50-year record and solid state speciation of mercury in natural and contaminated reservoir sediment

Contaminated fluvial sediments represent both temporary sinks for river-borne pollutants and potential sources in case of natural and/or anthropogenic resuspension. Reservoir lakes play a very important role in sediment dynamics of watersheds and may offer great opportunities to study historical records of river-borne particles and associated elements transported in the past. The fate and potential environmental impact of Hg depends on its abundance, its carrier phases and its chemical speciation. Historical Hg records and solid state Hg speciation were compared in sediments from two contrasting reservoirs of the Lot River (France) upstream and downstream from a major polymetallic pollution (e.g. Cd, Zn) source. Natural (geochemical background) and anthropogenic Hg concentrations and their relationships with predominant carrier phases were determined. The results reveal important historical Hg contamination (up to 35 mg kg⁻¹) of the downstream sediment, reflecting the historical evolution of industrial activity at the point source, i.e. former coal mining, Zn ore treatment and post-industrial remediation work. Single chemical extractions (ascorbate, H₂O₂, KOH) suggest that at both sites most (∼75%) of the Hg is bound to organic and/or reactive sulphide phases. Organo-chelated (KOH-extracted) Hg, representing an important fraction in the uncontaminated sediment, shows similar concentrations (∼0.02 mg kg⁻¹) at both sites and may be mainly attributed to natural inputs and/or processes. Although, total Hg concentrations in recent surface sediments at both sites are still very different, similar mono-methylmercury concentrations (up to 4 μg kg⁻¹) and vertical distributions were observed, suggesting comparable methylation-demethylation processes. High mono-methylmercury concentrations (4–15 μg kg⁻¹) in 10–40 a-old, sulphide-rich, contaminated sediment suggest long-term persistence of mono-methylmercury. Beyond historical records of total concentrations, the studied reservoir sediments provided new insights in solid state speciation and carrier phases of natural and anthropogenic Hg. In case of sediment resuspension, the major part of the Hg historically stored in the Lot River sediments will be accessible to biogeochemical recycling in the downstream fluvial-estuarine environment.     

Irrigation produces elevated arsenic in the underlying groundwater of a semi-arid basin in Southwestern Idaho

The shallow aquifer beneath the Western Snake River Plain (Idaho, USA) exhibits widespread elevated arsenic concentrations (up to 120 μg L⁻¹). While semi-arid, crop irrigation has increased annual recharge to the aquifer from approximately 1 cm prior to a current rate of >50 cm year⁻¹. The highest aqueous arsenic concentrations are found in proximity to the water table (all values >50 μg L⁻¹ within 50 m) and concentrations decline with depth. Despite strong vertical redox stratification within the aquifer, spatial distribution of aqueous species indicates that redox processes are not primary drivers of arsenic mobilization. Arsenic release and transport occur under oxidizing conditions; groundwater wells containing dissolved arsenic at >50 μg L⁻¹ exhibit elevated concentrations of O₂ (average 4 mg L⁻¹) and NO₃ (average 8 mg L⁻¹) and low concentrations of dissolved Fe (<20 μg L⁻¹). Sequential extractions and spectroscopic analysis of surficial soils and sediments indicate solid phase arsenic is primarily arsenate and is present at elevated concentrations (4–45 mg kg⁻¹, average: 17 mg kg⁻¹) relative to global sedimentary abundances. The highest concentrations of easily mobilized arsenic (up to 7 mg kg⁻¹) are associated with surficial soils and sediments visibly stained with iron oxides. Batch leaching experiments on these materials using irrigation waters produce pore water arsenic concentrations approximating those observed in the shallow aquifer (up to 152 μg L⁻¹). While As:Cl aqueous phase relationships suggest minor evaporative enrichment, this appears to be a relic of the pre-irrigation environment. Collectively, these data indicate that infiltrating irrigation waters leach arsenic from surficial sediments to the underlying aquifer.     

The universal ratio of boron to chlorinity for the North Pacific and North Atlantic oceans

We report seawater boron concentration (mg kg⁻¹) and chlorinity (‰) values measured in seawater samples (n = 139) collected at various depths in the North Pacific and North Atlantic oceans and the East/Japan Sea (located in the western temperate North Pacific). Our results indicate that variations in seawater boron concentration are strongly coupled to variations in chlorinity (and salinity), yielding a mean boron to chlorinity ratio of 0.2414 ± 0.0009 mg kg⁻¹ ‰⁻¹ (boron to salinity ratio = 0.1336 ± 0.0005 mg kg⁻¹ ‰⁻¹). This ratio was surprisingly universal throughout the water column in the three marine basins and across widely different ocean surface regimes, but differs from the generally accepted ratio of 0.232 ± 0.005 mg kg⁻¹ ‰⁻¹ determined by Uppström (1974), which was based on only 20 measurements at four sites in the tropical Pacific Ocean. In converting total alkalinity to carbonate alkalinity (and vice versa) for thermodynamic calculations, the difference between these two ratios leads to a difference of 5 μmol kg⁻¹ in estimates for ocean surface waters, where the contribution of borate to total alkalinity is typically greatest. We suggest the use of the new boron to chlorinity ratio for predicting seawater boron concentrations using chlorinity (or salinity) data.     

Rhizosphere and flooding regime as key factors for the mobilisation of arsenic and potentially harmful metals in basic,mining-polluted salt marsh soils

The occurrence of mining areas in the vicinities of salt marshes may affect their ecological functions and facilitate the transfer of pollutants into the food chain. The mobilisation of metals in salt marsh soils is controlled by abiotic (pH, redox potential) and biotic (influence of rhizosphere) factors. The effect of the rhizosphere of two plant species (Sarcocornia fruticosa and Phragmites australis) and different flooding regimes on potentially harmful metals and As mobilisation from salt marsh soil polluted by mining activities were investigated (total concentrations: 536 mg kg⁻¹ As, 37 mg kg⁻¹ Cd, 6746 mg kg⁻¹ Pb, 15,320 mg kg⁻¹ Zn). The results show that the changes in redox conditions (from 300 mV to −100 mV) and pH after flooding and rewetting periods may mobilise the contaminant elements into soil solution (e.g., 100 μg L⁻¹ Cd, 30 μg L⁻¹ Pb, 7 mg L⁻¹ Zn), where they are available for plants or may be leached from the soil. Drying periods generated peaks of concentrations in the soil solution (up to 120 μg L⁻¹ Cd and 50 μg L⁻¹ Pb). The risk assessment of As and metal-polluted salt marshes should take into account flood dynamics in order to prevent metal(loid) mobilisation.     

Environmental geochemistry of an active Hg mine in Xunyang,Shaanxi Province,China

The Xunyang Hg mine (XMM) situated in Shaanxi Province is an active Hg mine in China. Gaseous elemental Hg (GEM) concentrations in ambient air were determined to evaluate its distribution pattern as a consequence of the active mining and retorting in the region. Total Hg (HgT) and methylmercury (MeHg) concentrations in riparian soil, sediment and rice grain samples (polished) as well as Hg speciation in surface water samples were measured to show local dispersion of Hg contamination. As expected, elevated concentrations of GEM were found, ranging from 7.4 to 410 ng m⁻³. High concentrations of HgT and MeHg were also obtained in riparian soils, ranged from 5.4 to 120 mg kg⁻¹ and 1.2 to 11 μg kg⁻¹, respectively. Concentrations of HgT and MeHg in sediment samples varied widely from 0.048 to 1600 mg kg⁻¹ and 1.0 to 39 μg kg⁻¹, respectively. Surface water samples showed elevated HgT concentrations, ranging from 6.2 to 23,500 ng L⁻¹, but low MeHg concentrations, ranging from 0.022 to 3.7 ng L⁻¹. Rice samples exhibited high concentrations of 50–200 μg kg⁻¹ in HgT and of 8.2–80 μg kg⁻¹ in MeHg. The spatial distribution patterns of Hg speciation in the local environmental compartments suggest that the XMM is the source of Hg contaminations in the study area.     

Arsenic contamination in agricultural soils surrounding mining sites in relation to geology and mineralization types

A national-scale survey of the environment in and around mines was conducted to evaluate the status of total As contamination in agricultural soils surrounding numerous abandoned metal mines in Korea. This survey aimed to compare As concentrations in soils in relation to geology and mineralization types of mines. A total of 16,386 surface soil (0–15 cm in depth) samples were taken from agricultural lands near 343 abandoned mines (within 2 km of each mine). These samples were decomposed by aqua regia and analyzed for As by AAS with a hydride-generation (HG) device. To compare As levels in soils meaningfully with geology and mineralization types, three sub-classification criteria were adapted: (1) five mineralization types, (2) four valuable ore mineral types, and (3) four parent rock types. The average concentration of As in all the soils was 11.6 mg kg⁻¹ with a range of 0.01–4230 mg kg⁻¹. Based on the mineralization types, average As concentrations (mg kg⁻¹) in the soils decreased in the order of pegmatite (18.2) > hydrothermal replacement (14.5) > sedimentary deposits (12.4) > hydrothermal vein (10.7) > skarn (4.08). In terms of the valuable ore mineral types, the concentrations decreased in the order of Sn, W, Mo, Fe and Mn mines > Au, Ag, and base metal mines > Au and Ag mines ≈ base metal mines. For parent rock types, soils from metamorphic rocks and heterogeneous rocks exhibited enhanced As levels related to both igneous and sedimentary rocks. Therefore, it can be concluded that soils from highly altered rocks subject to metamorphic and igneous activities contained relatively high concentrations of As in the surface environment.     

Particulate-associated potentially harmful elements in urban road dusts in Xi’an,China

Sixty five urban road dust samples were collected from different land use areas of ∼240 km² in Xi’an, China. The concentrations of Ag, As, Cr, Cu, Hg, Pb, Sb and Zn were determined to investigate potentially harmful element (PHE) contamination, distribution and possible sources. In addition, the concentrations in different size fractions were measured to assess their potential impact on human health. The highest concentrations were found in the fraction with particle diameters between 80 μm and 101 μm, the finest particles (<63 μm) were not the most important carriers for Ag, As, Cd, Cr, Cu, Hg, Pb and Zn. The percentages of these elements in particles with diameters less than 63 μm (PM₆₃) and less than 101 μm (PM₁₀₁) were in the range of 7–15%, and 30–55%, respectively. Three main factors influencing element distributions have been identified: (a) industrial activities; (b) prior agricultural land use; and (c) other activities commonly found in urban areas, such as traffic, coal combustion, waste dumping, and building construction/renovation. The highest concentrations were found in industrial areas for As (20 mg kg⁻¹), Cr (853 mg kg⁻¹), Cu (1071 mg kg⁻¹), Pb (3060 mg kg⁻¹) and Zn (2112 mg kg⁻¹), and in previous agricultural areas for Ag and Hg, indicating significant contributions from industrial activities and prior agricultural activities.     

Methane microseepage from different sectors of the Yakela condensed gas field in Tarim Basin,Xinjiang, China

Methane microseepage is the result of natural gas migration from subsurface hydrocarbon accumulations to the Earth’s surface, and it is quite common in commercial petroleum fields. While the role of microseepage as a pathfinder in petroleum exploration has been known for about 80 a, its significance as an atmospheric CH₄ source has only recently been studied, and flux data are currently available only in the USA and Europe. With the aim of increasing the global data-set and better understanding flux magnitudes and variabilities, microseepage is now being extensively studied in China. A static flux chamber method was recently applied to study microseepage emissions into the atmosphere in four different sectors of the Yakela condensed gas field in Tarim Basin, Xinjiang, China, and specifically in: (a) a faulted sector, across the Luntai fault systems; (b) an oil–water interface sector, at the northern margin of the field; (c) an oil–gas interface sector, in the middle of the field; (d) an external area, outside the northern gas field boundaries. The results show that positive CH₄ fluxes are pervasive in all sectors and therefore, only part of the CH₄ migrating from the deep oil–gas reservoirs is consumed in the soil by methanotrophic oxidation. The intensity of gas seepage seems to be controlled by subsurface geologic settings and lateral variabilities of natural gas pressure in the condensed gas field. The highest CH₄ fluxes, up to ∼14 mg m⁻² d⁻¹ (mean of 7.55 mg m⁻² d⁻¹) with higher spatial variability (standard deviation, σ: 2.58 mg m⁻² d⁻¹), occur in the Luntai fault sector. Merhane flux was lower in the oil–water area (mean of 0.53 mg m⁻² d⁻¹) and the external area (mean of 1.55 mg m⁻² d⁻¹), and at the intermediate level in the gas–oil sector (mean of 2.89 mg m⁻² d⁻¹). These values are consistent with microseepage data reported for petroleum basins in the USA and Europe. The build-up of methane concentration in the flux chambers is always coupled with an enrichment of ¹³C, from δ¹³C₁ of −46‰ to −42.5‰ (VPDB), which demonstrates that seeping methane is thermogenic, as that occurring in the deep Yakela reservoir. Daily variations of microseepage are very low, with minima in the afternoon, corresponding to higher soil temperature (and higher methanotrophic consumption), and maxima in the early morning (when soil temperatures are lowest). A preliminary and rough estimate of the total amount of CH₄ exhaled from the Yakela field is in the order of 10² tonnes a⁻¹.     

Mobility of metals in nickel mine spoil materials

An understanding of the biogeochemical behaviour of metals in mine spoil materials is a prerequisite to rehabilitate Ni mining sites. The objective of this study was to characterize the fate of metals in different Ni ore spoil materials as influenced by hydrological conditions and fertilisation practices. In tropical ultramafic complexes, the different stages of lateritic weathering lead to two types of ores, and therefore, to two spoil types. They are mainly either a clay-rich saprolite, so-called “garnierite”, enriched in phyllosilicates, or a limonitic material, enriched in Fe oxides. Lysimeter columns were designed to monitor leaching waters through both spoil materials. The garnieritic spoil released higher concentrations of Mg (mean = 2.25 mg L⁻¹), Ni (0.39 mg L⁻¹) and Cr (1.19 mg L⁻¹) than the limonitic spoil (Mg = 0.5 mg L⁻¹; Ni = 0.03 mg L⁻¹ and Cr = 0.25 mg L⁻¹). Chromium was mainly in an anionic form in leaching solutions. As exchangeable pools of Cr(VI) in limonite (980 mg kg⁻¹ of KH₂PO₄-extractable Cr) are considerable its release in water may still occur in the case of a pH increase. In mixed spoil, metal concentrations were almost as low as in the limonitic one. The effect of mineral-N fertilisation was a strong release of cations (Ni, Mg) into the leachate. Phosphate amendment did not affect the soil solution composition under experimental conditions.     

Mercury contamination due to zinc smelting and chlor-alkali production in NE China

Zinc smelting and chlor-alkali production are major sources of Hg contamination to the environment, potentially leading to serious impacts on the health of the local population. Huludao, NE China has been heavily contaminated by Hg due to long-term Zn smelting and chlor-alkali production. The aim of this work was to determine Hg accumulation in the aquatic and terrestrial environment, as well as in the human population of Huludao. The investigation included: (a) Hg accumulation in sediments, Spirogyra algae, crucian carp and shrimp, (b) Hg distribution in soil, vegetables and corn, and (c) assessment of potential health effects of Hg exposure associated with total Hg (T-Hg) concentrations in human hair. Measured T-Hg concentrations in sediments of Wuli River ranged from 0.15 to 15.4 mg kg⁻¹, with the maximum Hg concentration in sediment exceeding the background levels in Liaoning Province by 438 times. The maximum T-Hg levels in Spirogyra, crucian carp and shrimp were 13.6, 0.36, and 0.44 mg kg⁻¹, respectively. Total-Hg concentrations in hair of the human population varied from 0.05 to 3.25 mg kg⁻¹ (average 0.43 mg kg⁻¹). However, the frequency of paraesthesia to most inhabitants in Huludao was estimated to be lower than 5%, with only one person rated at 50%. The results indicated minimal adverse health effects of Hg exposure to the inhabitants of Huludao, despite the serious Hg contamination of the environment.     

Alteration of As-bearing phases in a small watershed located on a high grade arsenic-geochemical anomaly (French Massif Central)

At a watershed scale, sediments and soil weathering exerts a control on solid and dissolved transport of trace elements in surface waters and it can be considered as a source of pollution. The studied subwatershed (1.5 km²) was located on an As-geochemical anomaly. The studied soil profile showed a significant decrease of As content from 1500 mg kg⁻¹ in the 135–165 cm deepest soil layer to 385 mg kg⁻¹ in the upper 0–5 cm soil layer. Directly in the stream, suspended matter and the <63 μm fraction of bed sediments had As concentrations greater than 400 mg kg⁻¹. In all these solid fractions, the main representative As-bearing phases were determined at two different observation scales: bulk analyses using X-ray absorption structure spectroscopy (XAS) and microanalyses using scanning electron microscope (SEM) and associated electron probe microanalyses (EPMA), as well as micro-Raman spectroscopy and synchrotron-based micro-scanning X-ray diffraction (μSXRD) characterization. Three main As-bearing phases were identified: (i) arsenates (mostly pharmacosiderite), the most concentrated phases As in both the coherent weathered bedrock and the 135–165 cm soil layer but not observed in the river solid fraction, (ii) Fe-oxyhydroxides with in situ As content up to 15.4 wt.% in the deepest soil layer, and (iii) aluminosilicates, the least concentrated As carriers. The mineralogical evolution of As-bearing phases in the soil profile, coupled with the decrease of bulk As content, may be related to pedogenesis processes, suggesting an evolution of arsenates into As-rich Fe-oxyhydroxides. Therefore, weathering and mineralogical evolution of these As-rich phases may release As to surface waters.     

Dissolved metals and associated constituents in abandoned coal-mine discharges,Pennsylvania, USA. Part 1: Constituent quantities and correlations

Complete hydrochemical data are rarely reported for coal-mine discharges (CMD). This report summarizes major and trace-element concentrations and loadings for CMD at 140 abandoned mines in the Anthracite and Bituminous Coalfields of Pennsylvania. Clean-sampling and low-level analytical methods were used in 1999 to collect data that could be useful to determine potential environmental effects, remediation strategies, and quantities of valuable constituents. A subset of 10 sites was resampled in 2003 to analyze both the CMD and associated ochreous precipitates; the hydrochemical data were similar in 2003 and 1999. In 1999, the flow at the 140 CMD sites ranged from 0.028 to 2210 L s⁻¹, with a median of 18.4 L s⁻¹. The pH ranged from 2.7 to 7.3; concentrations (range in mg/L) of dissolved (0.45-μm pore-size filter) SO₄ (34–2000), Fe (0.046–512), Mn (0.019–74), and Al (0.007–108) varied widely. Predominant metalloid elements were Si (2.7–31.3 mg L⁻¹), B (<1–260 μg L⁻¹), Ge (<0.01–0.57 μg L⁻¹), and As (<0.03–64 μg L⁻¹). The most abundant trace metals, in order of median concentrations (range in μg/L), were Zn (0.6–10,000), Ni (2.6–3200), Co (0.27–3100), Ti (0.65–28), Cu (0.4–190), Cr (<0.5–72), Pb (<0.05–11) and Cd (<0.01–16). Gold was detected at concentrations greater than 0.0005 μg L⁻¹ in 97% of the samples, with a maximum of 0.0175 μg L⁻¹. No samples had detectable concentrations of Hg, Os or Pt, and less than half of the samples had detectable Pd, Ag, Ru, Ta, Nb, Re or Sn. Predominant rare-earth elements, in order of median concentrations (range in μg/L), were Y (0.11–530), Ce (0.01–370), Sc (1.0–36), Nd (0.006–260), La (0.005–140), Gd (0.005–110), Dy (0.002–99) and Sm (<0.005–79). Although dissolved Fe was not correlated with pH, concentrations of Al, Mn, most trace metals, and rare earths were negatively correlated with pH, consistent with solubility or sorption controls. In contrast, As was positively correlated with pH.     

Background concentrations of elements in surface soils and their changes as affected by agriculture use in the desert-oasis ecotone in the middle of Heihe River Basin,North-west China

The concentrations of twenty four chemical elements in the surface layer of natural desert soils and the cultivated farmland soils were measured at a desert-oasis ecotone in the middle of Heihe river basin, north-west China. Background values were estimated for (a) major elements (Si 335.3 g kg^− 1, Al 49.4 g kg^− 1, Fe 19.1 g kg^− 1, Ca 29.4 g kg^− 1, Mg 8.9 g kg^− 1, K 20.1 g kg^− 1, Na 17.5 g kg^− 1 and P 0.338 g kg^− 1), (b) heavy metals and non-metals (Cr 55.8 mg kg^− 1, Mn 404.8 mg kg^− 1, Ni 17.7 mg kg^− 1, Cu 5.1 mg kg^− 1, Zn 33.7 mg kg^− 1, Pb 15.5 mg kg^− 1 and As 5.2 mg kg^− 1) and (c) other trace elements (Ti 2.0 mg kg^− 1, V 55.3 mg kg^− 1, Co 5.7 mg kg^− 1, Rb 82.4 mg kg^− 1, Sr 232.9 mg kg^− 1, Y 14.7 mg kg^− 1, Zr 194.9 mg kg^− 1, Nb 7.8 mg kg^− 1 and Ba 720.6 mg kg^− 1). After natural desert soil was cultivated for agricultural use, significant changes in element concentrations occurred under tillage, irrigation and fertilisation management. Compared to natural soil, the for the levels of Si, K, Na, Sr, Zr and Ba decreased, and no changes were observed for Rb, while the values of the other 17 elements increase in agricultural soil from 1.2 to 3.5 times. However, their absolute concentrations are still low, suggesting that the arable soil in this region remains comparatively a clean soil. The increased silt, clay and organic carbon content, under long-term irrigation, enriched the fine-grained materials, and application of fertilisers and manure contributed to the accumulation of most elements in arable soil. The accumulation of elements in agricultural soil increased with increasing cultivation years and extent of soil development.     

Estimating specific surface area of fine stream bed sediments from geochemistry

Specific surface area (SSA) of headwater stream bed sediments is a fundamental property which determines the nature of sediment surface reactions and influences ecosystem-level, biological processes. Measurements of SSA – commonly undertaken by BET nitrogen adsorption – are relatively costly in terms of instrumentation and operator time. A novel approach is presented for estimating fine (<150 μm) stream bed sediment SSA from their geochemistry – after removal of organic matter – for agricultural headwater catchments across 15,400 km² of central England, UK. From a regional set of 1972 stream bed sediment sites with common characteristics for which geochemical data were available, 60 samples were selected – based on maximising their variation in Al concentrations – and their BET SSA measured by N₂ adsorption. After careful selection of potential regression predictors following a principal component analysis and removal of a subset of samples with the largest Mo concentrations (>2.5 mg kg⁻¹), four elements were identified as significant predictors of SSA (ordered by decreasing predictive power): V > Ca > Al > Rb. The optimum model from these four elements accounted for 73% of the variation in bed sediment SSA (range 6–46 m² g⁻¹) with a root mean squared error of prediction – based on leave-one-out cross-validation – of 6.3 m² g⁻¹. It is believed that V is the most significant predictor because its concentration is strongly correlated both with the quantity of Fe-oxides and clay minerals in the stream bed sediments, which dominate sediment SSA. Sample heterogeneity in SSA – based on triplicate measurements of sub-samples – was a substantial source of variation (standard error = 2.2 m² g⁻¹) which cannot be accounted for in the regression model.     

Enrichment of metals in soils subjected to different land uses in a typical Mediterranean environment (Murcia City, southeast Spain)

Industrialization, urbanization, and agricultural practices are 3 of the most important sources of metal accumulations in soils. Concentrations of Cr, Mn, Ni, Cu, Pb, Zn and Cd were determined in surface soils collected under different land uses, including urban (UR), industrial (IN-1 and IN-2), agricultural (AG), abandoned unused (AB), and natural (NA) sites to examine the influence of anthropogenic activities on metals in soils formed in a typical Mediterranean environment. The highest concentrations of Cr, Cd, and Pb observed in the NW industrial area (IN-2) were 63.7, 3.34 and 2330 mg metal kg⁻¹ soil, for each metal, respectively. The SW industrial area (IN-1) contained the highest Zn content at 135 mg kg⁻¹. However, soils with the highest concentrations of Ni and Cu were located in AG sites at 30.9 and 64.9 mg kg⁻¹ soil, respectively. Sampling locations with the highest concentrations of Mn were identified in AB sites. Using the concentrations of metals at the NA sites as the baseline levels, soils collected from all other land uses in the study area exhibited significantly higher total contents of Zn, Mn, Cr and Ni. Metal enrichment was attributed to fertilizer and pesticide applications, industrial activities, and metal deposition from a high volume of vehicular traffic (for Pb and Cd). High concentrations of Mn in some samples were attributed to parent materials. The study demonstrated that anthropogenic activities associated with various land uses contribute to metal accumulation in soils and indicated a need to closely monitor land management practices to reduce human and ecological risks from environmental pollution.     

Sorption of lead by phlogopite-rich mine tailings

The Pb sorption capacity of apatite ore mine tailings and its potential to act as a remediation agent in a Pb polluted areas were investigated. The tailings, originating from the Siilinjärvi carbonatite complex in Finland, consist mainly of phlogopite and calcite accompanied by apatite residues. The ability of the tailings to retain Pb from an aqueous solution was investigated using an isotherm technique. Furthermore, in a 3-month incubation experiment, uncontaminated mineral soil was amended with untreated tailings and with tailings artificially weathered with acid to increase the quantity of Al and Fe (hydr)oxides. Tailings of two particle-sizes (∅ > 0.2 mm and ∅ < 0.2 mm) somewhat differing in their mineralogical composition were investigated as separate amendments. All tailings materials were added to the soil in two dosages (5 g and 10 g of tailings per 125 g of soil). Following incubation, tailings-induced changes in the Pb sorption capacity of the soil were investigated with the isotherm technique. Finally, to investigate the distribution of sorbed Pb among various chemical pools, the soil samples amended with tailings were contaminated with Pb and then subjected to sequential fractionation analysis. The results revealed efficient removal of Pb from an aqueous solution by the tailings, presumably through precipitation and surface complexation mechanisms. Amending the soil with the tailings increased the mass-based maximum Pb sorption capacity from 10.8 mg kg⁻¹ of the control soil to 14–20.5 mg kg⁻¹ for the untreated tailings and to 32.1–72.1 mg kg⁻¹ for the acid-treated material. The tailings transferred Pb from the exchangeable pool to the non-extracted one and thereby substantially decreased its bioavailability. The material with a particle diameter of less than 0.2 mm had a higher mass-based Pb sorption capacity than the large-sized material. The results suggest that the tailings may potentially serve as an immobilizing agent in polluted areas.     

Mercury contamination and its potential health effects in a lead-zinc mining area in the karst region of Guangxi, China

Mercury contamination of the environment is of worldwide concern because of its global presence and its potent neurotoxicity. Mining, smelting and the electronics industry are the main sources of Hg pollution. However, few studies have been performed to investigate systemic Hg contamination in metal mining regions. In this study, concentrations of Hg in air, farmland soil, and crops were measured in a Pb-Zn mining area in the karst region of Guangxi, China. Key factors that could affect Hg distribution, such as the fate of waste ore and waste residue, were analyzed. Geo-statistical methods were adopted to analyze the characteristics of spatial structure and distribution of Hg. The results show that Hg contamination in this region is serious. The total mercury (T-Hg) content is far higher than the Level II Limit Value of Chinese Soil Standards of 0.30 mg kg⁻¹, showing obvious directional characteristics from WNW to ESE. Highest Hg concentrations were found in the WNW portion of the study area. The contamination of paddy soil is higher than that in dry farmland soil. The vertical distribution of T-Hg and its decrease with depth suggest that the important sources are waste water irrigation and the improper disposal of the waste ore and waste rock. The T-Hg concentrations in the agricultural products examined exceed the Chinese tolerance value (0.02 mg kg⁻¹ for rice and 0.01 mg kg⁻¹ for vegetables), indicating the seriousness of the problem. The ecological environment and the safety of food grown in this mining area are being affected, with the result that human health is possibly being affected.     

Streamwater chemistry in three contrasting monolithologic Czech catchments

Hydrochemical patterns resulting from differing bedrock geochemistry were ascertained by concurrent streamwater sampling in three small catchments, each underlain by geochemically contrasting silicate rock types in the western Czech Republic, Central Europe in 2001–2010. The catchments are situated 5–7 km apart in the Slavkov Forest and are occupied by Norway spruce (Picea abies) plantations. They have similar altitude, area, topography, mean annual air temperature, and atmospheric deposition fluxes. The amount of base cations oxides (Ca + Mg + Na + K) is markedly different among the three studied rocks (leucogranite 8%, amphibolite 22%, serpentinite 36%). The leucogranite contains a very small amount of MgO, while the serpentinite contains extremely large amounts of MgO. The amphibolite contains an intermediate amount of MgO and elevated CaO. The Lysina, on leucogranite, exhibited very small concentrations of Mg (median 0.4 mg L⁻¹) in streamwater; Pluh?v Bor, on serpentinite, contained extremely high concentrations of streamwater Mg (18 mg L⁻¹). Streamwater in the Na Zeleném catchment, on amphibolite, contained an intermediate amount of Mg and an elevated Ca. Very low pH (4.2), negative alkalinity (−60 μeq L⁻¹) and high inorganic monomeric Al concentrations (0.3 mg L⁻¹) were found in the stream draining leucogranite. Serpentinite streamwater exhibited the highest pH (7.6), alkalinity (+940 μeq L⁻¹) and Ni concentrations (100 μg L⁻¹). Aquatic chemistry reflected the composition of the underlying rocks within the studied catchments. Contrasting streamwater compositions of the studied catchments were generated according to the MAGIC model simulations mainly by differences in chemical weathering rates of base cations (65 meq m⁻² a⁻¹ at Lysina, 198 meq m⁻² a⁻¹ at Na Zeleném, and 241 meq m⁻² a⁻¹ at Pluh?v Bor).     

Incorporation of lead into calcium carbonate granules secreted by earthworms living in lead contaminated soils

The influence of soil organisms on metal mobility and bioavailability in soils is not currently fully understood. We conducted experiments to determine whether calcium carbonate granules secreted by the earthworm Lumbricus terrestris could incorporate and immobilise lead in lead- and calcium-amended artificial soils. Soil lead concentrations were up to 2000 mg kg⁻¹ and lead:calcium ratios by mass were 0.5-8. Average granule production rates of 0.39 ± 0.04 mg_calcite earthworm⁻¹ day⁻¹ did not vary with soil lead concentration. The lead:calcium ratio in granules increased significantly with that of the soil (r² = 0.81, p = 0.015) with lead concentrations in granules reaching 1577 mg kg⁻¹. X-ray diffraction detected calcite and aragonite in the granules with indications that lead was incorporated into the calcite at the surface of the granules. In addition to the presence of calcite and aragonite X-ray absorption spectroscopy indicated that lead was present in the granules mainly as complexes sorbed to the surface but with traces of lead-bearing calcite and cerussite. The impact that lead-incorporation into earthworm calcite granules has on lead mobility at lead-contaminated sites will depend on the fraction of total soil lead that would be otherwise mobile.     

Effects of anthropopressure and soil properties on the accumulation of polycyclic aromatic hydrocarbons in the upper layer of soils in selected regions of Poland

Fifty soil samples collected from agricultural land in four regions of Poland with different anthropopressure were analysed for their content of 16PAHs by GC/MS. The regions correspond to Polish administrative units (voievodeships): Podlaskie and Lubelskie are situated in the rural East part of the country and more industrialised Slaskie and Dolnoslaskie voievodeships – in the South-West part. Basic physicochemical properties as well as the content of selected potentially harmful metals (Pb and Zn) were included in the soil analysis. Overall accumulation of Σ16PAHs in the upper soil layer was within the range 73–1800 μg kg⁻¹ with a geometric mean (GM) of 252 μg kg⁻¹, while the mean benzo(a)pyrene (BaP) load was 20 μg kg⁻¹. This corresponds with data for other European countries. Carcinogenic compounds contributed nearly in 50% to the total PAHs loads. In uncontaminated rural regions the mean Σ16PAHs and BaP contents were 113–159 μg kg⁻¹ and 11–13 μg kg⁻¹, respectively. Regional conditions strongly influenced the accumulation of PAHs ?4-rings, which were highly dependent (over 95%) on local anthropopressure expressed as dust and 4PAHs emission indexes. Soil acidity was the main soil parameter related to the accumulation of higher molecular weight PAHs in soils. In more contaminated regions a significant link between soil OM and PAH loads was noted. The same regions were characterised by associations between PAHs and potentially harmful metals implying common sources of pollution. Those relationships were not observed in the uncontaminated part of the country. The lower molecular weight PAHs contributed to a smaller extent (about 20%) to the total PAHs content in soils, and were less affected by anthropogenic factors.