Effects of long-term radionuclide and heavy metal contamination on the activity of microbial communities, inhabiting uranium mining impacted soils

Potential applications of microbial genomics in nuclear non-proliferation

As nuclear technology evolves in response to increased demand for diversification and decarbonization of the energy sector, new and innovative approaches are needed to effectively identify and deter the proliferation of nuclear arms, while ensuring safe development of global nuclear energy resources. Preventing the use of nuclear material and technology for unsanctioned development of nuclear weapons has been a long-standing challenge for the International Atomic Energy Agency and signatories of the Treaty on the Non-Proliferation of Nuclear Weapons. Environmental swipe sampling has proven to be an effective technique for characterizing clandestine proliferation activities within and around known locations of nuclear facilities and sites. However, limited tools and techniques exist for detecting nuclear proliferation in unknown locations beyond the boundaries of declared nuclear fuel cycle facilities, representing a critical gap in non-proliferation safeguards. Microbiomes, defined as "characteristic communities of microorganisms" found in specific habitats with distinct physical and chemical properties, can provide valuable information about the conditions and activities occurring in the surrounding environment. Microorganisms are known to inhabit radionuclide-contaminated sites, spent nuclear fuel storage pools, and cooling systems of water-cooled nuclear reactors, where they can cause radionuclide migration and corrosion of critical structures. Microbial transformation of radionuclides is a well-established process that has been documented in numerous field and laboratory studies. These studies helped to identify key bacterial taxa and microbially-mediated processes that directly and indirectly control the transformation, mobility, and fate of radionuclides in the environment. Expanding on this work, other studies have used microbial genomics integrated with machine learning models to successfully monitor and predict the occurrence of heavy metals, radionuclides, and other process wastes in the environment, indicating the potential role of nuclear activities in shaping microbial community structure and function. Results of this previous body of work suggest fundamental geochemical-microbial interactions occurring at nuclear fuel cycle facilities could give rise to microbiomes that are characteristic of nuclear activities. These microbiomes could provide valuable information for monitoring nuclear fuel cycle facilities, planning environmental sampling campaigns, and developing biosensor technology for the detection of undisclosed fuel cycle activities and proliferation concerns.

The effect of bacteria on uranium sequestration stability by different forms of phosphorus

Immobilisation of uranium (U (VI)) by direct precipitation of uranyl phosphate (U-P) exhibits a great potential application in the remediation of U (VI)-contaminated environments. However, phosphorus, vital element of bacteria's decomposition, absorption and transformationmay affect the stability of U (VI) with ageing time. The main purpose of this work is to study the effect of bacteria on uranium sequestration mechanism and stability by different forms of phosphorus in a water sedimentary system. The results showed that phosphate effectively enhanced the removal of U (VI), with 99.84%. X-Ray Diffraction (XRD), Scanning Electron Microscopy and Energy Dispersive Spectrometer (SEM-EDS), and X-ray Photoelectron Spectroscopy (XPS) analyses imply that U (VI) and U (IV) co-exist on the surface of the samples. Combined with BCR results, it demonstrated that bacteria and phosphorus have a synergistic effect on the removal of U (VI), realising the immobilisation of U (VI) from a transferable phase to a stable phase. However, from a long-term perspective, the redissolution and release of uranium immobilisation of U (VI) by pure bacteria with ageing time are worthy of attention, especially in uranium mining environments rich in sensitive substances. This observation implies that the stability of the uranium may be impacted by the prevailing environmental conditions. The novel findings could provide theoretical evidence for U (VI) bio-immobilisation in U (VI)-contaminated environments.

Assessing the chronic effect of the bioavailable fractions of radionuclides and heavy metals on stream microbial communities: A case study at the Rophin mining site

This study aimed to assess the potential impact of long-term chronic exposure (69 years) to naturally-occurring radionuclides (RNs) and heavy metals on microbial communities in sediment from a stream flowing through a watershed impacted by an ancient mining site (Rophin, France). Four sediment samples were collected along a radioactivity gradient (for 238U368 to 1710 Bq.Kg-1) characterized for the presence of the bioavailable fractions of radionuclides (226Ra, 210Po), and trace metal elements (Th, U, As, Pb, Cu, Zn, Fe). Results revealed that the available fraction of contaminants was significant although it varied considerably from one element to another (0 % for As and Th, 5-59 % for U). Nonetheless, microbial communities appeared significantly affected by such chronic exposure to (radio)toxicities. Several microbial functions carried by bacteria and related with carbon and nitrogen cycling have been impaired. The high values of fungal diversity and richness observed with increasing downstream contamination (H' = 4.4 and Chao1 = 863) suggest that the community had likely shifted toward a more adapted/tolerant one as evidenced, for example, by the presence of the species Thelephora sp. and Tomentella sp. The bacterial composition was also affected by the contaminants with enrichment in Myxococcales, Acidovorax or Nostocales at the most contaminated points. Changes in microbial composition and functional structure were directly related to radionuclide and heavy metal contaminations, but also to organic matter which also significantly affected, directly or indirectly, bacterial and fungal compositions. Although it was not possible to distinguish the specific effects of RNs from heavy metals on microbial communities, it is essential to continue studies considering the available fraction of elements, which is the only one able to interact with microorganisms.

Effects of uranium mining on soil bacterial communities and functions in the Qinghai-Tibet plateau

The microecological effects of plateau uranium mining are still unknown. In this study, we used 16S rRNA high-throughput sequencing to analyze the impact of plateau uranium mining on the microbial diversity and community structure of tailings soil, tunnel soil, and soil at different depths in an open pit. The results showed that uranium mining significantly reduced soil microbial community richness and diversity indicators, including Chao1, Pielou evenness, and Shannon index (P < 0.05). Uranium mining activities significantly reduced the abundance of RB41, Vicinamidactaceae, and Nitrospira (P < 0.05). Interestingly, the abundance of Thiobacillus, Sphingomonas, and Sulfuriferula significantly increased in the soil samples from various environments and depths during uranium mining (P < 0.05). Beta diversity analysis found that uranium mining resulted in the differentiation of soil microbial communities. Functional enrichment analysis found that uranium mining resulted in the functional enrichment of DNA binding response regulator, DNA helicase, methyl-accepting chemotaxis protein, and Helicase conserved C-terminal domain, whereas cell wall synthesis, nonspecific serine/threonine protein kinase, RNA polymerase sigma-70 factor, and ATP binding cassette transporter were significantly affected by uranium mining (P < 0.05). In addition, we also found that different uranium mining environments and soil depths enriched diverse microbial populations and functions to cope with the environmental pressures that were elicited by uranium mining, including Gaiella, Gemmatimonas, Lysobacter, Pseudomonas, signal transformation histidine kinase, DNA-directed DNA polymerase, and iron complex outer membrane receptor protein functions (P < 0.05). The results have enhanced our understanding of the impact of uranium mining on plateau soil microecological stability and the mechanism of microbial response to uranium mining activities for the first time and aided us in screening microbial strains that can promote the environmental remediation of uranium mining in plateaus.

Feasibility of uranium tailings for cemented backfill and its environmental effects

Surface storage of uranium tailings presents a potential threat to the environment and human health. Cemented backfill can be used to dispose of tailings and control the ground pressure of stopes, providing a new approach for the in-situ seal of heap leaching uranium tailings (HLUTs). The backfilling characteristics of HLUTs were investigated by analyzing the release mechanism of sulfuric acid in HLUTs, the rheological properties of backfill slurry, as well as the strength development and microscopic characteristics of cemented HLUTs backfill (CUTB). The environmental effects of the CUTB were also assessed, and a novel filling process was presented. The results showed that the release rate of sulfuric acid in HLUTs decreased logarithmically, and the content of free sulfuric acid in coarse particles surfaces and ultrafine particles is high, which can be pretreated with 0.1 % quicklime. Slurry with a mass concentration of 74 % ~ 76 % can satisfy the requirements for pipeline transport. The CUTB's strength raised quickly in the former 90d, then decreased to a different extent after 150d, adding 50 wt% FA can enhance its later stability. The leaching level of uranium in CUTB cured for 28d is below the stipulated limit (GB 23727-2009) under different test conditions, having little impact on the underground environment. The hydration products of CUTB are mainly gypsum and C-S-H gel. Gypsum causes later degradation in strength; numerous C-S-H gels generated by the secondary hydration of FA enhance the resistance to sulfate corrosion. These findings have demonstrated that cemented backfill has a high inclusion ratio and low cost for HLUTs, which is of great significance to the HLUTs minimization and the safety of mining while promoting the environmentally friendly development of uranium mines and mills.

Environmental impact of e-waste management in Indian microscale informal sectors

Inappropriate e-waste processing in the informal sector is a serious issue in developing countries. Field investigations in microscale informal recycling sites have been performed to study the impact of hazardous metal(loid)s (released from e-waste dismantling) on the environment (water and soil). Eight hazardous metal(loid)s (Pb, Cd, Cu, Zn, As, Hg, Ni, and Cr) were primarily found in the monitored water and soil samples (Sangrampur, West Bengal) because of widespread informal e-waste handling and primitive processing. Elevated concentrations of Cd, Pb, As, Cu, and Cr were observed in pond water samples (0.04, 1.62, 0.03, 1.40, 1.74 mg/L respectively). These ponds, which are regularly used for e-waste handling/dismantling, are usually flooded during the monsoon season mixing with further larger water resources - posing a serious threat to public health. Enriched levels of Pb, Cd, Cu, and Zn were detected in collected soil samples, both top surface soil (Pb up to 2042.27 ± 206.80, Cd up to 25.90 ± 9.53, Cu up to 6967.30 ± 711.70, and Zn up to 657.10 ± 67.05 mg/Kg) and deeper subsurface soil (Pb, 419.70 ± 44.70; Cd, 18.34 ± 3.81; Cu, 3928.60 ± 356.40; and Zn, 134.40 ± 33.40 mg/Kg), compared to the levels of As, Hg, Ni, and Cr. Seasonal variation of soil metal(loid) content indicated that higher levels of most of the metal(loids) were detected in the pre-monsoon (Nov-May) season, possibly due to the monsoonal dilution effect, except for Pb and Cd. The results highlighted that the composition and the handling of e-waste were important factors affecting the metal(loid) concentrations. E-waste policy and legislation have great influence on the handling and disposal procedures. An improved e-waste management practice has been proposed to encourage eco-friendly and safe e-waste disposal. It is recommended that regulatory agencies and manufacturers should create a road map to convince the informal sector to develop a systematic approach towards a more standardized formal e-waste management practices at the microscale field level.

Enhancement effects of decabromodiphenyl ether on microbial sulfate reduction in eutrophic lake sediments: A study on sulfate-reducing bacteria using dsrA and dsrB amplicon sequencing

Although sulfate (SO₄^2-) reduction by sulfate-reducing bacteria (SRB) is an important sulfur cycling processes, little is known about how the persistent organic pollutants affect the SO₄^2- reduction process in the eutrophic lake sediments. Here, we carried out a 120-day microcosm experiment to explore the effects of decabromodiphenyl ether (BDE-209) on SO₄^2- reduction mediated by SRB in sediment collected from Taihu Lake, a typical eutrophic lake in China. The results showed that BDE-209 contamination significantly enhanced the activity of dissimilatory sulfite reductase (DSR) (r = 0.83), which led to an increased concentration of sulfide produced by SO₄^2- reduction. This stimulatory effect of BDE-209 on DSR activity was closely related to variations in the dsrA- and dsrB-type SRB communities. The abundances and diversities of the dsrA- and dsrB-containing SRB increased and their community composition varied in response to BDE-209 contamination. The gene copies (r = 0.72), Chao 1 (r = 0.50), Shannon (r = 0.55), and Simpson (r = 0.70) indices of dsrB-containing SRB was positively correlated with BDE-209 contamination. Co-occurrence network analysis revealed that network complexity, connectivity, and the interspecific cooperative relationship in SRB were strengthened by BDE-209 contamination. The keystone species identified in the SRB community mainly belonged to the genera Candidatus Sulfopaludibacter for the dsrA-containing SRB and Desulfatiglans for the dsrB-containing SRB, and their relative abundances were positively correlated with DSR activity in the sediment. The relative abundance of the keystone species and SRB diversity were important microbial factors directly contributing to the variations in DSR activity based on structural equation modeling analysis. Notably, the results of abundance, community structure, and interspecific relationships showed that the dsrB-containing SRB may be more sensitive to the BDE-209 contamination than the dsrA-containing SRB. These results will help us understand the effects of BDE-209 on microbial sulfate reduction in eutrophic lakes.

Molecular Mechanisms Underlying Bacterial Uranium Resistance

Environmental uranium pollution due to industries producing naturally occurring radioactive material or nuclear accidents and releases is a global concern. Uranium is hazardous for ecosystems as well as for humans when accumulated through the food chain, through contaminated groundwater and potable water sources, or through inhalation. In particular, uranium pollution pressures microbial communities, which are essential for healthy ecosystems. In turn, microorganisms can influence the mobility and toxicity of uranium through processes like biosorption, bioreduction, biomineralization, and bioaccumulation. These processes were characterized by studying the interaction of different bacteria with uranium. However, most studies unraveling the underlying molecular mechanisms originate from the last decade. Molecular mechanisms help to understand how bacteria interact with radionuclides in the environment. Furthermore, knowledge on these underlying mechanisms could be exploited to improve bioremediation technologies. Here, we review the current knowledge on bacterial uranium resistance and how this could be used for bioremediation applications.

Phosphorus-modified biochar cross-linked Mg-Al layered double-hydroxide composite for immobilizing uranium in mining contaminated soil

The decommissioning of uranium mill tailings (UMTs) is usually accompanied by uranium (U) contamination in soil, which poses a serious threat to human health and ecological safety. In this study, a novel phosphorus-modified bamboo biochar (PBC) cross-linked Mg-Al layered double-hydroxide (LDH) composite ("PBC@LDH") was successfully prepared by phosphate pre-impregnation and a hydrothermal method with Mg-Al LDH. Physicochemical analysis revealed that phosphorus-containing functional groups and Mg-Al LDH were grafted onto the pristine biochar (BC) matrix. Laboratory-scale incubation and column leaching experiments were performed on the prepared BC, PBC, and PBC@LDH. The results showed that, at a dosage of 10%, the PBC@LDH composite had a commendable ability to immobilize U in soil. After 40 days of incubation with the stabilizer, the more mobile U was converted into immobilized species. Furthermore, during a column leaching experiment with simulated acid rain, the cumulative loss and leaching efficiency of U were remarkably reduced by PBC@LDH treatment compared with the control, reaching 53% and 54%, respectively. Surface complexation, co-precipitation, and reduction described the adsorption and immobilization mechanisms. In conclusion, this research demonstrates that the PBC@LDH composite offers a potentially effective amendment for the remediation of U contaminated soil.

Study of pollutant accumulation characteristics and microbial community impact at three bioretention facilities

In this paper, three bioretention facilities (BT, RG1-A, and RG1-B) were selected for on-site testing and experimental analysis. Of which, BT is a roadside bioretention tank with layered filler, while RG1-A and RG1-B are rain gardens with conventional filler (Bioretention soil media, BSM) and modified filler (BSM+10% Water treatment residuals,WTR), respectively. The effect of pollutant accumulation on the soil microbial community structure in the facilities, and the risk of heavy metal contamination over several years of bioretention facility operation were studied. Results showed that the water quality pollutant load reduction in BT was fluctuating. This is related  to the poor water quality of road stormwater flowing into BT and the facility filler. Because RG1-B uses modified filler, RG1-B was more effective than RG1-A in regulating water quality and quantity; the changes in soil physical and chemical properties in BT, RG1-A, and RG1-B were influenced by external factors. Next, BT was at high risk of heavy metal contamination than other facilities. The microbial community structure of the facility had the following characteristics: at the phylum level, Proteobacteria was the dominant phylum in the bioretention facility, accounting for 29-45%; and at the genus level, Blastocatella was the dominant phylum, and the relative abundance in situ was higher than that in the bioretention facility. The results of the correlation analysis combining filler environmental factors and microbial community structure indicated that SMC was a highly influential factor among the three facilities.

Soil microbial community structure and functionality changes in response to long-term metal and radionuclide pollution

Microbial communities are essential for a healthy soil ecosystem. Metals and radionuclides can exert a persistent pressure on the soil microbial community. However, little is known on the effect of long‐term co‐contamination of metals and radionuclides on the microbial community structure and functionality. We investigated the impact of historical discharges of the phosphate and nuclear industry on the microbial community in the Grote Nete river basin in Belgium. Eight locations were sampled along a transect to the river edge and one location further in the field. Chemical analysis demonstrated a metal and radionuclide contamination gradient and revealed a distinct clustering of the locations based on all metadata. Moreover, a relation between the chemical parameters and the bacterial community structure was demonstrated. Although no difference in biomass was observed between locations, cultivation‐dependent experiments showed that communities from contaminated locations survived better on singular metals than communities from control locations. Furthermore, nitrification, a key soil ecosystem process seemed affected in contaminated locations when combining metadata with microbial profiling. These results indicate that long‐term metal and radionuclide pollution impacts the microbial community structure and functionality and provides important fundamental insights into microbial community dynamics in co‐metal‐radionuclide contaminated sites.

On-line microcolumn-based dynamic leaching method for investigation of lead bioaccessibility in shooting range soils

In this work, a miniaturized flow-through leaching test is presented for rapid screening of potential chemical extractants to explore the bioaccessibility of lead (Pb) in contaminated shooting range soils in Valkeala, Finland. The method combines the versatility of microcolumn-based extraction methods with on-line inductively coupled plasma optical emission spectrometry (ICP OES) analysis for expedient assessment of the magnitude of the bioaccessible pools and the leaching kinetics of lead from polluted soils under variable physicochemical scenarios. Acids and salt solutions were studied as potential extractants. The efficiency of the extractants relative to the initial total amount of lead in the soil sample (509 ± 21 mg/kg) were found to increase in the following order: 0.11 M acetic acid (55%) < 1 M MgCl₂ (58%) < 0.1 M NH₂OH·HCl (61%) < 0.1 M citric acid (93%) < 0.1 M HCl (96%). The proposed on-line microcolumn-based method was further explored for implementation of the modified BCR (now termed Standards, Measurements and Testing Programme, SM&T) sequential extraction procedure to avail the information about different fractions available in the solid sample, and validated by mass balance calculations. The equivalent sequential procedure in a batch format was then studied and compared against the on-line microcolumn extraction method. The on-line dynamic extraction system presented in this work accepts a substantial amount of sample (2.5 g) as compared to previous flow-through mini-column setups (generally accommodating < 0.25 g of sample), thus maintaining sample representativeness and fostering comprehension of the extraction patterns for non-homogenous soil materials. The use of cotton buds and Teflon membranes and holders in the microcolumn setup facilitates the repeatable flow-through leaching of trace elements and restrict formation of preferential channels. Monitoring of the leachable trace elements in real time delivers detailed insight into the ongoing extraction process and provides a time-saving assessment of potential chemical extractants.

Effects of soil heavy metal pollution on microbial activities and community diversity in different land use types in mining areas

Microbial activities and community structures play crucial roles in the soil environment and can be served as effective indicators to assess the ecological influence of heavy metal pollution in soil. This article selected soil samples from five land use types (mining area, mineral processing area, heap mining area, tailing area, and vegetable area) in the Shizishan mining area in Tongling, Anhui Province, China. The physicochemical properties, pollution characteristics, enzyme activities (catalase, urease, alkaline phosphatase, neutral phosphatase, cellulase, and sucrase), microbial biomass carbon (MBC), basal respiration (SBR), and metabolic entropy (qCO₂) in soil were determined and compared, and the relationship between environmental factors and the microbial activities and community diversity was analyzed. The results showed that, according to the Nemerow's Pollution Index (P_N), the values were the heap mining area (24.47) > mineral processing area (12.55) > mining area (9.81) > tailings area (6.02) > vegetable area (4.51). With the increase of heavy metal contamination in the sampling area, the six enzyme activities, MBC and SBR decreased, but the qCO₂ increased. Principal coordinate analysis (PCoA) and canonical correlation analysis (CCA) showed that the land use types, soil moisture content (MC), heavy metal content, pH, MBC, SBR, and qCO₂ were significantly affected by the microbial community. The most dominant phyla were Proteobacteria (34.73%), Bacteroidetes (9.25%), Acidobacteria (8.99%), and Chloroflexi (8.68%) at the phylum (0.01) level by a total of 18 phyla. It was also found that Firmicutes and Phormidium were more tolerant to heavy metals. These results contributed to an insight into key environmental variables shaping the microbial activities, community structure, and diversity under various land use types in mining area.

Effects of decabromodiphenyl ether on activity, abundance, and community composition of phosphorus mineralizing bacteria in eutrophic lake sediments

Polybrominated diphenyl ethers (PBDEs) are typical persistent organic pollutants (POPs) in the environment. However, little is known about their effects on phosphorus mineralizing bacteria (PMB) in eutrophic lake sediments, despite the critical role of PMB in phosphorus (P) biogeochemical cycling. In this study, we carried out a 60-day microcosm experiment to understand the effects of 2 and 20 mg kg^-1 dry weight decabromodiphenyl ether (BDE-209) on the activity, abundance, diversity, and community composition of PMB in the sediment of Taihu Lake, a typical eutrophic lake in China. The results showed that BDE-209 contamination, regardless of the contamination levels, significantly increased the orthophosphate concentration in overlying water and available phosphorus concentration in sediments on day 60. Such increases may be explained by the stimulatory effects of BDE-209 on alkaline phosphatase (ALP) activity and PMB abundance. Moreover, based on Miseq sequencing of the phoD gene encoding ALP, Actinobacteria was the dominant PMB phylum in all treatments, and BDE-209 significantly increased the diversity of PMB and altered their community composition. In particular, the relative abundances of some PMB genera such as Bradyrhizobium were increased significantly after 60 days of the High treatment. A co-occurrence network analysis further revealed that the high level of BDE-209 contamination strengthened the connectivity and interspecific co-operative relationships in the PMB community. These results will help us to understand the effects of POPs on P biogeochemical cycling in eutrophic lakes and the associated microbial mechanisms.

Trace metal pollution and ecological risk assessment in agricultural soil in Dexing Pb/Zn mining area, China

Surface agricultural soil samples obtained from Dexing Pb/Zn mining area in Jiangxi province were analyzed for trace metals to assess their pollution status and potential ecological risk. The spatial distributions and the major trace metals pollution sources were described and identified with the combination of chemical measures and geographic information systems technology. The level of pollution in seven metals is decreasing in the following order: zinc (Zn 128.9 mg/kg) > chromium (Cr 64.1 mg/kg) > lead (Pb 58.4 mg/kg) > arsenic (As 45.3 mg/kg) > copper (Cu 41.9 mg/kg) > nickel (Ni 31.3 mg/kg) > cadmium (Cd 1.5 mg/kg). Trace metal spatial distribution maps established by geographic information system techniques displayed two high-pollution zones around mining sites in the study area. Multivariate statistical analyses were also applied, and the results demonstrated that Cd, As, Pb, Cu and Zn in the soils originated from mining activities, whereas Cr and Ni primarily originated from natural sources. The values of pollution index ranged from 4.79 to 71.59, and the values of modified pollution index ranged from 1.98 to 24.69. Moreover, the potential ecological risk values ranged from 264.0 to 3263.5, which indicated considerable ecological risk to very high ecological risk. The potential ecological risk values and other soil contamination indices showed similar patterns that the high-risk areas were around Dexing Pb/Zn mining site. The surface agricultural soil in study area is heavily to extremely polluted , with Cd that made the most dominant contribution.

Impacts of heavy metals and soil properties at a Nigerian e-waste site on soil microbial community

Heavy metal contamination is a serious problem worldwide threatening soil environment and human health. In the present study, concentrations of 6 heavy metals at an electronic waste (e-waste) site in Nigeria were correlated to their mobility, showing distinct distribution pattern between surface soils and subsoils. Proteobacteria, Firmicutes, Acidobacteria and Planctomycetes dominated the indigenous soil microbial communities, and there was significant discrimination of bacterial taxonomic composition between the heavy metal contaminated and uncontaminated areas. The abundance of most bacterial taxa changed with heavy metal contamination level to different extent. The multivariate regression tree (MRT) analyses illustrated that main environmental variables influencing bacterial taxonomic composition included soil texture (31%) and organic carbon (14%), whereas microbial diversity was affected by soil pH (32%) and soil texture (14%). Our results surprisingly indicated that soil properties were more influential in determining soil bacterial composition and diversity than heavy metals even at the e-waste site which was seriously contaminated by heavy metals. The present study contributes to a deeper insight into the key environmental variables shaping the diversity and composition of soil microbes at heavy metal contaminated e-waste sites.

Toxicity of enrofloxacin, copper and their interactions on soil microbial populations and ammonia-oxidizing archaea and bacteria

Enrofloxacin (EFX) is one of the most frequently used broad-spectrum veterinary drugs, and copper (Cu) is a heavy metal that could easily bind to certain antibiotic molecules. Hence EFX and Cu were chosen as representatives of antibiotics and heavy metals to explore the abundance and variation of soil microbial populations with a plate-counting technique, as well as the copy numbers of amoA gene in ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) by quantitative PCR methods in Argosols samples. Treatments of applied EFX (0.05, 0.20, 0.80 mmol/kg), Cu (1.60 mmol/kg) and combined EFX and Cu (at molar ratios of 1:32,1:8,1:2) exhibited various effects on different soil microorganisms. The toxicity of combined EFX and Cu was more strongly expressed on both soil microbial populations and amoA gene (AOA and AOB) compared to the EFX treatment alone, in most cases, time and dose effects were observed. With respect to the amoA gene, the AOA-amoA gene was more abundant than the AOB-amoA gene, and the ratio ranged from ~8 to ~11. Moreover, the interaction types of EFX and Cu were more likely to be antagonistic (64.29%) than synergistic (35.71%) on soil abundance and function, which may be related to the incubation time and the ratio of EFX to Cu in the soil.

Revitalisation of metal-contaminated, EDTA-washed soil by addition of unpolluted soil, compost and biochar: Effects on soil enzyme activity, microbial community composition and abundance

Soil remediation mitigates hazards from contaminants but could deprive soils of initial biota and enzymes. Historically contaminated acidic soil from Arnoldstein (Austria) and calcareous soil from Meza (Slovenia) were washed with 30 and 100 mmol kg^-1 ethylenediaminetetraacetate (EDTA) to remove 78 and 60% of Pb as a main pollutant. Remediation of the Arnoldstein soil decreased urease activity and increased β-glucosidase activity, measured in a 15-week experiment. The dehydrogenase activity and microbial gene abundances were not significantly impeded compared to the original soil. Conversely, the use of a high dose of EDTA in the Meza soil, necessary for effective remediation of calcareous soils, resulted in pronouncedly decreased enzyme activities (3.2 times on average) and repressed fungal ITS and increased bacterial 16S rRNA gene abundance. Remediation shifted the microbial community composition in both soils. For revitalisation, the remediated soils were amended with compost, inocula of un-contaminated soil and (Arnoldstein soil) biochar enriched with soil extract. Amendments inconsistently affected the Arnoldstein soil: compost increased the dehydrogenase activity and altered the microbial community composition, biochar enhanced the β-glucosidase activity, and all amendments decreased the microbial abundance (1.6 times on average). In contrast, amendments efficiently revitalised the remediated Meza soil; compost and soil inoculum returned the enzyme activities back to the baseline in the original soil, increased the fungal abundance above that in the original soil and restored the microbial community composition.

Bacterial community profile of contaminated soils in a typical antimony mining site

The soils around the world's largest antimony mine have been contaminated by high concentrations of Sb and As, which might influence microbial diversity in the surrounding soils. The ecological effects of bioavailable Sb and As on the composition and diversity of microbial community in soils remain unknown. In this study, the relative abundance, taxonomic diversity and composition of bacterial community in soils from a typical Sb mine area, and the relationship between the bacterial community and bioavailable concentrations as well as environmental factors have been investigated comprehensively using high-throughput sequencing (HTS) and diffusive gradients in thin films (DGT). The results indicated that Proteobacteria, Acidobacteria, Chloroflexi, Bacteroidetes, Actinobacteria, Gemmatimonadetes, and Cyanobacteria were the dominant bacterial populations at phylum level in all soil samples, accounting for more than 80% of the bacteria sequenced. The abundance and diversity of bacterial community vary along a metal contamination gradient. Redundancy discriminate analysis (RDA) revealed that 74.74% of bacterial community variation in the contaminated soils was explained by six environmental factors (pH, Sb_DGT, As_DGT, potential ecological risk index (RI), TC, TN), among which pH, Sb_DGT, and As_DGT were dominant factors influencing the composition and diversity of bacteria. This study contributes to our understanding of microbial diversity in a local ecosystem and introduces the option of studying bioavailable Sb and As using DGT.