Pasi Peltola

Effect of weathering on abundance and release of potentially toxic elements in soils developed on Lower Cambrian black shales, P. R. China

This paper examines the geochemical features of 8 soil profiles developed on metalliferous black shales distributed in the central parts of the South China black shale horizon. The concentrations of 21 trace elements and 8 major elements were determined using ICP-MS and XRF, respectively, and weathering intensity (W) was calculated according to a new technique recently proposed in the literature. The data showed that the black shale soils inherited a heterogeneous geochemical character from their parent materials. A partial least square regression model and EFbedrock (enrichment factor normalized to underlying bedrock) indicated that W was not a major control in the redistribution of trace metals. Barium, Sn, Cu, V, and U tended to be leached in the upper soil horizons and trapped by Al and Fe oxides, whereas Sb, Cd, and Mo with negative EF values across the whole profiles may have been leached out during the first stage of pedogenesis (mainly weathering of black shale). Compared with the Chinese average soils, the soils were strongly enriched in the potentially toxic metals Mo, Cd, Sb, Sn, U, V, Cu, and Ba, among which the 5 first listed were enriched to the highest degrees. Elevated concentrations of these toxic metals can have a long-term negative effect on human health, in particular, the soils in mining areas dominated by strongly acidic conditions. As a whole, the black shale soils have much in common with acid sulfate soils. Therefore, black shale soils together with acid sulfate soils deserve more attention in the context of metal exposure and human health.

Effects of land use and climate change on erosion intensity and sediment geochemistry at Lake Lehmilampi, Finland:

This paper aims to evaluate the possible relationships between erosion intensity and changes in climate and land use during the past 5.5 cal. k years at Lake Lehmilampi, eastern Finland. In this study we compare a detailed geochemical sediment record with (1) forest and land use history inferred from the first pollen and charcoal records from Lake Lehmilampi, and (2) existing archaeological surveys and independent proxy-records of climate change in the study region. The physical and geochemical sediment parameters examined include grain size analysis data and 23 chemical elements, determined with four selective extractions and ICP-MS. There are indications of possible human impact in the lake catchment as early as the Neolithic period, c. 3000–2550 bc, but the first undisputable signs are dated to 1800–100 bc. Cereal pollen reappears at c. ad 1700 and increases rapidly until c. ad 1950. The Holocene Thermal Maximum, its end c. 2000 bc, and the ‘Medieval Climate Anomaly’ were major climate events that had a prominent effect on erosion intensity, while human impact was a more significant factor during the period 3000 bc–ad 800 and from ad 1500 onwards. Although signs of changes in erosion intensity found in the sediment were small in this small catchment, they were significant enough to have a clear impact on the fraction of potentially mobile element species. This fraction increases with decreasing erosion intensity, which is probably related to a higher degree of chemical weathering and leaching during periods of decreased erosion.

Concentrations and leachability of chemical elements in estuarine sulfur-rich sediments, W. Finland.

Concentrations, distributions and mobility of chemical elements were investigated in reduced sulfur-rich estuarine sediments located in western Finland. The main objective was to determine the possible extent of metal leaching when dredged masses of these sulfur-rich sediments are dumped on the land and thus exposed to air. When dredged, the reduced sulfur in the sediments oxidises resulting in a lowering of pH, which in turn is expected to leach metals. The study area is an artificial lake claimed from the Botnian sea in 1962. In this lake, several mass-kills of fish have occurred, believed partly to be due to dredging. Two sediment samples (0-50 and 50-100 cm) were taken from 39 sampling points in the lake. These samples were leached in aqua regia (2:2:2 HNO3/HCl/H2O1) and analysed for Fe, Al, Mg, Ca, K, P, Na, Mn, Zn, Ba, V, Sr, Cr, Ni, Cu, Co, As, Pb, B, Mo and Cd with ICP-AES. Sulfur and organic carbon were analysed with Leco. In a controlled laboratory experiment, the sediments were allowed to oxidise for 1 year while moisturised with deionised water every month. The pH and conductivity were determined in the beginning of the experiment (reduced state) and in the end (oxidised state). In the supernatants in the oxidised states the amount of leached metals (Na, Al, Mn, Zn, Sr, Co, Ni, Cu, Cd, Cr, Pb, U, Li, Rb and As) were determined with ICP-MS. The sediments were found to contain low levels of toxic metals but, as expected, high concentrations of sulfur. In the experiment, pH was lowered (down to 3.0) and the conductivity increased in all samples due to oxidation and release of metal ions. The extent of leaching varied between 0.03% for As and 12.3% for Na. Critical pH values, at which high amounts of metals begin to leach, were obtained graphically. These values varied between 4.8 (Ni) and 3.3 (Cr). Not all elements were controlled by pH, e.g. Mn correlated well with its aqua regia leachable concentration. In a planned dredging operation in the area some 23,300 t (10,500 m3) (dry wt.) of sediments will be dredged. The amounts of metals likely to be leached, according to the results from this study, are as follows (kg): Al (1710), Mn (1230), Zn (59), Sr (39), Co (13), Ni (12), Cu (2) and less than 1 kg of Cd-Cr-As-Pb.

Arsenic removal from contaminated brackish sea water by sorption onto Al hydroxides and Fe phases mobilized by land-use.

This study examines the spatial and temporal distribution patterns of arsenic (As) in solid and aqueous materials along the mixing zone of an estuary, located in the south-eastern part of the Bothnian Bay and fed by a creek running through an acid sulfate (AS) soil landscape. The concentrations of As in solution form (<1 kDa) increase steadily from the creek mouth to the outer estuary, suggesting that inflowing seawater, rather than AS soil, is the major As source in the estuary. In sediments at the outer estuary, As was accumulated and diagenetically cycled in the surficial layers, as throughout much of the Bothnian Bay. In contrast, in sediments in the inner estuary, As concentrations and accumulation rates showed systematical peaks at greater depths. These peaks were overall consistent with the temporal trend of past As discharges from the Rönnskär smelter and the accompanied As concentrations in past sea-water of the Bothnian Bay, pointing to a connection between the historical smelter activities and the sediment-bound As in the inner estuary. However, the concentrations and accumulation rates of As peaked at depths where the smelter activities had already declined, but a large increase in the deposition of Al hydroxides and Fe phases occurred in response to intensified land-use in the mid 1960s and early 1970s. This correspondence suggests that, apart from the inflowing As-contaminated seawater, capture by Al hydroxides, Fe hydroxides and Fe-organic complexes is another important factor for As deposition in the inner estuary. After accumulating in the sediment, the solid-phase As was partly remobilized, as reflected by increased pore-water As concentrations, a process favored by As(V) reduction and high concentrations of dissolved organic matter.

Exposure to contaminated sediments during recreational activities at a public bathing place

More and more time is spent on recreational activities, but few risk assessments focus specifically on these situations and exposure factor data are often scarce. To assess exposure to contaminants at a public bathing place in an urban environment, we have compiled literature data, conducted observation studies, and analyzed water and sediment samples. The levels of anthropogenic contaminants are high in urban environments and traffic frequently plays an important role. In this study, to characterize variability and uncertainty, the deterministic exposure calculations for metal pollutants were supplemented by a probability bounds analysis for the polycyclic aromatic hydrocarbons (PAH). The results from these calculations show that oral intake is the major exposure route for metals, while skin absorption, with present assumptions, is more important for the PAH. The presently measured levels of contaminants, at this public bathing place, cannot be anticipated to cause any significant adverse influence on public health. This assessment methodology is easy to adapt and can be used routinely in other situations with more heavily contaminated surface sediments and lake water.

Niobium in boreal stream waters and brackish-water sediments

The focus is on ‘non-detrital’ Nb in boreal stream waters (dissolved fraction and acid-available particulate fraction) and brackish-water/lacustrine sediments (aqua regia extractable fraction). Spatial patterns, temporal trends and speciation experiments all point to dissolved humic substances and colloidal Fe as the main control of Nb concentrations in stream waters. In addition, clay-silt deposits and/or ore deposits may be responsible for producing local streamwater Nb anomalies. In groundwater in overburden (glacial till) overlying Proterozoic granitoids, dissolved Nb concentrations were about an order of magnitude higher than in stream waters and strongly correlated with dissolved Fe. In the brackish-water sediments, the Nb concentrations (1.33–4.20 ppm) were higher than in the lacustrine ones (0.25–0.53 ppm). To explain this, we assessed the potential role of organic material, biological processes, sulphide mineralogy, silicate mineralogy and input factors. However, none of them could satisfactorily explain the observed Nb geochemical features. Although Nb can be considered relatively immobile, the data presented in this paper show that under certain conditions its abundance in the aquatic environment increases.

Uranium in surface and groundwaters in Boreal Europe

ABSTRACT This study focuses on uranium (U) in surface and groundwaters in Boreal Europe (Sweden, Finland, Russia). Data from recently completed regional hydrogeochemical surveys and from site-specific studies were combined, in order to enhance the current understanding of U behaviour in the catchments and water bodies of these northerly latitudes. Over Precambrian areas (dominated by igneous and metamorphic rocks) the aqueous U concentrations in general increased in a downward direction, i.e. from stream waters to overburden groundwaters to bedrock groundwaters, and they were correlated with the U abundance in the surrounding overburden (mainly glacial till). Over Phanerozoic areas (dominated by terrigene deposits containing or composed of limestone) the aqueous U concentrations were, in contrast, unrelated to overburden U concentrations and strongly correlated with dissolved Ca and HCO3− concentrations. There is thus an overall geochemical and hydrochemical control, respectively, related to the underlying lithology. At geologically specific and local sites there is a range of correlations and control mechanisms of aqueous U. From acid sulphate soils, occurring abundantly on coastal plains, runoff below pH 4.0 is enriched in U (up to 55 μg/l) most likely due to oxidation of U(IV) minerals followed by subsequent limited sorption of U(VI) in the acidic environment. In a studied black shale setting, characterized by high U concentrations (up to >200 ppm), U levels increased in groundwater (up to 200 μg/l) and surface water (up to 80 μg/l) as the conditions changed from reducing to oxidizing. In an unmineralized granitic setting, proposed as a repository for spent nuclear fuel, elevated U concentrations in surface waters (up to 25 μg/l) reflect a regional stream-hydrochemical anomaly and in bedrock groundwaters (up to >100 μg/l), most likely mobilization of uranyl from U-rich fracture coatings. In the Baltic Sea, which has unique brackish water, the ratio of U to Cl− is similar to that in the oceans but contrasting near-coastal U trends exist, characterized by an inverse relationship between U and Cl− concentrations. These coastal-water anomalies are most likely caused by high U levels in inflowing streams, and possibly to some extent submarine discharge of U-enriched waters.

Abundance, correlations and spatial patterns of nutrients and metals in till, humus, moss and pine needles in a boreal forest, western Finland

Moss, humus, till and needle samples from coniferous forests at 87–103 sites were used to elucidate how natural processes and human activities throughout a 500 km2 area in western Finland have affected the content, accumulation and dispersion of P, K, Ca, Mg, Fe, S, B, Cu, Zn, Mn, Cd, Cr, Ni and Pb in the environment. Abundance, correlations and spatial trends between and within the organic, biological and inorganic compartments were determined. No evident spatial trends existed for K, P, S, Mn, Mg and Ca. The distribution of these macronutrients in and between the media is controlled, to a high degree, by biological cycling; thus the nutrient levels are optimized in the various media. Low correlation coefficients for Ca, P, K, S and Mg between humus and moss, and the low spread of these nutrients in moss and needles, are other strong indications of efficient recycling. No correlation existed between the concentrations of B and the distance from the coast, suggesting that the B patterns are unaffected by deposition of marine salts. There was a strong spatial pattern for B in humus, moss and needles, probably connected with anthropogenic emissions from a nearby town centre. Geogenic dust affected the spatial distribution and the high correlation between Fe and Cr in moss, while natural processes were associated with the Fe anomaly found in the needles. The spatial accumulation patterns of Zn, Cd, Cu, Ni and Pb in humus and moss were strong and diverse and related to current industry, the former steel industry, traffic, coal combustion, and natural geochemical processes. An intriguing Cu anomaly in moss, probably caused by corrosion of the railway lines electric cables, was identified.