite and nickelous carbonate when analyzed under XRD. It was proven that during precipitation of calcite, Ni2+ with an ion radius close to Ca2+ was incorporated into the CaCO3 crystal. The biominerals were also characterized by using SEM-EDS to observe the crystal shape and Raman-FTIR spectroscopy to predict responsible bonding during bioremediation with respect to Ni immobilization. The electronic structure and chemical-state information of the detected elements during MICP bioremediation process was studied by XPS. This is the first study in which microbial carbonate precipitation was used for the large-scale remediation of metal-contaminated industrial soil.
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•Microbial carbonate precipitation for large-scale remediation of metal-contaminated soil.•Soluble-exchangeable Ni fraction was reduced to 38 mg kg−1 after treatment from 898 mg kg−1.•Ni transformation from mobile species into stable biominerals, mainly calcite and NiCO3.•Characterization of biominerals by SEM-EDS, Raman-FTIR spectroscopy and XRD.
Microbial carbonate precipitation for nickel remediation was studied. Soluble-exchangeable Ni fraction from contaminated industrial soil was reduced from initial 898 mg kg−1 to 38 mg kg−1.
•Stepwise reduction of redox potential incrementally increased leachable soil colloids.•Fine and nano colloid fractions retained more soil organic carbon than particulates.•Leachate colloids had 4X ...greater carbon loading capacity than soil colloids.•Organic carbon in fine colloids was more degradable than in other size fractions.
Release and transport of organic carbon (OC), a large portion of which is complexed with mineral colloids, can lead to long-term C sequestration. However, the role of mobile colloids in carbon cycling is not well understood. In this study, we conducted experiments using syringe columns to measure size-dependent colloid mobility and associated OC loadings under stepwise reductions of redox potential, representing existence of different electron acceptors. Colloids were extracted from both leachate and soil samples, designated as leachate colloids and soil colloids, respectively, and fractionated into different sizes: particulates (450–1000 nm), fine colloids (100–450 nm) and nano colloids (2–100 nm) using sequential centrifugation and ultrafiltration techniques. Increases in leachate solution pH and ionic strength (IS) with decreasing redox potential promoted colloid release, as indicated in the increase in turbidity values, due to increased electrostatic repulsion between colloids and soil matrix. The average OC loading by colloids, i.e., the amount of OC associated with per unit mass of colloids, in leachate colloids was up to four times that of soil colloids for the same size fraction. In addition, fine colloids had ∼2 times higher OC loading (∼0.4 mg C mg−1 colloids) than particulates (∼0.2 mg C mg−1 colloid) for leachate colloids. Moreover, measurements of C:N ratio and the natural abundance of stable δ13C and δ15N isotope signatures of soil colloids showed that the fine-colloid fraction experienced more significant fluctuations in these measurements as redox potential decreased than the other two fractions (i.e., particulates and nano colloids). The results of this study demonstrated that OC loading, composition and reactivity all varied with size and strongly influenced by redox conditions. This knowledge can help improve the understanding of how different phases of OC, e.g., dissolved vs. colloidal OC, may impact C sequestration and transport in soils.
Corncob powder possessing its superiority in environmental sustainability and cost, was approved with strong capability of being a replacement of biochar in facilitating the microbial carbonate ...precipitation process. In this study, the ureolytic bacterial strain Bacillus sp. WA isolated from a pre-acquired metal contaminated soil in Guiyu, China, was showed to be well attached on the surfaces of corncob powder, indicating the carrier's role as a durable shelter for bacterial cells. The efficient immobilization helped develop biochemical composite material (BCM) and proven to function better the calcite precipitation. Afterwards, the mechanism and multi-directional benefits of BCM in edaphic cadmium remediation were examined through pot experiment and compared with corncob powder/bacterial strain/nutrient media as control groups. Integrated lab-scale analyses emphasized the advantages of BCM by the maximum soil urease activity (up to 3.440 U/mg and increased by 214% in 28 days), maximal bacterial propagation (most abundant population in fluorescence microscopy), richest surface functional group (most remarkable OC bond and CO bond in FTIR result), notable calcite precipitation (clear calcite crystals on the surface of BCM compared to control group under SEM-EDS), and highest Cd immobilization rate (exchangeable Cd decreased by 68.54%), among all treatments. The pH and electroconductivity measurements additionally led to the mechanism of corncob powder and NBU promoting pre-existed ureolytic bacteria in soil, which demonstrated the added value of corncob to be fine carbon source and residence shelter for soil microorganism, revealing its potential in developing agricultural materials.
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•Ureolytic bacterium was immobilized on Corncob powder to prepare biochemical composite (BCM).•The ion exchangeable phase of cadmium in soil decreased by 50% with BCM during remediation.•BCM showed significant soil urease activity, calcite precipitation and Cd immobilization rate.•Mechanism of BCM in soil Cd immobilization was elucidated.
Ureolytic bacteria can be a promising mediator used for the immobilization of potentially toxic elements via microbially-induced carbonate precipitation (MICP) process from biodegradable ions to ...carbonate form. Electronic waste (E-waste) environment is very complex compared to general metal contaminated soil, however, MICP has not been studied under such an environment. In this study, three bacterial strains were successfully isolated from an E-waste area in Guiyu, China, and indicated to have positive ureolytic behavior with significant heavy metal resistance (specific to Cu and Pb), among which, a strain of Lysinibacillus sp. was proven to show a great persistence in heavy metal immobilization. This featured strain can tolerate up to 100 ppm copper and 1000 ppm lead according to minimal inhibitory concentration (MIC) results, and its urease activity was well-adapted to metal effects. Results also revealed the positive correlation (R2 = 0.9819) between metal concentrations and surface layer protein content present in bacterial cells. The underlying mechanism on the role of S-layer protein in heavy metal immobilization during biocalcification was elucidated. The metabolic system of heavy metal resistance for these E-waste derived isolates is novel and represents a point of interest for possible environmental applications to immobilize toxic heavy metals from electronic waste sites.
•Lysinibacillus sp. of E-waste area showed a great persistence in heavy metal immobilization.•Biocalcification by ureolytic Lysinibacillus lead to immobilization of 100 ppm Cu and 1000 ppm Pb.•The metal concentrations and bacterial S-layer protein content were positively correlated.•The role of S-layer protein in metal immobilization during biocalcification was elucidated.
Microbially induced carbonate precipitation (MICP) is a biomineralization process that has various applications in environmental pollution remediation and restoration of a range of building ...materials. In this study, a ureolytic bacterium, Lysinibacillus sp. GY3, isolated from an E-waste site, was found as a promising catalyst for remediation of heavy metals via the MICP process. This bacterial isolate produced significant amounts of urease and showed a great persistence in immobilization of potentially toxic elements. A reference ureolytic strain, Bacillus megaterium VS1, was selected in order to compare the efficiency of Lysinibacillus sp. GY3. Study on urease localization indicated 80 % more urease activity secreted extracellularly as for Lysinibacillus sp. GY3 compared to B. megaterium VS1. From the investigation on effects of metals on both intra- and extra-cellular urease, it was clear that Lysinibacillus sp. GY3 produced the most stable urease under conditions of metal pressure, especially retaining more than 70 % activity in the presence of 1 g/L Pb2+ and Zn2+. These results suggest that this isolated microorganism could be promisingly introduced in the MICP process to stabilize complex heavy metal pollutions, with reference to the regulating ability under harsh conditions to stabilize urease activity. This species is so important both for its biological features and environmental impacts. In addition, the present study will bring new insight in the field of metal remediation coupled with enzyme engineered biotechnology.
•Lysinibacillus sp. GY3, of an E-waste site, produced the most stable urease in presence of metals.•Urease localization indicated 80 % more urease activity for Lysinibacillus sp. than B. megaterium.•Lysinibacillus sp. harboring urease operon with more Glu and Trp residues adapted with metals.•Lysinibacillus sp. is promising in MICP process to stabilize complex heavy metal pollutions.
An overexploitation of earth resources results in acid deposition in soil, which adversely impacts soil ecosystems and biodiversity and affects conventional heavy metal remediation using ...immobilization. A series of column experiments was conducted in this study to compare the cadmium (Cd) retention stability through biotic and abiotic carbonate precipitation impacted by simulated acid rain (SAR), to build a comprehensive understanding of cadmium speciation and distribution along soil depth and to elucidate the biogeochemical bacteria-soil-heavy metal interfaces. The strain of Sporosarcina pasteurii DSM 33 was used to trigger the biotic carbonate precipitation and cultivated throughout the 60-day column incubation. Results of soil pH, electrical conductivity (EC), and quantitative CdCO3/CaCO3 analysis concluded that the combination of biotic and abiotic soil treatment could reinforce soil buffering capacity as a strong defense mechanism against acid rain disturbance. Up to 1.8 ± 0.04 U/mg urease enzyme activity was observed in combination soil from day 10, confirming the sustained effect of urease-mediated microbial carbonate precipitation. Cadmium speciation and distribution analyses provided new insights into the dual stimulation of carbonate-bound and Fe/Mn-bound phases of cadmium immobilization under microbially induced carbonate precipitation (MICP). As confirmed by the microbial community analysis, outsourcing urea triggered diverse microbial metabolic responses, notably carbonate precipitation and dissimilatory iron metabolism, in both oxygen-rich topsoil and oxygen-depleted subsurface layers. The overall investigation suggests the feasibility of applying MICP for soil Cd remediation under harsh environments and stratagem by selecting microbial functionality to overcome environmental challenges.
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•A series column experiment was conducted to compare the Cd retention stability in soil.•Biotic and abiotic carbonate precipitation impacted by simulated acid rain (SAR) was studied.•The combined precipitation treatment could reinforce soil buffering capacity against acid rain.•Dual stimulation of both carbonate-bound and Fe/Mn-bound phases of cadmium immobilization was observed.
Methane (CH4) is the second most important greenhouse gas, 27 times as potent as CO2 and responsible for >30% of the current anthropogenic warming. Globally, more than half of CH4 is produced ...microbially through methanogenesis. Pyrogenic black carbon possesses a considerable electron storage capacity (ESC) and can be an electron donor or acceptor for abiotic and microbial redox transformation. Using wood-derived biochar as a model black carbon, we demonstrated that air-oxidized black carbon served as an electron acceptor to support anaerobic oxidation of organic substrates, thereby suppressing CH4 production. Black carbon-respiring bacteria were immediately active and outcompeted methanogens. Significant CH4 did not form until the bioavailable electron-accepting capacity of the biochar was exhausted. An experiment with labeled acetate (13CH3COO – ) yielded 1:1 13CH4 and 12CO2 without biochar and predominantly 13CO2 with biochar, indicating that biochar enabled anaerobic acetate oxidation at the expense of methanogenesis. Methanogens were enriched following acetate fermentation but only in the absence of biochar. The electron balance shows that approximately half (∼2.4 mmol/g) of biochar’s ESC was utilized by the culture, corresponding to the portion of the ESC > +0.173 V (vs SHE). These results provide a mechanistic basis for quantifying the climate impact of black carbon and developing ESC-based applications to reduce CH4 emissions from biogenic sources.
Release and transport of organic carbon (OC), a large portion of which can complexes with mineral colloids, often leads to long-term C sequestration. Despite colloids' potential importance, the role ...of mobile colloids in carbon cycling is not well understood. In this study, we conducted experiments using syringe columns with objectives to understand 1) the dynamic formation and disassociation processes of mineral-organic associations (MOAs) and transport of OC in relation to soil colloid mobility, 2) the coupled physical and biogeochemical processes of soil OC under dynamic redox conditions. Regression analyses of chemical properties (pH, Eh, turbidity, ionic strength) for leachate solutions as functions of released water-dispersible colloids were all linear, indicating clear correlations between colloid release with aerobic and anaerobic conditions. Mobilized C and colloids in leachates were quantified by fractionating samples into two particle-size classes (450-1000 nm, 100-450 nm). Under all redox conditions, we found that a larger amount of OC was contained in the 100-450nm size fraction, and a decreased redox potential resulted in an increasing release of this size fraction. In addition, soils in the columns were fractionated into three particle sizes: 450-1000 nm, 100-450 nm, and 2.3-100 nm, and we found that the 2.3-100 nm fraction accumulated the highest C concentration. Moreover, analyses of C and N stocks and their natural abundance of δ13C, δ15 N in different sized aggregates indicated that, as redox potential decreased, the most significant change occurred in the 100-450 nm fraction. Overall, expending of oxygen in soil system enhances the release of colloids, which in turn facilitates C turnover in soil. The 100-450 nm colloidal fraction is the most important size fraction as the potential exchangeable or biogeochemical-reactive fraction due to its high loading capacity of organic carbon and its lability under dynamic redox conditions.
Low levels of high density lipoprotein-cholesterol (HDL-C) are associated with an elevated risk of arteriosclerotic coronary heart disease. Heritability of HDL-C levels is high. In this research ...discovery study, we used whole-exome sequencing to identify damaging gene variants that may play significant roles in determining HDL-C levels. We studied 204 individuals with a mean HDL-C level of 27.8 ± 6.4 mg/dl (range: 4–36 mg/dl). Data were analyzed by statistical gene burden testing and by filtering against candidate gene lists. We found 120 occurrences of probably damaging variants (116 heterozygous; four homozygous) among 45 of 104 recognized HDL candidate genes. Those with the highest prevalence of damaging variants were ABCA1 (n = 20), STAB1 (n = 9), OSBPL1A (n = 8), CPS1 (n = 8), CD36 (n = 7), LRP1 (n = 6), ABCA8 (n = 6), GOT2 (n = 5), AMPD3 (n = 5), WWOX (n = 4), and IRS1 (n = 4). Binomial analysis for damaging missense or loss-of-function variants identified the ABCA1 and LDLR genes at genome-wide significance. In conclusion, whole-exome sequencing of individuals with low HDL-C showed the burden of damaging rare variants in the ABCA1 and LDLR genes is particularly high and revealed numerous occurrences in HDL candidate genes, including many genes identified in genome-wide association study reports. Many of these genes are involved in cancer biology, which accords with epidemiologic findings of the association of HDL deficiency with increased risk of cancer, thus presenting a new area of interest in HDL genomics.
