Trace Elements In Soils Research Articles

Health risks of potentially toxic trace elements in urban soils of Manaus city, Amazon, Brazil.

The city of Manaus is the biggest industrial city of the north Brazilian region, and a haphazard urbanization process characterizes it. The continuous urbanization and industrialization processes have increased the levels of trace elements in the urban environment and have posed great threat on human health. It is, then, essential to assess the pollution levels and the potential risks of the trace elements presence in urban soils. Therefore, the purpose of this study was to investigate the status of trace elements soils pollution and their human health risks to the population of Manaus City. Twenty-two soil samples were collected from the surface layer (0-20cm), and the contents of Ba, Cr, Mn, Zn, Co, Ni, Cu, Cd and Pb were analyzed. Results showed the predominance of kaolinite, gibbsite and goethite as the main minerals of the clay fraction. The trace elements contents were affected by both natural sources and anthropic activities such as industrial operations and vehicular emissions. The soil contamination assessment by Enrichment Factor showed the existence of eight samples classified as considerably contaminated and two samples classified as highly contaminated. Geoaccumulation index also showed the existence of eight samples exhibiting considerable contamination and one sample showing high contamination. The non-carcinogenic health risk was considered low (HI < 1) to both children and adults. However, the carcinogenic risk of Cd and Pb was higher than the safety limits (CRtotal > 1 × 10-6), indicating that the long exposure to contaminated soils increases the probability of children's cancer occurrence.

Community Structure and Soil Mineral Concentration in Relation to Plant Invasion in a Subtropical Urban and Rural Ecotone

Alien species invasion affects local community biodiversity and stability considerably, and ecosystem services and functions will accordingly be dramatically changed. Many studies have reported a correlation between invasibility and the chemical nature of soil, but the influences of understory plant community structure and soil trace element concentrations on invasibility have not been fully explored. Landscape heterogeneity in the urban and rural ecotone may alter the invasion process, and assessing the invasibility of different types of native forests may lead to a better understanding of the mechanisms by which native species resist invasion. We compared the composition, structure, diversity and stability of the understory community in abandoned fallows, severely invaded by Mikania micrantha and Borreria latifolia, and adjacent natural and planted forests in the urban and rural ecotone of Eastern Guangzhou, China. Additionally, we quantified mineral element concentrations in the topsoil (0–25 cm) most influenced by the root system of understory communities in the forest stand types. Abandoned fallows had the highest concentrations of available ferrum (Fe) and available boron (B) and the lowest concentration of total mercury (Hg) Hg among the three stand types. In contrast to various species diversity indices, the understory structure of the three stands better explained differences in community invasibility. Average understory cover significantly differed among the three stand types, and those types with the greatest number of stems in height and cover classes 1 and 2 differed the most, indicating that seedling establishment may deter invasion to a certain extent. CCA (canonical correspondence analysis) results better reflected the distribution range of each stand type and its relationship with environmental factors, and available Fe, available B, exchangeable calcium (Ca), exchangeable magnesium (Mg), cover, available copper (Cu) and total Hg , were strongly related the distribution of native and exotic understory species. Invasion weakened community stability. The stability index changed consistently with the species diversity index, and abandoned fallows understory community stability was lower than the other stand types. According to our results, both soil mineral element concentrations and community structure are related to alien species invasion. Against the backdrop of urbanization and industrialization, this information will provide forest management and planning departments with certain reference points for forest protection and invasive plant management.

Tolerance and phytoremediation potential of Calopogonium mucunoides to boron

AbstractSoil contamination by trace elements (TEs) is a problem of great concern since the industrial revolution. However, not all TEs are essentially toxic, and several micronutrients such as boron (B) play essential roles during plant development and, in this case, B acts in plants as a structural element. Soil B levels above 3.0 mg dm–3 may be toxic to many plants and the greatest input of B to the environment occurs through the anthropic way. An environmentally promising alternative is phytoremediation, in which contaminant‐tolerant plants are used to remove or stabilize TEs in soils. Therefore, this work has been carried out to aim C. mucunoides’ tolerance to increasing B concentrations and its potential as a phytoremediator. We found out that C. mucunoides tolerates B doses up to 480 mg dm−3, the B uptaken is transported at a 1:1 ratio between root and shoot, suggesting that C. mucunoides can be used as a phytostabilizer and phytoextractor due to its potential to be used in phytoremediation techniques because it can tolerate toxic concentrations of B.

Trace elements in the system “soil-plants” and optimization of their use in agrocenoses of the Omsk Irtysh Land

The data on the content and reserves of trace elements (Mn, Cu, Zn, Co, Mo, B) in soils, reveals patterns of their distribution and quantitative characteristics of relationships in the “soil-plants” system in agrocenoses of the Omsk Irtysh Land have been systematized in the article. The assessment of trace elements in soils and plants has been carried out from the ecological and agrochemical positions. The peculiarities of the intake and accumulation of trace elements in plants depending on zonal soil and climatic conditions have been revealed. Indicators for evaluating the potential of trace elements entering plants have been proposed, and its comparison for diff erent trace elements in the “soil-microfertilizerplant” system has been given. The use of this indicator in calculating and normalizing fertilizer doses and predicting the accumulation of trace elements in plants has been justified. The regularities of the distribution and shape of boron in diff erent types of soils of saline complexes have been studied. For the fi rst time a comprehensive assessment of the effect of high boron concentrations on crop productivity was carried out. A system of indicators for diagnosing the toxic eff ect of the element on plants and a scale of their borostability has been developed. The factors affecting the intake of boron in plants and their resistance to excess of the element have been revealed. Quantitative parameters of the eff ect of chemical reclamation on the boron content in the “soil-meliorant-plants” system have been obtained. The scheme of soil-geochemical zoning of the territory of the Omsk region reflecting the availability of trace elements in the soil has been developed. New data on the availability of trace elements in the main arable soils of the surveyed territory have been presented. The values of optimal levels of trace elements for agricultural crops were corrected. The economic and bioenergetic effi ciency of methods for optimizing plant nutrition with trace elements under the environments of agrocenoses of the Omsk Irtysh Land have been revealed.

Exploratory analysis of trace elements in soils and plants affected by a gossan in the Semiarid

ABSTRACT Trace elements in high concentrations are a huge problem worldwide. Monitoring of natural areas with a high concentration of these elements, such as soils under the influence of gossans, is important since there is little information available. This study aimed to evaluate the pseudo total and available concentrations of Fe, Mn, Pb, and Zn in the soil and its accumulation in native and cultivated plants in the area under the influence of gossan in the Semiarid region in Brazil. Soil samples (0-20 cm) were collected in the North, South, and center areas of the gossan and five transections separated by 1000 m. The pseudo total (EPA3050A) and available concentration (DTPA, Mehlich) of Fe, Mn, Pb, and Zn were determined. In the same points, plant samples were collected and processed to determine the concentration and bioconcentration factor of Fe, Mn, Pb, and Zn. Soils under the influence of the gossan had high Pb and Zn concentration (exceeding soil reference values), indicating that care should be taken in these areas to prevent any risk for the local community. Plants showed different accumulation patterns, with a higher accumulation of trace elements in the shoot (Fe, Mn, Zn), while Pb was primarily accumulated in the roots. Even though soil concentrations were high, plants showed in general, low bioconcentration factor of the potentially toxic elements, except for Zn, indicating that soil conditions limit their availability.

ТЯЖЕЛЫЕ МЕТАЛЛЫ В ГОРОДСКИХ ПОЧВАХ: ОЦЕНКА СОДЕРЖАНИЯ И ЭКОЛОГИЧЕСКОГО РИСКА

Актуальность исследования обусловлена необходимостью выявления особенностей накопления тяжелых металлов в почвах урболандшафтов Владивостока и Уссурийска и установления величины потенциального экологического риска. Целью работы является оценка геохимического состояния почв различных функциональных зон урболандшафтов с использованием нескольких индексов загрязнения. Методы. Валовое содержание элементов в почвах определяли методом рентгенфлуоресцентного анализа на спектрометре EDX-800HS (Shimadzu). Результаты. Под влиянием сильной техногенной нагрузки в верхних горизонтах почв урболандшафтов в наибольшей степени накапливаются хром, медь, цинк и свинец. Содержание ванадия, кобальта и никеля сравнимо с кларком или ниже его. Средние и максимальные значения комплексных коэффициентов загрязнения PLI и NPI свидетельствуют о деградации поверхностного слоя городских почв и сильной степени загрязнения тяжелыми металлами. Потенциальный экологический риск колеблется от незначительного до среднего. Степень загрязнения почв различных функциональных зон увеличивается в следующем ряду: рекреационная&lt;многоэтажной застройки&lt;транспортно-селитебная&lt;малоэтажной застройки, уровень загрязнения варьирует от оценки «чиста почва» до оценки «сильно загрязненная почва». В некоторых почвах рекреационной зоны выявлена слабая аккумуляция хрома, цинка и меди. В почвах зоны многоэтажной застройки во Владивостоке обнаружено накопление хрома, меди, свинца и цинка (от слабого до среднего), а в Уссурийске отмечено только накопление меди. В почвах транспортно-селитебной зоны и зоны малоэтажной застройки с разной степенью интенсивности аккумулируются хром, медь, свинец и цинк. Более высокие значения как индивидуальных (Igeo, EF, PI), так и комплексных показателей загрязнения (NPI, PLI, PERI) выявлены в почвах Владивосток.

Variability in plant trace element uptake across different crops, soil contamination levels and soil properties in the Xinjiang Uygur Autonomous Region of northwest China

This study investigated contamination status of eight trace elements (As, Cd, Cr, Hg, Pb, Cu, Zn and Ni) in farmland soils and crops at 535 sites across the Xinjiang Uygur Autonomous Region, Northwest China. Land use types of the sampling sites included vegetable patch, grain field and orchard. Our experimental results indicated all farmland soils were considered as trace element contamination based on the Nemerow comprehensive pollution index (NCPI > 1). However, 91.97% of the crop samples were uncontaminated according to the Chinese Risk Control Standard. Soils from the vegetable patch showed higher pollution level comparison with that from grain field and orchard. Health risks for both non-carcinogenic and carcinogenic risks were calculated through crop ingestion exposure pathway. Grain samples showed highest health risks, followed by melon and fruit, and vegetables. The health risks of crops were mainly driven by Cr and Cd. Crop consumption may pose risks for children but not adults. The source of trace element contamination in the different farmland soils varied and may be attributed to the different agricultural activities. Plant type had a greater influence on the trace element accumulation in crops compared with soil trace element contents and physicochemical properties.

Content of Trace Elements in Soils of Eastern Antarctica: Variability Across Landscapes.

Although Antarctica is considered one of the most pristine areas on Earth, an accelerating human presence in this remote continent, such as scientific operations and functioning of numerous scientific stations, logistics, and tourism activities, has increased the risks of environmental impacts in recent decades. During the 63rd Russian Antarctic expedition, 42 samples from topsoil horizons were collected from Larsemann Hills, Mirny station, and Fulmar Island, Eastern Antarctica. The purpose of this work was to analyze the accumulation levels 8 trace elements and to assess possible environmental risks associated with contamination of Antarctic soils. Various human activities have been found to be responsible for increase of metal levels in studied Antarctic environments. Our study also revealed a specific role of ornithogenic factor and moss cover in distribution of contaminants in severe conditions of Eastern Antarctica soils. Ornithogenic soils were characterized by higher rates of accumulation of some trace metals and metalloids (especially zinc and copper) compared with other investigated "pristine" sites without significantly visible traces of guano inputs. In general term, obtained geoaccumulation index for trace elements in all samples were under or slightly above the 0 level, indicating low to moderate pollution of the studied soils. Results of principal component analysis revealed the necessity for further detailed research on interactions of trace metals with soil organic matter for better understanding of their biogeochemistry in the Antarctic environment. Although most of contaminated sites were found in anthropogenically affected areas, accumulation of some elements in guano-derived and moss materials were associated with higher values for soil pollution indices in natural soils, as well.

Physico-chemical Characteristics and Heavymetal contents in Soil of South West EL-Fasher City,Western Sudan.

The objectives of this study were to assess levels of trace and heavy elements in South west EL-Fasher cityin North Darfur soils and to provide information regarding accumulation of these metalsin top and sub-soils and to determine the most important soil factors (chemical and physical) which influence trace and heavy elements concentrations in soil.Top and sub-soil samples were taken at various locations in South west EL-Fasher city. The soil characterization was carried out for parameters like pH, E.C, O.C, M.C, soil texture, and trace and heavy elements (Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb and Zn). The results obtained in this research work provides documentation of the relationship between physicochemical properties and heavy metals concentrations in soils of North Darfur. The pH was found to be slightly alkaline. The values of E.C indicated that all samples of the soils are non-saline. Fe, Mn, Cr, Zn and Cu were distributed in very high concentrations compared to other metals. This study will help the industrial section and can be benefit from it for commercial purposes.There were obvious differences in correlation coefficients among the selected criteria (65.6% from total number of correlated between pH and some other selected physicochemical characteristics, whereas 42.3% from the total number were positive correlated between soil texture and some other selected physicochemical characteristics. This study can serves as a database of trace and heavy elements build-up in soil, allowing preventive actions to be taken.

Detection of lead in soil implying sample heating and laser-induced breakdown spectroscopy.

The emission line intensities enhancement and sensitivity of laser-induced breakdown spectroscopy (LIBS) has been a subject of great interest for the last several years to improve the detection of the trace elements in soil and other environmental samples. Among several other methodologies, LIBS of the heated targets is emerging as one of the effective techniques to achieve the objective. We have investigated the effect of target heating (room temperature, 100°C, and 200°C) on the emission enhancement and plasma parameters of the laser-produced plasma on the soil sample containing 80 ppm lead. In addition, the limit of detection (LOD) of lead in soil has been determined at a fixed target temperature (200°C) and with varying lead concentration (20 ppm, 80 ppm, and 100 ppm) in the soil samples. With increasing the target temperature, not only do the emission line intensities, the excitation temperature, and electron number density increase, but also the spectral lines of Pb emerge, which were absent in the soil spectra recorded at room temperature. The limit of detection of lead in LIBS of the heated soil target has been determined as 3.8 ppm. This study reveals the potential application of the LIBS of a pre-heated target for the detection of lead with an improved LOD in the environmental sample.

Distribution of trace elements in soil and plants under the action of bio-organic and mineral fertilizers

The deficiency of trace elements in the soil is often among the factors limiting the degree of realization of the genetic potential of crops. As a rule, the availability of trace elements to plants from soil is determined by their concentration in it, which is in the easily hydrolyzed phase. At the same time, some trace elements with increasing concentration in soil are considered as one of the most dangerous pollutants. After exceeding the established maximum permissible concentrations (MPC) and approximate permissible concentrations (APC), some trace elements are classified as heavy metals.

УЧАСТКИ С ПОВЫШЕННЫМ ФИТОРАЗНООБРАЗИЕМ НА ПРОЙДЕННОЙ ПОЖАРАМИ ЧАСТИ КЕРЖЕНСКОГО ЗАПОВЕДНИКА: ЗНАЧЕНИЕ, ПРОИСХОЖДЕНИЕ, КАРТОГРАФИРОВАНИЕ

The position of the Nizhny Novgorod Trans-Volga region in vegetation zoning schemes has long been a subject of discussion, which is due to the peculiarities of its landscape structure and long-term anthropogenic impact. This study examines the role of areas of increased phytodiversity in the post-fire part of the Kerzhensky Nature Reserve as an important component of the communities’ recovery after fires, an also deals with their spatial structure and floristic composition. A combination of field observations (geobotanical descriptions, soil profiles) and cartographic materials were used as the main research methods. We have found that the studied complex of communities was formed along an ancient long hollow, within which, due to the peculiarities of the landscape structure, was formed environment with an increased content of trace elements in soils and a greater accumulation of snow, which determined the development of rich linden-pine forests. They reflect the zonal features of the vegetation in the sandy Trans-Volga region; their preservation and further study are necessary to understand the formation processes of the vegetation cover and landscapes of this territory.

Determining the characteristics and potential of plantbased biochars to reduce copper uptake in maize

Metal contamination problems have become common everywhere with several known cases of metal toxicity in the agriculture sector. Metals including copper (Cu) are important to plant metabolism in trace amounts; however, excessive amounts can cause toxicity to the plants. The biochars have potential to absorb these trace elements in soil. A study was conducted to determine the characteristics and potential of different plant-based biochars to control Cu uptake and influence on the growth of maize (Zea mays L.). Five biochars from different agricultural waste materials, such as rice husk (RH1 and RH2), empty fruit bunches (EFB1 and EFB2) and oil palm kernel (OPK), were selected in the study. Each biochar was applied at 20 t·ha–1 on Cu contaminated soil, and maize was grown for 56 days in pots with 10 kg of acidic soil. The rice husk biochar (RH1) with a substantial number of heterogenic functional groups (alcohols and phenols, carboxylic acids and derivatives, amines, saline, alkynes) on its surface and more porous structure was able to retain more nutrients. It also give the best results in terms of reducing the Cu concentrations (1.61 mg·kg–1) in plants and plant uptake (10.15 µg·pot–1). Other than that, the highest plant growth parameters were also perceived in rice husk biochar applications. Hence, RH1 biochar had the most promising results in terms of controlling the plants Cu uptake and improved maize plant growth. © 2021, Agronomic Institute of Campinas. All rights reserved.

GEOCHEMICAL FEATURES OF POST-PYROGENIC CHANGES OF POLISSYA SOILS (LOW FIRE)

Geochemical post-pyrogenic soil changes are one of the most important factors in determining the state of the forest ecosystem. For the first time the content of microelements (Hg, As, Ba, Mg, Mn, Mo, Cd, Co, Cr, Cu, Pb, Zn, V, Ni) in post-pyrogenic sod-podzolic soils under the pine forest of Zhytomyr Polissya (Ukraine) was determined by the ICP-MS method. The study is based on a comparison of the content of trace elements in the sod-podzolic soils of the background area and burnt areas (grassland fire in 2019). The analysis of microelements in the soil profile of the burned and background areas to a depth of 10 cm (after 1 cm) and set the limit - 3-5 cm (humus-eluvial horizon), after which you can record the accumulation or scattering of elements after a fire on the surface. By calculating the percentage change (relative to background soils), intensive accumulation (more than 20%) of elements in post-pyrogenic soils - Cu, Ni, Co, V and moderate accumulation (up to 10%) - Pb, Mo, Mg, Ba, Cr and intensive scattering - Hg, As, Cd, Zn, Mn. The increase in the pH of post-pyrogenic soils (from 4.2 to 7.5) was determined, spatial map-schemes were constructed, due to which the direction of the fire was revealed - from the south-east to the north-west. The change of the content of ionic forms of metals (Cu, Pb, Zn, Mn) in the soil solution at different pH values (from 4 to 8 with a step of 0.2) is modeled (PHREEQC program) and the current trend is revealed: Pb - linear dependence, Cu, Zn, Mn is polynomial. The pH limits are calculated, where there are free forms of metals that enter the plants: Pb 3.9-8.2; Zn 5.5-7.5; Cu 5-8.2; Mn 5-11.5. The post-fire transformation of soils was revealed, which is expressed in the increase of pH (before the fire - 4.2-4.8; after the fire - 6.5-7.2; a year after the fire - 4.5-5.5). The obtained results confirmed the need for geochemical monitoring of post-pyrogenic soils for ecosystem restoration and plant biodiversity.

Comparative study of the content of trace elements in the system soil - plants of meadow biocenoses

Comparative study of the content of trace elements in the system soil - plants of meadow biocenoses

Studying the Application and Advances of Diffusive Gradients in-Thin Films Techniques (DGTs) to Constrain Mobility and Bioavailability of Heavy Metals in Soils

The aim of this review is to investigate the application and latest developments of the Diffusive Gradients in-thin films (DGT) with a focus on the mobility and bioavailability of heavy metals in soil. Soil chemical extractions are extensively used to predict nutrients elements in the soil. However, these measurements have their weaknesses and shortcomings. Comparing DGT with conventional extraction methods, DGT is a sampling technique with significant advantages; including speciation capabilities, sensitivity, time-in- tegrated signal, low risk of contamination and time averaged concentrations. These findings have strengthened the usefulness of the DGT technique as a potential monitoring tool for soil with heavy metal contamination. Studies which have used the DGT technique to evaluate processes important to bioavailability have been booming in the last 13 years, especially its application in soils science. Some recent studies have shown a good relationship between the measurement of metals concentrations in soil and plant by DGT, and cohesive results have been obtained from these measurements when they are based on the DGT technique. DGT is a newly established procedure to assess the bioavailability of trace elements in sediments and soils, and its applications are still in the early stage of testing. Therefore, future application of DGT is likely to include the studies of HMs contamination in soil for risk assessment and transfer rates to the food chain, as some studies have indicated the potential of DGT in these areas.

Long-term effects of sewage sludge-derived biochar on the accumulation and availability of trace elements in a tropical soil.

Thermal treatment by pyrolysis has been proposed as a sustainable alternative to enable the agricultural use of sewage sludge. The solid product obtained via pyrolysis of sewage sludge is called sewage sludge biochar and presents several advantages for its use as a fertilizer or soil conditioner. However, there are concerns about the accumulation and dynamics of trace elements in soil amended with sewage sludge biochar over the years. This study examined the effect of sewage sludge biochar, under field conditions for 5 yr, on the accumulation and availability of trace elements in a tropical soil. For this, 15 t ha-1 of sewage sludge biochar produced at 300 and 500°C were applied in the first two growing seasons. Application was interrupted from the third to the fifth seasons to assess the residual effect of sewage sludge biochar in the soil. The total and available trace element concentrations were determined. The total contents of trace elements showed the following variation in the soil over the 5 yr (mg kg-1): Cd (16.8-20.0), Co (19.5-21.5), Cr (98.2-125.7), Cu (8.1-17.1), Mn (62.9-85.7), Ni (20.3-35.0), Pb (27.0-52.4), and Zn (20.3-35.8). There was no change in the availability of Cd, Cr, Ni, and Pb over the years. Additionally, a residual effect of the sewage sludge biochar was the increase in availability of trace elements that are considered essential (Cu, Mn, and Zn) and beneficial elements (Co) for plants. Therefore, in relation to contamination by trace elements, the pyrolysis of sewage sludge of domestic origin proved to be an adequate strategy to enable the safe use of this residue in tropical agriculture.

Comparing Trace Elements (As, Cu, Ni, Pb, and Zn) in Soils and Surface Waters among Montane, Upland Watersheds and Lowland, Urban Watersheds in New England, USA

Trace element biogeochemistry from soils to rivers is important for toxicity to aquatic ecosystems. The objective of this study was to determine whether trace element exports in contrasting watersheds are controlled by their abundance in soil, current land uses in the watershed, or geologic processes. Upland soils and river water samples were collected throughout the Deerfield watershed in southern Vermont and western Massachusetts and in the Quinebaug and Shetucket watersheds of eastern Connecticut. Soil concentrations were only an important predictor for dissolved Fe export, but no other trace element. Soil pH was not correlated with normalized dissolved exports of trace elements, but DOC was correlated with normalized dissolved Pb and Ni exports. The limited spatial and depth of soil sampling may have contributed to the poor correlation. Surprisingly, linear regressions and principal component analysis showed that human development was associated with higher soil trace metal concentrations but not significantly correlated with dissolved trace elements export. Instead, forest abundance was a strong predictor for lower Cu, Pb, and Zn soil concentrations and lower As, Fe, Ni and Pb dissolved exports across the watersheds. Dissolved exports of Al, K, and Si suggest that enhanced mineral dissolution in the montane watersheds was likely an important factor for matching or exceeding normalized pollutant trace element exports in more urbanized watersheds. Further studies are needed to evaluate subsurface/hyporheic controls as well as soil–surface water interface to quantify exchange and transport.

The occurrence and distribution of strontium in U.S. groundwater

Groundwater samples from 32 principal aquifers across the United States (U.S.) provide a broad spatial scope of the occurrence and distribution of strontium (Sr) and are used to assess environments and factors that influence Sr concentration. Strontium is a common trace element in soils, rocks, and water and is ubiquitous in groundwater with detectable concentrations in 99.8% of samples (n = 4,824; median = 225 μg/L). Concentrations in 2.3% of samples exceeded the 4,000 μg/L health-based screening level. The relative importance of controlling factors on Sr concentration are spatially variable and partly dependent on the type of groundwater well. Three case settings illustrate controls on Sr concentration. For drinking-water supply wells, most high concentrations (>4,000 μg/L) were measured in samples from carbonate aquifers that resulted from water-rock interaction with Sr-bearing rocks and minerals. High Sr concentrations from monitoring wells were more common in unconsolidated sand and gravel aquifers in arid or semi-arid setting where shallow groundwater is affected by irrigation and evaporative concentration of dissolved constituents in combination with lithologic or applied Sr sources. Upwelling saline groundwater is also a source of Sr in some locations. Total dissolved solids concentration is an indicator of high Sr in all settings. An estimated 2.2 million people in the conterminous U.S. are potentially supplied water from public-supply wells with high Sr concentration, ~86% of whom use carbonate aquifers (with more than half supplied by the Floridan aquifer system). An additional 120,000 people are potentially supplied high-Sr-concentration water from domestic wells, more than half of whom (~58%) are in Texas. This study markedly expands the coverage of previous surveys of Sr in groundwater and is of interest given potential adverse human-health effects related to elevated concentrations of Sr and consideration of Sr for drinking-water regulation. Case settings with elevated Sr described for U.S. groundwater are likely indicative of settings and processes affecting Sr concentration in groundwater globally.

Rehabilitation of waste rock piles: Impact of acid drainage on potential toxicity by trace elements in plants and soil

The restoration of mining areas, in particular if they are located near towns or villages, is essential to reduce their potential risks for human health and to minimize their visual impacts. In this study, we assess the rehabilitation of a waste rock pile adjacent to the town of Tharsis (SW Spain). We measured vegetation cover and its diversity, and chemical composition of plants and soil, twelve years after remediation by lime amendments, added topsoil and planted vegetation. In general, the applied measures were successful covering with woody vegetation the upper part of the waste rock pile, and providing a greening visual landscape for the town nearby. The most abundant species were the gum rockrose (Cistus ladanifer) and the legume shrub Retama sphaerocarpa, this latter species most probably introduced in the seedbank of the added topsoil. Also in the soil seedbank, probably arrived the invasive Acacia saligna, of fast growth. In contrast, the lower part of the slopes was almost devoid of vegetation. We interpret that partial failure in the rehabilitation process as due to the acid mine drainage, which caused downslope a decrease of soil pH and increased availability of trace elements, thus impeding growth and establishment of plants. In addition, some plants, like C. ladanifer, growing at the base of the rock pile, had concentrations of Cd above the maximum tolerable level for animals, therefore representing a toxicity risk. Finally, we propose here an alternative technique to restore waste rock piles, by sorting and selectively handling the extractive wastes, thus reducing infiltration rates, seepages and the negative effect of the acid mine drainage. Those modified waste rock piles will be rehabilitated by the addition of topsoil and planted vegetation, as successfully worked out in the upper slopes of the study site.