Control of geochemical mobility of arsenic by liming in materials subjected to acid mine drainage

Background  Acid mine drainage (AMD) results from the exposure of sulfide materials to atmospheric water and oxygen. In addition to AMD, oxidation of arsenopyrite and other As-bearing sulfides can release arsenic (As) into the environment. In view of the risk to living organisms due to contamination of ground and surface water sources with As, this work was carried out to evaluate the effectiveness of lime (CaCO₃) in controlling the dispersion of this metalloid in the environment. Methods  Partially oxidized samples of sulfide bearing materials from gold mines in Brazil were used to evaluate the arsenic mobilization by leaching tests. Columns containing ground samples, with and without liming treatments, were leached with distilled water every two weeks over a 156-day period. Results and Discussion  The acid-base accounting (ABA) static tests classified the samples as potential acid forming materials. In the treatments without liming, As, Fe and S concentrations in the leachates were higher than after treatment with carbonate. Nevertheless, the effectiveness of liming and As mobilization were lower in the sample containing goethite. A high correlation between Fe and As concentrations in the leachates (r=0.749) suggests that iron (hydr)oxides retained arsenic in the solid phase. Oxidation rates of As bearing sulfides were increased at low pH (2.0–3.9), probably due to the enhanced activity of bacteria (Acidithiobacillus) and decreased rate of Fe precipitation, thus reinforcing generation of acid water, and consequently releasing As. Conclusions and Perspectives  Our results corroborate the use of lime to control the dispersion of As in AMD-affected environments. However, the effectiveness of the liming treatment seems to be dependent on the presence of iron (hydr)oxides in the sample. These findings can be useful to remediate areas affected by acid mine drainage and arsenic mobilization in partially oxidized sulfide materials. ESS-Submission Editor: Chengrong Chen, PhD (c.chen@griffith.edu.au)     

Chromium and arsenic in contaminated soils (Review of publications)

In the last decades, the chromium clarke in the world’s soils has been revised and reduced; at present, it is equal to 70 mg/kg. No maximal permissible concentration is accepted for the total chromium content in the soils of Russia; it appears reasonable to use the Western European and North American standards in Russia and to take the average value of the maximal permissible concentration equal to 200 mg Cr/kg. Chromium toxicity depends on its oxidizing status. The hazardous effect decreases with the reduction of Cr(VI) to Cr(III). There are various chemical reducers of Cr(VI), including sulfides, dissolved organic substance, aqueous Fe(II) and minerals enriched in Fe(II), and Fe(0). As-containing ore tailings represent a powerful source of technogenic arsenic. Significant environment contamination with natural As is registered in a number of Asian countries. The maximal permissible concentration of total arsenic is equal to 2 mg/kg in Russian soils; it is probably underestimated, because it is lower than the As clarke in soil (5 mg/kg). The approximately permissible concentration (APC) values for As look more reasonable. Arsenic toxicity depends on its oxidation degree: As(III) is 2–3 times more toxic than As(V).     

A pedological investigation of an archaeological site in Ontario,Canada, I. An examination of the soils in and adjacent to a former village

The Benson site is a former village which was inhabited by Huron Indians in the 1600's. It is located 90 km northeast of Toronto, Canada. The soils of a portion of the site were sampled on a 1-m grid 15 cm below the surface. These soils were then analyzed for magnesium, calcium, potassium, sodium, phosphorus, carbonates, pH and organic carbon. Three off-site soil profiles (Podzols) were sampled and analyzed for comparative purposes.Of the chemical attributes of soil materials studied at the Benson site amounts of magnesium, organic phosphorus, and inorganic phosphorus were sufficiently different to be useful in distinguishing formerly occupied soils from off-site soils. Such information may thus be an aid to archaeologists in determining the presence or absence of sites occupied in the past.     

Effects of ammonium sulphate fertilization on arsenic mobility,speciation, and toxicity in soils planted with barley

Journal of Soils and Sediments - Arsenic (As) is one of the most widespread toxic elements, affecting human health through consumption of contaminated water or food. This work studied the effects...     

Binding of Sb(III) by Sb-tolerant Bacillus cereus cell and cell-goethite composite: implications for Sb mobility and fate in soils and sediments

Journal of Soils and Sediments - Adsorption onto mineral and bacterial surfaces can profoundly affect the mobility and fate of dissolved ions in soils; however, currently, there is a poor...     

The historic man-made soils of the Generalife garden (La Alhambra, Granada, Spain)

We studied the soils of the Patio de la Acequia garden of the Generalife, a palatial villa forming part of La Alhambra, a World Heritage Site in Granada, Spain. This garden, which is estimated to be around 700 years old, is the oldest historical garden in the Western World. The soils are man‐made cumulimollihumic‐calcaric (hypereutric, anthric) Regosols. Noteworthy amongst the main pedogenic processes, in relation to the human activities of cultivation, irrigation and tillage, are horizonation, melanization (the contents of organic carbon varied between 0.59% and 8.87%, and those of P₂0₅ extracted with citric acid between 723 mg kg⁻¹ and 7333 mg kg⁻¹, with maximae in the Ap horizons) and structure formation. The soil fabric, studied at the ultramicroscopic level using scanning electron microscopy, is of laminar and partition‐walls’ type in the lower horizons, depending on the microped zones. The partition‐walls’ fabrics found are different to those of the possible pre‐existing sedimentary fabrics. These are numerous lithological discontinuities and at least two burials, leading us to deduce that there have been two main stages of filling with materials in the formation of these soils. The first is Arabic‐Medieval (13th century), when the garden was created, its surface being some 50 cm below the level of the paved area of the present patio. In the deeper parts, the materials employed in the fill are similar to the in situ soils of the zone, unaffected by the buildings. The second stage is Christian (15th century to the present day). During this period the Medieval garden was gradually buried under a layer of materials from the nearby soils and/or sediments mixed with manure until the surface was only just below the level of the paved area of the patio. In this work we discuss the difficult classification of these relatively little studied soils. In spite of their being clearly related to human activity, they are not classified as Anthrosols in the FAO system (1998) because soil materials cannot be classified as anthropopedogenic or as anthropogeomorphic.     

Effects of bacteria on metal bioavailability,speciation, and mobility in different metal mine soils: a column study

Purpose  

Successful phytoremediation depends mainly on the bioavailability of heavy metals in the soil. Recently, soil microbes possess several mechanisms that are able to change metal bioavailability in the soil, which provides a new strategy for investigating biogeochemical cycling of metals in contaminated soils. Three metal mines soils with elevated concentrations of Cd, Pb, and Zn from China were applied in this column study to (1) evaluate the effects of metal tolerant bacterial inoculation (Burkholderia cepacia, accession number: AB051408) on metal release, (2) monitor the migration of metals in the rhizospheric horizon (0–20 cm), and (3) investigate metal speciation and sequential fractions in soil.     

An integrated geochemical and mineralogical approach for the evaluation of arsenic mobility in mining soils

Purpose  

The assessment of risk related to the presence of potentially toxic elements in soils is strictly related to the knowledge of their form and mobility. These relevant properties depend on the complex interactions of the elements of concern with the soil particles that generally cannot be addressed by a single technique. This study presents an integrated approach implementing geochemical and mineralogical investigation techniques on samples from a former mining area (Tolfa Mountains district, northern Latium, Italy), where exploiting activities occurred until the recent past. In particular, the As total concentration and the As distribution in solid phases is studied with the aim to evaluate the possibility of environmental pollution and consequent risks for the health of people living in the area and possibly affected in case of significant mobilization of this toxic element.     

晋陕蒙接壤区露天矿层状土壤水分入渗特征与模拟

分析4种不同结构层状土水分入渗规律,为晋陕蒙接壤区露天矿排土场建设筛选合适的层状土体。设置沙土、砒砂岩、黄绵土和红黏土4种均质土柱以及黄-沙-红、黄-红-沙、沙-黄-砒、黄-砒-沙4种层状土,借助室内土柱自动观测系统测定矿区土壤的入渗过程,通过入渗速率、累积入渗量、湿润锋运移、剖面含水量变化分析不同结构层状土入渗特征,结合晋陕蒙接壤区自然条件,评价适合排土场建设的层状土体。结果表明:黄-沙-红、沙-黄-砒型层状土在短时间内能储存大量水分,且第三层土体阻水作用强,黄-沙-红型层状土下层红黏土阻水效果尤其显著,这两种层状土体是矿区排土场较理想的新土体结构。但是,黄-红-沙型层状土入渗速率慢,在强降雨条件下不能使水分迅速入渗。黄-砒-沙型层状土湿润锋到达第三层土体后运移速率仍很快,阻水效果差,水分容易渗漏到深层土壤,这两种层状土结构不宜应用到晋陕蒙矿区排土场建设中。最后探讨了HYDRUS-1D对入渗过程的模拟,利用均质土剖面含水量反演土壤水力参数模拟4种层状土的入渗过程,得到较好的模拟效果。本文对4种层状土入渗特征的测定与模拟,对于指导露天矿区排土场新土体构筑有一定的理论和现实意义。     

Copper and arsenic (enargite) contamination of soils along a toposequence in Chinkuashih,northern Taiwan

This study investigates the species of Cu and As (enargite) residues present in soils of the Chinkuashih area, northern Taiwan. Two pedons, on the shoulder and footslope along a toposequence, were examined for their metal partitioning and geochemical origins. The bulk soils were analyzed by sequential extraction combined with mineralogical analyses, including X-ray diffraction (XRD) and scanning electron microscopy ∕ energy dispersive spectrometer (SEM ∕ EDS) analyses. Soil pH ranged from 4.23 to 4.91 with low base saturation, and the soils can be classified as fine, mixed, thermic, Typic Kandiudults. Mineralogical study indicated that enargite and pyrite particles mainly coexisted in silt and sand fractions, particularly in lower soil horizons of the footslope, showing high contents of Cu and As. Kaolinite and illite were dominant minerals in clay fractions. The footslope accumulated more total Cu and As than that of shoulder pedon. The sequential extraction experiments resulted in high proportions of Cu remaining in residual fractions, while the most of As was bound in amorphous Fe and Al oxyhydroxide fraction. The risk analyses of Cu and As (enargite) contamination in soils of the Chinkuashih area merits further study.     

Urban domestic gardens (IX): Composition and richness of the vascular plant flora, and implications for native biodiversity

Garden floras interact with native biodiversity by providing resources for wildlife and by acting as a source of non-native species. Understanding the composition and richness of garden floras will help evaluate the relationships between these floras and the wider environment. The composition and richness of vascular plant floras were measured in a stratified sample of 61 urban, domestic gardens in Sheffield, UK, based on complete garden inventories. The entire garden flora contained 1166 species, of which 30% were native and 70% alien. Across gardens, aliens showed lower occupancy than natives, comprising 79% of the species recorded only once. The garden flora contained 146 plant families, which included 72% of the native, naturalised or recurrent casual families recorded in the wild in Britain and Ireland. Gardens contained on average 45% natives, irrespective of garden size. Garden area explained 30% of the variation in species richness within individual gardens. Doubling garden size led to an increase in species richness of 25%. The garden flora comprised 10% annuals, 63% biennial/perennials, 18% shrubs and 8% trees; shrubs were disproportionately composed of alien species. The floras of urban domestic gardens probably form the greatest source of potentially invasive alien plants. However, the plants found in domestic gardens have closer affinities with the uncultivated flora than is often perceived, and their role for wildlife in gardens deserves reassessment. Declines in garden size that result from recommendations on the density of new housing are unlikely to have major consequences for plant richness in gardens.     

Amelioration and reforestation of sulfurous mine soils in Lusatia (Eastern Germany)

In Germany nearly 1.550 km² have been claimed by brown coal mining until now. Mine soils formed of carboniferous and sulfurous overburden are classified as “sulfurous mine soils”. They remain vegetation-free for decades and may be cultivated only after soil amelioration. The objective of amelioration is a sustained improvement of soil reaction. Lime requirement for the achievement of a certain pH-value is calculated from acid-base-balance (SBB). Lime fertilizers and base-rich brown coal ashes are used for amelioration. As ashes have serveral advantages,their application is recommended. The ameliorative application of lime fertilizer or brown coal ash should be incorporated intensively into the soil to a depth of 60 cm, better 100 cm. Amelioration includes a mineral fertilization with N, P and K. Afforestations with Pinus sylvestris, Pinus nigra, Larix decidua, Larix eurolepis, Tilia cordata, Quercus rubra and Quercus petraea on ameliorated mine soils show surprising good results. Multi-species stands have very positive effects on soil formation. Raw humus is formed under pine and larch, and under deciduous trees moder and mull with higher bioactivity and better development of water and nutrient balance in the topsoil are found.     

Characterization of arsenic serious-contaminated soils from Shimen realgar mine area,the Asian largest realgar deposit in China

Purpose

Serious arsenic (As)-contaminated soils have the potential to cause contamination of ground water and surface water, being toxic to plant, animals, and human. The aim of study was to characterize As contamination in the soils from Shimen realgar mine area, the largest realgar deposit in Asia.

Materials and methods

Total As concentrations, As chemical fractionation, and As potential solubility both at various land use types (smelting and processing plants (SPP), mining site (MS), and agriculture land (AL)) and soil depths (0–100 cm) were investigated. As speciation in soil was examined using X-ray absorption fine structure (XAFS) analysis, and risk assessment was also carried out to evaluate potential ecological risk of As contamination.

Results and discussion

As concentrations in the studied area were extremely high, and the total As concentration reached up to 5240.8 mg kg^?1. Moreover, total As and NaHCO₃-extractable As concentrations in all soil layers for various land use were far beyond the range of the non-contaminated soil. The potential ecological risk level of As posed higher to serious risk to the environment based on ecological risk index values. Sequential extraction confirmed that As is mostly bonded with amorphous and poorly crystalline hydrous iron and aluminum oxides (65?～?70 %), and only a small proportion (about 11 %) is partitioned in residual fraction, suggesting high risk of As mobilization. According to XAFS analysis, As was predominantly present in the form of arsenate, and arsenite was also found in the samples from SPP, MS, and AL.

Conclusions

The results indicate that the extra high concentrations of As were caused by both natural geochemical enrichment and long-lasting ore mining, smelting, and processing, and land use can greatly influence As contents in surface soil. These findings can be important for risk assessment and for the development and implementation of suitable management and remediation strategies.

     

Assessment of potentially toxic element contamination in soils from Portman Bay (SE,Spain)

Purpose

The present study deals with the geochemical fractions of Pb, Cd, Zn, Cu and As present on profiles using chemical simple extraction process. This work was conducted on Portman Bay, located in the SE Spain and strongly affected by mining activities.

Materials and methods

Four simple extractions were applied to selected samples in order to evaluate the potential mobility of metals. X-ray diffraction (XRD) was applied to the characterisation of samples and the residues remaining after each extraction, providing additional information about the sediment phases carrying the elements studied.

Results and discussion

The results obtained after the extractions suggested that the highest potentially toxic element (PTE) content was obtained in the oxidising medium. The mineralogical composition is an important factor that should be taken into account in the evaluation of PTE mobility, firstly because the mineral phases react differently in the proposed situations depending on their chemical nature, and secondly, because the presence of a particular phase depends on the degree of weathering.

Conclusions

The evaluation of PTE mobility and mineralogical composition under different environmental conditions may be very important in the execution of restoration projects which could involve dredging and mobilisation of materials.

     

Field-applying an inexpensive, 13C-depleted,labile carbon source to study in situ fate and short-term effects on soils

Background

Labile carbon (C_labile) limits soil microbial growth and is critical for soil functions like nitrogen (N) immobilization. Most experiments evaluating C_labile additions use laboratory incubations. We need to field-apply C_labile to fully understand its fate and effects on soils, especially at depth, but high cost and logistical difficulties hinder this approach.

Aims

Here, we evaluated the impact of adding an in situ pulse of an inexpensive and ¹³C-depleted source of C_labile—crude glycerol carbon (C_glyc), a by-product from biodiesel production—to agricultural soils under typical crop rotations in Iowa, USA.

Methods

We broadcast-applied C_glyc at three rates (0, 216, and 866 kg C ha⁻¹) in autumn after soybean harvest, tracked its fate, and measured its impact on soil C and N dynamics to four depths (0–5, 5–15, 15–30, and 30–45 cm). Nineteen days later, we measured C_glyc in microbial biomass carbon (MBC), salt-extractable organic C, and potentially mineralizable C pools. We paired these measurements with nitrate N (NO₃⁻–N) and potential net N mineralization to examine short-term effects on N cycling.

Results

C_glyc was found to at least 45-cm depth with the majority in MBC (18%–23% of total C_glyc added). The δ¹³C values of the other measured C pools were too variable to accurately track the C_labile fate. NO₃⁻–N was decreased by 13%–57% with the 216 and 866 kg C ha⁻¹ rates, respectively, and was strongly related to greater microbial uptake of C_glyc (i.e., immobilization via microbial biomass). Crude glycerol application had minor effects on soil pH—the greatest rate decreased pH 0.18 units compared to the control.

Conclusions

Overall, glycerol is an inexpensive and effective way to measure in situ, C_labile dynamics with soil depth—analogous to how mobile, dissolved organic C might behave in soils—and can be applied to rapidly immobilize NO₃⁻–N.     

Natural regeneration of degraded soils and site changes on abandoned agricultural terraces in Mediterranean Spain

Abandonment of degraded and marginal agricultural land is a widespread phenomenon in Spain and other Mediterranean countries. To study soil development and site dynamics, a comparative investigation of field groups representing different ages of abandonment was realized in the Meastrazgo region of the Mediterranean province of Castellón. Analysis of soil samples for organic carbon and total nitrogen content and pH showed that a sufficient regeneration of organic matter is accomplished after 20 years of fallow. Contrary to this there is no build-up of ‘available’ phosphorus after abandonment. A fixation of phosphorus in unavailable forms in the first fallow years seems evident, and there is no re-enrichment through solution or mineralization of organically bound P thereafter. The vegetation of the fallow fields develops after passing through a low-cover therophyte stage within 10–20 years to nanophanerophyte-dominated \underline matorral (shrubs), in the best case within 40–50 years to a stone oak juniper association. Under intensive cattle grazing, grasslands rich in hemicryptophytes evolved. Rates of soil erosion estimated through application of the Universal Soil Loss Equation are of medium to low intensity and range between 2·2 t ha⁻¹ year⁻¹ in the first fallow years and 0·6 t ha⁻¹ year⁻¹ after establishment of vegetation cover. Under grassland erosion is negligible unless vegetative cover is destroyed through treading. © 1998 John Wiley & Sons, Ltd.     

Anthropogenic transformation of soils in the Pokrovskoe-Streshnevo Park (Moscow) and adjacent residential areas

The diversity of soils within the specially protected natural territory of Pokrovskoe-Streshnevo in Moscow is discussed. The soils of this large park are not affected by the modern construction activities that delete the features inherited from the early stages of the anthropogenic transformation of soils in Moscow. They are characterized by the book-like type of soil memory, which makes it possible to trace several sequences of the anthropogenic soil transformation. The background natural soils-rzhavozems (Chromic Cambisols)—have been transformed into agrogenic soils (agrosols) and postagrogenic soils (postagrosols) under abandoned plowlands, into urbo-soils and urbanozems in the areas of former or modern settlements, and into techno-soils in the areas of active excavation works and engineering reclamation. The change in the character of the land use without the accumulation of osediments on the surface leads to the development of polygenetic soil horizons.     

Mobility of sulphate in experimentally acidified soils from Galicia (NW Spain)

Retention of S0₄ ^2? was investigated in Galician soils throughout an intense regime of acidification. Experiments consisted of the addition of an H2SO4 solution (pH 2.7) to columns of 6 soils of contrasting properties over 1, 2, or 5 months. Leachates were obtained continuously throughout the experiment for analysis, and analysis made of the solid fractions after 1, 2 or 5 months. The greatest capacities for retention of S0₄ ^2? were found in soil developed from serpentine and micaschist; the lowest in soils from granite, slate and sandy sediments. The surface horizons, especially those rich in organic matter, displayed low retention of 5042-. The amount of S0₄ ^2? adsorbed throughout the experiment depended on the content of crystalline forms of Fe and with the Fe and Al extracted with dithionite-citrate.The low retention of S0₄ ^2? in the organic horizons and the slightly negative relation with the organic matter suggest an inhibitory effect of the organic matter on the S0₄ ^2? retention process. Results of the study show, that under conditions of moderate acidity, SO₄ ^2? retention occurs in the form of adsorption; in strongly acidic conditions, the precipitation of aluminium-sulphate minerals may provide an additional retention mechanism.     

Glyphosate and glufosinate-based herbicides: fate in soil,transfer to,and effects on land snails

Purpose  

The aim of this work was to assess the transfer and effects of two widely used herbicides on the land snail Helix aspersa during long-term exposure under laboratory conditions.     

Response of some soils of Galicia (NW Spain) to H2SO4 acidification

This paper presents the results of an acidification experiment, consisting of seven consecutive equilibrations of repesentative soils of Galicia with a H₂SO₄ solution (pH 3). Different responses to soil acidification, such as SO₄ retention and cation release, were evaluated. In soils derived from gabbro and amphibolite, SO₄ retention and Al release were the principal acid neutralization mechanisms, whereas in soils derived from granite, schist, shale and sandstone Al release was the main process. The SO₄ retention was significantly correlated with Al and Fe extracted with dihionite-citrate-bicarbonate and crystalline Fe. The released base cations came mainly from exchange sites, though sometimes also from other sources, probably by mineral weathering. The major sources of Al in these soils were metalorganic complexes and weatherable minerals. Solutions with pHs close to 4 are in equilibrium with gibbsite, kaolinite, jurbanite and alunite; at lower pH values, with jurbanite and alunite.