Soil-plant interactions and the uptake of Pb at abandoned mining sites in the Rookhope catchment of the N. Pennines, UK--a Pb isotope study

Study on the migration pathway and isotopic composition of Zn in soil, plant and water in mining area

Isotopic tracing has been widely used to identify the sources and migration processes of Zn in diverse environments. However, Zn isotope fractionation during the migration process within the mining area poses challenges to the accuracy of isotopic tracing. To address this issue, a representative Pb-Zn mining area in the karst region of southwestern China was selected as the study area, given its long-term tailings' pollution history and the extensive spatial distribution of Zn migration. End-member samples and environmental media (soil, plants, river water and groundwater) were systematically collected, and heavy metal concentrations and isotopic signatures were analyzed. The migration pathways of Zn and associated isotopic fractionation from end members to surrounding environments were comprehensively investigated. Results indicated that tailings constitute the dominant source of Zn, with ZnS weathering being the primary driver of Zn isotopic variability in soils. Eluviation process, characterized by selective transport of soluble Zn2+ enriched in heavy isotopes, was identified as the key mechanism governing Zn migration across the soil-plant-river continuum. Retention processes (adsorption by organic matter, plant uptake, and mineral interactions) exhibited minimal influence on soil Zn isotopic composition. These findings advance the understanding of Zn and Zn isotope cycling in karst ecosystems and provide a scientific basis for formulating pollution control strategies in mining areas.

Study on the variation mechanism of Zn isotope in polluted farmland soil

Zn isotope can help to clarify the migration, transformation and source contribution of Zn in farmland soil. However, the research on Zn isotope value of different end members in farmland soil is incomprehensive, and the variation of Zn isotope in farmland soil caused by different factors in different polluted areas is unclear, which hinders the usage of Zn isotope tracing method in farmland soil. Thus, a Pb-Zn mine polluted farmland in southwest China was selected as the research object and the end elements and farmland soil samples with different Zn contamination were systematically collected to analyse Zn content, fraction and isotopic composition. The effects of different end members and processes of eluviation, organic adsorption and inorganic adsorption on Zn isotopic composition in soil were analysed, and the relationship between these three processes and environmental variables was analysed to clarify the change mechanism. The results can enrich the fractionation mechanism of Zn isotopes, expand the application of Zn isotope in tracing the sources, and provide geochemical evidence for remediation of Zn pollution in farmland soil.

Compost amendment in urban gardens: elemental and isotopic analysis of soils and vegetable tissues

Urban horticulture poses a sustainable form of food production, fosters community engagement and mitigates the impacts of climate change on cities. Yet, it can also be tied to health challenges related to soil contamination. This work builds on a previous study conducted on eleven urban gardens in the city of Vienna, Austria. Following the findings of elevated Pb levels in some soil and plant samples within that project, the present study investigates the elemental composition of soil and plants from two affected gardens 1 year after compost amendment. Inductively coupled plasma mass spectrometry (ICP-MS) analysis of skin, pulp and seeds of tomato fruits revealed minor variations in elemental composition which are unlikely to have an impact on food safety. In turn, a tendency of contaminant accumulation in root tips and leaves of radishes was found. Washing of lettuce led to a significant reduction in the contents of potentially toxic elements such as Be, Al, V, Ni, Ga and Tl, underscoring the significance of washing garden products before consumption. Furthermore, compost amendments led to promising results, with reduced Zn, Cd and Pb levels in radish bulbs. Pb isotope ratios in soil and spinach leaf samples taken in the previous study were assessed by multi-collector (MC-) ICP-MS to trace Pb uptake from soils into food. A direct linkage between the Pb isotopic signatures in soil and those in spinach leaves was observed, underscoring their effectiveness as tracers of Pb sources in the environment.

The Impact of Pb from Ammunition on the Vegetation of a Bird Shooting Range

Hunting with lead ammunition represents a source of heavy metal pollution to the environment that can be potentially high at the local scale. Intensive hunting of small game species can concentrate high levels of ammunition discharging in small areas. This type of hunting is a relevant economic resource for private landowners in some regions of Spain, and current legislation allows the use of lead ammunition in these scenarios. It becomes, therefore, highly relevant to study whether this activity may pose concerns to the conservation of the environment in the areas where it takes place. Using a red-legged partridge (Alectoris rufa) shooting range as a study area, we examined the effect of intensive hunting on this species on the vegetation present. We found significantly higher lead levels in the sprouts of plants of shooting areas related to control sites of the same property where partridge shooting does not occur. We found differences in the presence of lead between sprouts of different plant species. In addition, old sprouts of existing vegetation in shooting areas also showed higher lead levels than newly emerged sprouts of the same plants. These results demonstrate the impact of lead ammunition on vegetation in terms of persistence over time and differences between species. Further analyses using chemical and ecotoxicological data are necessary to evaluate the extent of environmental pollution risks. Our results provide new support in favor of the use of alternative ammunition, with particular emphasis on scenarios where hunting activity is intensive.

Concentrations and isotopic analysis for the sources and transfer of lead in an urban atmosphere-plant-soil system

Lead pollution has attracted significant attention over the years. However, research on the transfer of lead between urban atmospheric particles, soils, and plants remains rare. We measured lead concentrations and lead isotope ratios in total suspended particles (TSP), soil, and plants in an urban wetland in Beijing. The study period was September 2016-August 2017- covering all four seasons. The concentrations of lead in the atmospheric particles vary from 3.13 to 6.68 mg/m3. It is significantly higher in autumn than that in spring and summer (P < 0.05). There is also a significant difference between summer and winter (P < 0.05). The soil lead concentrations range from 57 to 114 mg/kg, with the highest concentration in spring, followed by summer, winter and autumn. The lead concentrations are 1.28-7.75 mg/kg in plants. The concentration was highest in spring and significantly higher than in summer. The bioaccumulation factor of Phragmites australis was 0.064 (<0.1), indicating that lead is not easily transferred to plants. Unlike the bioaccumulation factors, translocation factors have much higher values, indicating a higher transfer within the plants. Results also indicate an interesting seasonal pattern with almost 97% of lead in plants during spring being of atmospheric origin, whereas in autumn, soilborne sources contribute almost 94%. The isotopic compositions of lead in the urban atmosphere-soil-plant system show that lead pollution results from the mixing of geogenic and anthropogenic materials. Vehicle exhaust, crustal rocks and ore deposits are likely primary sources of lead pollution within the study domain.

Temporal and spatial changes of Pb in soils in Cuihu wetland, Beijing, China

Protecting soil from Pb contamination has been a programme for a long time in China. However, research on lead pollution in wetlands remains rare. To understand the characteristics of Pb pollution in Beijing and the sources of contamination of different soil samples in wetlands, we collected samples during all four seasons from two soil horizons and analyzed their Pb concentrations and Pb isotope ratios. The average concentrations of Pb varied from 65.44 mg/kg in spring to 106.11 mg/kg in winter. Concentrations in autumn were significantly lower than those in spring and summer and were notably different between A and B Horizons (59.42 and 71.47 mg/kg, respectively). The Pb isotopic compositions show that Pb pollution results from a mixing of geogenic and anthropogenic materials. The ratios of ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁶Pb/²⁰⁸Pb evidenced that coal combustion and vehicle exhaust are the main sources of lead contamination in the two horizons. These results will help in reducing lead contamination in soil by knowing the temporal and spatial variations and sources of lead in Beijing.

Source tracing of potentially toxic elements in soils around a typical coking plant in an industrial area in northern China

Coking plants are a substantial source of potentially toxic elements (PTEs) in soil. In this study, we examined the concentration of PTEs, the soil physicochemical properties, and the Pb isotopes in the soil inside and around a coking plant in an industrial city in northern China. We analyzed the spatial distribution of PTEs and the pollution risk areas by I_geo index, the enrichment factor (EF), and the Nemerow index, and we quantitatively identified the contribution of PTE pollution sources in the soil on a small- and medium-scale (plant and work section). Our results indicated that the Hg concentration inside the plant and the Cd concentration in the agricultural land around the plant were both relatively high. A comprehensive analysis of the soil in the study area was performed using the positive matrix factorization model and Pb isotope (^206/207Pb, ^208/206Pb) tracing method, based on the MixSIAR model, this analysis indicated that burning coal was the main source of Pb both inside (46.8%) and outside (26.3%) the coking plant. The pollution emission sources with significant influence on the soil outside the coking plant were diesel vehicles (12.5%), gas tanks (12.4%), and coke ovens (11.5%), while the sources inside the plant were quenching sections (11.1%), atmospheric deposition (11.0%), coke oven sections (9.6%), and diesel vehicles (6.1%). The results of PTE pollution risk zoning and Pb isotope tracing indicated that pollution is more serious in the western part of the plant, which is the area where coking and gas production takes place, and the most serious pollution outside the plant is mainly distributed to the southeast. This study provides theoretical and practical data indicating the contribution of industrial enterprises to soil pollution, and will help identify pollution responsibility and the management of pollution sources.

Methyl jasmonate ameliorates lead toxicity in Oryza sativa by modulating chlorophyll metabolism, antioxidative capacity and metal translocation

Lead (Pb) not only negatively alters plant growth and yield but may also have potentially toxic risks to human health. Nevertheless, the interaction between rice (Oryza sativa L.) plants and the molecular cell dynamics induced by lead-methyl jasmonate (MJ) remains unknown. Here, plants were hydroponically exposed to Pb (150 and 300 µM) alone or in combination with 0.5 and 1 µM MJ. The application of MJ modulated the expression of the HMAs, PCS1, PCS2 and ABCC1 genes, thereby immobilizing the Pb in the roots and lessening its translocation to the aerial parts of the rice plant. The supplementation of MJ improved the growth and yield of Pb-stressed rice by adjusting the proline and chlorophyll metabolism, increasing the phytochelatins (PCs) accumulation and diminishing the accumulation of Pb in the shoots. the application of MJ alleviated the oxidative stress of rice plants exposed to Pb toxicity by enhancing the activity of antioxidant enzymes and enzymes of the glyoxalase system (glyoxalase I and II) and decreasing the endogenous levels of malondialdehyde (MDA), hydrogen peroxide (H2O2) and methylglyoxal (MG). Therefore, the results of the present study could provide a molecular insight and cellular interplay scheme for the development of a promising strategy in Pb-contaminated areas to produce healthy food.

Source Identification of Cd and Pb in Typical Farmland Topsoil in the Southwest of China: A Case Study

Cd and Pb in farmland topsoil are controlled by many factors. To identify the source of potential toxic metals in the farmland topsoil around Mianyuan River, the chemical analysis and multivariate statistical analysis are performed in this study. The results indicate the following: (1) The concentration of Cd and Pb in soil exceed the background value of Chinese soil elements. (2) Cd is significantly enriched in the whole region and Pb is locally enriched, both of them are more or less influenced by human activities. (3) The contents of Cd and Pb increase significantly following the flow direction of river. (4) Pb isotope analysis indicates that the main source of Pb in the soil include the air dust, coal and phosphate plant, and the contribution of them decreases successively. (5) Linear correlation analysis and principal component analysis show that the main sources of Cd in the soil are mining phosphate rock, air dust, phosphate plant and coal mining.

Do soil amendments used to improve agricultural productivity have consequences for soils contaminated with heavy metals?

This study presents an analysis of the effects of manure and lime commonly used to improve agricultural productivity and evaluates the potential for such soil amendments to mobilise/immobilise metal fractions in soils contaminated from nearby mine tailings in the Zambian Copperbelt. Lime and manure were applied at the onset of the study, and their effects were studied over two planting seasons, i.e. 2016-17 and 2017–18. Operationally defined plant-available Cd, Cu, Ni, Pb and Zn in the soil, were determined by extraction with DTPA-TEA (diethylenetriaminepentaacetic acid-triethanolamine) and 0.01 M Ca(NO₃)₂, before, and after, applying the amendments. In unamended soils, Cd was the most available and Ni the least. Lime application decreased extractable Cd, Cu, Ni, Pb and Zn. The response to lime was greater in soils with an initially acidic pH than in those with approximately neutral pH values. Manure increased DTPA extractable Zn, but decreased DTPA and Ca(NO₃)₂ extractable Cd, Cu and Pb. Combined lime and manure amendment exhibited a greater reduction in DTPA extractable Cd, Ni, Pb, Zn, as well as for Ca(NO₃)₂ extractable Cd compared to separate applications of lime and manure. The amendments had a significant residual effect on most of the soil fractions between season 1 and 2. The results obtained in this study showed that soil amendment with minimal lime and manure whilst benefiting agricultural productivity, may significantly reduce the mobility or plant availability of metals from contaminated agricultural soils. This is important in contaminated, typical tropical soils used for crop production by resource poor communities affected by mining or other industrial activities.

Determination of (Bio)-available mercury in soils: A review

Despite the mercury (Hg) control measures adopted by the international community, Hg still poses a significant risk to ecosystem and human health. This is primarily due to the ability of atmospheric Hg to travel intercontinentally and contaminating terrestrial and aquatic environments far from its natural and anthropogenic point sources. The issue of Hg pollution is further complicated by its unique physicochemical characteristics, most noticeably its multiple chemical forms that vary in their toxicity and environmental mobility. This meant that most of the risk evaluation protocols developed for other metal(loid)s are not suitable for Hg. Soil is a major reservoir of Hg and a key player in its global cycle. To fully assess the risks of soil Hg it is essential to estimate its bioavailability and/or availability which are closely linked to its toxicity. However, the accurate determination of the (bio)-available pools of Hg in soils is problematic, because the terms 'bioavailable' and 'available' are ill-defined. In particular, the term 'bioavailable pool', representing the fraction of Hg that is accessible to living organisms, has been consistently misused by interchanging with other intrinsically different terms e.g. mobile, labile, reactive and soluble pools. A wide array of physical, chemical, biological and isotopic exchange methods were developed to estimate the (bio)-available pools of Hg in soil in an attempt to offer a plausible assessment of its risks. Unfortunately, many of these methods do not mirror the (bio)-available pools of soil Hg and suffer from technical drawbacks. In this review, we discuss advantages and disadvantages of methods that are currently applied to quantify the (bio)-availability of Hg in soils. We recommended the most feasible methods and give suggestions how to improve the determination of (bio)-available Hg in soils.

Isotope tracers for lead and strontium sources in the Tieguanyin tea garden soils and tea leaves

The concentrations of Pb & Sr in Tieguanyin tea leaves and soils from 15 tea gardens of Anxi, China, were determined and the sources of Pb & Sr in soil and leaf samples were analysed using isotope tracing technology. The results showed pH in soils had significant correlations to both acid-extractable Pb & Sr in soils and new leaves. The Pb concentration in leaves was significantly lower than that in soils, especially the acid-extractable Pb in soils. The low Bio-concentration Factor (BCF) indicated the bioavailable Pb in soils could not easily be transferred to leaves. The contribution rates of parent material were 61%-100% and 45%-100% for total Pb isotope and acid-extractable Pb isotope in soils, respectively, indicating a low impact of human activity. A sizeable influence of parent material for leaves was also observed, suggesting that Pb may be present in the dust-fall. Although Sr concentrations in leaves were not high, they exceeded that in soils. The high BCF also indicated that tea has a high capacity to accumulate Sr, with the coincidence that Sr⁸⁷/Sr⁸⁶ in the acid-extractable isotope in soils were similar to new leaves. A Pb-Sr joint tracer indicated that Sr in old and new leaves may be influenced by parent material and anthropogenic sources, respectively.

Review: mine tailings in an African tropical environment-mechanisms for the bioavailability of heavy metals in soils

Heavy metals are of environmental significance due to their effect on human health and the ecosystem. One of the major exposure pathways of Heavy metals for humans is through food crops. It is postulated in the literature that when crops are grown in soils which have excessive concentrations of heavy metals, they may absorb elevated levels of these elements thereby endangering consumers. However, due to land scarcity, especially in urban areas of Africa, potentially contaminated land around industrial dumps such as tailings is cultivated with food crops. The lack of regulation for land-usage on or near to mine tailings has not helped this situation. Moreover, most countries in tropical Africa have not defined guideline values for heavy metals in soils for various land uses, and even where such limits exist, they are based on total soil concentrations. However, the risk of uptake of heavy metals by crops or any soil organisms is determined by the bioavailable portion and not the total soil concentration. Therefore, defining bioavailable levels of heavy metals becomes very important in HM risk assessment, but methods used must be specific for particular soil types depending on the dominant sorption phases. Geochemical speciation modelling has proved to be a valuable tool in risk assessment of heavy metal-contaminated soils. Among the notable ones is WHAM (Windermere Humic Aqueous Model). But just like most other geochemical models, it was developed and adapted on temperate soils, and because major controlling variables in soils such as SOM, temperature, redox potential and mineralogy differ between temperate and tropical soils, its predictions on tropical soils may be poor. Validation and adaptation of such models for tropical soils are thus imperative before such they can be used. The latest versions (VI and VII) of WHAM are among the few that consider binding to all major binding phases. WHAM VI and VII are assemblages of three sub-models which describe binding to organic matter, (hydr)oxides of Fe, Al and Mn and clays. They predict free ion concentration, total dissolved ion concentration and organic and inorganic metal ion complexes, in soils, which are all important components for bioavailability and leaching to groundwater ways. Both WHAM VI and VII have been applied in a good number of soils studies with reported promising results. However, all these studies have been on temperate soils and have not been tried on any typical tropical soils. Nonetheless, since WHAM VII considers binding to all major binding phases, including those which are dominant in tropical soils, it would be a valuable tool in risk assessment of heavy metals in tropical soils. A discussion of the contamination of soils with heavy metals, their subsequent bioavailability to crops that are grown in these soils and the methods used to determine various bioavailable phases of heavy metals are presented in this review, with an emphasis on prospective modelling techniques for tropical soils.

Enrichment and source identification of Cd and other heavy metals in soils with high geochemical background in the karst region, Southwestern China

The geographical distributions of Cd and several other metals (Cu, Ni, Pb, Zn, and Cr) were characterized in 308 terra rossa samples across the Guangxi karst region. We found significant enrichments of heavy metals in the saprolites and terra rossa developed in 30 profiles, which is mainly caused by the weathering of Cd-enriched carbonate rocks, while the subsequent pedogenic processes were the dominant factor of the enrichments for Cu, Ni, Pb, Zn, and Cr. Sequential extraction analysis indicated that geogenic Cd and Pb in terra rossa mostly distributed in the residual fractions and exhibited low mobility, whereas the amorphous Fe/Mn oxide fraction was the principal Cd-bearing phase in Cambisols. The good correlation of Fe, Al, and Ti in related bedrocks, saprolites, and terra rossa suggested that in-situ pedogenetic processes provided most of the parent materials for terra rossa. The residual accumulation during the special pedogenesis in the karst region, caused elevated Cd and Pb concentrations with increasing weathering intensity, which was indicated by chemical index of alternation (CIA). In addition, results of Pb isotopic fingerprinting confirmed that terra rossa mainly derived from insoluble residues of underlying carbonate rocks. The allochthonous input of Pb also occurred during pedogenesis, whereas the transport and deposition of non-carbonate materials (clasolite/granite derived soils) was only a minor source to Pb input in terra rossa and the anthropogenic impact seemed to be negligible.

Deciphering source contributions of trace metal contamination in urban soil, road dust, and foliar dust of Guangzhou, southern China

Trace metal contamination prevails in various compartments of the urban environment. Understanding the roles of various anthropogenic sources in urban trace metal contamination is critical for pollution control and city development. In this study, the source contribution from various contamination sources to trace metal contamination (e.g., Cu, Pb, Zn, Co, Cr and Ni) in different environmental compartments in a typical megacity, Guangzhou, southern China, was investigated using the receptor model (Absolute Principal Component Scores-Multiple Linear Regression, APCS-MLR) coupled with the Kriging technique. Lead isotopic data and APCS-MLR analysis identified industrial and traffic emissions as the major sources of trace metals in surface soil, road dust, and foliar dust in Guangzhou. Lead isotopic compositions of road dust and foliar dust exhibited similar ranges, implying their similar sources and potential metal exchange between them. Re-suspended soil contributed to 0-38% and 25-58% of the trace metals in the road dust and foliar dust, respectively, indicating the transport of the different terrestrial dust. Spatial distribution patterns implied that Cu in the road dust was a good indicator of traffic contamination, particularly with traffic volume and vehicle speed. Lead and Zn in foliar dust indicated mainly industrial contamination, which decreased from the emission source (e.g., a power plant and steel factory) to the surrounding environment. The spatial influence of industry and traffic on the contamination status of road dust/foliar dust was successfully separated from that of other anthropogenic sources. This study demonstrated that anthropogenic inputs of trace metals in various environmental compartments (e.g., urban soil, road dust, and foliar dust) can be evaluated using a combined APCS-MLR receptor model and geostatistical analysis at a megacity scale. The coupled use of APCS-MLR analysis, geostatistics, and Pb isotopes successfully deciphered the spatial influence of the contamination sources in the urban environment matrix, providing some important information for further land remediation and health risk assessment.

Disentangling the factors of contrasting silver and copper accumulation in sporocarps of the ectomycorrhizal fungus Amanita strobiliformis from two sites

Amanita strobiliformis (European Pine Cone Lepidella) is an ectomycorrhizal fungus of the Amanitaceae family known to hyperaccumulate Ag in the sporocarps. Two populations (ecotypes) of A. strobiliformis collected from two urban forest plantations in Prague, Czech Republic, were investigated. The concentrations of Ag, Cu, Cd, and Zn were determined in the mushrooms. The metal mobility and fractionation in the soils was investigated by single extractions and sequential extraction. The soil distribution of A. strobiliformis mycelium was assessed by quantitative polymerase chain reaction (qPCR). The metal uptake from the soil into the mushroom sporocarps was traced by Pb isotopic fingerprinting. The findings suggested that A. strobiliformis (i) accumulates primarily Ag from the topsoil layer (circa 12cm deep) and (ii) accumulates Ag associated with the "reducible soil fraction". The concentrations of all metals, particularly Ag and Cu, were significantly higher in the A. strobiliformis sporocarps from one of the investigated sites (Klíčov). The elevated concentrations of Ag in the sporocarps from Klíčov can possibly be attributed to the higher Ag content in the topsoil layer found at this site. However, the simultaneously elevated concentrations of Cu in A. strobiliformis from Klíčov cannot be explained by the differences in the geochemical background and should be attributed to biological factors.

Role of P-type ATPase metal transporters and plant immunity induced by jasmonic acid against Lead (Pb) toxicity in tomato

The phytohormone jasmonic acid (JA) plays an imperative role in plants by modulating the activity of their antioxidative defense system under stress conditions. Here, we explored the role of JA-induced alterations in the growth and transcript levels of antioxidative enzymes in tomato seedlings exposed to different Pb concentrations (0.25, 0.50, and 0.75 mM). Pb treatment caused a dose-dependent reduction in their root and shoot lengths. Treatment of 0.75 mM Pb showed an increase in the contents of malondialdehyde (MDA), superoxide anion (O₂^•-), and hydrogen peroxide (H₂O₂) as compared to the untreated seedlings. Pb uptake was enhanced with an increase in Pb concentration. The seeds primed with JA showed reduction in Pb uptake and improvement in growth under Pb toxicity. The seedlings treated with both JA (100 nM) and Pb (0.75 mM) showed a decline in the levels of MDA, O₂^•-, and H₂O₂ as compared to the seedlings treated with 0.75 mM Pb alone. These results suggested that JA (100 nM) mitigated the oxidative damage by lowering the expression of the RBO and P-type ATPase transporter genes and by modulating antioxidative defense system activity. The biochemical and molecular analyses showed that JA plays a crucial role in plant defense responses against Pb stress.

Microbial functional diversity and carbon use feedback in soils as affected by heavy metals

Soil microorganisms are an important indicator of soil fertility and health. However, our state of knowledge about soil microbial activities, community compositions and carbon use patterns under metal contaminations is still poor. This study aimed to evaluate the influences of heavy metals (Cd and Pb) on soil microorganisms by investigating the microbial community composition and carbon use preferences. Metal pollution was approached both singly and jointly with low (25 and 2500 mg kg^-1) and high (50 and 5000 mg kg^-1) concentrations of Cd and Pb, respectively, in an artificially contaminated soil. In a laboratory incubation experiment, bio-available and potentially bio-available metal concentrations, selected soil properties (pH, electrical conductivity, total organic carbon and total nitrogen), and microbial parameters (microbial activity as basal respiration, microbial biomass carbon (MBC) and microbial functional groups) were determined at two sampling occasions (7 and 49 days). Metal contamination had no effect on the selected soil properties, while it significantly inhibited both microbial activity and MBC formation. Contaminated soils had higher microbial quotient (qCO₂), suggesting there was higher energy demand with less microbially immobilized carbon as MBC. Notably, the efficiency of microbial carbon use was repressed as the metal concentration increased, yet no difference was observed between metal types (p > 0.05). Based on the microbial phospholipid fatty acids (PLFA) analysis, total PLFAs decreased significantly under metal stress at the end of incubation. Heavy metals had a greater negative influence on the fungal population than bacteria with respective 5-35 and 8-32% fall in abundances. The contaminant-driven (metal concentrations and types) variation of soil PLFA biomarkers demonstrated that the heavy metals led to the alteration of soil microbial community compositions and their activities, which consequently had an adverse impact on soil microbial carbon immobilization.

Jasmonic acid induced changes in physio-biochemical attributes and ascorbate-glutathione pathway in Lycopersicon esculentum under lead stress at different growth stages

Lead (Pb) is one of most toxic heavy metals that adversely affect growth and developmental in plants. It becomes necessary to explore environment safe strategies to ameliorate its toxic effects. Phytohormones play an imperative role in regulating stress protection in plants. Jasmonic acid (JA) is recognized as a potential phytohormone which mediates immune and growth responses to enhance plant survival under stressful environment. The present study was undertaken to evaluate the effect of JA on the growth, metal uptake, gaseous exchange parameters, and on the contents of pigments, osmolytes, and metal chelating compounds in tomato plants under Pb stress during different stages of growth (in 30-, 45-, and 60-day-old plants). We observed a decrease in shoot and root lengths under Pb stress. Treatment of JA improved the shoot and root lengths in the Pb-treated plants. The Pb uptake was increased with the increasing concentrations of Pb, however, seeds pretreated with JA reduced the Pb uptake by the plants. The chlorophyll and carotenoid contents increased by JA treatment in plants under Pb stress. Pre-soaking of seeds in JA, improved gaseous exchange parameters, such as internal CO₂ concentration, net photosynthetic rate, stomatal conductance, and transpiration rate under Pb stress. JA enhanced the enzyme activity of ascorbate-glutathione cycle and reduced H₂O₂ concentration in Pb-treated plants. The contents of osmolyte and metal chelating compounds (total thiols, and non-protein and protein-bound thiols) were increased with the increase in Pb stress. In seeds primed with JA, the contents of osmolytes and metal chelating compounds were further increased in the Pb-treated plants. Our results suggested that treatment of JA ameliorated the toxic effects of Pb stress by reducing the Pb uptake and improving the growth, photosynthetic attributes, activity of ascorbate-glutathione cycle and increasing the contents of osmolytes and metal chelating compounds in the tomato plants.

Contamination of heavy metals and isotopic tracing of Pb in surface and profile soils in a polluted farmland from a typical karst area in southern China

Farmland top soils and soil profiles situated in the karst area of Guilin, Guangxi Zhuang Autonomous Region, southern China, reveal different degrees of heavy metal pollution, both in respect to the lateral as well as the vertical dimension. Pb isotope ratios clearly identify that heavy metal contributions to the soil represent the legacy of former Pb-Zn mining and smelting in the area. Depending upon soil properties, differences in the intensity of the vertical penetration of heavy metal pollution are discernible. Top soil coverage by local farmers provides little remediation. Consequently, hazardous conditions for the regional ecology, for agricultural usage and ultimately for human health remain in place. Based on chemical and isotopic results obtained, more effective remediation strategies need to be developed.

Investigating the Role of Wind in the Dispersion of Heavy Metals Around Mines in Arid Regions (a Case Study from Kushk Pb-Zn Mine, Bafgh, Iran)

The Kushk Pb-Zn mine is located in Central Iran and it has been in operation for the last 75 years. To investigate the role of wind dispersion of heavy metal pollutants from the mine area, dust samples were collected during 1 year and topsoil samples were collected around the mine. Results showed that the topsoil is polluted with Pb and Zn to about 1500 m away from the mine. It was also found that there was not a significant difference between the metal concentrations in topsoil and dust samples. The Pb and Zn concentrations in the dust samples exceeded 200 mg kg^-1 and their lateral dispersion via wind was estimated to be about 4 km away from the mine. It has been shown that a combination of mining activities and mechanical dispersion via water and wind have caused lateral movement of heavy metals in this area.

Effects of mining activities on evolution of water chemistry in coal-bearing aquifers in karst region of Midwestern Guizhou, China: evidences from δ13C of dissolved inorganic carbon and δ34S of sulfate

The generation of acid mine drainage (AMD) may accelerate watershed erosion and promote the migration of heavy metals, then threaten local ecosystems such as aquatic life and even human health. Previous studies have focused primarily on influence of AMD in surface environment. In order to reveal the acidizing processes in karst high-sulfur coalfield in Southwest China, this study, by contrast, focused on the hydrogeochemical evolution process and acidification mechanism of mine water in Zhijin coalfield, western Guizhou Province. The oxidation of pyrite and other sulfides induced strong acidification of mine water according to the water chemical analysis. As a result, a series of geochemical processes such as dissolution of carbonates and silicates, hydrolysis of metal ions, and degassing of CO₂ complicated water chemical evolution. The dissolution of silicates controlled the chemical composition of mine water, but more carbonates might be dissolved during the acidification of mine water. The sources of sulfate are quite different in water samples collected from the two selected mine. According to sulfur isotope analysis, the dissolution of gypsum is the primary source of sulfate in samples from Hongfa mine, whereas sulfide oxidation contributed a large amount of sulfate to the mine water in Fenghuangshan mine. The dissolution of carbonates should be an important source of DIC in mine water and CO₂ originating from organic mineralization might also have a certain contribution. This study elucidated the groundwater chemical evolution processes in high-sulfur coal-bearing strata and provided a foundation for further study of carbonates erosion and carbon emission during acidification of mine water.

Lead in Egyptian soils: Origin, reactivity and bioavailability measured by stable isotope dilution

The current availability of Pb in Egyptian soils and associated plants were studied in 15 locations (n=159) that had been historically subjected to industrial and automobile Pb emissions. Isotopic dilution with enriched ²⁰⁴Pb was used to estimate the soil Pb labile pool (Pb_E); results showed that %Pb_E values were mostly <25% which is likely due to the alkaline nature of the soils. Nonetheless, lability of Pb was significantly higher in urban and industrial locations indicating greater reactivity of anthropogenic Pb in comparison to geogenic-Pb. A plot of ²⁰⁶Pb/²⁰⁷Pb vs ²⁰⁸Pb/²⁰⁷Pb showed that all soils were aligned close to a virtual binary line between two apparent end member signatures (petrol and geogenic-Pb) suggesting that they are the major sources of Pb in the Egyptian environment. Soils with greater Pb concentrations (urban and industrial locations) displayed a significantly greater ratio of labile petrol-Pb to labile geogenic-Pb in comparison to less-contaminated soils. However, this difference was marginal (±5%) suggesting that historically emitted petrol-Pb has substantially mixed with geogenic-Pb into a common pool as a result of prolonged contact with soil. The proportion of petrol-Pb in fruits and leaf vegetables was significantly (P<0.005) greater than that of the associated soils suggesting preferential uptake of the more labile petrol-Pb as opposed to the relatively immobile geogenic-Pb. However, it is also possible that the major source of Pb intake by Egyptian consumers is extraneous Pb dust enriched with petrol Pb rather than systematic Pb via roots uptake.

The endogenous plant hormones and ratios regulate sugar and dry matter accumulation in Jerusalem artichoke in salt-soil

The changes in content of endogenous hormones in stolons and tubers of Jerusalem artichoke (Helianthus tuberosus L.) regulate tuber growth, but the specific knowledge about the importance of balance among the endogenous hormones is lacking. Two varieties of Jerusalem artichoke (NY-1 and QY-2) were tested for the endogenous zeatin (ZT), auxins (IAA), gibberellins (GA₃) and abscisic acid (ABA) in regulating sugar and dry matter accumulation in tubers. The dry matter content and sugar accumulation in tubers were correlated positively with endogenous ZT and negatively with GA₃ content and GA₃/ABA and IAA/ABA content ratios. Throughout the tuber formation, ZT content was higher in NY-1 than QY-2 tubers, whereas ABA content was higher in QY-2 than NY-1 tubers. The content ratios GA₃/ABA and IAA/ABA were greater in NY-1 than QY-2 before tuber initiation, but QY-2 surpassed NY-1 during the tuber growth stage. The GA₃/ABA and IAA/ABA content ratios declined during tuber growth. The results suggested that a dynamic balance of endogenous hormones played an important role in tuber development.

Balance between salt stress and endogenous hormones influence dry matter accumulation in Jerusalem artichoke

Salinity is one of the most serious environmental stresses limiting agricultural production. Production of Jerusalem artichoke on saline land is strategically important for using saline land resources. The interaction between plant hormones and salinity stress in governing Jerusalem artichoke (Helianthus tuberosus) growth is unclear. Jerusalem artichoke (variety Nanyu-1) was grown under variable salinity stress in the field, and a role of endogenous hormones [zeatin (ZT), auxins (IAA), gibberellins (GA3) and abscisic acid (ABA)] in regulating sugar and dry matter accumulation in tubers was characterized. Under mild salt stress (≤2.2gNaClkg(-1) soil), Nanyu-1 grew well with no significant alteration of dry matter distribution to stems and tubers. In contrast, under moderate salt stress (2.7gNaClkg(-1) soil), the distribution to stem decreased and to tubers decreased significantly. Mild salt stress induced sugar accumulation in tubers at the beginning of the tuber-expansion period, but significantly inhibited (i) transfer of non-reducing sugars to tubers, and (ii) polymerization and accumulation of fructan during the tuber-expansion stage. Under different salinity stress, before the stolon growth, the ratio of IAA/ABA in leaves increased significantly and that of GA3/ABA increased slightly; during tuber development, these ratios continued to decrease and reached the minimum late in the tuber-expansion period. While, salt stress inhibited (i) underground dry matter accumulation, (ii) tuber dry matter accumulation efficiency, (iii) transport of non-reducing sugars to tubers, and (iv) fructan accumulation efficiency during the tuber-expansion period; these effects were accompanied by significantly decreased tuber yield with an increase in salinity. With soil salinity increasing, the synthesis of IAA and GA3 was inhibited in leaves and tubers, while ABA synthesis was stimulated. In brief, tuber yield would significantly decreased with the increase of salinity.

Comparison of 265 nm Femtosecond and 213 nm Nanosecond Laser Ablation Inductively Coupled Plasma Mass Spectrometry for Pb Isotope Ratio Measurements

The analytical performance of 265 nm femtosecond laser ablation (fs-LA) and 213 nm nanosecond laser ablation (ns-LA) systems coupled with multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) for Pb isotope ratio measurements of solder were compared. Although the time-resolved signals of Pb measured by fs-LA-MC-ICPMS showed smoother signals compared to those obtained by ns-LA-MC-ICPMS, similar precisions on Pb isotope ratio measurements were obtained between them, even though their operating conditions were slightly different. The mass bias correction of the Pb isotope ratio measurement was carried out by a comparison method using a Pb standard solution prepared from NIST SRM 981 Pb metal isotopic standard, which was introduced into the ICP by a desolvation nebulizer (DSN) via a dual-sample introduction system, and it was successfully demonstrated for Pb isotope ratio measurements for either NIST 981 metal isotopic standard or solder by fs-LA-MC-ICPMS since the analytical results agreed well with the certified value as well as the determined value within their standard deviations obtained and the expanded uncertainty of the certified or determined value. The Pb isotope ratios of solder obtained by ns-LA-MC-ICPMS also showed agreement with respect to the determined value within their standard deviations and expanded uncertainty. From these results, it was evaluated that the mass bias correction applied in the present study was useful and both LA-MC-ICPMS could show similar analytical performance for the Pb isotope ratio microanalysis of metallic samples such as solder.

Field isotopic study of lead fate and compartmentalization in earthworm-soil-metal particle systems for highly polluted soil near Pb recycling factory

Earthworms are important organisms in soil macrofauna and play a key role in soil functionality, and consequently in terrestrial ecotoxicological risk assessments. Because they are frequently observed in soils strongly polluted by metals, the influence of earthworm bioturbation on Pb fate could therefore be studied through the use of Pb isotopes. Total Pb concentrations and isotopic composition ((206)Pb, (207)Pb and (208)Pb) were then measured in earthworms, casts and bulk soils sampled at different distance from a lead recycling factory. Results showed decreasing Pb concentrations with the distance from the factory whatever the considered matrix (bulk soils, earthworm bodies or cast samples) with higher concentrations in bulk soils than in cast samples. The bivariate plot (208)Pb/(206)Pb ratios versus (206)Pb/(207)Pb ratios showed that all samples can be considered as a linear mixing between metallic process particulate matter (PM) and geochemical Pb background. Calculated anthropogenic fraction of Pb varied between approximately 84% and 100%. Based on Pb isotopic signatures, the comparison between casts, earthworms and bulk soils allowed to conclude that earthworms preferentially ingest the anthropogenic lead fraction associated with coarse soil organic matter. Actually, soil organic matter was better correlated with Pb isotopic ratios than with Pb content in soils. The proposed hypothesis is therefore a decrease of soil organic matter turnover due to Pb pollution with consequences on Pb distribution in soils and earthworm exposure. Finally, Pb isotopes analysis constitutes an efficient tool to study the influence of earthworm bioturbation on Pb cycle in polluted soils.

Metals and possible sources of lead in aerosols at the Dinghushan nature reserve, southern China

RATIONALE

Aerosols play an important role in depositing metals into forest ecosystems. Better understanding of forest aerosols with regard to their metal content and their possible sources is of great significance for air quality and forest health.

METHODS

Particulate matter with an aerodynamic diameter less than 2.5 µm (PM(2.5)) in aerosols was collected every month for 20 months using moderate-volume samplers in the Dinghushan (DHS) nature reserve in southern China. The concentrations of metals (Al, Cd, Mn, Ni, Pb, and Zn) as well as the Pb isotopic ratios in the PM(2.5) samples were measured by inductively coupled plasma mass spectrometry (ICP-MS).

RESULTS

Moderate pollution with aerosol PM(2.5) was detected at the DHS nature reserve with the air mass from mainland China being the predominant PM(2.5) source. The high enrichment factors (EFs) for the heavy metals Pb, Cd, and Zn, as well as the PM(2.5) mass concentrations, coupled with backward trajectory analysis, indicated the anthropogenic origins of the PM(2.5) and of the heavy metals in the PM(2.5). The Pb isotopic ratios revealed the contributions from various Pb sources, which varied between seasons.

CONCLUSIONS

Industrial emissions and automobile exhaust from the Pearl River Delta (PRD) primarily contributed to the anthropogenic Pb in PM(2.5), although there was occasionally a contribution from coal combustion during the wet season. Pb isotopic ratios analyses are helpful for air quality assessment and Pb source tracing.

Lability, solubility and speciation of Cd, Pb and Zn in alluvial soils of the River Trent catchment UK

Alluvial soils can store a wide range of metal contaminants originating from point and diffuse sources. The biological health of these soils is important as they act as an interface between terrestrial and aquatic environments, therefore playing an important role in maintaining the quality of surface waters. The aim of this work was to examine the lability, solubility and bioavailability of Pb, Zn and Cd in the top (0-15 cm) and sub soil (35-50 cm) of metal contaminated alluvial soils from the Trent catchment, U.K. Samples (n = 46) were collected from within 10 m of the river bank. Sources of contamination include historical mining, industry, sewage treatment works and energy production. Enrichment factors based on total metal concentrations showed that contamination in soils declined with distance from the mining areas before rising again as a result of general urbanisation and identified point sources (e.g. river dredging activities). Pore waters were extracted and isotopic dilution and single extraction assays were undertaken on the soils to assess the lability and solubility of the metals. Multi-element isotopic dilution assays were used to determine the labile pool or E-value of these metals in the soil. E-value concentrations were found to range between 0.5 and 14 mg kg(-1), 11-350 mg kg(-1) and 25-594 mg kg(-1) for Cd, Pb and Zn, respectively. Comparison of the E-value assay with the EU standard extraction assay for trace element availability (0.05 M EDTA) showed that EDTA extractions generally over-estimated the E-value for Zn and Pb, with the difference being greater as contamination levels increased. Bioavailability of the metals was assessed by speciating the pore waters [MSol] using WHAM 7 to obtain estimates of free ion activities (M(2+)). Values of (M(2+)) were compared to published 'median critical limits' for soils that estimate levels of protection for 95% of biological species. For each of the three metals, (M(2+)) was found to exceed these critical limits at some sites. Solubility of the metals are reported using Kd values expressed using both the total and E-value as the solid phase. Finally we examine the use of different metal pools (total, E-value, EDTA-extractable) and different measures of Fe oxide pools (total, free total, free amorphous), in predicting [MSol] concentrations and (M(2+)) using WHAM 7 in assemblage modelling mode. Overall best simultaneous model predictions for the three metals were obtained using the E-values. Larger over-estimates of [MSol] and (M(2+)) were produced using the EDTA and total metal pools whereas a better fitting in the prediction was obtained when models used either the total or the free total FeOx pools.

Lead bioaccessibility in topsoils from lead mineralisation and urban domains, UK

Predictive linear regression (LR) modelling indicates that total Pb is the only highly significant independent variable for estimating Pb bioaccessibility in "mineralisation domains" located in limestone (high pH) and partly peat covered (low pH) shale-sandstone terrains in England. Manganese is a significant minor predictor in the limestone terrain, whilst organic matter and sulphur explain 0.5% and 2% of the variance of bioaccessible Pb in the peat-shale-sandstone terrain, compared with 93% explained by total Pb. Bootstrap resampling shows that LR confidence limits overlap for the two mineralised terrains but the limestone terrain has a significantly lower bioaccessible Pb to total Pb slope than the urban domain. A comparison of the absolute values of stomach and combined stomach-intestine bioaccessibility provides some insight into the geochemical controls on bioaccessibility in the contrasting soil types.

Sources, lability and solubility of Pb in alluvial soils of the River Trent catchment, U.K

Alluvial soils are reservoirs of metal contaminants such as Pb that originate from many different sources and are integrated temporally and spatially through erosional and depositional processes. In this study the source, lability and solubility of Pb were examined in a range of alluvial soils from the middle and lower River Trent and its tributary the River Dove using Pb isotope apportionment and isotopic dilution. All samples were collected within 10 m of the river bank to represent the soil that is most likely to be remobilised during bank erosion. Paired samples were taken from the topsoil (0-15 cm) and subsoil (35-50 cm) to assess differences with depth. Lead concentrations in soil ranged from 43 to 1282 mg/kg. The lability of soil Pb varied between 9 and 56% of total metal concentration whilst Pb concentrations in pore water varied between 0.2 and 6.5 μg/L. There was little difference in the % Pb lability between paired top and sub soils, possibly because soil characteristics such as pH, iron oxides and clay content were generally similar; a result of the recycling of eroded and deposited soils within the river system. Soil pH was found to be negatively correlated with % Pb lability. Source apportionment using (206)Pb/(207)Pb and (208)Pb/(207)Pb ratios showed that the isotopic ratios of Pb in the total, labile and solution pools fitted along a mixing line between Broken Hill Type ('BHT') Pb, used as an additive in UK petrol, and the local coal/Southern Pennine ore Pb. Various anomalies were found in the Pb isotopes of the bankside alluvial soils which were explained by point source pollution. Statistically significant differences were found between (i) the isotopic composition of Pb in the total soil pool and the labile/solution pools and (ii) the isotopic composition of Pb in the labile and solution pools, suggesting an enrichment of recent non-Pennine sources of Pb entering the soils in the labile and solution pools.