Effects of heavy metal contamination upon soil microbes: lead-induced changes in general and denitrifying microbial communities as evidenced by molecular markers

Poisoned in their homes - Red blood cell abnormalities in lead-exposed residents of a Pakistani Industrial Zone

The present study investigated the clinical and hematological effects of chronic lead exposure in the population residing in Shadi Pura, a small industrial zone in Lahore, Pakistan. A cross-sectional analysis of 149 participants recruited through health camps was conducted to explore the hematological manifestations of environmental lead exposure, focusing on various red blood cell (RBC) indices and morphology. Moreover, the study examined the differences in the impact of lead exposure on RBC indices and morphology between men, women, and children. Participants exhibited symptoms of lead poisoning, including fatigue, muscle pain, and headache, with a significant percentage of women (44%) reporting miscarriages. Iron deficiency anemia was highly prevalent among all sub-groups of the study population, with adult females showing a significantly higher prevalence than adult males. Male children were the most affected subgroup, with 93% displaying anemia. The RBC count in children remained unchanged, while 31% of male and 7% of female participants displayed elevated RBC counts. RBC indices, mainly mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH), were below normal levels, with children being more affected than adults and adult males being the least affected group. Furthermore, RBC morphology was severely affected, with a considerable proportion of females and children displaying hypochromic microcytic morphology. Our results highlight variations in the hematological impacts of lead exposure in different sex and age cohorts. Overall, our findings underscore the urgency of addressing the issue of environmental lead exposure in similar industrial zones. It is critical to implement appropriate measures to reduce lead exposure and enhance the infrastructure for safe drinking water and waste disposal to protect the health of populations in such areas.

Assessment of heavy metal pollution in soils of Jebba Area, Nigeria: Concentrations, source analysis and implications for ecological and human health risks

This comprehensive research investigates heavy metal contamination in the rapidly developing town of Jebba in north-central Nigeria, which is essential to the nation's economy due to its agro-allied and non-agro-allied businesses. The research focuses on soil samples, collecting and analyzing 137 surface soil samples to assess the presence of 25 distinct metals. After statistical analysis and simple mathematical models are applied to the data, the amounts of harmful metals and their probable causes are revealed. The study identifies geogenic and anthropogenic origins of toxic metals, with some elements exceeding average crustal concentrations. Non-homogeneous metal dispersion is shown in the region by spatial distribution maps. The geo-accumulation index reflects various amounts of contamination, with particular metals posing significant threats to the ecosystem. Additionally, the study compares results with worldwide studies, revealing distinct pollution patterns in Jebba. The research delves into weathering processes, employing chemical indices to quantify the level of soil weathering and uncovering a prominent role of geogenic activities in metal release. Bivariate correlation and principal component analysis indicate links and possibly common sources among heavy metals, emphasizing anthropogenic contributions. In addition, assessments of ecological and medical risks are conducted, indicating possible threats to human wellness and the ecosystem. Children, in particular, are regarded as especially vulnerable to non-carcinogenic health concerns, with various heavy metals posing potential threats through diverse exposure routes. The study emphasizes the need to implement remediation procedures to address the risks to public health and the environment related to metal pollution.

Molecular and eco-physiological responses of soil-borne lead (Pb2+)-resistant bacteria for bioremediation and plant growth promotion under lead stress

Lead (Pb) is the 2nd known portentous hazardous substance after arsenic (As). Being highly noxious, widespread, non-biodegradable, prolonged environmental presence, and increasing accumulation, particularly in arable land, Pb pollution has become a serious global health concern requiring urgent remediation. Soil-borne, indigenous microbes from Pb-polluted sites have evolved diverse resistance strategies, involving biosorption, bioprecipitation, biomineralization, biotransformation, and efflux mechanisms, under continuous exposure to Pb in human-impacted surroundings. These strategies employ a wide range of functional bioligands to capture Pb and render it inaccessible for leaching. Recent breakthroughs in molecular technology and understanding of lead resistance mechanisms offer the potential for utilizing microbes as biological tools in environmental risk assessment. Leveraging the specific affinity and sensitivity of bacterial regulators to Pb2+ ions, numerous lead biosensors have been designed and deployed worldwide to monitor Pb bioavailability in contaminated sites, even at trace levels. Besides, the ongoing degradation of croplands due to Pb pollution poses a significant challenge to meet the escalating global food demands. The accumulation of Pb in plant tissues jeopardizes both food safety and security while severely impacting plant growth. Exploring Pb-resistant plant growth-promoting rhizobacteria (PGPR) presents a promising sustainable approach to agricultural practices. The active associations of PGPR with host plants have shown enhancements in plant biomass and stress alleviation under Pb influence. They thus serve a dual purpose for plants grown in Pb-contaminated areas. This review aims to offer a comprehensive understanding of the role played by Pb-resistant soil-borne indigenous bacteria in expediting bioremediation and improving the growth of Pb-challenged plants essential for potential field application, thus broadening prospects for future research and development.

Soil depth and physicochemical properties influence microbial dynamics in the rhizosphere of two Peruvian superfood trees, cherimoya and lucuma, as shown by PacBio-HiFi sequencing

The characterization of soil microbial communities at different depths is essential to understand their impact on nutrient availability, soil fertility, plant growth and stress tolerance. We analyzed the microbial community at three depths (3 cm, 12 cm, and 30 cm) in the native fruit trees Annona cherimola (cherimoya) and Pouteria lucuma (lucuma), which provide fruits in vitamins, minerals, and antioxidants. We used PacBio-HiFi, a long-read high-throughput sequencing to explore the composition, diversity and putative functionality of rhizosphere bacterial communities at different soil depths. Bacterial diversity, encompassing various phyla, families, and genera, changed with depth. Notable differences were observed in the alpha diversity indices, especially the Shannon index. Beta diversity also varied based on plant type and depth. In cherimoya soils, positive correlations with Total Organic Carbon (TOC) and Cation Exchange Capacity (CEC) were observed, but negative ones with certain cations. In lucuma soils, indices like the Shannon index exhibited negative correlations with several metals and specific soil properties. We proposed that differences between the plant rhizosphere environments may explain the variance in their microbial diversity. This study provides insights into the microbial communities present at different soil depths, highlighting the prevalence of decomposer bacteria. Further research is necessary to elucidate their specific metabolic features and overall impact on crop growth and quality.

A Potential Involvement of Metallothionein in the Zinc Tolerance of Trichoderma harzianum: Experimental Findings

Metallothioneins are a group of cysteine-rich proteins that play an important role in the homeostasis and detoxification of heavy metals. The objective of this research was to explore the significance of metallothionein in Trichoderma harzianum tolerance to zinc. At the inhibitory concentration of 1000 ppm, the fungus adsorbed 16.7 ± 0.4 mg/g of metal. The HPLC and SDS-PAGE electrophoresis data suggested that the fungus production of metallothionein was twice as high in the presence of zinc as in the control group. The examination of the genes; metallothionein expression activator (MEA) and Cu fist revealed that the MEA, with a C2H2 zinc finger domain, increased significantly in the presence of zinc. It was observed that in T. harzianum, the enhanced expression of the metallothionein gene was managed by the metallothionein activator under zinc overload conditions. According to our knowledge, this is the first report on the role of metallothionein in the resistance of T. harzianum to zinc.

Single and Combined Effects of Phenanthrene and Silver Nanoparticles on Denitrification Processes in Coastal Marine Sediments

The increasing production and utilization of polycyclic aromatic hydrocarbons (PAHs) and commercial silver nanoparticles (AgNPs) have raised concerns about their potential environmental release, with coastal sediments as a substantial sink. To better understanding the effects of these contaminants on denitrification processes in coastal marine sediments, a short-term exposure simulation experiment was conducted. We investigated the effects of single and combined contamination of phenanthrene (Phe) and AgNPs on denitrification processes in a coastal marine sediment. Results showed that all contaminated treatment groups had different degrees of inhibitory effect on denitrification activity, denitrifying enzyme activity, total bacteria count and denitrifying genes. The inhibitory effect sequence of each treatment group was combined treatment > AgNPs treatment > Phe treatment. Moreover, the inhibitory effects of denitrifying genes were much larger than that of total bacteria count, indicating that the pollutants had specific toxic effects on denitrifying bacteria. The sequence of sensitivity of three reduction process to pollutants was N2O > NO2- > NO3-. All contaminated treatment groups could increase NO3-, NO2- and N2O accumulation. Furthermore, according to the linear relationship between functional gene or reductase and denitrification process, we also found that the abundance of denitrifying genes could better predict the influence of Phe and AgNPs on sediment denitrification than the denitrifying bacterial diversity. In addition, at the genus level, the community structure of nirS- and nosZ-type denitrifying bacteria changed dramatically, while changes at the phylum level were comparatively less pronounced. Single and combined contamination of Phe and AgNPs could reduce the dominance of Pseudomonas, which may lead to a potential slow-down in the degradation of Phe and inhibition of denitrification, especially the combined contamination. Overall, our study revealed that combined contamination of Phe and AgNPs could lead to an increase in NO3-, NO2- and N2O accumulation in coastal sediment, which poses a risk of eutrophication in coastal areas, exacerbates the greenhouse effect and has adverse effects on global climate change.

Exploring the relationship between metal(loid) contamination rate, physicochemical conditions, and microbial community dynamics in industrially contaminated urban soils

Increasing metal(loid) contamination in urban soils and its impact on soil microbial community have attracted considerable attention. In the present study, the physicochemical parameters and the effects of twelve metal(loid) pollution on soil microbial diversity, their ecotoxic effects, and human health risk assessment in urban soils with different industrial background were studied in comparison with an unpolluted forest soil sample. Results showed that urban soils were highly contaminated, and metal(loid) contamination significantly influenced structure of the soil microbial communities. In all samples the bacterial community was dominated by Proteobacteria, and on the level of phyla characteristic differences were not possible to observe between polluted and control sampling sites. However, clear differences emerged at class and genus level, where several rare taxa disappeared from contaminated urban soils. Simper test results showed that there is 71.6 % bacterial OTU and 9.5 % bacterial diversity dissimilarity between polluted and control samples. Ratio of Patescibacteria, Armatimonadetes, Chlamydiae, Fibrobacteres, and Gemmatimonadetes indicated a significant (p < 0.05) positive correlation with soil Zn, Cr, Pb, Sn, Cu, Mn content, suggest that metal(loid)s strongly influence the structure of microbial community. In contrast, the presence of metal(loid) contamination in urban soils has been found to significantly reduce the population of Archaeal communities. This can be attributed to the depletion of organic matter caused by contamination that reached a minimum of 0.5 m/m% for nitrate and 0.9 m/m% for total organic carbon. The values of urban soil pH were close to neutral, ranging from 5.9 to 8.3. The findings of ecotoxicology test are alarming, as all the studied urban soil sites were cytotoxic to soil microorganisms, and in one site metal(loid) contamination reached genotoxic level. Moreover, all the metal(loid) contaminated sites pose severe and persistent health risk to children, highlighting the urgent need for effective measures to mitigate metal(loid) pollution in urban areas.

Insights on the assembly processes and drivers of soil microbial communities in different depth layers in an abandoned polymetallic mining district

Soil microbes, which play crucial roles in maintaining soil functions and restoring degraded lands, are impacted by heavy metal pollution. This study investigated the vertical distribution of bacterial communities along the soil profiles across four types of areas (heavy metal pollution level: tailings heap area > phytoremediation area > natural restoration area > original forest area) in an abandoned polymetallic mining district by 16S rRNA sequencing, and aimed to disentangle the assembly mechanisms and key drivers of the vertical variation in bacterial community structure. Bacterial diversity and composition were found to vary remarkably between the depth layers in all types of areas, with heterogeneous selection dominated the vertical distribution pattern of soil bacterial communities. Pearson correlation analysis and partial Mantel test revealed that soil nutrients mainly shaped the vertical distribution of bacterial microbiota along soil profiles in the original forest and natural restoration areas. Ni, As, and bioavailable As were the key drivers regulating the vertical variation of bacterial assemblages in the phytoremediation area, whereas Pb, pH, soil organic carbon, and available nitrogen were crucial drivers in the tailings heap area. These findings reveal the predominant assembly mechanisms and drivers governing the vertical distribution of soil bacterial microbiota and indicate the efficiency of phytoremediation and ecological restoration on ameliorating edaphic micro-ecosystems in heavy metal-contaminated areas.

Hormones and the antioxidant transduction pathway and gene expression, mediated by Serratia marcescens DB1, lessen the lethality of heavy metals (As, Ni, and Cr) in Oryza sativa L

Microorganisms have recently gained recognition as efficient biological tool for reducing heavy metal toxicity in crops. In this experiment, we isolated a potent heavy metal (As, Ni, and Cr) resistant rhizobacterium Serratia marcescens DB1 and detected its plant growth promoting traits such as phosphate solubilization, gibberellin synthesis, organic acid production and amino acid regulation. Based on these findings, DB1 was further investigated for application in a rice var. Hwayeongbyeo subjected to 1 mM As, 4 mM Ni, and 4 mM Cr stress. The rice plants treated with Cr and Ni appeared healthy but were lethal, indicating unfitness for consumption due to toxic metal deposition, whereas the plants treated with > 1 mM As instantaneously died. Our results showed that DB1 inoculation significantly decreased metal accumulation in the rice shoots. Particularly, Cr uptake dropped by 16.55% and 22.12% in (Cr + DB1) and (Cr + As + Ni + DB1), respectively, As dropped by 48.90% and 35.82% in (As + DB1) and (Cr + As + Ni + DB1), respectively, and Ni dropped by 7.95% and 19.56% in (Ni + DB1) and (Cr + As + Ni + DB1), respectively. These findings were further validated by gene expression analysis results, which showed that DB1 inoculation significantly decreased the expression of OsPCS1 (a phytochelatin synthase gene), OsMTP1 (a metal transporting gene), and OsMTP5 (a gene for the expulsion of excess metal). Moreover, DB1 inoculation considerably enhanced the morphological growth of rice through modulation of endogenous phytohormones (abscisic acid, salicylic acid, and jasmonic acid) and uptake of essential elements such as K and P. These findings indicate that DB1 is an effective biofertilizer that can mitigate heavy metal toxicity in rice crops.

Assessing the toxicity of contaminated soils via direct contact using a gas production bioassay of thiosulfate utilizing denitrifying bacteria (TUDB)

A direct contact bioassay of thiosulfate utilizing denitrifying bacteria (TUDB) based on inhibition of gas production was deployed to assess the toxicity of naturally contaminated field soils and soils artificially contaminated with heavy metals. Test procedure producing optimal conditions responsible for maximum gas production was 0.5 mL test culture, 1 g soil sample, 80 RPM, and 48 h reaction time. Similarly, the concentrations which generated a 50% reduction in gas production by TUDB for the tested heavy metals were 3.01 mg/kg Cr⁶⁺; 15.30 mg/kg Ni²⁺;15.50 mg/kg Cu²⁺;16.60 mg/kg Ag⁺; 20.60 mg/kg As³⁺; 32.80 mg/kg Hg²⁺; 54.70 mg/kg Cd²⁺; and 74.0 mg/kg Pb²⁺. Because soil toxicity is usually influenced by various physicochemical characteristics, ten reference soils were used to determine the toxicity threshold for evaluating the toxicity of naturally contaminated field soils. All eight contaminated soils were toxic to the TUDB bioassay because their levels of inhibition ranged between 72% and 100% and exceeded the determined toxicity threshold of 10%. Compared to other direct contact assays, the newly developed assay TUDB proved to be very robust, producing highly sensitive data while the different soil physicochemical properties exerted minimal influence on the gas production activity of TUDB. Additionally, the simplicity of the developed methodology coupled with the elimination of pretreatment procedures such as elutriation, and ability to perform generate sensitive data in turbid and highly colored samples makes it, cost-effective, and easily adaptable for the assessment of heavy metal and field contaminated soils when compared with other conventional assays which require sophisticated instrumentation and prolonged testing procedures and times.

Effects of metal contamination with physicochemical properties on the sediment microbial communities in a tropical eutrophic-hypereutrophic urban reservoir in Brazil

We investigated the effects of metals and physicochemical variables on the microbes and their metabolisms in the sediments of Guarapiranga reservoir, a tropical eutrophic-hypereutrophic freshwater reservoir located in a highly urbanized and industrialized area in Brazil. The metals cadmium, copper, and chromium showed minor contribution to changes in the structure, composition, and richness of sediment microbial communities and functions. However, the effects of metals on the microbiota are increased when taken together with physicochemical properties, including the sediment carbon and sulfur, the bottom water electrical conductivity, and the depth of the water column. Clearly, diverse anthropic activities, such as sewage discharge, copper sulfate application to control algal growth, water transfer, urbanization, and industrialization, contribute to increase these parameters and the metals spatially in the reservoir. Microbes found especially in metal-contaminated sites encompassed Bathyarchaeia, MBG-D and DHVEG-1, Halosiccatus, Candidatus Methanoperedens, Anaeromyxobacter, Sva0485, Thermodesulfovibrionia, Acidobacteria, and SJA-15, possibly showing metal resistance or acting in metal bioremediation. Knallgas bacteria, nitrate ammonification, sulfate respiration, and methanotrophy were inferred to occur in metal-contaminated sites and may also contribute to metal removal. This knowledge about the sediment microbiota and metabolisms in a freshwater reservoir impacted by anthropic activities allows new insights about their potential for metal bioremediation in these environments.

Effects of heavy metal pollution and soil physicochemical properties on the Sphagnum farmland soil microbial community structure in Southern Guizhou, China

Farmland soil pollution is a serious problem worldwide threatening environment and human health. Microbial communities plays a key role in soil function. The purpose of this study was to analyze the relationship between microbial structure and soil physicochemical properties under different heavy metal pollution levels, find out heavy metal tolerant species under different environmental conditions, then provide useful reference for the bioremediation of contaminated farmland. In this study, 16s rRNA high-throughput sequencing technology was used, multiple comparisons and correlation analyses of the data were performed using R software. The results showed that study area A was contaminated by heavy metal Cd, and study area A, B and C were contaminated by heavy metal Hg. From the analysis of the community structure of the samples, it can be seen that the dominant bacterial phyla were Proteobacteria, Acidobacteriota, Chloroflexi, Actinobacteria, and 10 others. Correlation and RDA analysis of samples showed that the heavy metals Hg and As in peat were related to dominant bacteria phyla, and the physicochemical properties of soil potential of hydrogen (pH), total nitrogen (TN), available nitrogen (AN), available phosphorus (AP), available potassium (AK), and soil organic matter (SOM) were significantly positively correlated with the bacteria (Acidobacterta and Chloroflexi). Moreover, Chloroflexi was more tolerant to the heavy metals Hg and As. There was a significant correlation between bacterial community abundance and diversity in the four study areas. Soil heavy metal concentration and soil physicochemical properties affected the main phyla, bacterial community abundance and bacterial diversity of peat soil. These results indicate that some microorganisms have strong tolerance to heavy metal pollution and certain heavy metal digestion ability, which can create a good environment for farmland soil remediation.

Phytoextraction of anthropogenic heavy metal contamination of the Blesbokspruit wetland: Potential of wetland macrophytes

Blesbokspruit wetland is one of the least conserved ecosystems in the Southern Africa region with active and latent threats of anthropogenic contamination stretching over decades of mining wastewater discharge, agricultural run-off, and a consistent influx of untreated sewage. This study provides an insight into the present-day spatial distribution of heavy metal contamination and the role of localised macrophytes in their phytoremediation. With exception of the first sampling point, the concentration of heavy metals in water samples throughout the wetland was within limits however findings from sediment samples were the inverse. The concentrations of Chromium and Nickel significantly exceeded both effect range low (ERL) and effect range medium (ERM) limits (250-430 mg/Kg and 73-151 mg/Kg respectively) as set out by international sediment quality guidelines. Emergent- Phragmites australis, Typha capensis, and free-flowing-Eichhornia crassipes macrophytes, which are naturally localised to the wetland were found to have varying bioaccumulation potential for different heavy metals; Bioconcentration of heavy metals in emergent macrophytes was relatively low especially for Nickel and Chromium compared to free-flowing macrophytes. E. crassipes accumulated significant amounts of the heavy metals with root concentrations of up to 17.23, 116.6, 330.5, and 342.9 mg/Kg for Arsenic, Lead, Nickel, and Chromium respectively. The emergent macrophytes were however found to bioconcentrate Arsenic up to 1.15 L/Kg (T. capensis) and 9.9 L/Kg (P. Australis) at sites 4 and 5 respectively.   Findings with regards to bioconcentration especially of the E. crassipes, validate recommendations for the utilization of hyperaccumulating macrophytes for the natural recovery of these heavy metals towards alleviating the anthropogenic stress on this valuable ecosystem.

Dietary lead modulates the mouse intestinal microbiome: Subacute exposure to lead acetate and lead contaminated soil

The effect of dietary lead on the intestinal microbiome has not been fully elucidated. To determine if there was an association between microflora modulation, predicted functional genes, and Pb exposure, mice were provided diets amended with increasing concentrations of a single lead compound, lead acetate, or a well characterized complex reference soil containing lead, i.e. 6.25-25 mg/kg Pb acetate (PbOAc) or 7.5-30 mg/kg Pb in reference soil SRM 2710a having 0.552 % Pb among other heavy metals such as Cd. Feces and ceca were collected following 9 days of treatment and the microbiome analyzed by 16 S rRNA gene sequencing. Treatment effects on the microbiome were observed in both feces and ceca of mice. Changes in the cecal microbiomes of mice fed Pb as Pb acetate or as a constituent in SRM 2710a were statistically different except for a few exceptions regardless of dietary source. This was accompanied by increased average abundance of functional genes associated with metal resistance, including those related to siderophore synthesis and arsenic and/or mercury detoxification. Akkermansia, a common gut bacterium, was the highest ranked species in control microbiomes whereas Lactobacillus ranked highest in treated mice. Firmicutes/Bacteroidetes ratios in the ceca of SRM 2710a treated mice increased more than with PbOAc, suggestive of changes in gut microbiome metabolism that promotes obesity. Predicted functional gene average abundance related to carbohydrate, lipid, and/or fatty acid biosynthesis and degradation were greater in the cecal microbiome of SRM 2710a treated mice. Bacilli/Clostridia increased in the ceca of PbOAc treated mice and may be indicative of increased risk of host sepsis. Family Deferribacteraceae also was modulated by PbOAc or SRM 2710a possibly impacting inflammatory response. Understanding the relationship between microbiome composition, predicted functional genes, and Pb concentration, especially in soil, may provide new insights into the utility of various remediation methodologies that minimize dysbiosis and modulate health effects, thus assisting in the selection of an optimal treatment for contaminated sites.

Do heavy metals affect bacterial communities more in small repeated applications or in a single large application?

Heavy metals from anthropogenic sources accumulate slowly but steadily, leading to high metal concentration levels in soil. However, the effect of each heavy metal on soil bacterial communities is usually assessed in laboratories by a single application of individually spiked metals. We evaluated the differences between single individual application and repeated individual applications of Cr, Cu, Ni, Pb, and Zn on bacterial communities, through pollution-induced community tolerance (PICT), using bacterial growth as the endpoint (³H-leucine incorporation method). We found that PICT development was higher when soil was spiked in individual single application than individual repeated applications for Cu, Ni and Zn. In contrast, bacterial communities did not show different tolerance between singly or repeatedly when soil was spiked with Cr. In the case of Pb any increase of bacterial community tolerance to this metal was found despite high doses applied (up to 2000 mg kg^-1). These results are relevant for the interpretation of the effects of heavy metals on soil microbes in order to avoid laboratory overestimations of the real effects of heavy metals on soil microbes.

Potentially toxic elements in iron mine tailings: Effects of reducing soil pH on available concentrations of toxic elements

Tailings from iron mining are characterized by high concentrations of iron and manganese oxides, as well as high pH values. With these characteristics, most of the potentially toxic elements (PTE) contained in the tailings are somewhat unavailable. The aim of the present study was to evaluate how a reduction in the pH of iron mine tailings may affect PTE availabilities. The tailings were collected on the banks of the Gualaxo do Norte River (Mariana, MG, Brazil), one of the main areas impacted by the rupture of the Fundão Dam (Barragem de Fundão). A completely randomized experimental design was used, including five pH values (6.4, 5.4, 4.3, 3.7, and 3.4) and five replications. The concentrations of the PTE (Ba, Cr, Cd, Co, Cu, Fe, Mn, Pb, Ni, and Zn) were determined after extraction following different methodologies: USEPA 3051A, DTPA, Mehlich-1, Mehlich-3, and distilled water. A comparison of the available concentrations of the elements in the tailings with those in a soil not impacted by tailings shows that Cr, Cd, Cu, Fe, Mn, Ni, Ba, and Co were higher in the soil impacted by the tailings. The different methods used for evaluating the availability of PTE in the tailings at various pH exhibited the following decreasing order in relation to the quantity extracted: Mehlich-3 > Mehlich-1 > DTPA > distilled water. However, regarding sensitivity to change in pH, the order was DTPA > water > Mehlich-1 > Mehlich-3. The increases in the concentrations of PTE due to the reduction in the pH of the tailings did not lead to concentrations that exceed the limits of Brazilian regulations. The DTPA extractant exhibited higher coefficients of correlation between the PTE concentrations and the pH of the tailings, proving to be suitable for use in areas affected by the deposition of iron mine tailings.

Response addition is more protective of biogeochemical cycles of carbon and phosphorus compared to concentration addition

In soils, enzymes are crucial to catalyzing reactions and cycling elements such as carbon (C), nitrogen (N), and phosphorus (P). Although these soil enzymes are sensitive to metals, they are often disregarded in risk assessments, and regulatory laws governing their existence are unclear. Nevertheless, there is a need to develop regulatory standards for metal mixtures that protect biogeochemical cycles because soil serve as a sink for metals and exposures occur as mixtures. Using a fixed ratio ray design, we investigated the effects of 5 single metals and 10 quinary mixtures of Zn, Cu, Ni, Pb, and Co metal oxides on two soil enzymes (i.e., acid phosphatases [ACP] and beta glucosidases [BGD]) in two acidic Canadian soils (S1: acid sandy forest soil, and S2: acid sandy arable soil), closely matched to EU REACH standard soils. Compared to BGD, ACP was generally the more sensitive enzyme to both the single metals and the metal mixtures. The effective concentration inhibiting 50% enzyme activity (EC₅₀) estimates for single Cu (2.1-160.7 mmol kg^-1) and Ni (12-272 mmol kg^-1) showed that those were the most toxic to both enzymes in both soils. For metal mixtures, response addition (RA) was more conservative in predicting metal effects compared to concentration addition (CA). For both additivity models, antagonism was observed except at lower concentrations (≤10,000 mg/kg) where synergism was observed. At higher concentrations (>10,000 mg/kg), free and CaCl₂ extractable Cu protected both enzymes against the toxicity of other metals in the mixture. The results suggest that assuming CA at concentrations less than EC₅₀ does not protect biogeochemical cycling of C and P. And Cu in soil may protect soil enzymes from other toxic metals and thus may have an overall positive role.

A novel gas production bioassay of thiosulfate utilizing denitrifying bacteria (TUDB) for the toxicity assessment of heavy metals contaminated water

This study reports for the first-time the possibility of deploying gas production by thiosulfate utilizing denitrifying bacteria (TUDB) as a proxy to evaluate water toxicity. The test relies on gas production by TUDB due to inhibited metabolic activity in the presence of toxicants. Gas production was measured using a bubble-type respirometer. Optimization studies indicated that 300 mg NO₃^--N/L, 0.5 mL acclimated culture, and 2100 mg S₂O₃^2-/L were the ideal conditions facilitating the necessary volume of gas production for sensitive data generation. Determined EC₅₀ values of the selected heavy metals were: Cr⁶⁺, 0.51 mg/L; Ag⁺, 2.90 mg/L; Cu²⁺, 2.90 mg/L; Ni²⁺, 3.60 mg/L; As³⁺, 4.10 mg/L; Cd²⁺, 5.56 mg/L; Hg²⁺, 8.06 mg/L; and Pb²⁺, 19.3 mg/L. The advantages of this method include operational simplicity through the elimination of cumbersome preprocessing procedures which are used to eliminate interferences caused by turbidity when the toxicity of turbid samples is determined via spectrophotometry.

Uncovering the structure and function of specialist bacterial lineages in environments routinely exposed to explosives

Environmental contamination by hexahydro-1, 3, 5-trinitro-1, 3, 5-triazine (RDX), and Octahydro-1, 3, 5, 7-tetranitro-1, 3, 5, 7-tetrazocine (HMX), the two most widely used compounds for military operations, is a long-standing problem at the manufacturing and decommissioning plants. Since explosives contamination has previously been shown to favour the growth of specific bacterial communities, the present study attempts to identify the specialist bacterial communities and their potential functional and metabolic roles by using amplicon targeted and whole-metagenome sequencing approaches (WMS) in samples collected from two distinct explosives manufacturing sites. We hypothesize that the community structure and functional attributes of bacterial population are substantially altered by the concentration of explosives and physicochemical conditions. The results highlight the predominance of Planctomycetes in contrast to previous reports from similar habitats. The detailed phylogenetic analysis revealed the presence of OTU's related to bacterial members known for their explosives degradation. Further, the functional and metabolic analyses highlighted the abundance of putative genes and unidentified taxa possibly associated with xenobiotic biodegradation. Our findings suggest that microbial species capable of utilizing explosives as a carbon, energy, or electron source are favoured by certain selective pressures based on the prevailing physicochemical and geographical conditions.

Plants-Microorganisms-Based Bioremediation for Heavy Metal Cleanup: Recent Developments, Phytoremediation Techniques, Regulation Mechanisms, and Molecular Responses

Rapid industrialization, mine tailings runoff, and agricultural activities are often detrimental to soil health and can distribute hazardous metal(loid)s into the soil environment, with harmful effects on human and ecosystem health. Plants and their associated microbes can be deployed to clean up and prevent environmental pollution. This green technology has emerged as one of the most attractive and acceptable practices for using natural processes to break down organic contaminants or accumulate and stabilize metal pollutants by acting as filters or traps. This review explores the interactions between plants, their associated microbiomes, and the environment, and discusses how they shape the assembly of plant-associated microbial communities and modulate metal(loid)s remediation. Here, we also overview microbe-heavy-metal(loid)s interactions and discuss microbial bioremediation and plants with advanced phytoremediation properties approaches that have been successfully used, as well as their associated biological processes. We conclude by providing insights into the underlying remediation strategies' mechanisms, key challenges, and future directions for the remediation of metal(loid)s-polluted agricultural soils with environmentally friendly techniques.

Interactive effects of biochar amendment and lead toxicity on soil microbial community

This study determined the interactive effects of biochar and lead toxicity on the soil microbial community in a phytoextraction experiment. Arranged with a completely randomized design in a greenhouse, banana liners were planted singly in a sandy soil spiked with Pb(NO3)2 at 0, 400 and 1200 mg kg-1 and amended with bamboo biochar (pyrolyzing at 600 °C) at 0, 1, 3%. Soil samples were taken from triplicated pots five months after planting and measured for (i) content of lead and organic carbon; (ii) lead speciation; and (iii) microbial community composition through 16S rRNA gene sequencing. DNA sequencing results showed that lead and biochar treatments had significant individual and interactive effects on soil microbial dissimilarities from taxonomic levels of phyla to genera. While some specific taxa were lead resistant, biochar addition apparently alleviated lead toxicity and increased their richness (e.g., Alkanibacter, Muciaginibacter, Burkholderiaceae, and Beggiatoaceae). Soil analysis data indicated that biochar not only helped retain more lead in the soil matrix but created a soil environment inducive for transformation of lead into highly insoluble pyromorphite. This study highlights the effectiveness of biochar for lead remediation and the sensitivity of soil microorganisms in sensing changes in soil environment and lead bioavailability.

Deposition of Lead Phosphate by Lead-Tolerant Bacteria Isolated from Fresh Water near an Abandoned Mine

Specialist bacteria can synthesize nanoparticles from various metal ions in solution. Metal recovery with high efficiency can be achieved by metal-tolerant microorganisms that proliferate in a concentrated metal solution. In this study, we isolated bacteria (Pseudomonas sp. strain KKY-29) from a bacterial library collected from water near an abandoned mine in Komatsu City, Ishikawa Prefecture, Japan. KKY-29 was maintained in nutrient medium with lead acetate and synthesized hydrocerussite and pyromorphite nanoparticles inside the cell; KKY-29 also survived nanoparticle synthesis. Quantitative PCR analysis of genes related to phosphate metabolism showed that KKY-29 decomposed organic phosphorus to synthesize lead phosphate. KKY-29 also deposited various metal ions and synthesized metal nanoparticles when incubated in various metal salt solutions other than lead. The present study considers the development of biotechnology to recover lead as an economically valuable material.

Fire effects on the distribution and bioavailability of potentially toxic elements (PTEs) in agricultural soils

In the last years, uncontrolled fires are frequently occurring in forest and agricultural areas as an indirect effect of the rising aridity and global warming or caused by intentional illegal burnings. In addition, controlled burning is still largely used by farmers as an agricultural practice in many parts of the world. During fire events, soil can reach very high temperatures at the soil surface, causing dramatic changes of soil properties and elements biogeochemistry. Among soil elements, also potentially toxic elements (PTEs) can be affected by fires, becoming more or less mobile and bioavailable, depending on fire severity and soil characteristics. Such transformations could be particularly relevant in agricultural soils used for crop productions since fire events could modify PTEs speciation and uptake by plants and associated (micro)organisms thus endangering the whole food-chain. In this review, after describing the effects of fire on soil minerals and organic matter, the impact of fires on PTEs distribution and speciation in soils is presented, as well as their influence on soil microorganisms and plants uptake. The most common experimental methods used to simulate fires at the laboratory and field scale are briefly illustrated, and finally the impact that traditional and innovative agricultural practices can have on PTEs availability in burned agricultural soils is discussed in a future research perspective.

Effects of Abiotic Stress on Soil Microbiome

Rhizospheric organisms have a unique manner of existence since many factors can influence the shape of the microbiome. As we all know, harnessing the interaction between soil microbes and plants is critical for sustainable agriculture and ecosystems. We can achieve sustainable agricultural practice by incorporating plant-microbiome interaction as a positive technology. The contribution of this interaction has piqued the interest of experts, who plan to do more research using beneficial microorganism in order to accomplish this vision. Plants engage in a wide range of interrelationship with soil microorganism, spanning the entire spectrum of ecological potential which can be mutualistic, commensal, neutral, exploitative, or competitive. Mutualistic microorganism found in plant-associated microbial communities assist their host in a number of ways. Many studies have demonstrated that the soil microbiome may provide significant advantages to the host plant. However, various soil conditions (pH, temperature, oxygen, physics-chemistry and moisture), soil environments (drought, submergence, metal toxicity and salinity), plant types/genotype, and agricultural practices may result in distinct microbial composition and characteristics, as well as its mechanism to promote plant development and defence against all these stressors. In this paper, we provide an in-depth overview of how the above factors are able to affect the soil microbial structure and communities and change above and below ground interactions. Future prospects will also be discussed.

Lead acetate ecotoxicity in tropical soils

Lead acetate (AcPb) is an important raw material used in chemical industries worldwide. The potential toxicity of AcPb is generally attributed to the presence of Pb. However, the effect of AcPb on the environment as a whole is still poorly known. This study aimed to evaluate AcPb toxicity on three standard species of soil invertebrates and two plant species using ecotoxicology tests. Three tropical soils (Oxisol, Inceptisol, and Tropical Artificial Soil (TAS)) were contaminated with different concentrations of AcPb and one dose of K-acetate (positive control). These soils were used in tests with Eisenia andrei (earthworm), Folsomia candida (springtail), Enchytraeus crypticus (enchytraeid), Zea mays (maize), and Phaseolus vulgaris (common bean). Dose-response curves obtained in the laboratory tests were used to estimate the EC₅₀ values for each species. Among invertebrates, the highest sensitivity to AcPb was observed for E. crypticus in the TAS (EC₅₀ = 29.8 mg AcPb kg^-1), whereas for E. andrei and F. candida the highest sensitivity was observed in the Oxisol (EC₅₀ = 141.9 and 1835 mg AcPb kg^-1, respectively). Folsomia candida was the least sensitive invertebrate species to AcPb in all soils. Among plant species, Z. mays was less sensitive (EC₅₀ = 1527.5 mg AcPb kg^-1) than P. vulgaris (EC₅₀ = 560.5 mg AcPb kg^-1) in the Oxisol. The present study evidenced that the toxicity of AcPb should not be attributed uniquely to the presence of Pb, as the treatment containing uniquely Ac provoked the same toxicity as the highest dose of AcPb.

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.

Metal-Fungus interaction: Review on cellular processes underlying heavy metal detoxification and synthesis of metal nanoparticles

The most adverse outcome of increasing industrialization is contamination of the ecosystem with heavy metals. Toxic heavy metals possess a deleterious effect on all forms of biota; however, they affect the microbial system directly. These heavy metals form complexes with the microbial system by forming covalent and ionic bonds and affecting them at the cellular level and biochemical and molecular levels, ultimately leading to mutation affecting the microbial population. Microbes, in turn, have developed efficient resistance mechanisms to cope with metal toxicity. This review focuses on the vital tolerance mechanisms employed by the fungus to resist the toxicity caused by heavy metals. The tolerance mechanisms have been basically categorized into biosorption, bioaccumulation, biotransformation, and efflux of metal ions. The mechanisms of tolerance to some toxic metals as copper, arsenic, zinc, cadmium, and nickel have been discussed. The article summarizes and provides a detailed illustration of the tolerance means with specific examples in each case. Exposure of metals to fungal cells leads to a response that may lead to the formation of metal nanoparticles to overcome the toxicity by immobilization in less toxic forms. Therefore, fungal-mediated green synthesis of metal nanoparticles, their mechanism of synthesis, and applications have also been discussed. An understanding of how fungus resists metal toxicity can provide insights into the development of adaption techniques and methodologies for detoxification and removal of metals from the environment.

Microbial diversity and activity assessment in a 100-year-old lead mine

Mining activities frequently leave a legacy of residues that remain in the area for long periods causing the pollution of surroundings. We studied on a 100 year-old mine, the behavior of potentially toxic elements (PTEs) and their ecotoxicological impact on activity and diversity of microorganisms. The PTEs contamination assessment allowed the classification of the materials as highly (reference- and contaminated-samples) and very highly polluted (illegal spill of olive mill wastes (OMW), tailings, and dumps). OMW presented the lowest enzymatic activities while tailings and dumps had low dehydrogenase and arylsulfatase activities. All the α-diversity indices studied were negatively impacted in dumps. Tailings had lower Chao1 and PD whole tree values as compared to those of reference-samples. β-diversity analysis showed similar bacterial community composition for reference- and contaminated-samples, significantly differing from that of tailings and dumps. The relative abundance of Gemmatimonadetes, Bacteroidetes, and Verrucomicrobia was lower in OMW, tailings, and dumps as compared to reference-samples. Fifty-seven operational taxonomic units were selected as responsible for the changes observed between samples. This study highlights that assessing the relationship between physicochemical properties and microbial diversity and activity gives clues about ongoing regulating processes that can be helpful for stakeholders to define an appropriate management strategy.

Mechanistic Aspects of Microbe-Mediated Nanoparticle Synthesis

In recent times, nanoparticles (NPs) have found increasing interest owing to their size, large surface areas, distinctive structures, and unique properties, making them suitable for various industrial and biomedical applications. Biogenic synthesis of NPs using microbes is a recent trend and a greener approach than physical and chemical methods of synthesis, which demand higher costs, greater energy consumption, and complex reaction conditions and ensue hazardous environmental impact. Several microorganisms are known to trap metals in situ and convert them into elemental NPs forms. They are found to accumulate inside and outside of the cell as well as in the periplasmic space. Despite the toxicity of NPs, the driving factor for the production of NPs inside microorganisms remains unelucidated. Several reports suggest that nanotization is a way of stress response and biodefense mechanism for the microbe, which involves metal excretion/accumulation across membranes, enzymatic action, efflux pump systems, binding at peptides, and precipitation. Moreover, genes also play an important role for microbial nanoparticle biosynthesis. The resistance of microbial cells to metal ions during inward and outward transportation leads to precipitation. Accordingly, it becomes pertinent to understand the interaction of the metal ions with proteins, DNA, organelles, membranes, and their subsequent cellular uptake. The elucidation of the mechanism also allows us to control the shape, size, and monodispersity of the NPs to develop large-scale production according to the required application. This article reviews different means in microbial synthesis of NPs focusing on understanding the cellular, biochemical, and molecular mechanisms of nanotization of metals.

Response of carbon and microbial properties to risk elements pollution in arctic soils

A 180-day incubation study was conducted to evaluate the effects of risk elements (REs) on organic carbon use and microbial activities in organic soils in the Arctic during the summer snowmelt period. Soils were artificially spiked with Cd, Pb, Cr, Ni, Cu, As, and a combination of these REs according to the levels measured in Arctic soils from REs-polluted industrial sites. During the incubation period, microbial activities and microbial biomass carbon (MBC) formation were inhibited, and microbial quotient (qCO2) values were relatively high in the spiked soils indicating that more energy was used by microbes for maintenance under REs stress. Meanwhile, microbial metabolism was significantly restrained. Microbial Specific phospholipid fatty acids (PLFAs) were reduced in RE spiked soils relative to the control, especially in the As- and multi-RE-spiked soils. The abundance of both fungi and bacteria was reduced in response to RE amendments by 14-24% and 1-55%, respectively. PLFA biomarkers indicated a shift in soil microbial community structure and activities influenced by REs, consequently having a negative effect on soil organic carbon degradation. This study addresses the knowledge gap regarding the alternation of biochemical reactions in Arctic soils under anthropogenic REs with relevant contamination levels.

Effects of Land Use and Pollution Loadings on Ecotoxicological Assays and Bacterial Taxonomical Diversity in Constructed Wetlands

Freshwater ecosystems are affected by anthropogenic alterations. Different studies have extensively studied the concentrations of metals, nutrients, and water quality as measurements of pollution in freshwater ecosystems. However, few studies have been able to link these pollutants to bioindicators as a risk assessment tool. This study aimed to examine the potential of two bioindicators, plant ecotoxicological assays and sediment bacterial taxonomic diversity, in ecological risk assessment for six freshwater constructed wetlands in a rapidly urbanizing watershed with diverse land uses. Sediment samples were collected summer, 2015 and 2017, and late summer and early fall in 2016 to conduct plant ecotoxicological assays based on plant (Lepidium, Sinapis and Sorghum) growth inhibition and identify bacterial taxonomical diversity by the 16S rRNA gene sequences. Concentrations of metals such as lead (Pb) and mercury (Hg) (using XRF), and nutrients such as nitrate and phosphate (using HACH DR 2800TM spectrophotometer) were measured in sediment and water samples respectively. Analyses of response patterns revealed that plant and bacterial bioindicators were highly responsive to variation in the concentrations of these pollutants. Hence, this opens up the scope of using these bioindicators for ecological risk assessment in constructed freshwater wetland ecosystems within urbanizing watersheds.

The ecological roles of microbial lipopeptides: Where are we going?

Lipopeptides (LPs) are secondary metabolites produced by a diversity of bacteria and fungi. Their unique chemical structure comprises both a peptide and a lipid moiety. LPs are of major biotechnological interest owing to their emulsification, antitumor, immunomodulatory, and antimicrobial activities. To date, these versatile compounds have been applied across multiple industries, from pharmaceuticals through to food processing, cosmetics, agriculture, heavy metal, and hydrocarbon bioremediation. The variety of LP structures and the diversity of the environments from which LP-producing microorganisms have been isolated suggest important functions in their natural environment. However, our understanding of the ecological role of LPs is limited. In this review, the mode of action and the role of LPs in motility, antimicrobial activity, heavy metals removal and biofilm formation are addressed. We include discussion on the need to characterise LPs from a diversity of microorganisms, with a focus on taxa inhabiting 'extreme' environments. We introduce the use of computational target fishing and molecular dynamics simulations as powerful tools to investigate the process of interaction between LPs and cell membranes. Together, these advances will provide new understanding of the mechanism of action of novel LPs, providing greater insights into the roles of LPs in the natural environment.

Distribution and speciation of Sb and toxic metal(loid)s near an antimony refinery and their effects on indigenous microorganisms

Although several studies have investigated the effects of Sb contamination on surrounding environments and indigenous microorganisms, little is known about the effect of co-contamination of Sb and toxic metal(loid)s. In this study, the occurrence of Sb and other toxic metal(loid)s near an operating Sb refinery and near-field landfill site were investigated. Topsoil samples near the refinery had high Sb levels (∼3250 mg kg^-1) but relatively low concentrations of other toxic metal(loid)s. However, several soil samples taken at greater depth from the near-field landfill site contained high concentrations of As and Pb, as well as extremely high Sb contents (∼21,400 mg kg^-1). X-ray absorption fine structure analysis showed that Sb in the soils from both sites was present as Sb(V) in the form of tripuhyite (FeSbO₄), a stable mineral. Three-dimensional principal coordinate analysis showed that microbial community compositions in samples with high toxic metal(loid)s concentrations were significantly different from other samples and had lower microbial populations (∼10⁴ MPN g^-1). Sequential extraction results revealed that Sb is present primarily in the stable residual fraction (∼99 %), suggesting low Sb bioavailability. However, microbial redundancy analysis suggested that the more easily extractable Pb might be the major factor controlling microbial community compositions at the site.

The Transcriptomic Landscape of Cupriavidus metallidurans CH34 Acutely Exposed to Copper

Bacteria are increasingly used for biotechnological applications such as bioremediation, biorecovery, bioproduction, and biosensing. The development of strains suited for such applications requires a thorough understanding of their behavior, with a key role for their transcriptomic landscape. We present a thorough analysis of the transcriptome of Cupriavidus metallidurans CH34 cells acutely exposed to copper by tagRNA-sequencing. C. metallidurans CH34 is a model organism for metal resistance, and its potential as a biosensor and candidate for metal bioremediation has been demonstrated in multiple studies. Several metabolic pathways were impacted by Cu exposure, and a broad spectrum of metal resistance mechanisms, not limited to copper-specific clusters, was overexpressed. In addition, several gene clusters involved in the oxidative stress response and the cysteine-sulfur metabolism were induced. In total, 7500 transcription start sites (TSSs) were annotated and classified with respect to their location relative to coding sequences (CDSs). Predicted TSSs were used to re-annotate 182 CDSs. The TSSs of 2422 CDSs were detected, and consensus promotor logos were derived. Interestingly, many leaderless messenger RNAs (mRNAs) were found. In addition, many mRNAs were transcribed from multiple alternative TSSs. We observed pervasive intragenic TSSs both in sense and antisense to CDSs. Antisense transcripts were enriched near the 5' end of mRNAs, indicating a functional role in post-transcriptional regulation. In total, 578 TSSs were detected in intergenic regions, of which 35 were identified as putative small regulatory RNAs. Finally, we provide a detailed analysis of the main copper resistance clusters in CH34, which include many intragenic and antisense transcripts. These results clearly highlight the ubiquity of noncoding transcripts in the CH34 transcriptome, many of which are putatively involved in the regulation of metal resistance.

Changes in electricity production and microbial community evolution in constructed wetland-microbial fuel cell exposed to wastewater containing Pb(II)

Two constructed wetland microbial fuel cell (CW-MFC) devices, experimental group (EG, with 5 mg/L Pb(II) addition) and control group (CG) were built to explore the changes in power generation, wastewater purification and microbial community structure under Pb(II) stress. The voltage of EG (343.16 ± 12.14 mV) was significantly higher (p < 0.01) than that of CG (295.49 ± 13.91 mV), and the highest power density of the EG and CG were 7.432 mW·m^-2 and 3.873 mW·m^-2, respectively. There was no significant difference in the removal of common pollutants between these groups except for the NH₄⁺-N removal efficiency, which was probably caused by the inhibition of the bioactivity of Comamonas (AOB) in the anode of the experimental group by Pb(II). Pb(II) was effectively removed by CW-MFC (84.86 ± 3%), and the abundant amount of fulvic acid-like matter in the extracellular polymeric substance (EPS) of the EG contributed to its removal. The presence of Pb(II) had a negative effect on both microbial community diversity and species richness. The abundance of a lead resistance gene, pbrT, decreased with long-term Pb(II) pressure. This is evidence of microbial adaptation to Pb(II).

Microbial community shift under exposure of dredged sediments from a eutrophic bay

Microbial communities occur in almost every habitat. To evaluate the homeostasis disruption of in situ microbiomes, dredged sediments from Guanabara Bay-Brazil (GB) were mixed with sediments from outside of the bay (D) in three different proportions (25%, 50%, and 75%) which we called GBD25, GBD50, and GBD75. Grain size, TOC, and metals-as indicators of complex contamination-dehydrogenase (DHA) and esterase enzymes (EST)-as indicators of microbial community availability-were determined. Microbial community composition was addressed by amplifying the 16S rRNA gene for DGGE analysis and sequencing using MiSeq platform (Illumina).We applied the quality ratio index (QR) to the GB, D, and every GBD mixture to integrate geochemical parameters with our microbiome data. QR indicated high environmental risk for GB and every GBD mixture, and low risk for D. The community shifted from aerobic to anaerobic profile, consistent with the characteristics of GB. Sample D was dominated by JTB255 marine benthic group, related to low impacted areas. Milano-WF1B-44 was the most representative of GB, often found in anaerobic and sulfur enriched environments. In GBD, the denitrifying sulfur-oxidizing bacteria, Sulfurovum, was the most representative, typically found in suboxic or anoxic niches. The canonical correspondence analysis was able to explain 60% of the community composition variation and exhibit the decrease of environmental quality as the contamination increases. Physiological and taxonomic shifts of the microbial assemblage in sediments were inferred by QR, which was suitable to determine sediment risk. The study produced sufficient information to improve the dredging plan and management.

Heavy metal concentrations in Brazilian port areas and their relationships with microorganisms: can pollution in these areas change the microbial community?

The objectives of this study were to analyze the difference in ways in which metals polluting Brazilian port areas influence bacterial communities and the selection of resistant strains. The hypothesis tested was that port areas would have microbial communities significantly different from a pristine area, mainly due to a greater load of metals found in these areas. Sediment samples were collected in two port areas (Santos and São Sebastião) and one pristine area (Ubatuba). Total DNA was extracted and MiSeq sequencing was performed. A hundred strains were isolated from the same samples and were tested for metal resistance. The community composition was similar in the two port regions, but differed from the pristine area. Microbial diversity was significantly lower in the port areas. The phyla Proteobacteria, Cyanobacteria, and Thermodesulfobacteria exhibited positive correlations with copper and zinc concentrations. Chloroflex, Nitrospirae, Planctomycetes, and Chlorobi exhibited negative correlations with copper, chromium, and zinc. Cr and Zn had higher concentrations at port areas and were responsible to select more metal-resistant strains. Some genera were found to be able to easily develop metal resistance. The most isolated genera were Bacillus, Vibrio, and Pseudomonas. This type of study can illustrate, even in very complex natural environments, the influence of pollution on the community as a whole and the consequences of these changes.

A comprehensive review of biogeochemical distribution and fractionation of lead isotopes for source tracing in distinct interactive environmental compartments

Lead (Pb) is a non-essential and extremely noxious metallic-element whose biogeochemical cycle has been influenced predominantly by increasing human activities to a great extent. The introduction and enrichment of this ubiquitous contaminant in the terrestrial-environment has a long history and getting more attention due to its adverse health effects to living organisms even at very low exposure levels. Its lethal-effects can vary widely depending on the atmospheric-depositions, fates and distribution of Pb isotopes (i.e., ²⁰⁴Pb, ²⁰⁶Pb, ²⁰⁷Pb &²⁰⁸Pb) in the terrestrial-environment. Thus, it is essential to understand the depositional behavior and transformation mechanism of Pb and the factors affecting Pb isotopes composition in the terrestrial-compartments. Owing to the persistence nature of Pb-isotopic fractions, regardless of ongoing biogeochemical-processes taking place in soils and in other interlinked terrestrial-compartments of the biosphere makes Pb isotope ratios (Pb-IRs) more recognizable as a powerful and an efficient-tool for tracing the source(s) and helped uncover pertinent migration and transformation processes. This review discusses the ongoing developments in tracing migration pathway and distribution of lead in various terrestrial-compartments and investigates the processes regulating the Pb isotope geochemistry taking into account the source identification of lead, its transformation among miscellaneous terrestrial-compartments and detoxification mechanism in soil-plant system. Additionally, this compendium reveals that Pb-pools in various terrestrial-compartments differ in Pb isotopic fractionations. In order to improve understanding of partition behaviors and biogeochemical pathways of Pb isotope in the terrestrial environment, future works should involve investigation of changes in Pb isotopic compositions during weathering processes and atmospheric-biological sub-cycles.

Contamination, sources and risk assessments of metals in media from Anka artisanal gold mining area, Northwest Nigeria

Mining is a major human activity that has contributed significantly to high degree of environmental and human health degradation. This study was done to uncover the degree of contamination and risks associated with metals in environmental media collected from Anka area, Northwest Nigeria. A total of eighty-two (82) samples which include 42 soils, 22 stream sediments, 13 tailings and 5 plants were collected. Media were air-dried, pulverized and sieved to collect fine particles. They were digested and analyzed for toxic metal contents using High Performance Liquid Chromatography-Inductively Coupled Plasma Mass Spectrometer (HPLC-ICPMS). Metals analyzed include As, Cd, Co, Cr, Cu, Hg, Ni, Pb, Sb, Zn and Fe. From the results, degree of contamination in samples were obtained using pollution indices, while ecological and health risks were calculated using acceptable risk indices. Average concentrations of metals in the soils were: As: 0.64 μg/g; Cr: 42.55 μg/g; Pb: 131.76 μg/g; Hg: 0.85 μg/g while in sediments, the average concentration were As: 15.46 μg/g; Cr: 111.82 μg/g; Pb: 2234.02 μg/g; Hg: 2.12 μg/g. In tailings, the mean concentration were As: 4.79 μg/g; Cr: 96.95 μg/g; Pb: 2802.56 μg/g; Hg: 1.25 μg/g. Metals in plants are above acceptable limits. Metals in the media are both from geogenic and mining activities, and they pose high ecological risks. High carcinogenic (>10^-4) and non-carcinogenic (>1) health risks are associated with metals in media from this area. Further epidemiological studies should be carried to know the extent of occurrence of diseases associated with mining in the area.

Potential ecological and health risks of toxic metals associated with artisanal mining contamination in Ijero, southwest Nigeria

This investigation was done to decide the concentrations, sources and potential risks of metals in media around Ijero area. A total of 80 samples including topsoils, sediments, tailings and whole plants were gathered from this territory while control samples were taken from zone with less human exercises. Samples were pounded, sieved and chemically analyzed utilizing Agilent High Plasma Liquid Chromatography Inductively Coupled Plasma-Mass Spectrometer. Results demonstrated that the mean concentrations of lead (Pb) and zinc (Zn) in soils are 30.61 and 123.71 µg/g individually. In tailings the mean distribution of Pb and Zn are 33.16 and 22.44 µg/g each. Toxic units in all media were less than 4, indicating low effect on the ecosystem. Bivariate correlation, hierarchical cluster and principal component analyses revealed that metals in media from this area originated from mining and mineral processing activities, mixed and geogenic sources. Study revealed that metals in the media pose high degree of contamination and moderate to high ecological hazard. Also, there is high cancer-causing hazard index (HI) (10^-6-10^-4) and non-cancer-causing (HI > 1) dangers which is more articulated in kids than the grown-ups. It is important to introduce measures that will decrease the negative impacts associated with mining in the area.

Community Composition of Nitrite Reductase Gene Sequences in an Acid Mine Drainage Environment

Denitrifying microbial communities play a central role in the nitrogen cycle, contribute to greenhouse gas production, and provide ecosystem services through the mitigation of nitrogen pollution. The impacts of human-induced acid mine drainage (AMD) and naturally occurring acid rock drainage (ARD), both characterized by low pH and high metal concentrations, on denitrifying microbial communities is not well understood. This study examined denitrifying microbes within sediments impacted by acidic and metal-rich AMD or ARD in the Iron Springs Mining District (10 sites across four regions over four time points) located in Southwest Colorado, USA. Denitrification functional gene sequences (nirS and nirK coding for nitrite reductase) had a high number of observed OTUs (260 for nirS and 253 for nirK) and were observed at sites with pH as low as 3.5 and metals > 2 mg/L (including aluminum, iron, manganese, strontium, and zinc). A majority of the nirK and nirS OTUs (> 60%) were present in only one sampling region. Approximately 8% of the nirK and nirS OTUs had a more cosmopolitan distribution with presence in three or more regions. Phylogenetically related OTUs were found across sites with very different chemistry. The overall community structure for nirK and nirS genes was correlated to conductivity and calcium (respectively), which may suggest that conductivity may play an important role in shaping the distribution of nirK- and nirS-type denitrifiers. Overall, these findings improve upon our understanding of the potential for denitrification within an ecosystem impacted by AMD or ARD and provide a foundation for future research to understand the rates and physiology of denitrifying organisms in these systems.

Phytoremediation of Heavy Metal-Contaminated Sites: Eco-environmental Concerns, Field Studies, Sustainability Issues, and Future Prospects

Environmental contamination due to heavy metals (HMs) is of serious ecotoxicological concern worldwide because of their increasing use at industries. Due to non-biodegradable and persistent nature, HMs cause serious soil/water pollution and severe health hazards in living beings upon exposure. HMs can be genotoxic, carcinogenic, mutagenic, and teratogenic in nature even at low concentration. They may also act as endocrine disruptors and induce developmental as well as neurological disorders, and thus, their removal from our natural environment is crucial for the rehabilitation of contaminated sites. To cope with HM pollution, phytoremediation has emerged as a low-cost and eco-sustainable solution to conventional physicochemical cleanup methods that require high capital investment and labor alter soil properties and disturb soil microflora. Phytoremediation is a green technology wherein plants and associated microbes are used to remediate HM-contaminated sites to safeguard the environment and protect public health. Hence, in view of the above, the present paper aims to examine the feasibility of phytoremediation as a sustainable remediation technology for the management of metal-contaminated sites. Therefore, this paper provides an in-depth review on both the conventional and novel phytoremediation approaches; evaluates their efficacy to remove toxic metals from our natural environment; explores current scientific progresses, field experiences, and sustainability issues; and revises world over trends in phytoremediation research for its wider recognition and public acceptance as a sustainable remediation technology for the management of contaminated sites in the twenty-first century.

Advances in characterizing microbial community change and resistance upon exposure to lead contamination: Implications for ecological risk assessment

Recent advancement in molecular techniques has spurred waves of studies on responses of microorganisms to lead contamination exposure, leveraging detailed phylogenetic analyses and functional gene identification to discern the effects of lead toxicity on microbial communities. This work provides a comprehensive review of recent research on (1) microbial community changes in contaminated aquatic sediments and terrestrial soils; (2) lead resistance mechanisms; and (3) using lead resistance genes for lead biosensor development. Sufficient evidence in the literature, including both in vitro and in situ studies, indicates that exposure to lead contamination inhibits microbial activity resulting in reduced respiration, suppressed metabolism, and reduced biomass as well as altered microbial community structure. Even at sites where microbial communities do not vary compositionally with contamination levels due to extremely long periods of exposure, functional differences between microbial communities are evident, indicating that some microorganisms are susceptible to lead toxicity as others develop resistance mechanisms to survive in lead contaminated environments. The main mechanisms of lead resistance involve extracellular and intracellular biosorption, precipitation, complexation, and/or efflux pumps. These lead resistance mechanisms are associated with suites of genes responsible for specific lead resistance mechanisms and may serving as indicators of lead contamination in association with dominance of certain phyla. This allows for development of several lead biosensors in environmental biotechnology. To promote applications of these advanced understandings, molecular techniques, and lead biosensor technology, perspectives of future work on using microbial indicators for site ecological assessment is presented.

Reducing chromium uptake through application of calcium and sodium in spinach

In peri-urban areas, the use of wastewater for crop production is a common practice due to water scarcity. Moreover, in the recent years, large quantity of wastewater generation and discharge as industrial effluent in water resources is another issue for reduction of water quality. The leather industries are significantly contributing chromium (Cr) in effluent, whereas, other industries may have salt and cationic load in their discharges are mixed up. Therefore, it is mandatory to study the interactive effect of different effluent constituents on crop plants. In this connection, a pot culture experiment was conducted at the ICAR-Indian Institute of Soil Science, Bhopal to compute the effect of application of calcium (Ca) and sodium (Na) ions on Cr uptake by spinach crop in Vertisol of central India. Three levels of Cr (0, 50, 100 mg kg^-1), calcium (0, 2, 4 mM), and sodium (0, 40, 80 mM) were applied in combinations. The spinach variety All Green was used as a test crop and harvested at full maturity. Results showed that application of Ca and Na reduced the Cr uptake in spinach crop. The reduction of Cr uptake was more in the root than shoot. Applied calcium acted as an essential plant nutrient and enhanced the crop biomass. Sole applications of Na adversely affected the crop biomass and Cr uptake in both root and shoot of spinach. In conclusion, application of Ca fertilizers reduced the Cr toxicity in spinach and could be used as a strategy for the safe utilization of tannery industrial effluents for crop production.

Heavy metal pollution and co-selection for antibiotic resistance: A microbial palaeontology approach

Frequent and persistent heavy metal pollution has profound effects on the composition and activity of microbial communities. Heavy metals select for metal resistance but can also co-select for resistance to antibiotics, which is a global health concern. We here document metal concentration, metal resistance and antibiotic resistance along a sediment archive from a pond in the North West of the United Kingdom covering over a century of anthropogenic pollution. We specifically focus on zinc, as it is a ubiquitous and toxic metal contaminant known to co-select for antibiotic resistance, to assess the impact of temporal variation in heavy metal pollution on microbial community diversity and to quantify the selection effects of differential heavy metal exposure on antibiotic resistance. Zinc concentration and bioavailability was found to vary over the core, likely reflecting increased industrialisation around the middle of the 20th century. Zinc concentration had a significant effect on bacterial community composition, as revealed by a positive correlation between the level of zinc tolerance in culturable bacteria and zinc concentration. The proportion of zinc resistant isolates was also positively correlated with resistance to three clinically relevant antibiotics (oxacillin, cefotaxime and trimethoprim). The abundance of the class 1 integron-integrase gene, intI1, marker for anthropogenic pollutants correlated with the prevalence of zinc- and cefotaxime resistance but not with oxacillin and trimethoprim resistance. Our microbial palaeontology approach reveals that metal-contaminated sediments from depths that pre-date the use of antibiotics were enriched in antibiotic resistant bacteria, demonstrating the pervasive effects of metal-antibiotic co-selection in the environment.

Animal residues found on tiny Lower Paleolithic tools reveal their use in butchery

Stone tools provide a unique window into the mode of adaptation and cognitive abilities of Lower Paleolithic early humans. The persistently produced large cutting tools (bifaces/handaxes) have long been an appealing focus of research in the reconstruction of Lower Paleolithic survival strategies, at the expenses of the small flake tools considered by-products of the stone production process rather than desired end products. Here, we use use-wear, residues and technological analyses to show direct and very early evidence of the deliberate production and use of small flakes for targeted stages of the prey butchery process at the late Lower Paleolithic Acheulian site of Revadim, Israel. We highlight the significant role of small flakes in Lower Paleolithic adaptation alongside the canonical large handaxes. Our results demonstrate the technological and cognitive flexibility of early human groups in the Levant and beyond at the threshold of the departure from Lower Paleolithic lifeways.

The negative impact of cadmium on nitrogen transformation processes in a paddy soil is greater under non-flooding than flooding conditions

Nitrification and denitrification are two important processes in the nitrogen (N) cycle. Under heavy-metal pollution with water management of paddy soils, these two processes are not well understood. This study aimed to examine the effect of cadmium (Cd) on N transformation under flooding and non-flooding conditions. A paddy soil was incubated under two water regimes (flooding and non-flooding) and four Cd levels (0, 2, 5 and 10 mg kg^-1). The availability of Cd was higher in the non-flooding than flooding conditions. Cadmium contamination significantly (p ≤ 0.05) decreased the copy number of archaeal and bacterial amoA genes, bacterial nirS, nirK and nosZ genes under both conditions with the decrease being greater under non-flooding. High level of Cd (10 mg kg^-1) was more toxic in non-flooding than flooding conditions to the nitrifiers and denitrifiers, which in turn decreased N transformation through microbially-mediated processes. Its contamination decreased N₂O emission initially under both water regimes but the effect was greater under the non-flooding condition. However, the non-significant stimulatory effect of Cd on N₂O emission was observed during the late phase. The microbial community structure was changed with time and water regimes. Irrespective of water regime, the dominated fungal phyla were Ascomycota and Basidiomycota while the dominated bacteria phyla were Actinobacteria, Proteobacteria, Firmicutes and Acidobacteria. In summary, water regimes and Cd bioavailability changed soil N transformations via microbial mediated processes.

Diagnosis of soil contamination using microbiological indices: A review on heavy metal pollution

Heavy metal contamination of soil has become a serious global issue because of their persistence in the environment and the non-biodegradable nature leading to their accumulation to toxic levels. In order to achieve early warning and prevent soil quality from deteriorating, it is necessary to select suitable indices to diagnose heavy metal pollution. Microbiological indices for monitoring soil pollution by heavy metals are gaining attention. However, the related researches are scattered, and critical review is imperative. This review is mainly to provide readers with an in-depth understanding of the merits and limitations of microbiological indices for heavy metals contaminated and remediated soils. Microbiological indicators include microbial abundance, community diversity and structure, functional activity. The changes of different microbiological indices and the mechanism of microbial response to heavy metal stress in soils are comprehensively summarized. Furthermore, research gaps and future directions of the microbial ecotoxicological diagnosis of soil contamination by heavy metals are also proposed and discussed.

The role of selenium on mitigating arsenic accumulation, enhancing growth and antioxidant responses in metallicolous and non-metallicolous population of Isatis cappadocica Desv. and Brassica oleracea L

A hydroponic experiment was conducted to explore the interactive effects of selenium (Se) supplementation (0, 5, and 10 μM) and arsenic (As) toxicity (0, 200, and 400 μM) on the growth, accumulation, and oxidative damage along with defense mechanisms of metallicolous (MP) and non-metallicolous population (NMP) of Isatis cappadocica, an As-hyperaccumulator, and Brassica oleracea as reference brassica. The results revealed that As stress significantly hampered plant growth particularly in B. oleracea. It reduced plant growth due to enhanced oxidative load of As-stressed plants. Between the two Isatis populations, metallicolous plants accumulated significantly higher As, however with considerably low growth defects. Furthermore, Se supplementation counteracted the adverse effects of stress on growth and physiological performance of all studied plants. Addition of Se, particularly at higher dose (10 μM), significantly suppressed root As uptake and slightly its accumulation in shoots of B. oleracea plants treated with 400 μM As, and thus improved growth characteristics of stressed plants. Under As stress, Se supplementation increased the activities of enzymatic (peroxidase (POD) and glutathione reductase (GR)) and non-enzymatic (anthocyanins and total flavonoids) antioxidants, thereby suggesting relieved As stress by reduced oxidative damage. Taken together, these results support the beneficial role of Se in the regulation of As stress by improving growth, physiology, and antioxidant capacity, and highlight its significance for plants grown on such metal-contaminated soils.