High Concentrations Of Toxic Metals Research Articles

Legacy copper/nickel mine tailings potentially harbor novel iron/sulfur cycling microorganisms within highly variable communities.

The oxidation of sulfide-bearing mine tailings catalyzed by acidophilic iron and sulfur-oxidizing bacteria releases toxic metals and other contaminants into soil and groundwater as acid mine drainage. Understanding the environmental variables that control the community structure and metabolic activity of microbes indigenous to tailings (especially the abiotic stressors of low pH and high dissolved metal content) is crucial to developing sustainable bioremediation strategies. We determined the microbial community composition along two continuous vertical gradients of Cu/Ni mine tailings at each of two tailings impoundments near Sudbury, Ontario. 16S rRNA amplicon data showed high variability in community diversity and composition between locations, as well as at different depths within each location. A temporal comparison for one tailings location showed low fluctuation in microbial communities across 2 years. Differences in community composition correlated most strongly with pore-water pH, Eh, alkalinity, salinity, and the concentration of several dissolved metals (including iron, but not copper or nickel). The relative abundances of individual genera differed in their degrees of correlation with geochemical factors. Several abundant lineages present at these locations have not previously been associated with mine tailings environments, including novel species predicted to be involved in iron and sulfur cycling.IMPORTANCEMine tailings represent a significant threat to North American freshwater, with legacy tailings areas generating acid mine drainage (AMD) that contaminates rivers, lakes, and aquifers. Microbial activity accelerates AMD formation through oxidative metabolic processes but may also ameliorate acidic tailings by promoting secondary mineral precipitation and immobilizing dissolved metals. Tailings exhibit high geochemical variation within and between mine sites and may harbor many novel extremophiles adapted to high concentrations of toxic metals. Characterizing the unique microbiomes associated with tailing environments is key to identifying consortia that may be used as the foundation for innovative mine-waste bioremediation strategies. We provide an in-depth analysis of microbial diversity at four copper/nickel mine tailings impoundments, describe how communities (and individual lineages) differ based on geochemical gradients, predict organisms involved in AMD transformations, and identify taxonomically novel groups present that have not previously been observed in mine tailings.

Air pollution biomonitoring in an urban-industrial setting (Taranto, Italy) using Mediterranean plant species

This study presents the first report on the elemental composition of five Mediterranean plant species (Pinus pinaster, Eucalyptus camaldulensis, Nerium oleander, Olea europaea and Pittosporum heterophyllum) to trace industrial emissions in Taranto, Italy, a mixed-use industrial and urban setting. Potential metal sources include vehicular traffic, steel and cement plants, and a petrochemical refinery. Samples were collected from 29 sites covering the Tamburi-Lido Azzurro neighbourhood and the historical quarter Città Vecchia-Borgo. High concentrations of toxic metals were observed in all samples, with marked inter-species variability. Model based clustering identified two distinct groups, one dominated by pine needles with higher metal concentrations than the other group composed of the other four plant species. The contamination factor (CF) and pollution load index (PLI) indices which use background samples to standardise the level of pollution, were used to remove species effect allowing for direct site comparison. Spatial analysis of CF and PLI data identified pollution hotspots near industrial areas and major roads, with areas of little to no air pollution near green spaces. Statistical analysis of the CFs revealed the contribution of different sources to element emissions. Ni and Cr were primarily emitted from the steel plant and petrochemical refinery, while Fe and Al were associated with road traffic emissions, and geogenic elements Ca, Mg, K, and Na were linked to marine spray and Saharan dust. This study demonstrates that combining multiple plant species with pollution indices can be a cost-effective biomonitoring approach for assessing air pollution and creating a high-density spatial monitoring network.

Removal of toxic metals using iron sulfide particles: A brief overview of modifications and mechanisms

Growing mechanization has released higher concentrations of toxic metals in water and sediment, which is a critical concern for the environment and human health. Recent studies show that naturally occurring and synthetic iron sulfide particles are efficient at removing these hazardous pollutants. This review seeks to provide a concise summary of the evolution in the production of iron sulfide particles, specifically nanoparticles, through the years. This review presents an outline of the synthesis process for the most dominant forms of iron sulfide: mackinawite (FeS), pyrite (FeS2), pyrrhotite (Fe1-x S), and greigite (Fe3S4). The review confirms that both natural forms of iron sulfide and modified forms of iron sulfide are highly effective at removing different heavy metals and metalloids from water. Concurrently, this review reveals the interaction mechanism between toxic metals and iron sulfide, along with the impact of conditions for remedy and rectification. None the less, modifications and future investigations into the synthesis of novel iron sulfides, their use to adsorb diverse environmental pollutants, and their fate after injection into polluted aquifers, remain crucial to maximizing pollution control.

The provenance of microorganisms adapted to extreme salinity, extreme temperature, and toxic metals within the Montney shale formation.

Introduction Shale oil reservoirs are hypothesized to be sterile due to the extremely high temperature, pressure and salinity within these formations (Evans et al. 2018). High concentrations of toxic metals also pose challenges that demand specific microbial adaptions (Boyd and Barkay 2012, White and Gadd 1998, Ben Fekih et al. 2018). While some microorganisms are introduced into and are selected for within shale formations during hydraulic fracturing, the possibility that certain microorganisms are pre-existing inhabitants of these formations is less clear. Here, we followed the microbial diversity of input and output fluids injected into a Montney formation shale reservoir to assess the distribution and transport of microbial populations during hydraulic fracturing. Enrichment cultures distinguished various metabolisms in the microbial populations found in different sample types, and adaptations allowing them to colonize such niches. Material and methods Fracturing fluid, drilling muds (3302 m, 3350 m and 3400 m depths), shale cuttings (rinsed from the drillings muds), shale core plugs and produced water samples (12-month period) were sampled from a Montney shale oil reservoir. Microbial community compositions were analyzed by amplicon sequencing. Metal content was analyzed by inductively coupled plasma-mass spectrophotometry. High salinity enrichments at 90°C of the drilling muds or rinsed shale samples were set up in triplicate and amended with glucose and guar gum (a mannose/galactose-based polymer used during hydraulic fracturing). Sugars were measured through spectrophotometric assays. Metagenomic analyses were performed to assess microbial gene content. Results/Discussion Provenance of microorganisms from the Montney shale formation Provenance of microorganisms from the Montney shale formation Input fluids (fracturing fluid, drilling muds) were revealed to be the likely source of most of the microbial diversity. However, some microorganisms were only detected in the subsurface samples. ASVs affiliated with Aurantimonas, Caminicella, BRH-c8a (Family Desulfallas) and Geotoga exhibited occurrence patterns consistent with being derived from subsurface shale formations. Geotoga has only ever been reported from oil reservoirs (Semenova et al. 2020). Analysis of produced water revealed ASVs from these groups increasing in abundance during hydraulic fracturing operations, suggesting selective pressure from oil reservoir conditions (e.g., toxic metal presence, input of saline water, temperature and pressure fluctuations). Incubations set up from drilling muds showed a preference for glucose while incubations of the rinsed shale cuttings showed a microbial preference for guar gum (i.e., mannose production; Fig. 0), reinforcing the presence of different populations being derived from surface and subsurface samples. Adaptations for life in Montney shale Adaptations for life in Montney shale When considering adaptations of microorganisms for environmental conditions found in oil reservoirs, it is relevant to note the presence of toxic metals such as arsenic, cadmium and mercury. Levels of all three metals were found to vary over time within the 28-day shale microbial enrichments and 12-month produced water time course analyses (Suppl. material 1). Metagenomics revealed various genes for the internalization and metabolism of all three metals within the shale microbiome (i.e., arsenate reductases, arsenite transporters, metallothioneins, mercuric reductases). In conclusion, the results of this study suggest that shale reservoirs thus might not be sterile environments, and host microorganisms are able to contend with major perturbations.

Transport of Ba, Sr, Cd, Pb, and As in dolomite saline aquifers injected with petroleum produced water

Predicting the transport of toxic metals in dolomite saline aquifers where petroleum produced water (PW) is commonly injected is important to prevent underground sources of drinking water contamination. This study presents new experimental results on the degree and impact of precipitation and sorption reactions on the transport of high concentrations of toxic metals (80-100 mg-Ba/L, 80-100 mg-Sr/L, 70-100 mg-Cd/L, 2-100 mg-Pb/L, and 80-100 mg-As/L) in dolomite injected with PW of variable alkalinity (0–200 mg/L), total dissolved solids (1700–77,000 mg/L), and pH (2–7). Changes in the elemental and mineral composition of dolomite surface were measured by BSEs SEM, SEM-EDS, and high-resolution XRD analyses. The results reveal a key role of alkalinity generated from the dissolution of dolomite. We show that a short initial stage where the removal of toxic metals is driven by the initial pH and alkalinity of PW is followed by a prolonged stage where the removal of toxic metals by sorption and precipitation reactions is driven by the alkalinity and pH that results from the kinetic dissolution of dolomite. Precipitated/coprecipitated metals were carbonate minerals reflecting the metal composition of PW. Attained removal levels of tested toxic metals from 1 L of PW using a dolomite core made of 200 g were >90% for Pb, >50% for As, >30% for Cd, and >5% for Ba and Sr. Apparently, the in-situ generation of alkalinity (carbonate ions) and sorption reactions of metals on dolomite catalyzes the precipitation of toxic metals as carbonate minerals. This catalytic effect of dolomite is different with PW and fresh water (FW) of low salinity (NaCl). Precipitation reactions are more prominent with FW than with PW, whereas sorption reactions are more prominent with PW than with FW.

Using benthic macroinvertebrates as bioindicators to evaluate the impact of anthropogenic stressors on water quality and sediment properties of a West African lagoon

This study aimed to investigate the impact of anthropogenic stressors (landfilling, navigation for transport of goods, cooling in fossil fuel, urbanization, industrial expansion, agriculture activities, and recreational activities) on environmental variables, microbiological quality, and sediment properties using benthic macroinvertebrates as a bioindicator within Lagos Lagoon, Nigeria. Four (4) sampling stations were established with respect to their importance/anthropogenic activities within the Lagos Lagoon. Surface water, bottom substrates, and benthic macroinvertebrate fauna samples were collected bimonthly from each sampling station for a year and analyzed using appropriate standard methods and procedures. The highest pH range of 7.96–8.01 (7.98 ± 2.35) was recorded at Site IV, while the lowest range of 6.41–7.01 (6.15 ± 1.14) was observed at Site II, and there was a significant difference (p < 0.05) among the pH mean values across the sites. High values of salinity, chloride, sodium, COD, BOD, manganese, nickel, cadmium, and nitrate were recorded among the surface water physicochemical parameters, which were above WHO (2011) permissible limits, while the high concentrations of toxic metals (Pb, Cr, Zn, and Cd) was recorded in sediment. A total of 26 species of benthic macroinvertebrates were recorded during this study, which belongs to eight (8) classes. Gastropoda recorded the highest percentage contribution of 39.12%, followed by polychaeta accounting for 30.34%, while malacostraca contributed 2.63%. The highest abundance of macroinvertebrates was recorded at Site I (256 Indiv/m2), followed by Site IV (252 Indiv/m2), and the least was observed at Site II (195 Indiv/m2). Based on the results of the physico-chemical, heavy metals, microbial quality, and macroinvertebrates assemblage obtained from this study revealed the adverse effect of anthropogenic activities on water quality degradation. It plays a significant role in the distribution and diversity of benthic macroinvertebrates in an aquatic environment.

Potency of Jatropha integerrima Jacq., Hibiscus rosa-sinensis L. and Ruellia tweediana as Absorbants of Lead (Pb) in Air

Air pollution is an atmospheric condition with high concentrations of toxic metals that exceed normal limits and are harmful to humans, animals or plants. Jatropha integerrima Jacq., Hibiscus rosa-sinensis L., and Ruellia tweediana have the potential to absorb (Pb) in the air. The aim of the study to analyze the levels of (Pb), chlorophyll, and the relationship between levels of (Pb) and chlorophyll in the three plant species at different locations. Samples were obtained from three locations with different traffic volumes Mayjend Yono Soewoyo street (100346.50 units/day), Dr. Soetomo street (58997.80 units/day), and Polisi Istimewa street (25692.50 units/day) Surabaya. Each sample was taken as many as 15 leaves at the third node. Leaf (Pb) measurements were carried out by dry ashing method using Atomic Absorption Spectrophotometry (AAS) and chlorophyll content was measured extraction method followed analysis by Spectrophotometer. Data levels (Pb) and chlorophyll were analyzed using two-way ANOVA followed by Duncan’s test and correlation test with SPSS Statistics 26. The results showed that (1)Pb levels in the three plants from high to low J. integerrima (0.152±0.032 mg.L-1); H. rosa-sinensis (0.042±0.008 mg.L-1); and R. tweediana (0.007±0.006 mg.L-1), (2)chlorophyll content of plant leaves from high to low R. tweediana (33.891±0.510 mg.L-1); H. rosa-sinensis (28.499±0.32 mg.L-1), and J. integerrima (10.597±1.697 mg.L-1) high volume of vehicles followed by increasing levels of (Pb) and decreasing levels of chlorophyll, namely at Mayjend Yono Soewoyo street, Dr. Soetomo street, and Polisi Istimewa street, (3)there is a correlation between levels (Pb) and leaf chlorophyll content (0.524&gt;0.381). Can be concluded that J. integerrima, H. rosa-sinensis, and R. tweediana have the potential as absorbents (Pb) in the air.

Cadmium contributes to heat tolerance of a hyperaccumulator plant species Sedum alfredii

Hyperaccumulators are plant species that tolerate and accumulate very high concentrations of toxic metals, including Cd. Hyperaccumulation of heavy metals is reported to benefit plant biotic resistance; however, no prior study has examined the possible role of toxic metals on abiotic stress resistance in hyperaccumulators. A preliminary experiment found that Cd significantly improved plant growth of a hyperaccumulator, Sedum alfredii Hance, under heat stress. This study investigated the possible role of Cd in S. alfredii’s heat resistance, using infrared thermography, transmission electron microscopy (TEM), real-time quantitative polymerase chain reaction (RTqPCR), and high-throughput sequencing. The results showed that high temperatures irreversibly damaged stomatal function, chloroplast structure, photosynthesis in S. alfredii, and lowered survival rates to 25%. However, Cd application significantly decreased the leaf temperature of S. alfredii and increased the survival rate to 75%. Cd penetrated the guard cells, restored stomatal function, and mitigated excessive water loss from S. alfredii under heat stress. Moreover, it activated antioxidant enzymes, promoted phytohormone biosynthesis, and upregulated a series of unigenes, thereby augmenting heat resistance in S. alfredii. These results indicate that Cd effectively improved thermotolerance in S. alfredii by regulating stomatal movement and antioxidant systems via upregulation of phytohormones and heat shock proteins.

Vermicomposting of sewage sludge with organic bulking materials to improve its properties.

Adverse properties of sewage sludge such as high concentration of toxic metals and the presence of pathogens have limited its use in agriculture. In this study, the effect of vermicomposting on some important chemical properties of sewage sludge was investigated as a factorial arrangement based on a completely randomized design with three replications. The studied factors were bulking agents in three concentrations (0, 5, and 10% v/v), earthworm (Eisenia fetida) in 2 different concentrations (0 and 50 adult earthworms/6kg sewage sludge), and retention times in three levels (30, 60, and 90days). Sewage sludge was obtained from the lagoons of Ghahdarijan refinery in Isfahan province in Iran. The results showed that vermicomposting significantly (p < 1%) reduced the number of coliforms and concentrations of Ni, Cr, and Pb and increased the organic carbon percent and N of the sewage sludge. When comparing different treatments, vermicomposting of sewage sludge with rice husk 10% v/v during retention times of 60 and 90days were superior treatments in reducing the concentrations of Ni, Cr, and Pb and reducing the number of coliforms. Furthermore, the highest %OC was measured in the rice husk 10% + earthworm in the retention time of 90days which was about 41% more than the control treatment. In general, it is concluded that vermicomposting significantly reduced the adverse properties of sewage sludge for using in agriculture as an organic fertilizer.

Removal of toxic metals from petroleum produced water by dolomite filtration

We conducted experiments and reactive transport simulations to assess the removal of high concentrations of toxic metals (100 mg/L) commonly found in produced water from high saline waters (45,000–115,000 mg/L) using dolomite filters made of compressed powdered dolomite. The focus was on Ba, Sr, Cd, Pb, and As, as well as on guar gum as a metal complexing additive. We found that salinity has a significant impact on the removal of Sr and Ba but a mild impact on the removal of Cd. An increase of pH due the dissolution of dolomite increases the removal of Cd more significantly than the removal of Ba and Sr. The formation of guar-gum complexes of metals in the aqueous phase attenuates the removal of Sr, Ba, and Cd by dolomite filtration, this attenuation process is more significant for Cd than for Sr and Ba. The affinity sequence for the sorption of toxic metals at salinity levels of PW is Pb > Cd > As>Ba>Sr. Higher removal levels predicted for Sr than for Ba and over predictions of Cd removal using previously proposed surface complexation models for dolomite highlights the necessity of further experimental research to incorporate molecular scale surface crystal structure parameters into surface complexation models.

Retention dynamics of multi-metal contaminants from pond ash slurry onto fine grained soil

The coal fly ashes contain high concentration of toxic metals. The sorption plays crucial part to retard the movement of contaminants through the liner. In the present investigation to examine the potential of fine-grained soil as liner material, obtained from bank of River Ganga, was assessed in terms of its adsorption capability. Batch adsorption of Pb(II) and Cr(VI) were performed. Maximum adsorption of Cr(VI) (65.76%) at pH 3 for adsorbate and adsorbent dose of 5 ​mg/L and 2 ​g/L and maximum adsorption of Pb(II) (96.84%) at pH 5 for adsorbate and adsorbent dose of 5 ​mg/L and 1.5 ​g/L, respectively, were observed. Adsorption of Pb(II) and Cr(VI) follow Freundlich isotherm equation. The soil column studies were performed at various bed heights (2, 3 and 5 ​cm) in down flow mode. The tracer studies were conducted using NaCl to estimate the hydrodynamic parameters and they were considered as input parameters for modelling of fate and transport of contaminants in soil using HYDRUS 1D software for assessing the potential use of soil as liner material in ash pond structures.

Metal accumulation potential and tolerance responses in Alternanthera dentata grown under multi metal treatment

Present study investigates metal accumulation potential, enzymatic and non-enzymatic tolerance responses of a tropical perennial plant Alternanthera dentata grown under multi metal (Cr, Cd, As and Ni) treatment at different concentration i.e. 0, 5, 20 and 50 ppm for 60 d in pot culture with garden soil as control. Results revealed accumulation of appreciable amount of toxic metals in the root of Alternanthera dentata , as maximum concentration of Cr (2402.65 μ g g −1 dw), As (1485.81 μ g g −1 dw), Cd (1258.9 μ g g −1 dw) and Ni (1215 μ g g −1 dw) recorded at 50 ppm of multi metal treatment. High concentration of toxic metals in the biomass of Alternanthera dentata indicates its high potential for metal accumulation. Biochemical changes particularly increase in synthesis and concentration of phenol, carotenoid and cysteine in metal treated plant provide non-enzymatic tolerance. Similarly, increased antioxidant activities of Ascorbate Peroxidase (APX) and Guaiacol Peroxidase (GPX) provide better tolerance for growth and survival at higher concentration of toxic metals. The plant Alternanthera dentata grown worldwide, thrive in humid condition, has heat and metal tolerance, thus it could be efficiently used for metal removal globally. Therefore, Alternanthera dentata has emerged as an efficient metal accumulator plant with better tolerance to toxic metals and may be exploited as a bioresource in developing innovative and sustainable technology to remove toxic metals from soil, contaminated due to industrial discharge or geological processes for ecological restoration, environmental cleanup and health safety • The plant Alternanthera dentata showed better tolerance and growth under multi metal treatment. • Alternanthera dentata accumulate more metals in the root and leaves. • Maximum accumulation of Cr (2402.65 μ g g −1 dw) recorded in the roots. • As (1485.81), Cd (1258.9) and Ni (1215) μ g g −1 dw accumulated in roots. • Metal accumulation potential and tolerance indicate feasibility of Alternanthera dentata to be used in phytoremediation.

Distribution and dispersion of heavy metals in the rock-soil-moss system of the black shale areas in the southeast of Guizhou Province, China.

Black shales are easily exposed due to human activities such as mining, road construction, and shale gas development, which results in several environmental issues including heavy metal (HM) pollution, soil erosion, and the destruction of vegetation. Mosses are widely used to monitor metal pollution in the atmosphere, but few studies on the distribution and dispersion of HMs in the rock-soil-moss system are available. Here, mosses (Pohlia flexuosa Harv. in Hook), growing soils, and corresponding parent rocks were collected from black shale areas. After appropriate pretreatment, samples were analyzed for multiple elemental concentrations by ICP-AES and ICP-MS. The results show that black shale parent rocks have elevated HM concentration and act as a source of multiple metals. The overlying soil significantly inherits and accumulates heavy metals released from black shale. Significant positive correlations between HMs in P. flexuosa and the growing soils indicate that HMs are mainly originating from geological source rather than atmospheric deposition. Differential accumulation of HMs is observed between rhizoids and stems in our study. Moreover, P. flexuosa is able to cope with high concentrations of toxic metals without any visible negative effect on its growth and development. Finally, the bioconcentration factor (BCF) for all the HMs in P. flexuosa is less than 1, indicating that it has a tolerance and exclusion mechanism for these metals, especially for the non-essential elements As and Pb. Therefore, the luxuriant and spontaneous growth of P. flexuosa could be used as a phytostabilization pioneer plant in the black shale outcrop where vascular plants are rare.

Ecological Risk from Toxic Metals in Sediments of the Yangtze, Yellow, Pearl, and Liaohe Rivers, China.

In this study, the concentrations of six toxic metals (Cd, Cr, Cu, Ni, Pb, and Zn) in surface sediments within the Yangtze, Yellow, Pearl, and Liaohe rivers, China, were analyzed, and their associated pollution statuses and potential ecological risks were assessed using the geoaccumulation index (Igeo), sediment quality guidelines (SQGs), and the potential ecological risk index (RI). Relatively high toxic metal concentrations were observed in the Pearl and Yangtze rivers, whereas relatively low concentrations were observed in the Yellow and Liaohe rivers. In the Yangtze, Pearl, and Liaohe rivers, the concentrations of these six toxic metals were higher than their background values. Based on the SQGs, the concentrations of Cd, Cr, and Cu in the four rivers were found to be higher than the threshold effect levels (TELs) but lower than the probable effect levels (PELs); however, the concentration of Ni exceeded the PEL in the Pearl River sediments. The Igeo index indicated that all four rivers were heavily contaminated with Cd. The RI of the Pearl and Yellow rivers was classed as high and low, respectively, and that of the Yangtze and Liaohe rivers as moderate. The pollution status of the sediments in the four major rivers was explored in relation to the geochemical background, the ecological toxicity of metals, and the sensitivity of the local benthic communities. These results provide meaningful information for directing river management priorities.

Effect of acid mine drainage (AMD) on the alteration of hydrated Portland cement and calcareous sandstone

AMD is the acidic discharge generated by the oxidation of sulfide minerals from active or disused mine workings and contains high concentrations of toxic metals and sulfuric acid. Host rocks and concrete-based infrastructures in permanent contact with AMD are highly vulnerable to the geochemical processes caused by acidity (e.g. concrete corrosion). Experiments using columns filled with calcareous sandstone and hydrated Portland cement were performed to quantify these geochemical processes. AMD mono-ionic and poly-ionic solutions containing sulfate, Fe(II), Al, Ca, Mg and different divalent cations (Cd, Zn, Cu and Ni) and As(V) at pH 2 were injected in the columns.The temporal variation of the chemical composition of the output solutions was monitored. The retrieved solid samples were analyzed by X-Ray Diffraction (XRD), thin section petrography and Scanning Electron Microscopy (SEM). A quantitative interpretation of the reactions was carried out by means of 2D reactive transport modeling.Results indicated that the main reactions were the dissolution of portlandite (hydrated Portland cement) and calcite (rock). These two reactions, together with the pH variation, played a pivotal role (1) in the precipitation of gypsum, aragonite, brucite and Fe- and Al- poorly crystalline phases (e.g., basaluminite, schwertmannite and ferrihydrite) and (2) in the precipitation of Cd, Ni and Zn hydroxides and Zn carbonates and adsorption or co-precipitation of Cu and As on schwertmannite and ferrihydrite.

Spatial distribution characteristics of the microbial community and multi-phase distribution of toxic metals in the geochemical gradients caused by acid mine drainage, South China

Acid mine drainage (AMD) poses a potential environmental risk due to the low pH combined with high concentrations of toxic metals and sulfate. The Hengshi River in China is continually contaminated by the AMD from upstream mining areas and this river was selected as a study site to investigate the spatial distribution of Cu, Cd, Pb, Zn and the microbial communities in the paddy soil in vicinity of the river. Various geochemical parameters were determined for five sites, where river water was sampled together with paddy soil (at three depths) and soil pore water. The distribution of toxic metals at these sites was ranked as soil > river water > pore water. The metals in the soil samples were divided into five extractable fractions. With the increase of soil depth, F1Zn, F2Pb, F3Zn, F4Zn, F5Cu basically produced a decreasing trend. The sum of the F1 and the F2 fractions of the toxic metals followed the order of Cd > Pb > Cu > Zn. Among the predominant bacteria detected were Fe- and S- metabolizing genera, including Anaeromyxobacter, Thiobacillus, and Geobacter. Based upon canonical correspondence analysis, sand content, Cu and pH correlated most strongly with the composition of the microbial communities. Significant correlations were found between toxic metal fraction and environmental parameters such as organic matter and total S content, while Fe only had a minor effect. The toxic metal fractions were the dominant drivers in changing the soil microbial community. The potential ecological risk of the toxic metals was assessed as Cd > Cu > Pb > Zn. Collectively, these results suggest that the geochemical gradients caused by AMD altered the toxic metals speciation and enriched relevant soil microbiota which adapted to the different conditions.

Selective Removal of As(V) Ions from Acid Mine Drainage Using Polymer Inclusion Membranes

Acid mine drainage (AMD) is globally recognized as one of the environmental pollutants of the priority concern due to high concentrations of toxic metals and sulfates. More rigorous environmental legislation requires exploitation of effective technologies to remove toxic metals from contaminated streams. In view of high selectivity, effectiveness, durability, and low energy demands, the separation of toxic metal ions using immobilized membranes with admixed extractants could ameliorate water quality. Cellulose triacetate based polymer inclusion membranes (PIMs), with extractant and plasticizer, were studied for their ability to transport of As(V) ions from synthetic aqueous leachates. The effects of the type and concentration of extractant, plasticizer content, and sulfuric acid concentration in source phase on the arsenic removal efficiency have been assessed. Under the best of applied conditions, PIM with Cyanex 921 as extractant and o-nitrophenyl octyl ether (o-NPOE) as plasticizer showed high repeatability and excellent transport activity for selective removal of As(V) from AMD.

Chemical characteristics, oxidative potential, and sources of PM2.5 in wintertime in Lahore and Peshawar, Pakistan

The chemical characteristics, oxidative potential, and sources of PM2.5 were analyzed at the urban sites of Lahore and Peshawar, Pakistan in February 2019. Carbonaceous species, water soluble ions, and metal elements were measured to investigate the chemical composition and sources of PM2.5. The dithiothreitol (DTT) consumption rate was measured to evaluate the oxidative potential of PM2.5. Both cities showed a high exposure risk of PM2.5 regarding its oxidative potential (DTTv). Carbonaceous and some of the elemental species of PM2.5 correlated well with DTTv in both Lahore and Peshawar. Besides, the DTTv of PM2.5 in Lahore showed significant positive correlation with most of the measured water soluble ions, however, ions were DTT-inactive in Peshawar. Due to the higher proportions of carbonaceous species and metal elements, Peshawar showed higher mass-normalized DTT activity of PM2.5 compared to Lahore although the average PM2.5 concentration in Peshawar was lower. The high concentrations of toxic metals also posed serious non-carcinogenic and carcinogenic risks to the residents of both cities. Principle component analysis coupled with multiple linear regression was applied to investigate different source contributions to PM2.5 and its oxidative potential. Mixed sources of traffic and road dust resuspension and coal combustion, direct vehicle emission, and biomass burning and formation of secondary aerosol were identified as the major sources of PM2.5 in both cities. The findings of this study provide important data for evaluation of the potential health risks of PM2.5 and for formulation of efficient control strategies in major cities of Pakistan.

Assessment of foliar dust particle retention and toxic metal accumulation ability of fifteen roadside tree species: Relationship and mechanism

The resuspension of urban road dust particles with high concentration of toxic metals becomes one of the main sources of particulate matter that affects air quality and the health of human beings. To address this problem, foliar dust capture ability and toxic metal accumulation capacity are evaluated through 15 tree and shrub species collected from three main roads in Nanjing. The element analysis results show that traffic, industry and the combustion of chemical fuel are important sources of road dust and its bound Cu, Zn, Cr and Pb. Among the plants, Cedrus deodara has the highest dust retention ability of 75.4 μg cm−2d−1, followed by Nerium indicum and Acer palmatum, while Platamus orientalis exhibits the lowest dust capture ability of 9.19 μg cm−2d−1, which is related to the microstructure feature of the plant leaf. Leaf particles in different size fraction differ among the species, but fine particles (PM < 2.5 μm) predominate in most cases. Nerium indicum, Cerasus yedoensis and Salix babylonica are the three species that accumulate the highest amounts of Cu, Zn, Cr and Pb. Moreover, a significant positive correlation between foliar toxic metal and dust retention amounts (especially fine particles) was found, indicating foliar uptake of toxic metals after deposition of dust particles on the leaf surface. Taken together, plant leaves can simultaneously capture road dust and its bound toxic metals. Moreover, Nerium indicum could be used as an urban landscape barrier for road dust and toxic metals.

Shift in phagocytosis, lysosomal stability, lysozyme activity, apoptosis and cell cycle profile in the coelomocytes of earthworm of polluted soil near a tannery field of India.

Calcutta Leather Complex of the state of West Bengal, India has been designated as an industrially active zone with around 400 active tannery units. This area spanning 4.5 km2 is surrounded by human habitation. The soil of this region is contaminated with metal pollutants and exhibited an alteration in selected physicochemical parameters, namely cation exchange capacity, moisture content, pH, total nitrogen, total organic carbon and water holding capacity. Metaphire posthuma, a common variety of endogeic earthworm inhabiting this region is thus continuously exposed to these toxic metals. Coelomocytes, the chief immune effector cells of earthworm presented a shift in phagocytosis, lysosomal membrane stability, lysozyme and phosphatase activity, physiological apoptosis and cell cycle profile of M. posthuma sampled from the soil of tannery industry. Presence of high concentration of toxic metals and change in the physicochemical characteristics of soil led to a state of cellular stress and immunocompromisation in M. posthuma, a common inhabitant of soil of this region. Experimental endpoints bear ecotoxicological significance as biomarkers of physiological stress in earthworm for monitoring the health of soil around this tannery industrial zone.