Arsenic in the water–soil–plant system and the potential health risks in the coastal part of Chianan Plain,Southwestern Taiwan

The present study investigates the bioavailability, soil to plant transfer and health risks of arsenic (As) in the coastal part of Chianan Plain in southwestern Taiwan. Groundwater used for irrigation, surface soils from agricultural lands and locally grown foodstuffs were collected from eight locations and analyzed for As to assess the risks associated with consuming these items. The concentration of As in groundwater ranged from 13.8 to 881 μg/L, whereas surface soil showed total As content in the range of 7.92–12.7 mg/kg. The available As content in surface soil accounted for 0.06–6.71% of the total As content, and was significantly correlated with it (R² = 0.65, p < 0.05). Among the leachable fraction, the organic matter (3.23–54.8%) and exchangeable portions of oxides (6.03–38.4%) appear to be the major binding phases of As. The average As content in fourteen studied crops and vegetables varied from 10.3 to 151 μg/kg with maximum in mustard and minimum in radish. All the plants showed considerably higher As content (21.5 ± 3.64–262 ± 36.2 μg/kg) in their roots compared to the edible parts (9.15 ± 1.44–75.8 ± 22.9 μg/kg). The bioaccumulation factor (BAF) based on total As (ranging from 0.0009 to 0.144) and available As in soil (ranging from 0.039 to 0.571) indicate that mustard, rice, amaranth and spinach are the highest accumulators of As. Although the health risk index (HRI) of the studied crops and vegetables ranged from only 0.0068–0.454, with the maximum in rice, the combined HRI indicates an alarming value of 0.88. Therefore, the possible health risks due to long-term consumption of rice and other As-rich foodstuffs could be overcome by controlling the contamination pathways in the water–soil–plant system.     

Is silt the most influential soil grain size fraction?

The contribution of individual grain size fractions (2000–500, 500–250, 250–63, 63–2 and < 2 μm) to bulk soil surface area and reactivity is discussed with reference to mineralogical and oxalate and dithionite extractions data. The 63–2 μm fraction contributed up to 56% and 67% of bulk soil volume and BET surface area, respectively. Consideration of these observations and the mineralogy of this fraction suggest that the 63–2 μm fraction may be the most influential for the release of elements via mineral dissolution in the bulk soil.     

The nature and distribution of Cu,Zn, Hg,and Pb in urban soils of a regional city: Lithgow,Australia

This study investigates the concentration and spatial distribution of Cu, Zn, Hg and Pb in the surface (0–2 cm) soils of a regional city in Australia. Surface soils were collected from road sides and analysed for their total Cu, Zn, Hg and Pb concentrations in the <180 μm and <2 mm grain size fractions. The average metal concentration of surface soils, relative to local background soils at 40–50 cm depth, are twice as enriched in Hg, more than three times enriched in Cu and Zn, and nearly six times as enriched in Pb. Median surface soil metal concentration values were Cu – 39 mg/kg (682 mg/kg max), Zn – 120 mg/kg (4950 mg/kg max), Hg – 44 μg/kg (14,900 μg/kg max) and Pb – 46 mg/kg (3490 mg/kg max). Five sites exceeded the Australian NEPC (1999) 300 mg/kg guideline for Pb in residential soils. Strong positive correlations between Cu, Zn and Pb, coupled with the spatial distribution of elevated soil concentrations towards the city centre and main roads suggest traffic and older housing as major sources of contamination. No spatial relationships were identified between elevated metal loadings and locations of past or present industries.     

Impact of former mining activities on the uranium distribution in the River Saale (Germany)

In the lower part of the River Saale, Germany, U shows concentrations of up to 4 μg/L. Former mining activities and their still existing dewatering systems in the drainage basin of the River Saale are responsible for the high salt and trace metal concentrations in the water of some tributaries. An old adit from the Mansfeld mining district flowing into the Schlenze Stream with mean U concentrations of about 60 μg/L increases the U concentration of the River Saale by 0.5 μg/L. The U concentrations in the running waters of the study area can be explained by mixing processes. Uranium from the adit and the Schlenze is mainly transported in the <0.45 μm fraction as a carbonate complex.     

Biogeochemical indicators of buried mineralization under cover,Talbot VMS Cu–Zn prospect,Manitoba

Results are presented of a surficial geomicrobiological investigation of glacial cover overlying buried mineralization at the Talbot prospect, Manitoba, Canada, where previous surficial geochemistry surveys indicated anomalous concentrations of elements above the buried mineralization. The Cu–Zn volcanogenic massive sulfide (VMS) occurrence is overlain by 100 m of Paleozoic dolomites and Quaternary glacial cover. The geomicrobiological investigation demonstrates that there is a distinct microbial ecology at the anomalous sampling locations, especially directly overlying buried mineralization. The combined geochemical and geomicrobiological analyses reveal the presence of an anomaly directly over mineralization due to oxidation of the buried ore. Specifically, geomicrobiological analyses yield an inverse correlation between Zn in the clay-size (<2 μm) fraction and total microbial biomass and a direct correlation between Cu in the clay-size (<2 μm) fraction and abundance of methanotrophic bacteria. These results demonstrate that microbiological analyses can be a useful addition to geochemical exploration by revealing metal transport and sequestration processes and enhancing surficial anomalies.     

High cadmium concentration in soil in the Three Gorges region: Geogenic source and potential bioavailability

This study investigated the distribution and sources of Cd in soils from a Cd-rich area in the Three Gorges region, China. The results showed that in the study area arable soils contain 0.42–42 mg kg⁻¹ Cd with 0.12–8.5 mg kg⁻¹ in the natural soils, corresponding to high amounts of Cd (0.22–42 mg kg⁻¹) in outcropping sedimentary rocks in the area. Both lognormal distribution and enrichment factor (EF) plots were applied in an attempt to distinguish between geogenic and anthropogenic origins of Cd in the local soils. The lognormal distribution plots illustrated that geogenic sources dominated in soils with low and moderate Cd concentrations (<8.5 mg kg⁻¹), whereas anthropogenic sources (agricultural activities, coal mining) significantly elevated Cd contents in some arable soils (>8.5 mg kg⁻¹). The enrichment factor plots illustrated that the majority of the soil samples had EF values of <5, pointing to a geogenic origin of Cd in the soils, whereas some arable soils had EF values >5, pointing to an additional anthropogenic input of Cd to the soils. Sequential extraction results showed that Cd soluble in water and weak acid (water-soluble, exchangeable and carbonate fraction of the soil) accounts for an average of 31% of the total soil Cd, which indicates high potential for Cd mobility and bioavailability. The findings point to a potential health risk from Cd in areas with high geogenic background concentrations of this metal.     

Direct characterization of airborne particles associated with arsenic-rich mine tailings: Particle size,mineralogy and texture

Windblown and vehicle-raised dust from unvegetated mine tailings can be a human health risk. Airborne particles from As-rich abandoned Au mine tailings from Nova Scotia, Canada have been characterized in terms of particle size, As concentration, As oxidation state, mineral species and texture. Samples were collected in seven aerodynamically fractionated size ranges (0.5–16 μm) using a cascade impactor deployed at three tailings fields. All three sites are used for recreational activities and off-road vehicles were racing on the tailings at two mines during sample collection. Total concentrations of As in the <8 μm fraction varied from 65 to 1040 ng/m³ of air as measured by proton-induced X-ray emission (PIXE) analysis. The same samples were analysed by synchrotron-based microfocused X-ray absorption near-edge spectroscopy (μXANES) and X-ray diffraction (μXRD) and found to contain multiple As-bearing mineral species, including Fe–As weathering products. The As species present in the dust were similar to those observed in the near-surface tailings. The action of vehicles on the tailings surface may disaggregate material cemented with Fe arsenate and contribute additional fine-grained As-rich particles to airborne dust. Results from this study can be used to help assess the potential human health risks associated with exposure to airborne particles from mine tailings.     

The use of water-extractable Cu,Mo, Zn,As, Pb concentrations and automated mineral analysis of flue dust particles as tools for impact studies in topsoils exposed to past emissions of a Cu-smelter

An exploratory study has been conducted to test the utility of automated mineral analysis observations to identify flue dust particles in topsoils exposed for several decades to emissions of a copper smelter. The methods used are readily available in mining countries. To identify the most impacted sites, the Cu, Zn, Pb, Mo and As levels in water and diluted sulphuric acid extractions of four topsoil size fractions (833–495 μm, 246–148 μm; 74–38 μm; <38 μm) were analysed. X-ray diffraction analyses were used to demonstrate the mineralogical degradation of smectite phases when approaching the smelter. Flue dust particles in different states of conservation in topsoils were directly observed by scanning electron microscopy (SEM) aided by energy dispersive detection of X-rays. Qemscan^® scanning of dispersed topsoil preparations (10,000 particles) pinpoints smelter particles by their density; flue dust pearls can be tracked by sorting particles according to their sphericity, clearly identifying them as pyrometallurgical products. When sorting soil particles by mineral groups (e.g. sulphides), an increase in this phase group can be observed when approaching the smelter. SEM resolution limits observations to particles larger than 2–3 μm. Smaller particles can be observed by transmission electron microscopy, although observer experience and the availability of equipment time are essential as is the case for SEM.     

Mobilization of arsenic from acid deposition – The Elbe River catchment,Czech Republic

Temporal changes of As concentration in surface waters were observed in some areas of the Czech Republic. Mobilized As originates from past atmospheric deposition. To understand the factors influencing As aqueous concentration and mobility the chemistry and runoff generation of a number of brooks, springs and rivers in the central part of the Elbe River catchment, Czech Republic, were monitored. Seasonal variations of As (from 0.5 to 10.5 μg L⁻¹), Fe (from 0.05 to 3.9 mg L⁻¹) and DOC (dissolved organic C – from 1.2 to 17.5 mg L⁻¹) were observed in monitored stream waters with maximum values of As and Fe in the summer months at pH values 7.6–7.8. The concentration of As in particles with a diameter < 60 μm correlates with the Fe concentration. There is no correlation between Fe and As in filtered samples (<0.45 μm). The As concentration in stream water colloids depends on an increase in DOC concentration and a decrease in ionic strength. The DOC stabilizes As in solution and reduces its re-adsorption on Fe colloids and consequently As concentration in the stream increases.     

Trace metals in Antarctic ecosystems: Results from the Larsemann Hills,East Antarctica

Sediments, mosses and algae, collected from lake catchments of the Larsemann Hills, East Antarctica, were analysed to establish baseline levels of trace metals (Ag, As, Cd, Co, Cr, Cu, Ni, Sb, Pb, Se, V and Zn), and to quantify the extent of trace metal pollution in the area. Both impacted and non-impacted sites were included in the study. Four different leaching solutions (1 M MgCl₂, 1 M CH₃COONH₄, 1 M NH₄NO₃, and 0.3 N HCl) were tested on the fine fraction (<63 μm) of the sediments to extract the mobile fraction of trace metals derived from human impact and from weathering of basement lithologies. Results of these tests indicate that dilute HCl partly dissolves primary minerals present in the sediment, thus leading to an overestimate of the mobile trace metal fraction. Concentrations of trace metals released using the other 3 procedures indicate negligible levels of anthropogenic contribution to the trace metal budget. Data derived from this study and a thorough characterisation of the site allowed the authors to define natural baseline levels of trace metals in sediments, mosses and algae, and their spatial variability across the area. The results show that, with a few notable exceptions, human activities at the research stations have contributed negligible levels (lower than natural variability) of trace metals to the Larsemann Hills ecosystem. This study further demonstrates that anthropogenic sources of trace metals can be correctly identified and quantified only if natural baselines, their variability, and processes controlling the mobility of trace metals in the ecosystem, have been fully characterised.     

The Diavik Waste Rock Project: Particle size distribution and sulfur characteristics of low-sulfide waste rock

Three large-scale instrumented waste rock piles were constructed at the Diavik Diamond Mine in the Northwest Territories, Canada. These experimental waste rock piles (test piles) are 15 m high and are part of an integrated field and laboratory research program to characterize and compare low-sulfide waste rock and drainage at various scales. During test pile construction, samples of the <50 mm fraction of waste rock were collected from two types of waste rock that are segregated during mining operations based on S content. The samples were analyzed for S content and particle size distribution. One test pile contained waste rock with an average of 0.035 wt.% S in the <50 mm fraction, within the operational S target of <0.04 wt.% S for the lower S waste rock type. The second test pile contained waste rock with an average of 0.053 wt.% S in the <50 mm fraction, lower than the operational S target of >0.08 wt.% S for the higher S waste rock type. The third test pile has a low permeability till layer and a low sulfide waste rock thermal layer covering a core of waste rock with average 0.082 wt.% S in the <50 mm fraction, which is within the operational S target of >0.08 wt.% S for the higher S waste rock. Particle size distributions for the lower and higher S waste rock are similar, but the higher S waste rock has a higher proportion of fine-grained particles. Sulfur determinations for discrete particle sizes of the <50 mm fraction illustrate higher S concentrations in smaller particles for both the lower S waste rock and the higher S waste rock. Similarly, S concentrations calculated for the >10 m scale, from composite blast hole cuttings, are lower than those calculated for the <50 mm scale. Acid–base accounting using standard methods and site-specific mineralogical information was used to calculate the ratio of neutralization potential to acid generating potential. A comparison of calculation approaches to pH and alkalinity data from humidity cell and test pile effluent suggest that ratios are very sensitive to the calculation method. The preferred calculation method was selected by comparing calculation results to pH and alkalinity data from humidity cell effluent collected over 95 weeks and test pile effluent collected over five field seasons. The preferred acid–base accounting values were obtained by calculating the average neutralization potential divided by the average acid potential of a sample set. This approach indicates that waste rock with >0.05 wt.% S is of uncertain acid-generating potential and effluent data indicate this waste rock generates acidic effluent; whereas lower S waste rock does not produce acidic effluent, consistent with the acid–base accounting predictions.     

Partitioning and mobility of trace metals in the Blesbokspruit: Impact assessment of dewatering of mine waters in the East Rand,South Africa

A suite of trace metals was analyzed in water and sediment samples from the Blesbokspruit, a Ramsar certified riparian wetland, to assess the impact of mining on the sediment quality and the fate of trace metals in the environment. Limited mobility of trace metals was observed primarily because of their high partition coefficient in alkaline waters. Nickel was most mobile with a mean K_d of 10^3.28 L kg⁻¹ whereas Zr was least mobile with a mean K_d of 10^5.47 L kg⁻¹. The overall trace metal mobility sequence, derived for the Blesbokspruit, in increasing order, is: Zr < Cr < Pb < Ba < V < Cu < Zn < Sr < Mn < U < Mo < Co < Ni. Once removed from the solution, most trace metals were preferentially associated with the carbonate and Fe–Mn oxide fraction followed by the exchangeable fraction of the sediments. Organic C played a limited role in trace metal uptake. Only Cu was primarily associated with the organic fraction whereas Ti and Zr were mostly found in the residual fraction. Compared to their regional background, Au and Ag were most enriched, at times by a factor of 20–400, in the sediments. Significant enrichment of U, Hg, V, Cr, Co, Cu and Zn was also observed in the sediments.The calculated geoaccumulation indices suggest that the sediments are very lightly to lightly polluted with respect to most trace metals and highly polluted with respect to Au and Ag. The metal pollution index (MPI) for the 20 sampled sites varied between 2.9 and 45.7. The highest MPI values were found at sites that were close to tailings dams. Sediment eco-toxicity was quantified by calculating the sediment quality guideline index (SQG-I). The calculated SQG-I values (0.09–0.69) suggest that the sediments at the study area have low to moderate potential for eco-toxicity.     

Characteristics of modern atmospheric dust deposition in snow in the Mt. Yulong region,southeastern Tibetan Plateau

We evaluated the concentration, size and distribution, and temporal variation of insoluble dust micro-particles in the snow, rainfall and water taken from the areas surrounding the Mt. Yulong to define the characteristics of modern atmospheric dust deposition and the contributions of different dust sources. The mean mass concentration (4511 μg kg⁻¹) of micro-particles with 0.57 < d < 26 μm, and the diameter (11.5 μm) of dust contained in the water bodies of the Mt. Yulong are roughly similar to those observed in other sites, implying that dust is primarily supplied through short-range transport from proximal source regions (several or hundreds of km distances). The mean mass concentrations of micro-particles with 0.57 < d < 26 μm is lower in the rainfall than in the snow and the river water, suggesting the rain water is an ideal source/carrier for detecting the characteristics of modern atmospheric micro-particles. Volume size distributions of micro-particles in the snow and water showed single modal structures having volume median diameters from 3 to 26 μm. Number concentrations of micro-particles in the snow were higher than that in the rainfall, the river water contains the least amount of micro-particles. Vertical profiles of the snowpits show that there is a strong lateral correlation among the dust peaks, indicating a regional uniformity of dust deposition and suitability of snow analysis for dust deposition. In addition, the bare rock of snow-free terrain in the Mt. Yulong region and the mineral particles from local rock weathering are also important sources for the dust deposition.     

Diel variation of arsenic,molybdenum and antimony in a stream draining natural As geochemical anomaly

The Mokrsko Stream in the central Czech Republic is an oxic and slightly alkaline stream that drains a natural As geochemical anomaly. Although long-term monitoring has characterized the general seasonal trends in trace element concentrations (i.e., As, Mo, Cu, Zn) in this stream, little is known about solubility controls and sorption processes that influence diel cycles in trace element concentrations. Trace elements (including As species, Cu, Mn, Mo, Pb and Sb) and other parameters were monitored over two 24-h periods in unfiltered and filtered (0.1 μm) samples collected in August 2010 and June 2011. Copper and Pb were predominantly (>92% of the mass) associated with the particulate fraction (>0.1 μm). Arsenic, Mo and Sb were predominantly (>88% of the mass) in the “dissolved” (<0.1 μm) form. Particulate-associated elements displayed up to a factor of 13 differences between minimum and maximum concentrations, most likely due to increased streamflow related to rainfall events. Dissolved concentrations of the trace metal cations (Cu, Fe, Mn and Pb) were consistently low and displayed no diel trends. Dissolved As(V), Mo and Sb varied on a diel cycle, with increased concentrations (up to 36%) during the late afternoon and decreased concentrations during the nighttime. Diel trends in trace anionic elements are explained by temperature-dependent sorption, as the diel changes in pH during base flow were very small (0.07 std. units). Very low concentrations of As(III), which have been shown to vary in a diel cycle, were attributed to enhanced hydraulic exchange with As(III)-rich hyporheic water during rainfall events.     

Metal mobility due to storm events on an impacted hillslope in Palmerton,PA

Water samples were collected continuously from perennial springs on a hillslope impacted by historical metal deposition to study the hydrologic and geochemical behavior of a watershed during storm events, and assess the natural attenuation of metals in soil. Water samples were collected throughout storm hydrographs for inorganic chemistry analyses, and a sequential extraction was performed on watershed soil samples. Despite 30 a of natural attenuation at the site, Zn is mobilized into streamwater during storm events, with concentrations ranging from 18 to 452 μg/L. While Cd and Pb concentrations in water samples remained relatively constant, Zn concentration increased corresponding with the peak in the hydrograph indicating this metal is being released from adsorption sites located in an unsaturated zone that is temporarily inundated during storm events. Zinc is held on exchangeable, water and acid soluble sites, and in the reducible fraction, further indicating Zn may be released as a result of the downward movement of water through the soil profile. Equilibrium geochemical modeling predicts Zn desorption with a decrease in pH, which may occur as a result of site re-vegetation. The long legacy of metal emissions from a historical smelting operation will continue to limit the attenuating ability of this site.     

Organic matter quality in reclaimed boreal forest soils following oil sands mining

Following surface mining of the Athabasca Oil Sands deposits in northeastern Alberta, Canada, land reclamation entails the reconstruction of soil-like profiles using salvaged soil materials such as peat and mining by-products. The overall objective of this research was to assess soil organic matter (SOM) quality in different reclamation practices as compared to undisturbed soils found in the region. Soil samples (0–10 cm) were taken from 45 plots selected to represent undisturbed reference ecosites and reclamation treatments. Soil OM pools were isolated using a combination of acid hydrolysis and physical separation techniques. Chemical composition of the low density fractions was characterized using ramped cross polarization (RAMP-CP) ¹³C nuclear magnetic resonance (NMR). Differences between disturbed and undisturbed sites reflected the influence of different botanical inputs (peat vs. forest litter) to SOM composition. Reconstructed soils were characterized by significantly lower alkyl over O-alkyl carbon (ALK/O-ALK) ratios (0.3) than undisturbed sites (0.5). For these reconstructed soils, a significantly higher proportion of soil carbon was present in the sand associated (Heavy sand) pool (49.2 vs. 37.3) and in the acid-unhydrolyzable residue (AUR) fraction (61.3 vs. 54.7). These SOM parameters were significantly related to time since reconstruction, with the AUR (p value = 0.012) and Heavy sand (p value = 0.05) fractions decreasing with time since reconstruction, while the ALK/O-ALK ratio increased (p value = 0.006). These findings suggest that the ALK/O-ALK, AUR, and Heavy sand parameters are suitable indicators for monitoring SOM quality in these reconstructed soils following oil sands mining.     

Significance of weathering and regolith/landscape evolution for mineral exploration in the NE Albany-Fraser Orogen,Western Australia

The Albany-Fraser Orogen (AFO), southeast Western Australia, is an underexplored, deeply weathered regolith-dominated terrain that has undergone complex weathering associated with various superimposed climatic events. For effective geochemical exploration in the AFO, integrating landscape evolution with mineralogical and geochemical variations of regolith and bedrock provides fundamental understanding of mechanical and hydromorphic dispersion of ore and pathfinder elements associated with the different weathering processes.In the Neale tenement, northeast of the AFO, a residual weathering profile that is 20-55 m thick was developed under warm and humid climatic conditions over undulating Proterozoic sheared granitoids, gneisses, schists and Au-bearing mafic rocks. From the base, the typical weathering profile consists of saprock, lower ferruginous saprolite, upper kaolinitic saprolite and discontinuous silcrete duricrust or its laterally coeval lateritic residuum. These types of duricrusts change laterally into areas of poorly-cemented kaolinitic grits or loose lateritic pisoliths and nodules.Lateritic residuum probably formed on remnant plateaus and was transported mechanically under arid climatic conditions over short distances, filling valleys to the southeast. Erosion of lateritic residuum exposes the underlying saprolite and, together with dilution by aeolian sands, constitutes the transported overburden (2-25 m thick). The reworked lateritic materials cover the preserved silcrete duricrusts in valleys. The lower ferruginous saprolite and lateritic residuum are well developed over mafic and sulphide-bearing bedrocks, where weathering of ferromagnesian minerals and sulphides led to enrichment of Fe, Cu, Ni, Cr, Co, V and Zn in these units. Kaolinitic saprolite and the overlying pedogenic silcrete are best developed over alkali granites and quartzofeldspathic gneisses, which are barren in Au and transition elements, and enriched in silica, alumina, rare earth and high field strength elements.A residual Au anomaly is formed in the lower ferruginous saprolite above a Au -bearing mafic intrusion at the Hercules prospect, south of the Neale tenement, without any expression in the overlying soil (< 20 cm). Conversely, a Au anomaly is recorded in the transported cover, particularly in the uppermost 3 m at the Atlantis prospect, 5 km southwest of the Hercules prospect. No anomalies have been detected in soils using five different size fractions (> 2,000 μm, 2,000-250 μm, 250-53 μm, 53-2 μm and < 2 μm). Therefore, soil cannot be efficiently applied as a reliable sampling medium to target mineralization at the Neale tenement. This is because mechanical weathering was interrupted by seasonal periods of intensive leaching under the present-day surface conditions and/or dilution by recently deposited aeolian sediments which obscure any signature of a potential Au anomaly in soils. Therefore, surface soil sampling should extend deeper than 20 cm to avoid dilution by aeolian sands and seasonal leaching processes. Regolith mapping and the distinction between the residual and transported weathering products are extremely significant to follow the distal or proximal mineralization.     

Strategic and rare elements in Cretaceous-Cenozoic cobalt-rich ferromanganese crusts from seamounts in the Canary Island Seamount Province (northeastern tropical Atlantic)

Thick ferromanganese (Fe-Mn) crusts from four Cretaceous seamounts (The Paps, Tropic, Echo and Drago) at the southern Canary Island Seamount Province (CISP) in the northeastern tropical Atlantic were recovered along the flanks and summits from 1700 to 3000 m water depths. CISP is composed of > 100 seamounts and submarine hills, is likely the oldest hotspot track in the Atlantic Ocean, and is the most long-lived of known hotspots globally. The Fe-Mn crusts grow on basalt-sedimentary rock substrates below the northeastern tropical Atlantic core of the oxygen minimum zone (OMZ) with a maximum thickness of 250 mm at a water depth of 2400 m. The mineralogical and chemical composition of these Fe-Mn crusts indicate a hydrogenetic origin. The main Mn minerals are vernadite with minor interlayered todorokite and asbolane-buserite. Fe oxides are essentially ferroxyhyte and goethite. The Fe-Mn crusts show high average contents in Fe (23.5 wt%), Mn (16.1 wt%), and trace elements like Co (4700 μg/g), Ni (2800 μg/g), V (2400 μg/g) and Pb (1600 μg/g). Rare earth elements plus yttrium (REY) averages 2800 μg/g with high proportions of Ce (1600 μg/g). Total platinum group elements (PGEs) average 230 ng/g, with average Pt of 182 ng/g. Two main types of growth layers form the crusts: 1) a dense laminae of oxides with high contents in Mn, Co and Ni associated with vernadite and Cu, Ni, and Zn associated with todorokite; 2) botryoidal layers with high contents in Fe, Ti, V and REY associated with goethite. The Fe-Mn crusts from the CISP region show higher contents in Fe, V, Pb and REY but lower Mn, Co, Ni and PGEs contents than Pacific or Indian ocean seamount crusts. The oldest maximum age of initiation of crust growth was at 76 Ma (Campanian, Late Cretaceous). Using a combination of high resolution Co-chronometer and geochemical data along an Electron Probe Micro Analysis (EPMA) transect, four stages in morphology, chemical contents and growth rates can be differentiated in the the Cenozoic crusts since 28 Ma, which we interpret as due to changes in the ventilation of the North Atlantic OMZ and to the increase of Saharian dust inputs. An earliest growth period, characterized by similar contents of Fe and Mn in the interval 27.8–24.45 Ma (late Oligocene-early Miocene) reflects slow precipitation related to a thick OMZ. An intermediate laminated zone with higher contents of Fe, Si and P, high growth rates reaching 4.5 mm/Ma, and precipitation of Fe-Mn oxides during the interval 24.5–16 Ma is related to periods of ventilation of the OMZ by intrusion of deep upwelling currents. Significant increase in Fe contents at ca. 16 Ma correlates with the onset of incursions of Northern Component Waters into the North Atlantic. Finally, since 12 Ma, the very low growth rates (< 0.5 mm/Ma) of the crust are related to a thick North Atlantic OMZ, an increase in Sahara dust input and a stable thermohaline circulation.     

Metal species in a Boreal river system affected by acid sulfate soils

The bioavailability of metals and their potential for environmental pollution depends not simply on total concentrations but on their chemical form. Consequently, knowledge of aqueous metal speciation is essential in investigating potential metal toxicity and mobility. Dissolved (<1 kDa), colloidal (1 kDa–0.45 μm) and particulate (>0.45 μm) size fractions of sulfate, organic C (OC) and 18 metals/metalloids were investigated in the extremely acidic Vörå River system in Western Finland, which is strongly affected by acid sulfate (AS) soils. In addition, geochemical modelling was used to predict the formation of free ions and complexes in these acidic waters. The most important finding of this study is that the very large amounts of elements known to be released from AS soils (including Al, Ca, Cd, Co, Cu, Mg, Mn, Na, Ni, Si and U) occur and can prevail mainly in toxic forms throughout acidic river systems; as free ions and/or sulfate-complexes. This has serious effects on the biota and particularly dissolved Al can be expected to have acute effects on fish and other organisms. In the study area, only the relatively forested upstream area (higher pH and contents of OC) had significant amounts of a few bioavailable elements (including Al, Cu, Ni and U) due to complexation with the more abundantly occurring colloidal OC in the upstream area. It is, however, notable that some of the colloidal/particulate metals were most likely associated with metal bearing phyllosilicates eroded from clay soils. Moreover, the mobilisation of Fe and As was small and As was predicted to be associated with Fe oxides, indicating a considerable influence of Fe oxides on the mobilisation/immobilisation processes of As. Elements will ultimately be precipitated in the recipient estuary, where the acidic metal-rich river water will gradually be diluted/neutralised with brackish seawater in the Gulf of Bothnia. According to speciation modelling, such a pH rise may first cause precipitation of Al, Cu and U together with organic matters closest to the river mouth, in line with previous sediment studies from the estuary.     

Behaviour of chromium(VI) in stormwater soil infiltration systems

The ability of stormwater infiltration systems to retain Cr(VI) was tested by applying a synthetic stormwater runoff solution with a neutral pH and high Cr(VI) concentrations to four intact soil columns excavated from two roadside infiltration swales in Germany. Inlet flow rates mimicked normal (10 mm in 2 h) and extreme (100 mm in 3 h) rain events. The objectives were to understand the behaviour of the anionic and toxic Cr(VI) in soil at neutral pH and to asses treatment efficiency towards Cr(VI). During normal rain events Cr(VI) was largely retained (more than 50%), even though pH was neutral, while under extreme rain events approximately 20% of Cr(VI) was retained. In both cases effluent concentrations of Cr(VI) would exceed the threshold value of 3.4 μg/L if the infiltrated water were introduced to freshwater environments. More knowledge on the composition of the stormwater runoff, and especially the occurrence of Cr(VI), is needed.