Geochemical controls on dispersion of U and Th in Quaternary deposits, stream water, and aquatic plants in an area with a granite pluton.

The weathering of U and/or Th rich granite plutons, which occurs worldwide, may serve as a potentially important, but as yet poorly defined source for U and Th in (sub-)surface environments. Here, we assessed the impact of an outcrop of such granite (5 km in diameter) and its erosional products on the distribution of U and Th in four nemo-boreal catchments. The results showed that (i) the pluton was enriched in both U and Th; and (ii) secondary U and Th phases were accumulated by peat/gyttja and in other Quaternary deposits with high contents of organic matter. Movement of the ice sheet during the latest glaciation led to dispersal of U- and Th-rich materials eroded from the pluton, resulting in a progressive increase in dissolved U and Th concentrations, as well as U concentrations in aquatic plants with increasing proximity to the pluton. The accumulation of U in the aquatic plants growing upon the pluton (100-365 mg kg-1, dry ash weight) shows that this rock represents a long-term risk for adjacent ecosystems. Dissolved pools of U and Th were correlated with those of dissolved organic matter (DOM) and were predicted to largely occur as organic complexes. This demonstrates the importance of DOM in the transport of U and Th in the catchments. Large fractions of Ca2UO2(CO3)30(aq) were modeled to occur in the stream with highest pH and alkalinity and thus, explain the strongly elevated U concentrations and fluxes in this particular stream. In future climate scenarios, boreal catchments will experience intensified runoff and warmer temperature that favor the production of hydrologically accessible DOM and alkalinity. Therefore, the results obtained from this study have implications for predicting the distribution and transport of Th and U in boreal catchments, especially those associated with U and/or Th rich granite plutons.

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 1960's and early 1970's. 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.

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 EF(bedrock) (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.

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.

Lead and Cu in contaminated urban soils: extraction with chemical reagents and bioluminescent bacteria and yeast.

Twenty urban soil samples, with a wide range of Pb (14-5323 mg/kg) and Cu (8-12987 mg/kg), were used to compare the operational speciation of a five-step sequential leach with the bioavailability determined with bioluminescent Pb (RN4220(pTOO24)) and Cu (MC1061(pSLcueR/pDNPcopAluc)) specific bacterial biosensors and a Cu specific yeast sensor. The bioavailable Pb concentrations were all similar or lower than the first sequential leach step (1M NaOAc). In contrast, in some samples the bioavailable concentrations of Cu clearly exceeded even the second sequential leach step (0.1 M Na4P2O7). With the yeast sensor 12/20 samples were below detection, however, the yeast sensor was capable of detecting all high Cu concentrations. The biosensors used in this study are not capable of detecting the natural soil concentrations of Pb and Cu in the studied area.

Urban geochemistry: a multimedia and multielement survey of a small town in northern Europe.

The concentrations and distributions of chemical elements (Ag, Al, As, Au, Ba, Bi, Ca, Cd, Co, Cr, Cu, Fe, Ga, Hg, K, La, Mg, Mn, Mo, Na, Ni, P, Pb, S, Sb, Sc, Se, Sr, Te, Th, Ti, Tl, U, V, W and Zn) were studied in till, humus and urban soil in Jakobstad, a small town (20,000 inhabitants) in W. Finland. The analyses were performed with ICP-MS after aqua regia leaching of till (n = 37), urban topsoil (n = 32) and subsoil (n = 32), and HNO3 leaching of humus (n = 37). The till and humus samples, collected at the same sites, were divided into urban and rural samples. The urban till was not significantly enriched in metals. In contrast, a majority of the elements occurred in higher concentrations in the urban than the rural humus samples. Statistical and spatial interpretations of the humus data revealed that traffic (Pb, V and Ni), metal industry (Pb, Zn, Bi, Sb and Cr), an abandoned shooting range (Pb and Sb) and other sources contribute to higher metal levels in the urban humus. The urban soil samples were collected at parks, yards, abandoned industrial sites, roadsides, etc. The topsoil samples were enriched in most elements, also by elements not enriched in the urban humus (e.g. Cd). At several sites, the concentrations far exceeded the limit concentrations for contaminated soils in Finland. A large variety of sources were identified or indicated.

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.