Mercury Isotope Fractionation during Dark Abiotic Reduction of Hg(II) by Dissolved, Surface-Bound, and Structural Fe(II).

Stable mercury (Hg) isotope ratios are an emerging tracer for biogeochemical transformations in environmental systems, but their application requires knowledge of isotopic enrichment factors for individual processes. We investigated Hg isotope fractionation during dark, abiotic reduction of Hg(II) by dissolved iron(Fe)(II), magnetite, and Fe(II) sorbed to boehmite or goethite by analyzing both the reactants and products of laboratory experiments. For homogeneous reduction of Hg(II) by dissolved Fe(II) in continuously purged reactors, the results followed a Rayleigh distillation model with enrichment factors of -2.20 ± 0.16‰ (ε202Hg) and 0.21 ± 0.02‰ (E199Hg). In closed system experiments, allowing reequilibration, the initial kinetic fractionation was overprinted by isotope exchange and followed a linear equilibrium model with -2.44 ± 0.17‰ (ε202Hg) and 0.34 ± 0.02‰ (E199Hg). Heterogeneous Hg(II) reduction by magnetite caused a smaller isotopic fractionation (-1.38 ± 0.07 and 0.13 ± 0.01‰), whereas the extent of isotopic fractionation of the sorbed Fe(II) experiments was similar to the kinetic homogeneous case. Small mass-independent fractionation of even-mass Hg isotopes with 0.02 ± 0.003‰ (E200Hg) and ≈ -0.02 ± 0.01‰ (E204Hg) was consistent with theoretical predictions for the nuclear volume effect. This study contributes significantly to the database of Hg isotope enrichment factors for specific processes. Our findings show that Hg(II) reduction by dissolved Fe(II) in open systems results in a kinetic MDF with a larger ε compared to other abiotic reduction pathways, and combining MDF with the observed MIF allows the distinction from photochemical or microbial Hg(II) reduction pathways.

Molecular Probing of DOM Indicates a Key Role of Spruce-Derived Lignin in the DOM and Metal Cycles of a Headwater Catchment: Can Spruce Forest Dieback Exacerbate Future Trends in the Browning of Central European Surface Waters?

Peatlands of the Northern Hemisphere and Central European coniferous forests experience significant environmental change. The resultant browning of surface waters, that is, elevated concentrations of dissolved organic matter (DOM) and metals, is of interest in the context of the global C cycle, peatland and forest management, and water treatment. In an attempt to identify the causes of this process in the Harz Mountains (Central Germany), we studied the spatiotemporal variations in DOM molecular composition (thermally assisted hydrolysis and methylation combined with GC-MS) and metal concentrations in headwater stream samples. We found strong relationships between DOM and metals and seasonal variations in the DOM quality and tentatively DOM-metal binding mode: during summer base flow, DOM and metal concentrations are low, and all elements other than the alkali and alkaline earth metals (Ca, Mg, Sr, K, and Na) are positively correlated to DOM, whereas during spring and autumn (high discharge), only metals with strong affinity for DOM (Fe, As, Cu, Cr, Pb, and Ti), but not weakly binding ones (Al, Cd, La, Mn, Ni, Zn, and Zr), are correlated to DOM, indicative of selectivity in DOM-metal interactions. The products of polyphenols are the key ingredients of the DOM-metal complexes. We argue the importance of spruce lignin-derived vanillic acid moieties, which are involved in weak (all seasons) and strong, multidentate and/or colloidal, binding (spring and autumn) of metals. Considering the ongoing spruce forest dieback and climate change acceleration, it is tempting to conclude that spruce necromass and forest soils may release vast amounts of lignin-derived DOM and associated metals to headwater streams. This would have significant implications for forest soil C stocks and the management of connected drinking water reservoirs.

Mercury Isotope Fractionation in the Subsurface of a Hg(II) Chloride-Contaminated Industrial Legacy Site.

To understand the transformations of mercury (Hg) species in the subsurface of a HgCl2-contaminated former industrial site in southwest Germany, Hg isotope analysis was combined with an investigation of Hg forms by a four-step sequential extraction protocol (SEP) and pyrolytic thermodesorption. Data from two soil cores revealed that the initial HgCl2 was partly reduced to metallic Hg(0) and that Hg forms of different mobility and oxidation state coexist in the subsurface. The most contaminated sample (K2-8, 802 mg kg-1 Hg) had a bulk δ202Hg value of around -0.43 ± 0.06‰ (2SD), similar to published average values for industrial Hg sources. Other sample signatures varied significantly with depth and between SEP pools. The most Hg-rich samples contained mixtures of Hg(0) and Hg(II) phases, and the water-extractable, mobile Hg pool exhibited heavy δ202Hg values of up to +0.18‰. Sequential water extracts revealed slow dissolution kinetics of mobile Hg pools, continuously releasing isotopically heavy Hg into solution. This was further corroborated by heavy δ202Hg values of groundwater samples. Our results demonstrate that the Hg isotope signature of an industrial contamination source can be significantly altered during the transformations of Hg species in the subsurface, which complicates source tracing applications but offers the possibility of using Hg isotopes as process tracers in contaminated subsurface systems.

Mercury concentrations in bats (Chiroptera) from a gold mining area in the Peruvian Amazon.

In the southeastern Peruvian Amazon, artisanal and small-scale gold mining (ASGM) is estimated to have released up to 300 tonnes of mercury (Hg) to the environment between 1995 and 2007 alone, and is claimed to be responsible for Hg concentrations above international thresholds for aquatic wildlife species. Here, we examined whether Hg concentrations in bat populations are potentially related to regional ASGM-Hg releases. We determined Hg concentrations in the fur of bats collected at three different distances from the major ASGM areas in Peru. Our findings from 204 individuals of 32 species indicate that Hg concentrations in bat fur mainly resulted from differences in feeding habits, because Hg concentrations were significantly higher in omnivorous bats than in frugivorous bats. At least in two species, populations living in ASGM-affected sites harbored higher Hg concentrations than did populations in unaffected sites. Because Hg concentrations reflect Hg dietary exposure, Hg emissions from amalgam roasting sites appear to deposit locally and enter the terrestrial food web. Although our study demonstrates that ASGM activities (and Hg point sources) increase Hg exposure in wildlife, the overall Hg concentrations reported here are relatively low. The measured Hg concentrations were below the toxicity threshold at which adverse neurological effects have been reported in rodents and mink (>10 µg g-1), and were in the range of Hg concentrations in the fur of bats from nonpoint source affected sites in other latitudes. This study emphasizes the importance of considering feeding habits when evaluating Hg concentrations in bats and other vertebrates.

Geochemical investigation of potentially harmful elements in household dust from a mercury-contaminated site, the town of Idrija (Slovenia).

A comprehensive geochemical investigation of potentially harmful elements (PHEs) in household dust from the town of Idrija (Slovenia), once a world-famous Hg mining town that is now seriously polluted, was performed for the first time. After aqua regia digestion, the content of mercury (Hg), arsenic (As), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), molybdenum (Mo), nickel (Ni), lead (Pb) and zinc (Zn) was measured. PHE-bearing particles were recognised and observed by scanning electron microscopy and energy-dispersive spectrometry before and after exposure to simulated stomach acid (SSA). Mercury binding forms were identified by Hg thermal desorption technique and gastric bioaccessible Hg was estimated after SSA extraction by ICP-MS. With regard to rural and urban background values for Slovenia, high Hg content (6-120 mg/kg) and slightly elevated As content (1-13 mg/kg) were found. Mercury pollution is a result of past mining and ore processing activities. Arsenic content is potentially associated with As enrichment in local soils. Four Hg binding forms were identified: all samples contained Hg bound to the dust matrix, 14 samples contained cinnabar, two samples contained metallic Hg (Hg0), and one sample assumingly contained mercury oxide. After exposure to SSA, Hg-bearing phases showed no signs of dissolution, while other PHE-bearing phases were significantly morphologically and/or chemically altered. Estimated gastric Hg bioaccessibility was low (<0.006-0.09 %), which is in accordance with identified Hg binding forms and high organic carbon content (15.9-31.5 %) in the dust samples.

Comparing Modeled and Measured Mercury Speciation in Contaminated Groundwater: Importance of Dissolved Organic Matter Composition.

In addition to analytical speciation, reliable Hg species modeling is crucial for predicting the mobility and toxicity of Hg, but geochemical speciation codes have not yet been tested for their prediction accuracy. Our study compares analyses of Hg species in highly Hg-contaminated groundwater (Hgtot: 0.02-4 µmol·L(-1)) at three sites with predictions of Hg speciation obtained from three geochemical codes (WHAM, Visual MINTEQ, PHREEQC) with and without implementation of Hg complexation by dissolved organic matter (DOM). Samples were analyzed for chemical composition, elemental, inorganic, and DOM-bound Hg (Hg(0), Hginorg, HgDOM). Hg-DOM complexation was modeled using three approaches: binding to humic/fulvic acids, binding to thiol-groups, or a combination of both. Results of Hg(0) modeling were poor in all scenarios. Prediction accuracy for Hginorg and HgDOM strongly depended on the assumed DOM composition. Best results were achieved when weaker binding sites, simulated by WHAMs DOM submodel, were combined with strongly binding thiol groups. Indications were found that thiol-DOM ratios in groundwater are likely to be lower than in surface water, highlighting the need for analytical thiol quantification in groundwater DOM. This study shows that DOM quality is a crucial parameter for prediction of Hg speciation in groundwater by means of geochemical modeling.

Iron traps terrestrially derived dissolved organic matter at redox interfaces.

Reactive iron and organic carbon are intimately associated in soils and sediments. However, to date, the organic compounds involved are uncharacterized on the molecular level. At redox interfaces in peatlands, where the biogeochemical cycles of iron and dissolved organic matter (DOM) are coupled, this issue can readily be studied. We found that precipitation of iron hydroxides at the oxic surface layer of two rewetted fens removed a large fraction of DOM via coagulation. On aeration of anoxic fen pore waters, >90% of dissolved iron and 27 ± 7% (mean ± SD) of dissolved organic carbon were rapidly (within 24 h) removed. Using ultra-high-resolution MS, we show that vascular plant-derived aromatic and pyrogenic compounds were preferentially retained, whereas the majority of carboxyl-rich aliphatic acids remained in solution. We propose that redox interfaces, which are ubiquitous in marine and terrestrial settings, are selective yet intermediate barriers that limit the flux of land-derived DOM to oceanic waters.

Potential of Brass to Remove Inorganic Hg(II) from Aqueous Solution through Amalgamation.

Brass shavings (CuZn45) were tested for their efficiency to remove Hg(II) from contaminated groundwater through amalgamation. The study was focused on long-term retention efficiency, the understanding of the amalgamation process and kinetics, and influences of filter surface alteration. Column tests were performed with brass filters (thickness 3 to 9 cm) flushed with 1000 µg/L Hg solution for 8 hours under different flow rates (300 to 600 mL/h). Brass filters consistently removed >98% of Hg from solution independent of filter thickness and flow rate. In a long-term experiment (filter thickness 2 cm), Hg retention decreased from 96 to 92% within 2000 hours. Batch and column experiments for studying kinetics of Hg removal indicate ~100% Hg removal from solution within only 2 hours. Solid-phase mercury thermo-desorption analysis revealed that Hg(0) diffusion into the brass surface controls kinetics of mercury retention. Brass surface alteration could be observed, but did not influence Hg retention.

Urban sediment contamination in a former Hg mining district, Idrija, Slovenia.

Road sediments from gully pots of the drainage system and stream sediments from local streams were investigated for the first time in the urban area of Idrija town, the central part of the second largest and strongly contaminated Hg mining district in the world. Hg concentrations in road sediments were lower than in stream sediments. They ranged from 16 to 110 mg/kg (Md = 29 mg/kg) for <0.125 mm particles and from 7 to 125 mg/kg (Md = 35 mg/kg) for <0.04 mm particles, while Hg concentrations in stream sediments ranged from 10 to 610 mg/kg (Md = 95 mg/kg) for <0.125 particles and from 10 to 440 mg/kg (Md = 105 mg/kg) for <0.04 mm particles. High Hg loadings in stream sediments were successfully linked with identified mercury sources (rocks containing mercury ore, areas of former ore roasting sites, ore residue dumps), because they are located in the drainage areas of streams, from which the sediments were collected. Links between Hg loadings in road sediments and identified mercury sources were not recognized. Solid phases of Hg were determined by thermo-desorption technique and are similar for both types of sediments. Results show the occurrence of three different forms: elemental mercury, mercury bound to matrix components and cinnabar. Approximately 50 % of Hg in samples consist of non-cinnabar fractions. This is important, since they are potentially bioavailable. An interesting new discovery according to previous research of environmental media from Idrija area by solid-phase Hg thermo-desorption technique is that elemental mercury was determined in almost all investigated sediments in minor amounts (Md = 3 %).

Use and legacy of mercury in the Andes.

Both cinnabar (HgS) and metallic mercury (Hg(0)) were important resources throughout Andean prehistory. Cinnabar was used for millennia to make vermillion, a red pigment that was highly valued in pre-Hispanic Peru; metallic Hg(0) has been used since the mid-16th century to conduct mercury amalgamation, an efficient process of extracting precious metals from ores. However, little is known about which cinnabar deposits were exploited by pre-Hispanic cultures, and the environmental consequences of Hg mining and amalgamation remain enigmatic. Here we use Hg isotopes to source archeological cinnabar and to fingerprint Hg pollution preserved in lake sediment cores from Peru and the Galápagos Islands. Both pre-Inca (pre-1400 AD) and Colonial (1532-1821 AD) archeological artifacts contain cinnabar that matches isotopically with cinnabar ores from Huancavelica, Peru, the largest cinnabar-bearing district in Central and South America. In contrast, the Inca (1400-1532 AD) artifacts sampled are characterized by a unique Hg isotopic composition. In addition, preindustrial (i.e., pre-1900 AD) Hg pollution preserved in lake sediments matches closely the isotopic composition of cinnabar from the Peruvian Andes. Industrial-era Hg pollution, in contrast, is distinct isotopically from preindustrial emissions, suggesting that pre- and postindustrial Hg emissions may be distinguished isotopically in lake sediment cores.

Molecular fractionation of dissolved organic matter with metal salts.

Coagulation of dissolved organic matter (DOM) by hydrolyzing metals is an important environmental process with particular relevance, e.g., for the cycling of organic matter in metal-rich aquatic systems or the flocculation of organic matter in wastewater treatment plants. Often, a nonremovable fraction of DOM remains in solution even at low DOM/metal ratios. Because coagulation by metals results from interactions with functional groups, we hypothesize that noncoagulating fractions have a distinct molecular composition. To test the hypothesis, we analyzed peat-derived dissolved organic matter remaining in solution after mixing with salts of Ca, Al, and Fe using 15 T Electrospray Ionization Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry (ESI-FT-ICR-MS). Addition of metals resulted in a net removal of DOM. Also a reduction of molecular diversity was observed, as the number of peaks from the ESI-FT-ICR-MS spectra decreased. At DOM/metal ratios of ∼9 Ca did not show any preference for distinct molecular fractions, while Fe and Al removed preferentially the most oxidized compounds (O/C ratio >0.4) of the peat leachate. Lowering DOM/metal ratios to ∼1 resulted in further removal of less oxidized as well as more aromatic compounds ("black carbon"). Molecular composition in the residual solution after coagulation was more saturated, less polar, and less oxidized compared to the original peat leachate and exhibited a surprising similarity with DOM of marine origin. By identifying more than 9200 molecular formulas we can show that structural properties (saturation and aromaticity) and oxygen content of individual DOM molecules play an important role in coagulation with metals. We conclude that polyvalent cations not only alter the net mobility but also the very molecular composition of DOM in aquatic environments.

Over three millennia of mercury pollution in the Peruvian Andes.

We present unambiguous records of preindustrial atmospheric mercury (Hg) pollution, derived from lake-sediment cores collected near Huancavelica, Peru, the largest Hg deposit in the New World. Intensive Hg mining first began ca. 1400 BC, predating the emergence of complex Andean societies, and signifying that the region served as a locus for early Hg extraction. The earliest mining targeted cinnabar (HgS) for the production of vermillion. Pre-Colonial Hg burdens peak ca. 500 BC and ca. 1450 AD, corresponding to the heights of the Chavín and Inca states, respectively. During the Inca, Colonial, and industrial intervals, Hg pollution became regional, as evidenced by a third lake record approximately 225 km distant from Huancavelica. Measurements of sediment-Hg speciation reveal that cinnabar dust was initially the dominant Hg species deposited, and significant increases in deposition were limited to the local environment. After conquest by the Inca (ca. 1450 AD), smelting was adopted at the mine and Hg pollution became more widely circulated, with the deposition of matrix-bound phases of Hg predominating over cinnabar dust. Our results demonstrate the existence of a major Hg mining industry at Huancavelica spanning the past 3,500 years, and place recent Hg enrichment in the Andes in a broader historical context.

Biochemical and spectroscopic characterization of the human mitochondrial amidoxime reducing components hmARC-1 and hmARC-2 suggests the existence of a new molybdenum enzyme family in eukaryotes.

The mitochondrial amidoxime reducing component mARC is a newly discovered molybdenum enzyme that is presumed to form the catalytical part of a three-component enzyme system, consisting of mARC, heme/cytochrome b(5), and NADH/FAD-dependent cytochrome b(5) reductase. mARC proteins share a significant degree of homology to the molybdenum cofactor-binding domain of eukaryotic molybdenum cofactor sulfurase proteins, the latter catalyzing the post-translational activation of aldehyde oxidase and xanthine oxidoreductase. The human genome harbors two mARC genes, referred to as hmARC-1/MOSC-1 and hmARC-2/MOSC-2, which are organized in a tandem arrangement on chromosome 1. Recombinant expression of hmARC-1 and hmARC-2 proteins in Escherichia coli reveals that both proteins are monomeric in their active forms, which is in contrast to all other eukaryotic molybdenum enzymes that act as homo- or heterodimers. Both hmARC-1 and hmARC-2 catalyze the N-reduction of a variety of N-hydroxylated substrates such as N-hydroxy-cytosine, albeit with different specificities. Reconstitution of active molybdenum cofactor onto recombinant hmARC-1 and hmARC-2 proteins in the absence of sulfur indicates that mARC proteins do not belong to the xanthine oxidase family of molybdenum enzymes. Moreover, they also appear to be different from the sulfite oxidase family, because no cysteine residue could be identified as a putative ligand of the molybdenum atom. This suggests that the hmARC proteins and sulfurase represent members of a new family of molybdenum enzymes.

The role of hydrological conditions for riverine Hg species transport in the Idrija mining area.

Estimation of mercury (Hg) species fluxes in Hg contaminated rivers is crucial to predict Hg methylation in connected sediment sinks. Cinnabar (HgS) was mined and roasted for ∼500 years in the Idrija mining area, Slovenia, which is drained by the Idrijca River to the Gulf of Trieste (GT), Italy. Mining residues dumped into the Idrijca River caused high proportions of cinnabar in sediments, whereas soils containing high proportions of natural organic matter bound to Hg (NOM-Hg) are attributed to atmospheric Hg deposition. Previous calculations of Hg fluxes have been based on the erosion of cinnabar only, and neglected transport of NOM-Hg derived from soil. Here, we estimated NOM-Hg and cinnabar fluxes in the Idrijca River and evaluated the extent of variability under changing hydrological conditions. We estimated the discharge of NOM-Hg by Idrijca's tributaries and the importance of NOM-Hg fluxes for Hg methylation in the GT. Mass balance calculations reveal that approximately 11.2 Mg y-1 of NOM-Hg and 38.9 Mg y-1 of cinnabar are transported by the Idrijca River to the GT under median-flow conditions. In the past 520 years, a total of 53,000 tons of Hg have been released from the Idrija mining area, of which ∼32,000 tons were NOM-Hg. Under low-flow conditions, Idrijca's tributaries deliver more than 1280 kg y-1 of NOM-Hg. This study highlights the importance of Hg species analyses and their flux calculations to estimate risks of biological Hg uptake in sedimentary Hg sinks connected to Hg mining areas.

Mercury emission from industrially contaminated soils in relation to chemical, microbial, and meteorological factors.

The Minamata Convention entered into force in 2017 with the aim to phase-out the use of mercury (Hg) in manufacturing processes such as the chlor-alkali or vinyl chloride monomer production. However, past industrial use of Hg had already resulted in extensive soil pollution, which poses a potential environmental threat. We investigated the emission of gaseous elemental mercury (Hg0) from Hg polluted soils in settlement areas in the canton of Valais, Switzerland, and its impact on local air Hg concentrations. Most soil Hg was found as soil matrix-bound divalent Hg (HgII). Elemental mercury (Hg0) was undetectable in soils, yet we observed substantial Hg0 emission (20-1392 ng m-2 h-1) from 27 soil plots contaminated with Hg (0.2-390 mg Hg kg-1). The emissions of Hg0 were calculated for 1274 parcels covering an area of 8.6 km2 of which 12% exceeded the Swiss soil remediation threshold of 2 mg Hg kg-1. The annual Hg0 emission from this area was approximately 6 kg a-1, which is almost 1% of the total atmospheric Hg emissions in Switzerland based on emission inventory estimates. Our results show a higher abundance of Hg resistance genes (merA) in soil microbial communities with increasing soil Hg concentrations, indicating that biotic reduction of HgII is likely an important pathway to form volatile Hg0 in these soils. The total soil Hg pool in the top 20 cm of the investigated area was 4288 kg; hence, if not remediated, these contaminated soils remain a long-term source of atmospheric Hg, which is prone to long-range atmospheric transport.

Diatom ooze-A large marine mercury sink.

The role of algae for sequestration of atmospheric mercury in the ocean is largely unknown owing to a lack of marine sediment data. We used high-resolution cores from marine Antarctica to estimate Holocene global mercury accumulation in biogenic siliceous sediments (diatom ooze). Diatom ooze exhibits the highest mercury accumulation rates ever reported for the marine environment and provides a large sink of anthropogenic mercury, surpassing existing model estimates by as much as a factor of 7. Anthropogenic pollution of the Southern Ocean began ~150 years ago, and up to 20% of anthropogenic mercury emitted to the atmosphere may have been stored in diatom ooze. These findings reveal the crucial role of diatoms as a fast vector for mercury sequestration and diatom ooze as a large marine mercury sink.

Distribution of mercury species and mercury isotope ratios in soils and river suspended matter of a mercury mining area.

Mercury (Hg) released by mining activities can be dispersed in the environment, where it is subject to species transformations. Hg isotope ratios have been used to track sources in Hg contaminated areas, although it is unclear to what extent variations in δ-values are attributed to distinct Hg species. Hg was mined as Hg sulphide (cinnabar) in Idrija, Slovenia for centuries. Sediments are loaded with mining-residues (cinnabar and calcine), whereas contaminated soils mainly contain Hg bound to natural organic matter (NOM-Hg) related to atmospheric Hg deposition. Hg released from soils and sediments is transported as suspended matter (SM) in the Idrijca river to the Gulf of Trieste (GT), Italy. We determine Hg isotope ratios in river SM, sediments and soils from the Idrijca-catchment to decipher the Hg isotope ratio variability related to Hg species distribution in different grain-size fractions. δ202Hg values of SM collected from tributaries corresponded to those found in soils ranging from -2.58 to 0.19‰ and from -2.27 to -0.88‰, respectively. Speciation measurements reveal that fine fractions (0.45-20 µm) are dominated by NOM-Hg, while larger fractions contain more cinnabar. More negative δ202Hg values were related to higher proportions of NOM-Hg, which are predominant in soils and SM. Rain events increase SM-loads in the river, mainly due to resuspension of coarse grain-size fractions of bottom sediments bearing larger proportions of cinnabar, which leads to more positive δ202Hg values. The large magnitude of variation in δ202Hg and the smaller magnitude of variation in Δ199Hg (-0.37 to 0.09‰) are likely related to fractionation during ore roasting. Soil samples with high NOM-Hg content show more negative δ202Hg values and larger variation of Δ199Hg. More negative δ202Hg values in GT sediments were rather linked to distant sedimentation of soil derived NOM-Hg than to sedimentation of autochthonous marine material. Heterogeneity in the Idrija ore and ore processing likely produce large variations in the Hg isotopic composition of cinnabar and released metallic Hg, which complicate the differentiation of Hg sources. Combining Hg isotope measurements with solid phase Hg speciation reveals that Hg isotope ratios rather indicate different Hg species and are not necessarily symptomatic for Hg pollution sources.

Binding of mercury in soils and attic dust in the Idrija mercury mine area (Slovenia).

Total Hg concentrations and Hg speciation were determined in soils and attic dust in a 160 km2 area around Idrija mercury mine. Attic dust as well as a sample of soil was collected at 100 locations. Mercury phases were separated into cinnabar and non-cinnabar compounds via a thermo-desorption technique. The amount of the non-cinnabar fraction is important since it is potentially bioavailable and results are needed for further risk assessment studies. The concentrations of Hg in attic dust are many times higher than in surrounding soils and the attic dust/soil ratio changes with distance. The highest concentration ratios were identified at the greatest distance from the source of pollution and the lowest close to the source of pollution. This confirms the impact of air emissions on the wider area around Idrija. Furthermore the spatial mercury distribution in the attic dust shows that the influence of atmospheric emissions caused by the Idrija smelter resulted in impacts on the environment on a regional scale. The portions of non-cinnabar compounds increase with distance from the mercury source in both sampling media. Non-cinnabar fractions were found to be enriched in distant areas where fine grained material was deposited. There were two different transport mechanisms of dust particles and gaseous Hg(0) during the mercury production period. Obviously coarse grained particles, with mostly cinnabar-bound Hg settled in the immediate vicinity of the smokestack of the smelter, whereas the fine grained fraction could be dispersed further ahead. This is represented by the percentage of cinnabar-bound Hg in attic dust and soil decreasing with distance from the smelter. Gaseous Hg(0) is probably bound to fine and ultrafine aerosols with longer residence time against deposition. The consequence is that fine grained material with Hg2+ and Hg0 prevails in remote localities and is bound in soils and dust with matrix and organic matter as non-cinnabar mercury compounds. The distributions of mercury species in attic dust and soils along the Idrijca River show that in the region from Idrija to Spodnja Idrija the portions of cinnabar and non-cinnabar are about equal, while in the upper and in the lower Idrijca valley non-cinnabar bound mercury prevails. The applicability of attic dust for tracing the mercury halo in the Idrija area was successfully shown.

Mercury removal from contaminated groundwater: Performance and limitations of amalgamation through brass shavings.

Brass shavings have been proposed as a cost-effective filter material to remove Hg from contaminated groundwater. This method, which is based on the reduction of reactive Hg(II) and subsequent formation of amalgams, has been shown to be fast and effective in the short term. However, the effectiveness of brass filters and their stability over the long term, especially if used in passive filter systems such as permeable reactive barriers (PRB) under high flow conditions, is unknown. To evaluate the performance and limitations of brass shavings for Hg removal from contaminated groundwater, we performed long-term pilot scale filtration tests (6 and 28 months) at two former wood impregnation sites with severe groundwater contamination (up to 870 µg L(-1) Hg). The results showed that even under high flow conditions (>60 m d(-1)), 60-80% of the Hg was removed in the first 8 mm of the brass shavings filter bed. The kinetics of filtration, Hg total removal performance (>99.95%), and loading capacity (164 g L(-1)) surpassed those of a Hg-specific synthetic resin (LEWATIT(®)MonoPlus TP-214). However, under natural pH conditions (pH 6.4 and 6.7), Zn was leached from the brass and exceeded the threshold value (0.5 mg L(-1)) in the filter outflow by up to a factor of 40. Increasing pH (>8.5) decreased the Zn concentration (<0.05 mg L(-1)) but affected Hg removal due to the formation of Zn-hydroxide/carbonate coatings on the brass (up to 15% performance reduction). Thus, the use of brass shavings as an exclusive filter material in PRBs is restricted to aquifers with high pH. However, brass is ideal as a low-cost, thin-bed prefilter in onsite systems to remove the main Hg load from groundwater when Zn release is managed.

Solar Output Controls Periodicity in Lake Productivity and Wetness at Southernmost South America.

Cyclic changes in total solar irradiance (TSI) during the Holocene are known to affect global climatic conditions and cause cyclic climatic oscillations, e.g., Bond events and related changes of environmental conditions. However, the processes how changes in TSI affect climate and environment of the Southern Hemisphere, especially in southernmost South America, a key area for the global climate, are still poorly resolved. Here we show that highly sensitive proxies for aquatic productivity derived from sediments of a lake near the Chilean South Atlantic coast (53 °S) strongly match the cyclic changes in TSI throughout the Holocene. Intra-lake productivity variations show a periodicity of ~200-240 years coherent with the time series of TSI-controlled cosmogenic nuclide 10Be production. In addition TSI dependent periodicity of Bond events (~1500 years) appear to control wetness at the LH site indicated by mineral matter erosion from the catchment to the lake assumingly through shifts of the position of the southern westerly wind belt. Thus, both intra-lake productivity and wetness at the southernmost South America are directly or indirectly controlled by TSI.