Application of a modified BCR sequential extraction (three-step) procedure for the determination of extractable trace metal contents in a sewage sludge amended soil reference material (CRM 483), complemented by a three-year stability study of acetic acid and EDTA extractable metal content

Livestock and poultry manure influence thallium accumulation in chili peppers (Capsicum annuum) under complex toxic elements contamination in soil

Long-term mining activities in the mercury-thallium mining area of Lanmuchang, southwestern China, resulting in contamination of surrounding soils with complex toxic elements such as Tl, As, Sb, Hg, and Cd. While manure aids in pollution control and soil fertilization, its impact on Tl bioavailability in soil remains incompletely understood. This study explored the physiological changes and Tl accumulation in Capsicum annuum under combined pollution stress and application of livestock and poultry manure near the Lanmuchang mining area. The results showed that chicken manure promoted Tl accumulation in Capsicum annuum, whereas pig and cattle manure inhibited it, with pig manure exhibiting the strongest inhibitory effect. Both pig and cattle manure reduced the transpiration rate of Capsicum annuum, which decreased the driving force for Tl transport to the plant's upper parts. Additionally, manure increased organic acid secretion in Capsicum annuum roots and decreased soil Eh. This led to a reduction in Tl3+ to the more stable Tl+, which decreased the content of exchangeable Tl form and its activity. Pig manure significantly reduced Tl content in stems, leaves, and fruits by increasing the area of the Casparian bands in Capsicum annuum roots, which hindered Tl accumulation. In contrast, chicken manure had the opposite effect. The findings of this study provide important theoretical support for scientifically guiding agricultural production safety in areas contaminated with the heavy metal Tl.

The Use of Diatomite-Based Composites for the Immobilization of Toxic Heavy Metals in Industrial Wastes Using Post-Flotation Sediment as an Example

Composite materials based on diatomite (DT) with the addition of biochar (BC), dolomite (DL), and bentonite (BN) were developed. The effect of chemical modification on the chemical structure of the resulting composites was investigated, and their influence on heavy metal immobilization and the ecotoxicity of post-flotation sediments was evaluated. It was demonstrated that the chemical modifications resulted in notable alterations to the chemical properties of the composites compared to pure DT and mixtures of DT with BC, DL, and BN. An increase in negative charge was observed in all variants. The addition of BC introduced valuable chemically and thermally resistant organic components into the composite. Among the chemical modifications, composites with the addition of perlite exhibited the lowest values of negative surface charge, which was attributed to the dissolution and transformation of silicon compounds and traces of kaolinite during their initial etching with sodium hydroxide. The materials exhibited varying efficiencies in metal immobilization, which is determined by both the type of DT additive and the type of chemical modification applied. The greatest efficacy in reducing the mobility of heavy metals was observed in the PFS with the addition of DT and BC without modification and with the addition of DT and BC after the modification of H2SO4 and H2O2: Cd 8% and 6%; Cr 71% and 69%; Cu 12% and 14%; Ni 10% and Zn 15%; and 4% and 5%. In addition, for Zn and Pb, good efficacy in reducing the content of mobile forms of these elements was observed for DT and DL without appropriate modification: 4% and 20%. The highest reduction in ecotoxicity was observed in the PFS with the addition of DT and BC, followed by BN and DL, which demonstrated comparable efficacy to materials with DT and BN.

Evaluating ecological risks and metal bioavailability in post-dredging sediments of a wetland affected by artisanal gold mining

The evaluation of metal contamination, ecological risk, bioavailability, and the environmental dredging depth in sediments of two Colombian riverine systems impacted by artisanal gold mining and agricultural activities, was conducted following dredging processes. Results indicated significant contamination by Cd and Pb before dredging, based on the contamination factor (CF) and the geoaccumulation index (Igeo). Additionally, Cu and Hg were found to cause adverse biological effects according to sediment quality guidelines. Post-dredging, surface sediments exhibited a moderate ecological risk index (RI, 150-300), primarily due to increased contamination by Hg, Pb, and Cd. To mitigate this ecological risk (RI < 150), the environmental dredging depth needed to exceed 20 cm for all metals. On average, the bioavailable fraction increased 2.3 times within two months after dredging. However, the low environmental risk (%F1 = 1-10) calculated using risk assessment codes (RAC) indicates a potential risk due to metals entering the water column and bioaccumulating in organisms. These findings provide insights into the dynamics of metals and the impact of dredging activities on sediments in the Colombian Caribbean coast affected by various anthropogenic activities. The research underscores the importance of integrating sustainable practices in mining and agriculture to protect the ecological integrity of these riverine systems.

Detangling past and modern zinc anthropogenic source contributions in an urbanized coastal river by combining elemental, isotope and speciation approaches

The accumulation of trace metals in the environmental compartments of coastal rivers is a global and complex environmental issue, requiring multiple tools to constrain the various anthropogenic sources and biogeochemical processes affecting the water quality of these environments. The Valao fluvio-estuarine system (Rio de Janeiro, Brazil) presents a challenging case of a coastal river contaminated by both modern and historical anthropogenic metal sources, located in the land and in the intra-estuary, continuously mixed by tidal cycles. This study employed a combination of spatial distribution analysis of trace metals including gadolinium (Gd), zinc (Zn) isotopic analyses, and X-ray absorption spectroscopy (XAS) to distinguish between these sources. The concentrations of metals in both dissolved (water samples) and surficial sediment compartments (Suspended Particulate Matter and sediment samples) display an overall enrichment trend from upstream to downstream. Multivariate statistical analysis allows to discriminate geogenic elements derived from watershed geology (Ti, K, and Mg) vs anthropogenic contaminants from urban runoff and domestic sewage discharges (Cu, Cr, Pb, Zn, and Gd); and legacy metal contaminants (Zn and Cd) remobilized from ancient metallurgical wastes and transported upstream in the estuary during tidal cycles. The anthropogenic Gd concentration in the dissolved compartment increases along the watercourse, highlighting continuous ongoing sewage discharge. Zinc solid speciation also indicates that Zn contribution from legacy metallurgy waste is primarily associated with sulfide-Zn and Zn-phyllosilicate in the outlet estuary, while in upstream sediments of fluvio-estuarine system, Zn is found bound to organic matter. Zinc isotope systematically reveals a progressive downstream shift to heavier isotope compositions. Upstream, the relatively pristine site and the urbanized section of the river exhibit a relatively uniform δ66/64Zn value (+0.20 ± 0.07 ‰) in suspended particulate matter (SPM) and surficial sediments. These results indicate that domestic sewage discharges contribute to Zn enrichment in sediments of the Valao fluvio-estuarine system but without modifying its isotope signature in sediments. The sediment of the downstream estuarine section shows a heavier δ66/64Zn value (+0.48 ± 0.08 ‰), indicating the strong influence of the intra-estuarine source identified as the historical metallurgic contamination. An integrated view of the geochemical tracers allows thus inferring that the untreated sewage and legacy metallurgical contamination are the primary sources of anthropogenic Zn contamination. It highlights the progressive mixing along the estuarine gradient under tidal dynamics. The influence of the former source continuously expands from the headland towards the estuary.

Chromium cycle in Red Soil Critical Zone constrained by chromium isotopes

Chromium (Cr) isotopic system has been used to trace Cr pollution in the modern surface environment and redox change in the paleoenvironment. However, the transformation mechanism of Cr in soil and the accompanied Cr isotopic fractionation have not been clarified clearly. Here we measured Cr isotopic compositions (δ53Cr) of two paddy field profiles from the Red Soil Critical Zone Observatory in South China. The δ53Cr values of the young paddy fields, which have been cultivated for about 20 years, range from -0.34 ‰ to -0.22 ‰. The old paddy fields have been cultivated for >100 years and have more positive Cr isotopic compositions than the young paddy fields, from -0.20 ‰ to -0.06 ‰. The results of three-step leaching experiments show that iron and manganese oxides are enriched in heavy Cr isotopes, while organic matters have much lower Cr isotopic compositions, likely resulting from back reduction of Cr(VI). Our results suggest that Cr isotopic fractionation during the oxidation of Cr(III) is not the only reason for the depletion of heavy isotopes during oxidative weathering, and the partial back-reduction of generated Cr(VI) by organic matter plays an important role in Cr isotopic fractionation during weathering. Comparison between the old and young paddy fields further indicates that cultivation can significantly affect the Cr cycle in red soils. Paddy fields could be a potential sink for the Cr(VI) contaminant, and soils with a long history of cultivation would be more susceptible.

Granulometric and Geochemical Distribution of Arsenic in a Mining Environmental Liability in a Semi-arid Area

This study focuses on the "El Lavadero" tailings deposit, a mining environmental liability (MEL) located near the town of San Felipe de Jesús, Sonora, in northwest Mexico. The objective was to determine the total arsenic (As) content, its granulometric and geochemical distribution, as well as its mobilization capacity and bioavailability. The results from oxidized and unoxidized tailings showed low potential of hydrogen (pH) values (2.4-5.7) and high concentrations of total arsenic (8235-36,004 mg kg-1), predominantly in the finer granulometric fractions (< 0.05 mm). Arsenic also prevails in the finest fraction of agricultural soil (> 2 mm). These fine particles could present adverse environmental effects due to their potential to be transported by leaching and water suspension. In contrast, arsenic in the effluent sediments is primarily found in the coarser fraction (> 2 mm). A significant proportion of arsenic in the tailings (5-40%) was found in the non-residual geochemical fractions (I + II + III) (1106-7675 mg kg-1), indicating potential for mobilization and bioavailability. Depending on environmental conditions (redox potential and pH), arsenic can redissolve and exhibit high mobility in abiotic media, which may ultimately impact the environment and human health. Therefore, it is crucial to rehabilitate the "El Lavadero" MEL to prevent further environmental damage. This study provides useful information to understand some phenomena in other global mining environmental liabilities, such as mobilization and bioavailability of arsenic and its possible impact on the surrounding environment and biota, contributing to the worldwide research of ecosystems polluted by mining activity, especially in arid and semi-arid climates.

Nano zerovalent Fe did not reduce metal(loid) leaching and ecotoxicity further than conventional Fe grit in contrasting smelter impacted soils: A 1-year field study

The majority of the studies on nanoscale zero-valent iron (nZVI) are conducted at a laboratory-scale, while field-scale evidence is scarce. The objective of this study was to compare the metal(loid) immobilization efficiency of selected Fe-based materials under field conditions for a period of one year. Two contrasting metal(loid) (As, Cd, Pb, Zn) enriched soils from a smelter-contaminated area were amended with sulfidized nZVI (S-nZVI) solely or combined with thermally stabilized sewage sludge and compared to amendment with microscale iron grit. In the soil with higher pH (7.5) and organic matter content (TOC = 12.7 %), the application of amendments resulted in a moderate increase in pH and reduced As, Cd, Pb, and Zn leaching after 1-year, with S-nZVI and sludge combined being the most efficient, followed by iron grit and S-nZVI alone. However, the amendments had adverse impacts on microbial biomass quantity, S-nZVI being the least damaging. In the soil with a lower pH (6.0) and organic matter content (TOC = 2.3 %), the results were mixed; 0.01 M CaCl2 extraction data showed only S-nZVI with sludge as remaining effective in reducing extractable concentrations of metals; on the other hand, Cd and Zn concentrations were increased in the extracted soil pore water solutions, in contrast to the two conventional amendments. Despite that, S-nZVI with sludge enhanced the quantity of microbial biomass in this soil. Additional earthworm avoidance data indicated that they generally avoided soil treated with all Fe-based materials, but the presence of sludge impacted their preferences somewhat. In summary, no significant differences between S-nZVI and iron grit were observed for metal(loid) immobilization, though sludge significantly improved the performance of S-nZVI in terms of soil health indicators. Therefore, this study indicates that S-nZVI amendment of soils alone should be avoided, though further field evidence from a broader range of soils is now required.

Honey Bees and Associated Matrices as Biomonitors of Soil Trace Elements: Assessment of their Sensitivity in a Regional Rural Environment

Honey bees (Apis mellifera L.) represent a random biosampler integrating pollutants over space and time. An effective biomonitor for trace element (TE) pollution should provide a linear response to TE levels in the environment. However, uncertainties in detecting TEs originating in soil limit their use. To address this, nine experimental sites with multiple apiaries were established in the Upper Palatine Forest, Czech Republic. The soils surrounding the hives were characterized by estimations of the pseudototal and (bio)available pools of TEs. Our study aimed to (1) quantify the linear relationships between soil TE indices and TE contents in bees, bee bread, honey, and wax, and (2) verify the biobarrier function protecting honey from TE contamination. Lead (0.046-0.140 µg g-1 ) and nickel (0.12-4.30 µg g-1 ) contents in bees showed strong linear correlations with (bio)available Pb (0.012-0.254 µg g-1 ) and pseudototal Ni (17.1-36.4 µg g-1 ) in soil (Pearson's r = 0.95 and 0.88, p < 0.005), providing high spatial resolution. A weaker, insignificant correlation was observed for chromium (Cr; r = 0.65) and vanadium (V; 0.44), while no correlation was found for cadmium (Cd). However, the lack of associations for Cr, V, and Cd may result from the low soil TE levels in the region, negligible differences among the majority of sites, and temporal concerns related to different time scales of the biomonitors, impacting the linear model's sensitivity. Biochemical traits in bees, such as the biobarrier function, and different bioavailability of TEs from ingested matter may affect the matrix-to-matrix transfer of TEs in an element-dependent manner. Consequently, the linear response of bee-related biomonitors to TE levels in the environment may significantly deteriorate. Environ Toxicol Chem 2024;43:288-298. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

The intrinsic and extrinsic mechanisms regulated by functional carbon nanodots for the phytoremediation of multi-metal pollution in soils

Functional carbon nanodots (FCNs) were currently demonstrated to regulate plant behavior in the agricultural and environmental areas. However, their regulation mechanisms on the interactions of plant-soil system during phytoremediation remain unrevealed. Here, Solanum nigrum L. was employed to explore the intrinsic and extrinsic mechanisms regulated by FCNs in the phytoremediation of Cd-Pb co-contaminated soils. The mediation of FCNs on metal removal and plant growth showed a hormesis manner, wherein the maximum induction effect was contributed by 15 mg kg-1 FCNs. Cd/Pb removal were enhanced by 8.5% and 31.6%, respectively. Moreover, FCNs reallocate metal distribution in plant by immobilized metals in roots and suppressed metal translocation to leaves. Improving plant growth (by 82.8% for root), stimulating plant hormesis, and activating plant detoxification pathways are the intrinsic mechanism for the phytoremediation smartly regulated by FCNs. Notably, FCNs induced soil enzyme activities that associated with soil nutrients recycling, up-regulated the microbial diversity and the soil immune system, and regulated S. nigrum L. to recruit beneficial microbials in the rhizosphere. The above-mentioned comprehensive improvement of soil micro-environment is the extrinsic mechanism regulated by FCNs. This study provides new insights to evaluate the interactions of nanomaterials with plant-soil system under soil contamination.

Integrative application of biochar and arbuscular mycorrhizal fungi for enhanced chromium resistance in Medicago sativa

Soil chromium (Cr) contamination has become an environmental problem of global concern. However, the joint effects of combined utilization of biochar and arbuscular mycorrhizal (AM) fungal inoculum, which are considered as two promising remediation strategies of soil heavy metal pollutions, on plant Cr resistance are still poorly understood. In this study, a two-factor pot experiment was conducted to investigate how biochar and AM fungus Rhizophagus irregularis regulate Medicago sativa growth, physiological trait, nutrient and Cr uptake, relevant gene expressions, soil properties, and Cr speciation, independently or synergistically. The results showed that biochar notably decreased AM colonization, while biochar and AM fungus could simultaneously increase plant dry biomass. The greatest growth promotion was observed in mycorrhizal shoots at the highest biochar level (50 g kg-1 soil) by 91 times. Both biochar application and AM fungal inoculation enhanced plant photosynthesis and P nutrition, but the promoting effects of AM fungus on them were significantly greater than that of biochar. In addition, the combined application of biochar and AM fungus dramatically reduced shoot and root Cr concentrations by up to 92 % and 78 %, respectively, compared to the non-amended treatment. Meanwhile, down-regulated expressions were observed for metal chelating-related genes. Furthermore, Cr translocation from roots to shoots was reduced by both two soil amendments. Transcriptional levels of genes involved in reactive oxygen species and proline metabolisms were also regulated by biochar application and AM fungal colonization, leading to alleviation of Cr phytotoxicity. Furthermore, AM fungal inoculation slightly elevated soil pH but decreased plant-available soil P, which was, by contrast, lifted by biochar addition. The combined application reduced soil acid-extractable Cr concentration by 40 %. This study provides new insights into comprehensively understanding of the mechanisms of biochar and AM fungi combination on improving plant Cr tolerance.

Is the co-application of self-produced compost and natural zeolite interesting to reduce environmental and toxicological availability in metal-contaminated kitchen garden soils?

Composting can turn organic waste into a valuable soil amendment that can improve physical, chemical, and biological soil quality. Compost amendments can also contribute to the remediation of areas anthropogenically degraded by metals. However, it is well known that compost, particularly self-produced compost, can show enrichment in metals. An experimental study was conducted to examine the short- and long-term distribution and the mobility of metals in soils amended with a self-produced compost when it was added alone or in combination with different doses of a natural zeolite to soil. The aim was also to study the interest of managing moderately metal-contaminated kitchen garden soils by assessing the chemical extractability, phytoavailability, and oral bioaccessibility of metals. When zeolite was added to compost alone, it had the tendency to better reduce extractability of Cd and Zn at 25%, and those of Pb at 15%. When the self-produced compost alone or in co-application with zeolite at these doses was applied to soils, the results showed (1) a decrease of NH4NO3-extractable Zn; (2) a reduction of Pb environmental availability, but not Pb bioaccessibility, and (3) an increase of ryegrass biomass. Nevertheless, the risk posed by the self-produced compost was minimal when applied at the proper rate (0.6% w/w). In the selected experimental conditions, the study recommends that self-produced compost be mixed with 15% zeolite to maximize vegetal biomass and minimize environmental risk. The question of sustainability of the results with repeated compost addition is also raised.

Effect of organic acids and soil particle size on heavy metal removal from bulk soil with washing

To evaluate the effect of soil particle size on heavy metals removal by washing, two soil samples were collected around a lead-zinc mining area (SM) and lead-zinc smelter (SS). The total content of Cd, Pb and Zn in SM and SS were determined. And the effect of soil particle size on Cd removal by low molecular organic acids was studied. The results showed that Cd was the main pollutant and the total content of Cd in SS can reach to 24.8 mg Kg^-1. 68.4% of the total Cd in SM existed in the form of residual state, while 54.7% of the total Cd in SS was in weak acid extractable state. About 50.0% of the Cd distributed in < 2 μm soil size fraction. The washing results indicated that citric acid was a highly efficient eluent among the five low molecular weight organic acids (citric acid, malic acid, tartaric acid, oxalic acid and acetic acid). After washing, 40% and 69.6% of the total Cd in SS and SM can be removed by citric acid, respectively. While only 18.7-40.2% and 32.6-68.7% of Cd was removed from different size fractions of SM and SS, respectively. The species of Cd in soil size fractions affected the removal effect of citric acid. The citric acid can easily remove the weak acid extractable and reducible form of Cd in soil. After eluted by citric acid, the bioavailability of Cd in soil decreased markedly, and the highest decreasing rate reached 93%.

Effects of physical aging processes on the bioavailability of heavy metals in contaminated site soil amended with chicken manure and wheat straw biochars

The physicochemical properties of biochars undergo slow changes in soils due to the natural aging processes, which influences their interaction with heavy metals. The effects of aging on immobilization of co-existing heavy metals in contaminated soils amended with fecal and plant biochars possessing contrasting properties remain unclear. This study investigated the effects of wet-dry and freeze-thaw aging on the bioavailability (extractable by 0.01 M CaCl₂) and chemical fractionation of Cd and Pb in a contaminated site soil amended with 2.5% (w/w) chicken manure (CM) biochar and wheat straw (WS) biochar. Compared to that in the unamended soil, the contents of bioavailable Cd and Pb in CM biochar-amended soil decreased by 18.0% and 30.8%, respectively, after 60 wet-dry cycles, and by 16.9% and 52.5%, respectively, after 60 freeze-thaw cycles. CM biochar, which contained significant levels of phosphates and carbonates, effectively reduced the bioavailability of Cd and Pb and transformed them from the labile chemical fractions to the more stable ones in the soil during the accelerated aging processes, mainly through precipitation and complexation. In contrast, WS biochar failed to immobilize Cd in the co-contaminated soil in both aging regimes, and was only effective at immobilizing Pb under freeze-thaw aging. The changes in the immobilization of co-existing Cd and Pb in the contaminated soil resulted from aging-induced increase in oxygenated functional groups on biochar surface, destruction of the biochar's porous structure, and release of dissolved organic carbon from the aged biochar and soil. These findings could help guide the selection of suitable biochars for simultaneous immobilization of multiple heavy metals in co-contaminated soil under changing environmental conditions (e.g., rainfall, and freezing and thawing of soils).

Ryegrass extraction of heavy metals from municipal sewage sludge compost-amended soils assisted with citric acid

Land use is an effective way to reduce carbon emission in the recycling process of municipal sludge compost; meanwhile, heavy metals (HMs) in the sludge can be phytoextracted by ornamental plants. As an eco-friendly soil amendment, citric acid (CA) has been reported to be of great potential aid to phytoremediation, and its effect on ryegrass (Lolium perenne L.) extraction of HMs (Zn, Ni, Pb, Cu, and Cd) from municipal sewage sludge compost-amended (MSSC) soils has been investigated through pot experiments in the study. The growth of ryegrass was significantly promoted under 2 and 4 mmol kg^-1 CA treatments. The concentrations of HMs in MSSC soil after 45-day planting were significantly reduced ([Formula: see text]), and they were further reduced except for Cu while CA treated. The acid-extractable fraction of HMs in the soil was increased significantly as CA treated, and further improvement could be found when CA dose increased, which was due to the decreased soil pH and the complexation of CA with metal ions. The phytoremediation factor (PRF) was proposed to assess the phytoremediation efficiency, which was obtained as a ratio of the product of the biomass and metal concentration of plant shoot between the CA-treated group and the control group. When the CA dose was 6 mmol kg^-1, the average PRF of five heavy metals reached 2.29, and Cd was the highest (3.72), demonstrating that CA had great promotion on phytoremediation of heavy metals. This study made a contribution to the research of phytoremediation in sludge land use by demonstrating ryegrass as an ideal bioaccumulator for heavy metals, especially for Cd.

Metal Fractionation and Leaching in Soils from a Gold Mining Area in the Equatorial Rainforest Zone

In this article, a modified BCR procedure and a column leaching test were used to examine the bioavailability and mobility of heavy metals in soils collected from a gold mining area in Ghana. The results for the fractionation of Cd, Cr, Fe, and Mn indicated that high percentages of metals were found in the residual fraction. This implies that the concentrations of metals in the soil are stable under normal environmental conditions. The bioavailability of metals in the soils declined in the following order: Mn (92.4%) > Cd (64.6%) > Cr (46.4%) > Fe (39%). However, the concentrations of labile metals may pose no risk to the environment. In the column test, different rainwater conditions (i.e., natural rainwater and acidified rainwater) were used to imitate the leaching potential of the metals in the actual field. The pH of the soil primarily controlled metal migration into deeper layers. Cumulative metal concentrations in the leachates showed that Fe, Mn, and Cd were high in the tested soils but present at low concentrations, except for Cd. Cadmium showed a higher concentration than the WHO guideline for drinking water, and its seepage into deeper layers may affect the quality of groundwater.

Hydrodynamic release of Pb, Zn, and Cd from impermeable tailings as deduced from physical parameters evolution and multivariate statistical analysis: case study of Jbel Ressas mine waste (North Tunisia)

Tailings are one of the largest pollutant sources in the world. The wind and water leaching were often considered the main distribution tool of their pollutants. However, the carbonate crust precipitation has negated the trace toxic element (TTE) release. To identify the release mode of Pb, Zn, and Cd from mine wastes, the hydrodynamic evolution of waste piles was considered. The macroscopic and microscopic observation, the grain sizes, cohesion particles, density, hydraulic conductivity, and Pb, Zn, and Cd concentrations performed from eight drill cores of the two waste dumps and the principal component and the hierarchical cluster analysis showed that the physical properties of waste piles closely controlled the TTE mobility and migration from the tailings. The obtained data also showed that the upper carbonate layers were first eroded by wind and rainfall. Then, the formation of an impermeable carbonate crust limited the Pb, Zn, and Cd releases. However, the hydrodynamic evolution of the underneath layers was different. As the high pile waste sediments' weight meaning the lithostatic pressure (P_l), the geostatic ratios (λ = P_f/P_l) were in DII and DIII dumps superior to 0.29 and 0.26, respectively. Therefore, the overpressured fluids increased the mineral dissolution, including the sulfides and carbonates of metals, and hydraulic fracturing that raised the percentages of the mobile TTE and migration indexes. By the secondary pore and fracture volumes, the polluted fluids were progressively channeled towards the underpressured marge (dumps edge) by repetitive (polyphase) fluid pulsations.

Cadmium in the hyperaccumulating mushroom Thelephora penicillata: Intracellular speciation and isotopic composition

Thelephora penicillata is an ectomycorrhizal mushroom that can accumulate extraordinarily high concentrations of Cd, As, Cu, and Zn in its fruit-bodies. To better understand its element accumulation ability, we compared the element concentrations in T. penicillata with 10 distinct ectomycorrhizal mushroom species growing at the same site (Karlina Pila, Czech Republic). On average, T. penicillata accumulated 330, 2130, 26, and 4 times more Cd, As, Cu, and Zn, respectively, than other mushrooms. Size-exclusion chromatography and an electrophoretic analysis of T. penicillata cell extracts indicate that intracellular Cd may be present mainly in >1 kDa, presumably compartmentalized, Cd species, and partially binding with 6-kDa cysteinyl-containing peptide(s) resembling metallothioneins. The cadmium isotopic composition of mushroom fruit-bodies, soil digests, and soil extracts was investigated by thermal ionization mass spectrometry (TIMS) with double spike correction. The isotopic composition (δ^114/110Cd) of ectomycorrhizal mushrooms from Karlina Pila varied in a wide range of -0.37 to +0.14 ‰. However, remarkably low δ^114/110Cd values were observed in the majority of the investigated mushrooms when compared to the relatively homogeneous Cd isotopic composition of bulk soil (δ^114/110Cd = +0.09 ‰) and the comparatively heavy isotopic composition of soil extracts (mean δ^114/110Cd values of +0.11 ± 0.01 ‰ and +0.22 ± 0.01 ‰, depending on the extraction method). The isotopic composition of Cd hyperaccumulated in T. penicillata essentially matched the mycoavailable soil Cd fraction. However, most isotopic data indicates isotopic fractionation at the soil/fruit-body interface, which could be of environmental significance.

Exploring the impacts of physicochemical characteristics and heavy metals fractions on bacterial communities in four rivers

Heavy metals contamination in sediment poses serious threats to bacterial communities that play critical roles in sediment biogeochemical processes. However, the physicochemical factors and the major heavy metals fractions that affect sediment bacterial communities are still unclear. Here, we performed heatmap and redundancy analyses to examine the effects of physico-chemical characteristics and heavy metals fractions on the sediment bacterial community from rivers in the UK (River Tyne and Ouseburn) and India (River Ganga and Yamuna). The results revealed that physicochemical characteristics and heavy metals fractions altered the diversity, richness, and structures of the bacterial community. Moreover, the fractions of Co, Zn, Pb, Cr, and Cu played significant roles in shaping the bacterial community structure, and physicochemical variables, particularly NH₄⁺-N and NO₂^--N, also influenced the bacterial diversity and structure. Firmicutes showed strong associations with both physicochemical factors and heavy metals fractions. Chloroflexi and Actinobacteriota can be used as biomarkers for Zn contamination. Overall, our study identified the significance of sediment chemical characteristics and heavy metals fractions in determining the bacterial community structure as well as bioremediation and environmental management of metals contaminated sites.

Global deposition of potentially toxic metals via faecal material in seabird colonies

Seabirds are known to play an important role in the geochemical cycling of macronutrients; however, their role in cycling elements of environmental interest has not been investigated. Guano is an important source of marine-derived nutrients and trace metals in seabird nesting areas, but most of the available information on this topic is derived from local studies. In the present study, we used a bioenergetic model to estimate the amounts of cadmium (Cd), mercury (Hg) and lead (Pb) that are deposited via faecal material in seabird colonies worldwide. The findings showed that the seabirds excreted 39.3 Mg (Mg = metric ton or 1000 kg) of Cd, 35.7 Mg of Hg and 27.2 Mg of Pb annually. These amounts are of the same order of magnitude as those reported for other fluxes considered in the geochemical cycling of these elements (e.g. sea-salt spray, cement production, soil loss to oceans). Most of the deposition occurs in circumpolar zones in both hemispheres and, interestingly, high proportions of the metals in the excrements occur in geochemically labile forms, which can be easily leached into coastal waters and assimilated by marine organisms.

Environmental implications of agricultural abandonment on Fe cycling: Insight from iron forms and stable isotope composition in karst soil, southwest China

Land-use change influences the fate of nutrient elements, including iron (Fe), and then threaten soil security. In this study, Fe forms and stable isotope composition (δ⁵⁶Fe) in soils were investigated to identify the variations in the processes of Fe cycling during agricultural abandonment in a karst region of Southwest China. Soil δ⁵⁶Fe compositions varied from -0.05‰-0.02‰ in croplands, 0.05‰-0.12‰ in abandoned croplands, to 0.30‰-0.80‰ in the native vegetation lands. In the croplands, Fe oxidation-precipitation process is considered as the main contributor to Fe migration and isotope fractionation, leading to a relatively enrichment of heavier Fe isotope in deeper soil layer. In the abandoned croplands and native vegetation lands, Fe isotope in the organic-rich layer (0-10 cm) was significantly lighter than that in subsurface layer (20-30 cm), mainly due to the recovery of soil organic carbon (SOC) and macro-aggregate after cropland abandonment. Moreover, the eluviation process mainly caused a decrease in soil Fe contents and enrichment of heavy Fe isotope in deeper soils (below 40 cm). The positive correlation between oxidized Fe and SOC contents suggested the accumulation of mobile Fe in soils after agricultural abandonment, which is beneficial for Fe uptake and assimilation by plants. This study suggests that agricultural abandonment significantly reduce soil Fe leaching loss and improve plant Fe supply by SOC accumulation in surface soil, which gives an environmental implication for the management of soil nutrients.

Microbial community succession in response to sludge composting efficiency and heavy metal detoxification during municipal sludge composting

This study researched microbial community succession in response to sludge composting efficiency and heavy metal detoxification during municipal sludge co-composting with spent mushroom and spent bleaching. The change law of key physicochemical properties, the heavy metals contents and forms during composting were analyzed, and the passivation of heavy metals after composting was explored. High-throughput sequencing was used to analyze the microbial community structure of treat 2 during composting, and the correlation analysis of microbial community structure with heavy metal contents and forms were carried out. The results showed that the sludge of each treatment reached composting maturity after 26 days of composting. Organic matter content, electrical conductivity, pH and seed germination index of treat 2 were all in line with the standard limit of agricultural sludge. Because of the presence of compost bacteria addition, the passivating heavy metals performance of treat 2 satisfied the standard limit of agricultural sludge after composting, which was superior to that of treat 1 and treat 3. The diversity of microbial communities in treat 2 decreased during composting. Extensive bacteria such as Bacillus, Geobacter, Lactobacillus, and Pseudomonas, which possessed the abilities of heavy metal passivation and organic oxidizing, were dominant in treat 2 during the heating stage. However, as composting proceeded, Tuberibacillus with ability of organic oxidizing gradually became the most dominant species at the thermophilic and cooling stages. Changes in microbial function varied from changes of microbial community in treat 2, subsequently affected the performances of heavy metal passivation and organic oxidizing during composting.

The impact of the mountain barrier on the spread of heavy metal pollution on the example of Gorce Mountains, Southern Poland

The main objective of this study was to determine the content, mobility, and the variability of concentration of zinc, lead, and cadmium in soils from the Gorce Mountains (south Poland), located over 100 km south-east from the potential industrial sources of contamination-zinc-lead sulfide ore mine and smelter in Bukowno, as well as hard coal mines of Silesia region and Kraków Nowa-Huta steelwork. The abovementioned problem is crucial in the context of the traditional mountain farming still extant in the region, as well as intensively developing tourism. The geoaccumulation index and potential ecological risk index were adopted to evaluate soil pollution in the study area and the BCR sequential extraction technique to assess mobility of the abovementioned elements. The obtained results clearly show that the pollution from distant industrial sources in the mountains is detectable. Apart from the increased concentrations of the tested metals in the soil (especially available forms), there is also a strong correlation between the concentrations of lead, zinc, and cadmium, which proves their common source of origin. The main evidence is the fact that differences in the concentrations of the tested metals on the windward and leeward sides were statistically significant. This also means that the studied mountain area, despite relatively low altitudes (up to 1310 m above sea level), constitutes a measurable barrier to the spread of atmospheric pollutants.

Responses of Labile Organic Carbon and Extractable Cadmium Fractions in an Agricultural Soil Following Long-Term Repeated Application of Pig Manure and Effective Microbes

Long-term pig manure addition has been widely applied in red soil to improve soil fertility. However, the influence of combined utilization of pig manure and effective microbes (EM) on soil organic carbon (SOC) and Cd are not well understood. This study conducted a 23-year (1996-2019) long-term fertilization field trial to investigate the changes of different fractions of SOC and Cd under chemical fertilization (CF), pig manure (PM), and pig manure with effective microbes (PM + EM) treatments in an agricultural soil of Jiangxi Province, South China. The results showed that the pig manure addition significantly enhanced the contents of SOC and Cd in the soils compared with the CF treatments. Furthermore, with the increment of SOC, the PM + EM treatment significantly increased the contents of soil microbial biomass carbon, dissolved organic carbon and easily oxidizable carbon compared with the pig manure application alone. Meanwhile, compared with the CF treatments, the EM addition significantly enhanced the exchangeable and oxidizable fractions of Cd, thus the potential Cd environment risk due to pig manure application should be carefully assessed.

Sediment quality of the Ridracoli fresh water reservoir in Italy: Insights from aqua regia digestion and sequential extractions

The inter-element relationships and the forms in which metals exist strongly influence their mobility and, in turn, have a signature on the environment and human health. Located in the northern Apennines within the Emilia-Romagna region, the Ridracoli artificial lake is one of Italy's most important reservoirs that provides drinking water for about one million people. This work characterized the reservoir sediments by ICP-MS after aqua regia digestion (ARD), comparing the limits by law to assess environmental compliance and XRF data from the same sample-set taken as total concentrations. The Degree of Extraction (DE) from pseudo-total concentrations of ARD analysis allows assessing elements mobility and the associated environmental risk. Principal Component Analysis (PCA) on the obtained data helped to investigate inter-element relationships better; for example, we observed carbonate-sourced sediments, many trace elements (e.g., Ni, Zn) linked to FeMn oxyhydroxides, the importance of the grain size in elements distribution, and the central role of the organic matter in element partitioning. In addition, a Sequential Extraction Procedure (SEP) was applied to the sediment samples to understand the partitioning of many analytes, including Potentially Harmful Elements (PHE) such as Fe, Mn, Cu, Cr, Ni, Pb, and Zn. The results indicated that the most easily mobilized forms were predominant in the area near the dam, in correspondence to sediments affected by the formation of a seasonal anoxic layer.

Analysis of the heavy metals (As, Pb, Cu, Zn) by leaching and sequential extraction procedure from a municipal solid waste incinerator fly ash co-processing cement kiln plant

The municipal solid waste incineration (MSWI) fly ash has been a major problem with the rapid development of the cities in China. And the cement rotary kiln co-processing technique is accepted as an effective method to dispose detrimental heavy metals in MSWI fly ash. This study focused on presented the total leaching content and the morphological distribution of the heavy metals in cement solid samples doped with MSWI fly ash. These samples were collected from a MSWI fly ash co-processing cement rotary kiln plant. The leaching test and the sequential extraction procedure were adopted to measure the migration characteristic of As, Pb, Cu, and Zn. In addition, the leachability of clinker samples under different simulated environmental conditions was also detected to analyze the security of the cement product doped with MSWI fly ash. This work demonstrates the feasibility of the cement rotary kiln MSWI fly ash co-processing technique and provides a scientific guidance to related plant.

Phytoremediation of Soils Contaminated with Heavy Metals from Gold Mining Activities Using Clidemia sericea D. Don

Soils contaminated by potentially toxic elements (PTEs) as a result of anthropogenic activities such as mining are a problem due to the adverse effects on human and environmental health, making it necessary to seek sustainable strategies to remediate contaminated areas. The objective of this study was to evaluate the species Clidemia sericea D. Don for the phytoremediation of soils contaminated with PTEs (Hg, Pb, and Cd) from gold mining activities. The study was conducted for three months, with soils from a gold mining area in northern Colombia, and seeds of C. sericea, under a completely randomized experimental design with one factor (concentration of PTEs in soil) and four levels (control (T0), low (T1), medium (T2), and high (T3)), each treatment in triplicate, for a total of twelve experimental units. Phytotoxic effects on plants, bioconcentration (BCF), and translocation (TF) factors were determined. The results obtained for the tissues differed in order of metal accumulation, with the root showing the highest concentration of metals. The highest values of bioconcentration (BCF > 1) were presented for Hg at T3 and Cd in the four treatments; and of translocation (TF > 1) for Hg and Pb at T0 and T1; however, for Pb, the TF indicates that it is transferable, but it is not considered for phytoextraction. Thus, C. sericea demonstrated its potential as a phytostabilizer of Hg and Cd in mining soils, strengthening as a wild species with results of resistance to the stress of the PTEs evaluated, presenting similar behavior and little phytotoxic affectation on the growth and development of each of the plants in the different treatments.

Enhanced remediation of heavy metals contaminated soils with EK-PRB using β-CD/hydrothermal biochar by waste cotton as reactive barrier

Heavy metals in the soil are major global environmental problems. Waste cotton was used to synthesize a novel β-CD/hydrothermal biochar (KCB), which is a low-cost and environment-friendly adsorbent for heavy metal soil remediation. KCB were used as reactive materials of electrokinetic-permeable reactive barrier (EK-PRB) to explore the removal characteristics of heavy metals. FTIR and XPS analysis revealed that KCB contained large numbers of surface functional groups. Adsorption of KCB for Pb²⁺ and Cd²⁺ reached 50.44 mg g^-1 and 33.77 mg g^-1, respectively. Metal ions in contaminated soil were removed by reactive barrier through electromigration, electrodialysis and electrophoresis, the removal efficiency of Pb²⁺ and Cd²⁺ in soil reached 92.87% and 86.19%. This finding proves that KCB/EK-PRB can be used as a cheap and green process to effectively remediate soils contaminated with heavy metals.

Trace Elements Analysis of Tunisian and European Extra Virgin Olive Oils by ICP-MS and Chemometrics for Geographical Discrimination

The aim of this study was to investigate the levels of trace elements in olive oils from different locations and their use for geographical authentication. Concentrations of seventeen elements were determined in a total of 42 olive oils from Tunisia, Spain (Basque country), and southern France, and in nine soil samples from Tunisia by quadrupole inductively plasma mass spectrometry. The compilation of appropriate techniques integrated into the analytical procedure achieved a precision (RSD) between 2% and 15% and low limits of detection (between 0.0002 and 0.313 µg kg^-1). The accuracy of the analytical method applied for olive oil analysis was evaluated using SRM NIST 2387 Peanut butter. The recoveries obtained after microwave-assisted digestion for the certified elements ranged between 86% and 102%. Concentrations of non-certified elements (V, Cr, Co, Ni, Ba, Rb, Sr, Cd, Pb, and As) were presented. The use of Pearson correlation applied on paired Tunisian oil/soil samples has shown that several elements (Mg, Mn, Ni, and Sr) were significantly correlated. The multivariate statistics using principal component analysis have successfully discriminated against three studied origins. The most significant variables were the elemental concentrations of Cu, Cr, Fe, Mn, Sr, V, and Zn. This study shows the potential of applying trace elements profiles for olive oil geographical discrimination.

Application of co-pyrolysis biochar for the adsorption and immobilization of heavy metals in contaminated environmental substrates

Heavy metal pollution has been considered as a serious threat to the environment and human in the past decades due to its toxic and unbiodegradable properties. Recently, extensive studies have been carried out on the removal of heavy metals, and various adsorption materials have been successfully developed. Among, biochar is a promising option because of its advantages of various biomass sources, abundant microporous channels and surface functional groups, as well as its attractive economic feasibility. However, the application of pristine biochar is limited by its low adsorption capacity and nonregenerative property. Co-pyrolysis biochar, produced from the pyrolysis of biomass with the addition of another biomass or non-biomass precursor, is potential in overcoming the limitation of pristine biochar and achieving superior performance for heavy metal adsorption and immobilization. Therefore, this article summarizes the recent advances in development and applications of co-pyrolysis biochar for adsorption and immobilization of various heavy metals in contaminated environmental substrates. In details, the production, characteristics and advantages of co-pyrolysis biochar are initially presented. Subsequently, the adsorption behaviors and mechanisms of different heavy metals (including Hg, Zn, Pb, Cu, Cd, Cr, As, etc.) in flue gas and wastewater by co-pyrolysis biochar are reviewed, as well as factors influencing their adsorption capacities. Meanwhile, the immobilization of heavy metals in both biochar itself and contaminated soils by co-pyrolysis biochar is discussed. Finally, the limitations of current studies and future prospects are proposed. It aims at providing a guideline for the exploitation and application of cost-effective and environmental-friendly co-pyrolysis biochar in the decontamination of environmental substrates.

Mechanisms for potential Pb immobilization by hydroxyapatite in a soil-rice system

This study aimed to investigate the mechanism of lead (Pb) immobilization by hydroxyapatite (HAP) in a soil-rice system, a pot experiment was conducted using Pb-contaminated soil amended with various rates of HAP and planted with rice (Oryza sativa L.). The Pb species in the soil and rice roots were determined using Pb L3-edge X-ray absorption near edge structure (XANES). Application of HAP increased soil pH and induced the dissolution of phosphate, subsequently promoting the formation of chloropyromorphite, an insoluble Pb species, in the soil. Therefore, the acid soluble and DTPA-extractable Pb concentrations decreased significantly with increasing levels of applied HAP. HAP reduced the retention of Pb in the iron plaque on the root surface at maturity, thereby alleviating Pb uptake by rice roots. The amount of phosphate in roots were increased with increasing rate of application of HAP, but was negatively correlated with Pb in rice stems and leaves. Application of 32 g kg^-1 of HAP triggered the precipitation of Pb₅PO₄Cl in roots, limiting Pb translocation from roots to shoots. In addition, HAP may induce the redistribution of Pb in rice nodes, lowering the transfer factor of Pb from the stem (or leaf) to rice grains. When the rate of application of HAP exceeds 4 g kg^-1, the Pb concentration in brown rice could be reduced to less than the Chinese National Standard of 0.2 mg kg^-1 (GB2762-2017).

Assessment of the Environmental Impact of Acid Mine Drainage on Surface Water, Stream Sediments, and Macrophytes Using a Battery of Chemical and Ecotoxicological Indicators

Mining activities at the Portuguese sector of the Iberian Pyrite Belt (IPB) have been responsible for the pollution of water, sediments, and biota, caused by the acid mine drainage (AMD) from the tailing deposits. The impact has been felt for years in the rivers and streams receiving AMD from the Aljustrel mine (SW sector of the IPB, Portugal), such as at the Água Forte stream, a tributary of the Roxo stream (Sado and Mira Hydrographic Region). To evaluate the extent of that environmental impact prior to the remediation actions, surface water, sediments, and the macrophyte Scirpus holoschoenus L. were sampled at the Água Forte and the Roxo streams, upstream and downstream from the confluence. The surface water and the sediments were extremely acidic at the Água Forte stream (pH ranges 2.22–2.92 for the water and 2.57–3.32 for the sediment), with high As, Cu, Pb, and Zn concentrations of 2.1, 120, 0.21, and 421 mg kg−1, respectively, in the water, and 661, 1746, 539, and 1994 mg kg−1, respectively, in the sediment, in the location closer to the mine. Two aquatic bioassays evidenced the high ecotoxicity of the Água Forte water at that site, with very low EC50 values for Vibrio fischeri luminescence inhibition (<3.1% v/v) and Daphnia magna 48-hour immobilization/mortality assays (<6.3% v/v). The impact of the AMD was also evident in the sediments of the Roxo stream, but not so marked in the water, with circa neutral pH and lower As, Cu, Pb, and Zn concentrations. Consistently, the ecotoxicological response was only felt in the sampling point closer to the confluence of the Água Forte with the Roxo stream, with an EC20 of 27.0% (v/v) towards the V. fischeri. One of the dominant and well adapted macrophytes, S. holoschoenus L., presented low bioaccumulation factors for Cu (0.04) and Zn (0.15) in their emerging parts, and very low concentrations for As and Pb, making this plant a potential candidate to be used in phytoremediation actions to treat and control AMD in the IPB.

Source and risk assessment of heavy metals and microplastics in bivalves and coastal sediments of the Northern Persian Gulf, Hormogzan Province

The objectives of the current study are to investigate the concentration, biological risks, chemical speciation, and mobility of of heavy metals and also the determination of their distribution, physicochemical characteristics, and abundance of microplastics in coastal sediments and edible bivalves in the Persian Gulf, the coastal area of Hormozgan Province. Sampling points were selected considering the location of industrial, urban and Hara forest protected areas. In November 2017, a total of 18 sediment samples from coastal sediments (top 0-10 cm) and the most consumed bivalve species in the region were collected from two stations, Lengeh and Bandar Abbas Ports. The average concentration of heavy metals (except for Ni and Cd) in the sediments were lower than their average shale and the upper continental crust. Enrichment factors revealed significant enrichment of Ni, Mn, Cr, Cd and As. The fractionation of heavy metals using the Community Bureau of Reference (BCR) sequential extraction scheme indicated the high bioavailability of Zn, As, Mn, and Co. In general, the highest concentration of Mo, Cd, Pb, Zn, Cr, Cu, Mn, Hg, and Sb was detected in areas with frequent human activities including Shahid Rajaee Port, Shahid Bahonar Port, and Tavanir station. Shahid Rajaee and Shahid Bahonar Ports are the most important ports on the coast of Hormozgan province. The Risk Assessment Code calculated for the study elements indicates that As, Co, Zn, and Cu pose a moderate environmental risk a threat to the aquatic biota. Health risks of most heavy metals arising from bivalves consumption were safe, except for As which is associated with the high target cancer risk values. With reference to the type of microplastics found, they were mainly fibeours with lengths ranging between 100 and 250 μm in sediments and bivalves. Most of the microfibers found in the sediments were made of polyethylene terephthalate (PET) and polypropylene (PP), and the fibers found in the bivalves were made of PP.

The evaluation of immobilization behavior and potential ecological risk of heavy metals in bio-char with different alkaline activation

The bio-char was prepared by co-pyrolysis of municipal sewage sludge and biomass with chemical activation. The alkaline activating agents of KOH and K₂CO₃ were used to develop multilevel pore structure without heavy metal. The proximate analysis, ultimate analysis, SEM, and surface area and porosity analyzer were applied to present the physico-chemical properties and multilevel pore structure of bio-char. After impregnation pretreatment, the KOH provided more functional ingredients and reacted with C to expand pore structure for bio-chars. It was confirmed the specific surface area reached 2122.43 m²/g, and micropore area was 1674.85 m²/g after co-pyrolysis at 800 °C. Through the pretreatment of alkaline activation, the novel evaluation of heavy metal immobilization behavior in bio-char matrix were investigated by BCR sequential extraction and leaching tests. The KOH activation showed prominent immobilization behavior relatively, and the K₂CO₃ activation had more noticeable effects on leaching behavior. For Cu, Ni, Cr, Cd, Pb, and Zn, after co-pyrolysis at 900 °C, the proportion of unstable fraction decreased significantly, and the residual fractions of heavy metals were above 89.44% according to BCR sequential extraction procedure. Under optimal pyrolysis temperature, the E_r value of bio-char reduced to 41.93, and the potential ecological risks decreased from considerable risk to low risk to ensure the further eco-friendly application.

Effect of antimony in soils of an Sb mine on the photosynthetic pigments and antioxidant system of Dittrichia viscosa leaves

Antimony is a toxic element whose concentration in soil and water has been rising due to anthropogenic activities. This study focuses on its accumulation in leaves of Dittrichia viscosa growing in soils of an abandoned Sb mine, and the effect on oxidant/antioxidant systems and photosynthetic efficiency. The results showed leaves to have a high Sb accumulation capacity. The amount of total chlorophyll decreased depending on Sb concentration and of carotenoids increased slightly, with a consequent increase in carotenoid/chlorophyll ratio. Photosynthetic efficiency was unaffected. The amount of O ₂ ^.- rose, although there was no increase in cell membrane damage, with lipid peroxidation levels being similar to normal. This response may be due to considerable increases that were observed in total phenolics, PPO activity, and enzymatic antioxidant system. SOD, POX, and DHAR activities increased in response to increased Sb amounts in leaves. The ascorbate/glutathione cycle was also affected, with strong increases observed in all of its components, and consequent increases in total contents of the ascorbate and glutathione pools. However, the ratio between reduced and oxidized forms declined, reflecting an imbalance between the two, especially that between GSH and GSSG. Efficient detoxification of Sb may take place either through increases in phenolics, carotenoids, and components of the glutathione-ascorbate cycle or through the enzymatic antioxidant system. Since Dittrichia viscosa accumulates large amounts of Sb without suffering oxidative damage, it could be used for phytoremediation.

Fractionation and accumulation of selected metals in a tropical estuary, south-west coast of India

Estimating the fractional distribution of sediment-bound heavy metals is highly significant for its ecological risk assessment in contaminated aquatic systems, since environmental factors enhance the mobility of heavy metals and its accumulation in different ecological matrices. In this study, the fractional distribution of Zn, Cd, Pb and Cu in the sediments of the Cochin estuary, along the south-west coast of India, was estimated along with its accumulation in four edible crustaceans. The high mobility of heavy metals in the Cochin estuary was evident from the distribution in fractions other than residual fraction. The exchangeable fractions of Zn and Cd were high in the Cochin estuary, indicating its high bioavailability. Even though the exchangeable fraction is negligible, Pb poses the risk of bioaccumulation due to the presence of oxidisable and reducible fractions. The level of heavy metals varies in different species of edible prawns, and high accumulation of all metals was observed in Metapenaeus dobsoni. Various risk assessment indices show that Cd and Pb pose significant ecological and human health risks in the Cochin estuary.

Remediation of Cu-polluted soil with analcime synthesized from engineering abandoned soils through green chemistry approaches

Due to the large output and potential ecological risks, disposal of engineering abandoned soils (EAS) has become an enormous challenge for human society. Herein, EAS has been transformed into microporous analcime (ANA) zeolite material through a fast, energy-efficient, and straightforward conversion process. The as-synthesized ANA has been employed to remediate Cu-polluted soil, which shows a significant ecological restoration function in a vegetable pot experiment. With 25 g/kg ANA into Cu contaminated soil (total Cu concentration: 200 ppm), the Cu accumulation concentration in vegetables has been decreased from 5.60 down to 1.80 mg/kg (approaching the background Cu level 1.70 mg/kg in vegetables). Detailed mechanism study combining with DFT calculations reveals that the Cu²⁺ in soil has been captured both inside the ANA pore channels and on the surface via ion-exchange and surface adsorption mechanism. The whole process, including ANA synthesis and Cu polluted soil remediation, has been optimized to show a valuable conceptual model to recycle EAS resource and in-situ remediate Cu polluted soil.

Trace metal dynamics in an industrialized Brazilian river: A combined application of Zn isotopes, geochemical partitioning, and multivariate statistics

The Paraiba do Sul (PSR) and Guandu Rivers (GR) water diversion system (120 km long) is located in the main industrial pole of Brazil and supplies drinking water for 9.4 million people in the metropolitan region of Rio de Janeiro. This study aims to discern the trace metals dynamics in this complex aquatic system. We used a combined approach of geochemical tools such as geochemical partitioning, Zn isotopes signatures, and multivariate statistics. Zinc and Pb concentrations in Suspended Particulate Matter (SPM) and sediments were considerably higher in some sites. The sediment partition of As, Cr, and Cu revealed the residual fraction (F4) as the main fraction for these elements, indicating low mobility. Zinc and Pb were mostly associated with the exchangeable/carbonate (F1) and the reducible (F2) fractions, respectively, implying a higher susceptibility of these elements to being released from sediments. Zinc isotopic compositions of sediments and SPM fell in a binary mixing source process between lithogenic (δ^66/64Zn_JMC ≈ + 0.30‰) and anthropogenic (δ^66/64Zn_JMC ≈ + 0.15‰) end members. The lighter δ^66/64Zn_JMC values accompanied by high Zn concentrations in exchangeable/carbonate fraction (ZnF1) enable the tracking of Zn anthropogenic sources in the studied rivers. Overall, the results indicated that Hg, Pb, and Zn had a dominant anthropogenic origin linked to the industrial activities, while As, Cr, and Cu were mainly associated with lithogenic sources. This work demonstrates how integrating geochemical tools is valuable for assessing geochemical processes and mixing source effects in anthropized river watersheds.

Effect of aging on stabilization of Cd and Ni by biochars and enzyme activities in a historically contaminated alkaline agricultural soil simulated with wet-dry and freeze-thaw cycling

Natural aging alters the surface physicochemical properties of biochars, which can affect the retention of heavy metals. This work investigated the effect of biochar aging on stabilization of heavy metals (Cd and Ni) and soil enzyme activities simulated with laboratory wet-dry (WD) and freeze-thaw (FT) cycling. A wheat straw (WS) biochar and a corn straw (CS) biochar were subjected to 30 WD or FT cycles, and Cd- and Ni-contaminated alkaline soils amended with the two fresh biochars (at 5% w/w) were subjected to 30-day constant moisture incubation and 30 WD or FT cycles. WD and FT aging caused slight reduction in the pH of the biochars, significant increases in their O contents and surface areas, and formation of new carbonate minerals. WS biochar was more effective than CS biochar at reducing the phytoavailable Cd in the soil, with reduction of 12.1%, 14.6%, and 12.9% under constant moisture incubation, WD aging, and FT aging, respectively. Reduction in phytoavailability of Ni by the addition of biochars was observed only under WD aging, by 17.0% and 18.5% in the presence of WS and CS biochars, respectively. Biochar amendment also reduced the distribution of Cd in the acid soluble and reducible fractions in all aging regimes. The addition of biochars decreased catalase activity in almost all aging regimes and invertase activity under FT aging, but increased urease activity under FT aging. Comparison of the enzyme activities in the soils amended with biochars under constant moisture and accelerated aging conditions indicates WD aging significantly decreased the activities of catalase, invertase, and urease in all treatments, while FT aging significantly increased urease activity in all treatments. These findings suggest that biochars can stabilize Cd in alkaline soils under changing environmental conditions, although the activities of some soil enzymes could be negatively impacted.

Urban Soils and Road Dust—Civilization Effects and Metal Pollution—A Review

Urban soils have been changed much by human impacts in terms of structure, composition and use. This review paper gives a general introduction into changes from compaction, mixing, water retention, nutrient inputs, sealing, gardening, and pollution. Because pollutions in particular have caused concerns in the past, metal pollutions and platinum group metal inputs have been treated in more detail. Though it is not possible to cover the entire literature done on this field, it has been tried to give examples from all continents, regarding geochemical background levels. Urban metal soil pollution depends on the age of the settlement, current emissions from traffic and industry, and washout. It seems that in regions of high precipitation, pollutants are swept away to the watershed, leaving the soils less polluted than in Europe. Health hazards, however, are caused by ingestion and inhalation, which are higher in 3rd world countries, and not by concentrations met in urban soils as such; these are not treated within this paper in detail. With respect to pollutants, this paper is focused on metals. Contrary to many reviews of the past, which mix all data into one column, like sampling depth, sieved grain sizes, digestion and determination methods, these have been considered, because this might lead to considerable interpretation changes. Because many datasets are not Gaussian distributed, medians and concentration ranges are given, wherever possible. Urban dust contains about two to three fold the hazardous metal concentrations met in urban soils. Some data about metal mobilities obtained from selective and sequential leaching procedures, are also added. Soil compaction, pollution, sealings and run-offs cause stress situations for green plants growing at roadside locations, which is discussed in the Section 5. Environmental protection measures have led to decrease metal pollutions within the last decade in many places.

Potentially toxic elements in the Middle East oldest oil refinery zone soils: source apportionment, speciation, bioaccessibility and human health risk assessment

In this research, fifteen potentially toxic elements (PTEs) (Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Sb, Sc and Zn) were analysed and quantified in samples collected at 44 sites in an urban area of Iran. Sources were apportioned using enrichment factors (EFs), modified pollution index (MPI), principal component analysis (PCA), multivariate linear regression of absolute principal component scores (MLR-APCS) and speciation, with a focus on anthropogenic PTEs in the urban and industrial soils of the Arvand Free Zone area, an oil-rich zone in the country. Furthermore, the bioaccessibility and the human health risks of PTEs were investigated. The EF revealed a significant enrichment for elements such as Cd, Cu, Hg, Mo, Pb, Sb and Zn. Values of MPI showed that Abadan industrial district and Abadan petrochemical complex are the most polluted sites in the study area.The PCA/MLR analysis revealed four main sources: natural sources, fossil fuel combustion, traffic and oil derivatives and petroleum waste. The relative contribution of each source to PTE concentration varied from 32.3% of the natural sources to 30.6% of traffic and from 20.1% of petroleum waste to 17% of fossil fuel combustion. The source apportionment of metals generated using MLR-APCS receptor modelling revealed that 85.0% of Hg was generated by oil products. Chemical speciation results were compatible with the results obtained from PCA. Bioaccessibility of PTEs decreased from gastric to intestinal phase except Mo and Sb due to their different geochemical characteristics. Hazard index (HI) for non-cancer risk of PTEs for both children and adults based on total element concentrations was estimated to range from 2-fold to more than 10-fold higher than that of bioaccessible phases.

Potential Release of Zinc and Cadmium From Mine-Affected Soils Under Flooding, a Mesocosm Study

Metal-contaminated mining soils pose serious environmental and health risks if not properly managed, especially in mountainous areas, which are more susceptible to perturbation. Currently, climate change is leading to more frequent and intense rain events, which cause flooding episodes, thereby altering soil redox equilibria and contaminants stability. We evaluated the potential release of Zn and Cd (two of the most common inorganic contaminants) and the factors regulating their solubility and speciation in two heavily contaminated soils representative of a Zn-mining area. The soils were flooded under aerobic (for 24 h) and anaerobic (for 62 days) conditions using mesocosm experiments, sequential extractions, and geochemical modelling. Leaching trials under aerobic conditions showed a high release of Zn and Cd (10 times the legislative limits), with metals possibly migrating via water infiltration or runoff. Under anaerobic conditions Zn and Cd were initially released. Then, solution concentrations decreased gradually (Zn) or sharply (Cd) until the end of the experiment. Sequential extractions and multisurface modelling indicated that both metals precipitated mainly as carbonates. This was confirmed by a geochemical multisurface modelling, which also predicted the formation of sulphides after 60 days in one soil. The model calculated metals to be preferentially complexed by organic matter and well predicted the observed soil solution concentrations. The results showed that during flooding episodes contaminants could be promptly transferred to other environmental compartments. The use of multisurface modelling coupled with laboratory experiments provided useful indications on the potential release and speciation in case of anoxic conditions.

Persistent thallium contamination in river sediments, source apportionment and environmental implications

The adverse impacts of detrimental thallium (Tl) contamination are of increasing concerns to sustainable development. Herein, the contents, distributions and sources of Tl and potential toxic elements (PTEs) (Pb, As, Cr, Cu, Ni, Co, Sb, Cd and U) were investigated in sediments collected in Gaofeng River, which has been contaminated by long-term mining activities, located in Yunfu City, Southern China. Results indicated that excessive Tl levels were found in sediments (1.80-16.70 mg/kg). Sequential extraction procedure indicated that despite a large amount of Tl entrapped in residual fraction, a significant level of Tl (0.28-2.34 mg/kg) still exhibited in geochemically labile fractions, which was easy for Tl mobilization and availability. Pb isotope tracing method further confirmed that the pyrite exploitations may be the prime contaminated contributor (47-76%) to these sediments. These findings highlight that it is essential to establish more effective measures for Tl contamination control and call for engineered remediation countermeasures towards polluted river sediments.

Source identification of chromium in the sediments of the Xiaoqing River and Laizhou Bay: A chromium stable isotope perspective

Hexavalent chromium, Cr(VI), is a heavy metal contaminant and the reduction of Cr(VI) is accompanied by large isotopic fractionation. In this study, the sources of Cr were explored using the Cr isotopic composition of sediments from the Xiaoqing River, a heavily polluted river located in the Shandong Province of China, which flows into Laizhou Bay. The results show that δ⁵³Cr values of the sediments are the highest upstream near the pollution source, and gradually decrease along the river toward the range for igneous reservoirs observed near the estuary. Based on the calculation of authigenic Cr isotopic composition (δ⁵³Cr_auth) using the detrital index and leaching experiments, we suggest that the authigenic Cr in the sample near the pollution source with the highest δ⁵³Cr_auth value mainly comes from the reduction of Cr(VI) discharged by anthropogenic activity, and authigenic Cr in other samples in the midstream with δ⁵³Cr_auth values slightly higher than the range of igneous reservoirs may come from natural oxidative Cr weathering products. By introducing a Rayleigh model, we calculate that at least 31%-55% of Cr(VI) in the river water had been reduced to Cr(III) near the pollution source. Due to the self-purification ability of the river, Cr(VI) was reduced; thus, there is no record of high δ⁵³Cr_auth values in the downstream of the Xiaoqing River and Laizhou Bay, indicating no obvious Cr pollution in these locations. The limited variation of δ⁵³Cr values for samples from a sediment core in Laizhou Bay is also indicative of no obvious Cr pollution in the history. The Cr isotopic compositions of the river sediments are useful for the identification of Cr sources and can be used to advise environmental remediation on Cr pollution.

Remediation of Pb, Cd, and Cu contaminated soil by co-pyrolysis biochar derived from rape straw and orthophosphate: Speciation transformation, risk evaluation and mechanism inquiry

Biochars are widely used in the remediation of soil heavy metals, but there has been no clear understanding to the effects of novel co-pyrolysis biochars derived from biomass and orthophosphate on soil heavy metals. In this study, co-pyrolysis biochars derived from rape straw and orthophosphate (Ca (H₂PO₄)₂·H₂O/KH₂PO₄) were prepared and used to explore their effects on the speciations and ecological risks of Pb, Cd, and Cu in contaminated agricultural soil. The results showed that the addition of these co-pyrolysis biochars significantly decreased TCLP extracted concentrations (decreased by 5.9-81.7%) and ecological risks of heavy metals (Pb, Cd, and Cu) by transforming the metals from available speciation to stable speciation in soils. Co-pyrolysis biochar derived from rape straw and KH₂PO₄ showed the highest immobilization capacities, and the immobilization capacities of biochars for three metals were in the order of Pb > Cu > Cd. Co-pyrolysis biochars could precipitate and complex with heavy metals directly by the phosphate and -OH on their surface, and also could promote immobilization of heavy metals indirectly by increasing soil pH value and available P content. During incubation, the content of carboxyl groups on biochars increased significantly, which was beneficial to the further complexation of heavy metals. In summary, the application of co-pyrolysis biochar derived from rape straw and orthophosphate (especially for KH₂PO₄) could effectively reduce ecological risks of Pb, Cd, and Cu in contaminated soil.

Sources, Enrichment, and Geochemical Fractions of Soil Trace Metals in Ulaanbaatar, Mongolia

Mongolia is a rapidly developing country that has experienced growing industrialization and urbanization in recent decades. This study was conducted to evaluate the enrichment and labile fractions of metals in urban soils of Mongolia and to identify major sources of soil metal pollution. The concentrations and geochemical fractions of Al, Fe, Mn, Cr, Cu, Cd, Co, Zn, V, Mo, As, Sb, and Pb in soils of the city Ulaanbaatar were investigated. The results demonstrate that only Fe, Mn, Co, Mo, and V occur at natural levels with enrichment factors close to unity. The majority of investigated toxic metals, including Cu, Zn, Cr, Sb, As, Cd, and Pb, are serious pollutants in urban soils, with enrichment factors of up to 2.8, 5.1, 2.1, 16, 13, 15, and 11, respectively. Studies of the chemical fractions of metals demonstrate that Zn is mainly found in its labile form and is considered a high risk to humans and biota. Industrial release, household ash, coal combustion, and tire abrasion were identified as key sources of toxic metals entering into the soil of Ulaanbaatar City, which should be controlled effectively to prevent the population as well as pollution distribution over a wider area by long-range atmospheric transport.

Do Wildfires Cause Changes in Soil Quality in the Short Term?

Wildfires have high frequency and intensity in the Mediterranean ecosystems that deeply modify the soil abiotic (i.e., pH, contents of water, organic matter and elements) and biotic properties (i.e., biomass and activity). In 2017, an intense wildfire occurred inside the Vesuvius National Park (Southern Italy), destroying approximately 50% of the existing plant cover. So, the research aimed to evaluate the fire effects on soil quality through single soil abiotic and biotic indicators and through an integrated index (SQI). To achieve the aim, soil samples were collected inside the Vesuvius National Park at 12 sampling field points before fire (BF) and after fire (AF). The findings highlighted that in AF soil, the contents of water and total carbon, element availability, respiration and the dehydrogenase activity were lower than in BF soil; in contrast, pH and hydrolase activity were significantly higher in AF soil. The microbial biomass and activity were affected by Al, Cr and Cu availability in both BF and AF soils. Despite the variations in each investigated soil abiotic and biotic property that occurred in AF soil, the overall soil quality did not significantly differ as compared to that calculated for the BF soil. The findings provide a contribution to the baseline definition of the properties and quality of burnt soil and highlight the short-term effects of fire on volcanic soil in the Mediterranean area.

Transfer and bioaccumulation of mercury from soil in cowpea in gold mining sites

In this study, we evaluated the phytoremediation ability of three different genotypes of cowpea (Vigna unguiculata L. Walp) grown on mercury-contaminated soils from gold mining areas. In particular we compared a native genotype with two commercial lines L-019 and L-042. The plants were cultivated in soils amended at different concentrations of Hg (i.e. 0.2, 1, 2, 5 and 8 mg kg^-1). After three months exposure, we determined plant growth, seed production, and Hg accumulation in different plant tissues (root, leaf, seed and stem). Indices of soil-plant metal transfer such as translocation, bioconcentration and bioaccumulation factors were calculated. Results showed that the native variety presented the highest seed production (3.8 g), however the highest plant biomass (7.9 g) was observed in line L-019, both on Hg-contaminated soil of 1 mg kg^-1. The different plant tissues differed in terms of Hg concentration (root > leaf > stem). In the highest treated soil, the line L-042 accumulates higher Hg in both roots and leaves, while line L-019 accumulates more metal in stems. In line L-019, Hg concentrations in the fruit showed significant differences being higher in the valves than in the seeds. The transfer factors were generally lower than 1 and indicates the low accumulation of Hg by cowpeas. The estimated daily Hg intake through cowpea consumption showed values far below the threshold of 0.57 μg kg^-1 dw day^-1 recommended by the World Health Organization. Our results show cowpea V. unguiculata as a good protein-rich food substitute of Hg-contaminated fish for populations living near gold mining sites.

Distribution and Bioavailability of Heavy Metals in Soil Aggregates from the Fenhe River Basin, China

Accumulation, bioavailability and potential ecological risk of seven heavy metals - chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd) and lead (Pb) - have been analyzed in agricultural soil aggregates with particle size of > 1 mm, 0.25-1 mm, 0.05-0.25 mm, and < 0.05 mm from the Fenhe River Basin (FRB). Accumulation factor (AF) analysis demonstrated that heavy metals tend to be enriched in < 0.05 mm soil aggregate. The bioavailability to plants of Cu, Zn, and Cd was higher than that of other metals and increased with the decrease in soil aggregate particle sizes. Risk assessment code (RAC) of Ni, Cu, Zn and Cd were 13.84%-21.08%, 7.13%-13.74%, 32.08%-51.82% and 29.38%-43.82%, indicating that Cu, Zn, Cd and Ni had a low to very high risk to other ecosystems, and the smaller the particle size (0.05-0.25 mm and < 0.05 mm), the greater ecological risk.

Heavy metals in iron ore tailings and floodplain soils affected by the Samarco dam collapse in Brazil

In November 2015, the Fundão Dam collapsed releasing about 35 million m^-3 of iron ore tailings into the environment, which covered approximately 15 km² of floodplain soils. Four years later, there is still great concern and controversy regarding contamination by heavy metals in the affected areas. Thus, the present study sought to evaluate the heavy metal contents and its distribution in tailings and non-affected soils. Tailings samples were collected in the stretch between Bento Rodrigues and the Candonga hydroelectric plant, in addition to a sample inside the Fundão Dam. Non-affected soils and river sediments from the same region were also collected as a control group. The heavy metal contents in the tailings were lower than in non-affected samples from the same area, discarding the hypothesis of contamination by the tailings mud. The non-affected samples presented high levels of As, Ba, Co, Cr, Cu, Ni and Zn, with at least one sample exceeding the quality reference values (QRV's) established for Minas Gerais state, which indicated a scenario of pre-disaster contamination for the Doce River watershed. Most of the elements (As, Cr, Cu, Ni, V and Zn) were extracted in the residual fraction of the BCR sequential extraction, presenting low risk of release in nature. The health risk assessment for As estimated that all the non-affected soils and sediments from Gualaxo do Norte, Carmo and Doce rivers have carcinogenic risk higher than the acceptable value for children. From our results, it is more likely to conclude that the deposited tailings are not a time-bomb for heavy metals contamination in the region.