Article pubs.acs.org/est
Thallium Speciation and Extractability in a Thallium- and ArsenicRich Soil Developed from Mineralized Carbonate Rock Andreas Voegelin,*,† Numa Pfenninger,† Julia Petrikis,‡ Juraj Majzlan,‡ Michael Plötze,§ Anna-Caterina Senn,† Stefan Mangold,∥ Ralph Steininger,∥ and Jörg Göttlicher∥ †
Eawag, Swiss Federal Institute of Aquatic Science and Technology, Ueberlandstrasse 133, CH-8600 Duebendorf, Switzerland Friedrich-Schiller-University Jena, Institute of Geosciences, Mineralogy, Burgweg 11, D-07749 Jena, Germany § ETH Zurich, Institute for Geotechnical Engineering, CH-8093 Zurich, Switzerland ∥ Karlsruhe Institute of Technology, ANKA Synchrotron Radiation Facility, 76344 Eggenstein-Leopoldshafen, Germany ‡
S Supporting Information *
ABSTRACT: We investigated the speciation and extractability of Tl in soil developed from mineralized carbonate rock. Total Tl concentrations in topsoil (0−20 cm) of 100−1000 mg/kg are observed in the most affected area, subsoil concentrations of up to 6000 mg/kg Tl in soil horizons containing weathered ore fragments. Using synchrotron-based microfocused X-ray fluorescence spectrometry (μ-XRF) and X-ray absorption spectroscopy (μ-XAS) at the Tl L3-edge, partly Tl(I)substituted jarosite and avicennite (Tl2O3) were identified as Tl-bearing secondary minerals formed by the weathering of a Tl−As−Fe-sulfide mineralization hosted in the carbonate rock from which the soil developed. Further evidence was found for the sequestration of Tl(III) into Mn-oxides and the uptake of Tl(I) by illite. Quantification of the fractions of Tl(III), Tl(I)jarosite and Tl(I)-illite in bulk samples based on XAS indicated that Tl(I) uptake by illite was the dominant retention mechanism in topsoil materials. Oxidative Tl(III)uptake into Mn-oxides was less relevant, probably because the Tl loadings of the soil exceeded the capacity of this uptake mechanism. The concentrations of Tl in 10 mM CaCl2-extracts increased with increasing soil Tl contents and decreasing soil pH, but did not exhibit drastic variations as a function of Tl speciation. With respect to Tl in contaminated soils, this study provides first direct spectroscopic evidence for Tl(I) uptake by illite and indicates the need for further studies on the sorption of Tl to clay minerals and Mn-oxides and its impact on Tl solubility in soils.
■
kg.1 For 840 topsoils from across Europe, a median Tl concentration of 0.66 mg/kg has been determined.7 Elevated geogenic concentrations may be found in soils developed from K-rich rocks or rocks hosting metal sulfide mineralizations.7−9 Rarely, Tl occurs in Tl-rich metal-sulfide deposits, for example in Alsar, Macedonia, or Lanmuchang, China, and soils in such areas may contain up to several 1000 mg/kg of Tl.10,11 Anthropogenic Tl contamination of soils and water resources mainly results from nonferrous and ferrous metal mining,12,13 coal combustion,14 and cement production,15 with an estimated total annual release of 2000−5000 t of Tl.16,17 These Tl emissions largely exceed the current annual use of ∼15 t of Tl, which however may increase with new applications of Tl in different fields, as for example high-temperature superconductors.18
INTRODUCTION Thallium (Tl) is a highly toxic element classified as priority pollutant by the U.S. Environmental Protection Agency. In the environment, Tl typically occurs in the oxidation states Tl(I) and Tl(III).1 Tl(I) exhibits both chalcophile and lithophile character: Small amounts of Tl(I) are often found in metal sulfides, and Tl+ readily substitutes K+ in minerals such as K-feldspars or micas due to its similar ionic radius.1 Tl(I) is relatively soluble, mobile and bioavailable, similar to alkali metal cations. In aquatic environments at low Tl concentrations, Tl(I) tends to dominate over Tl(III), mostly in the form of hydrated Tl+ due to limited complexation.2 However, photochemically driven reactions in sunlit surface waters3 or microbiological processes4 may lead to Tl(I) oxidation, and Tl(III) may be stabilized by hydrolysis and colloid formation5 or sorption to Fe(III)-colloids.3 In contact with certain Mn(IV)-oxides, Tl(I) can be oxidized to Tl(III) and stabilized by incorporation into the Mn(IV)-oxide.6 Owing to its versatile biogeochemical behavior, Tl occurs ubiquitously in the environment, but typically at very low concentrations, with an average crustal abundance of ∼0.8 mg/ © XXXX American Chemical Society
Received: February 4, 2015 Revised: March 30, 2015 Accepted: April 1, 2015
A
DOI: 10.1021/acs.est.5b00629 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Article
Environmental Science & Technology
days. For chemical extractions and bulk speciation analyses, the (mostly clayey) samples were manually disintegrated and ground using a planetary ball mill with corundum jars (Retsch, Germany) or a mixer mill with ZrO2 jars (Retsch). For spatially resolved speciation analyses, undisturbed samples were embedded in epoxy resin and prepared as polished thin-sections on glass slides (Geoprep, Switzerland). Bulk Soil Analyses. To determine the elemental composition of bulk samples, 4 g powdered material was mixed with 0.9 g wax and pressed into a 32 mm diameter pellet for energydispersive X-ray fluorescence spectrometry (XRF; Xepos+, SPECTRO Analytical Instruments GmbH, Germany). Selected samples were digested (100−150 mg material in 2 mL HNO3, 3 mL HF, 3 mL HClO4 at 180 °C for 12 h in pressure digestion system (DAS, PicoTrace, Germany); evaporation at 180 °C for 14 h; redissolution in 2 mL HNO3, 0.6 mL HCl and 7 mL water at 150 °C for 8 h) and the digests diluted and analyzed by inductively coupled plasma mass spectrometry (ICP-MS; Varian 725 ES) and optical emission spectrometry (ICP-OES; Thermo XSeriesII). To determine oxalate-extractable element contents, powdered samples were extracted with 0.2 M NH4-oxalate adjusted to pH 3.25 (250 mg in 50 mL; 4 h reaction time; in the dark). The extracts were filtered, acidified with 0.65% HNO3 (0.14 M) and analyzed by ICP-MS (Agilent 7500ce, Agilent Technologies). Exchangeable Tl and major cations (Ca, Mg, K) were determined by extracting 2.5 g of soil material twice with 25 mL of 1 M NH4-acetate (adjusted to pH 7.0) for 30 min and analyzing the centrifuged, pooled, filtered, and acidified supernatant with ICP-MS. For the determination of soil pH and pseudo pore-water concentrations of Tl and K, 4 g of powdered soil material was suspended in 10 mL of a dilute 10 mM CaCl2 solution and equilibrated for 16 h. An aliquot was centrifuged (5 min at 4000 rpm) and the supernatant filtered (0.2 μm; nylon) and analyzed for Tl and K by ICP-MS, the remaining suspension was used to measure soil pH with a glass electrode. The bulk and clay mineralogy of selected soil samples was characterized by Xray diffraction (XRD). The XRD data were qualitatively evaluated by pattern matching and quantified by Rietveld refinement as described in the SI (section S3, Table S6). Synchrotron-Based Analyses. Tl L3-edge X-ray absorption spectra of the majority of the bulk samples and reference materials were recorded at the XAS beamline at the Angströmquelle Karlsruhe (ANKA, Eggenstein-Leopoldshafen, Germany). The measurements were performed at room temperature using ionization chambers to record the incident and transmitted beam intensity and a five-element solid-state Ge detector to record the fluorescence signal. A Si(111) double crystal monochromator (DCM) was used for monochromatization. The photon energy of the first maximum of the Tl L3-edge absorption spectrum of Tl 2 O 3 was set to 12 688 eV (corresponding to 12 658 eV for the first inflection point in the K-edge of gray Se(0)). Powdered soil samples were mixed with ∼20 mg of cellulose to a total mass of ∼200−250 mg and pressed into 13 mm diameter pellets. Concentrated soil samples and reference materials were diluted with cellulose to obtain an absorption edge step near unity. Thin-sections were analyzed by microfocused X-ray fluorescence spectrometry (μ-XRF) and X-ray absorption spectroscopy (μ-XAS) at the SUL-X beamline at ANKA. The X-ray beam was monochromatized with a Si(111) fixed-exit DCM and focused with a Kirkpatrick Baez mirror system. The incident and transmitted photon flux were measured with ionization chambers, and the fluorescence signal with a seven-element
Based on the ability of Tl to substitute for K in illite and the accumulation of Tl in certain Mn-oxides, it is commonly assumed that Tl(I) uptake by illite-type clay minerals and (oxidative) Tl scavenging by certain types of Mn oxides represent key Tl sorption mechanisms in pristine and contaminated soils.8,19 This assumption is supported by macroscopic observations such as correlations between the clay and Tl contents of soils,8 enrichment of Tl in the residual fraction of sequential extractions,9 or reduced Tl availability in Mn-oxide-amended soils.20 In addition, less specific cation exchange reactions on soil organic matter or clay minerals may contribute to the retention of Tl(I).13 Avicennite (Tl2O3)21 and dorallcharite (Tl(I)jarosite)22 have been identified as Tl-bearing secondary minerals near Tl-rich metal sulfide deposits and could also occur in mining-impacted soils. Knowledge on the forms of Tl in pristine and contaminated soils is essential for an improved understanding of the solubility, mobility and bioavailability of Tl in soils.23,24 To date, however, molecular-level studies on the speciation of Tl in soils are lacking. In the Swiss Jura Mountains, a site named Erzmatt (“ore meadow”) has been recognized for its high Fe contents and low fertility since Medieval times. More than 90 years ago, it was shown that the soils at this site contain exceptionally high levels of As that were attributed to soil formation from (hydrothermally) mineralized carbonate rock.25 In early 2013, local authorities found that the soils also contain extremely high levels of several 100 to several 1000 mg/kg Tl. These Tl levels by far exceed typical soil Tl contents of 60 cm depth. Trends in profile P2 fell between those in P1 and P3 (Figure 1). In all profiles, trace elements other than Tl and As in general did not markedly exceed typical background contents, except Zn which occurred at slightly elevated concentrations (SI Table S1). Soil Physicochemical Parameters. The topsoil samples (0−20 cm) from profiles P1 and P3 had a silty clay texture and contained 2.6% and 4.1% total organic carbon, respectively (TOC and clay fraction of selected samples are reported in SI Tables S2 and S6, respectively). The topsoil mineralogy was dominated by quartz, K-feldspar, minor amounts of Naplagioclase, anatase, and goethite, and the phyllosilicates illite +muscovite, interstratified illite/smectite, chlorite+hydroxyinterlayered vermiculite, and kaolinite (details in SI Table S6). Elevated goethite fractions and minor amounts of jarosite were observed in soil horizons whose elevated Tl and As contents suggested formation from ore-hosting parent material. On average, 11% ± 5% of the total Fe, and 73% ± 25% of the total Mn were oxalate-extractable, with trends toward higher extractable fractions in topsoils and lower fractions in horizons presumably formed from ore-hosting parent materials (all oxalate-extraction data in SI Table S3). Microfocused X-ray Analyses on Soil Thin Sections. Ten thin-sections from seven samples were screened using laboratory μ-XRF and two sections (SI Figure S3, Figure S4) selected for analysis by synchrotron-based μ-XRF and μ-XAS: (i)
One section of soil and weathered ore fragments from 60 cm depth in profile P1 and (ii) one section of soil from 50 cm depth from profile P3. Element distribution maps for Tl, Fe and Mn for three areas are shown in Figure 2, the Tl L3-edge μ-XANES spectra of four POI on these areas in Figure 3b. The first area revealed a ∼1 × 1 mm2-sized mineral grain rich in Fe, Tl, and As in the weathered ore material (Figure. 2a; POI 1; molar Tl:K:Fe:As ratio of 0.14:0.80:3:0.13 based on semiquantitative laboratory μ-XRF). The XANES spectrum of POI 1 perfectly matched the spectrum of Tl(I)-jarosite (Figure 3b), and the same was true for its EXAFS spectrum (SI Figure S7). In addition, Fe and As K-edge EXAFS spectra of POI 1 matched the Fe and As spectra of As-substituted jarosite (shown for Fe in SI Figure S10). POI 1 thus represented partly Tl(I)- and As(V)substituted jarosite. In the soil sample from profile P3, we identified a ∼1 mm-long needle-shaped particle with very high Tl content but no detectable As, Fe or Mn (Figure 2b. POI 2). The μ-XANES (Figure 3b) spectrum of POI 2 (as well as its μ-EXAFS spectrum; SI Figure S7) matched the spectrum of avicennite (Tl2O3) (after correcting the transmission spectrum of POI 2 for amplitude dampening by pinhole effects), in line with μ-XRD data collected on POI 2 that matched the pattern of avicennite (SI Figure S9). The avicennite needle was surrounded by a thin layer of Mn(III/ IV)-oxide (based on Mn K-edge μ-XAS; not shown) which probably formed via the oxidation of dissolved Mn2+ by Tl3+ released from the Tl2O3. In all studied sections, elevated levels of Tl were consistently associated with Mn-concretions in the soil matrix, as exemplified for one area on the sample from profile P1 (Figure 2c, POI 3). The μ-XANES (Figure 3b) and μ-EXAFS (SI Figure S7) spectra of POI 3 resembled the spectrum of Tl(III)-Hx-birn representing E
DOI: 10.1021/acs.est.5b00629 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Article
Environmental Science & Technology
Figure 4. Tl L3-edge XANES LCF results for bulk samples in (a) mg/kg Tl and (b) Tl fractions. Complete LCF results are listed in SI Table S7, the reconstructed LCF spectra are shown in Figure 3 (P1) and SI Figure S6 (P2, P3). Chemical data and sample descriptions are provided in Table 1 and SI Table S3.
Tl that has been oxidatively scavenged by hexagonal birnessite.6 Comparison of the Fourier-transformed EXAFS spectra of POI 3 and Tl(III)-Hx-birn revealed differences that may point to variations in the mode of Tl uptake by the Mn-concretion and synthetic hexagonal birnessite, possibly related to differences in Tl loading or Mn-oxide structure or to the presence of minor fractions of Tl(I) (SI Figure S9). Throughout the clayey soil matrix, synchrotron μ-XRF indicated the presence of Tl at low concentrations (not visible in Figure 2). The μ-XANES spectrum of POI 4 which represents this background Tl closely matched the spectrum of Tl(I)-illite (Figure 3b). The spectrum of Tl(I)-illite is distinctly different from the spectrum of Tl(I)-smectite (SI Figure S5), suggesting that most Tl(I) was indeed bound specifically to illite-type clay minerals, as expected based on the similar ionic radius of Tl+ and K+ and the well-known potassium-like behavior of Tl(I). Speciation of Tl in Bulk Soil Samples by XAS. The speciation of Tl in 19 bulk samples listed in Table 1 was investigated by XAS. The selection included samples from individual soil horizons (depth intervals), subsamples characterized by marked differences in color and texture, and weathered ore fragments associated with soil matrix. The XANES reference spectra corresponding to the four Tl species identified in thinsections (Figure 3ab) were found suitable for LCF analysis of the spectra of the bulk samples. Preliminary analyses, however, indicated that a fifth spectral component was required to accurately reproduce all sample spectra, especially spectra of samples with high Tl contents and high fractions of Tl(III). This spectral component most probably resulted from overabsorption within Tl2O3 (or another unknown Tl-rich Tl(III)-phase) in grains with diameters of a few tens of μm. We therefore included a second spectrum of Tl2O3 in the LCF analysis derived from the
measured spectrum by simulating overabsorption equivalent to an EXAFS amplitude reduction of 30% (SI Figure S5). Starting with the best 1-component fit based on these 5 reference spectra, the number of references in the LCF was increased as long as the normalized sum of squared residuals (NSSR = ∑(datai − fiti)2/ ∑(datai)2) of the best LCF decreased by at least 30%. This criterion was set to avoid spurious inclusion of references that did not visually improve the fits, taking the quality of the sample spectra and the spectral characteristics of the reference spectra into account. The LCF-derived fractions are displayed in Figure 4 (complete LCF results in SI Table S7). The reconstructed LCF spectra for samples from profile P1 are shown in Figure 3c (for profiles P2 and P3 in SI Figure S6). Due to the similarities in the XANES of Tl2O3 and Tl(III)-Hx-birn, potential overabsorption effects, and/or presence of another Tl(III) species, differentiation between Tl2O3 and Tl(III)-Hx-birn in bulk samples by LCF was uncertain, and mainly the sum of the two fractions was further interpreted as a measure of the fraction of Tl(III) in the samples. Owing to their distinct spectra (Figure 3a; SI Figure S5), identification of Tl(I)-illite and Tl(I)-jarosite in samples dominated by Tl(I) were considered reliable. The LCF results indicated high fractions of Tl(III) and Tl(I)jarosite in soil samples and weathered ore fragments with markedly elevated Tl contents (Figure 4). For the samples P1 60 Ore Y and P1 140−160 R, also the EXAFS spectra were evaluated by LCF analysis (SI Figure S7; Table S8). Both Tl2O3 and Tl(III)-Hx-birn were needed to describe the Tl(III)-component in the EXAFS spectrum of P1 140−160 R. Because sample P1 140−160 R has a high molar Tl/Mn ratio of 2.3 (Table 1), however, the fraction of Tl(III)-Hx-birn returned by LCF (0.38) was unrealistically high. This discrepancy most probably F
DOI: 10.1021/acs.est.5b00629 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Article
Environmental Science & Technology
Figure 5. (a) Oxalate-extractable Tl fractions as a function of Tl(III)-fractions derived from Tl L3-edge XANES LCF analysis. (b) Log value of the concentration of Tl in 10 mM CaCl2 extracts calculated from linear regression (eq 1) versus measured. In panel a, data are grouped according to total Tl content. In panel a, thin dashed 1:1 line is shown to guide the eye. In panel b, data are grouped according to LCF-derived Tl(I)-illite fractions, the thick solid lines indicates the 1:1 line, and the thin solid lines the uncertainty of the calculated values (±0.22, eq 1). The outlier sample PIII 60 Y (with 65% Tlillite; orange dot) was excluded from the linear regression.
Mn ratios (0.03, 0.11, and 0.25 for P1, P2, and P3, respectively). Even the lowest Tl level in the topsoil of profile P1 (119 mg/kg Tl) was 10−100 times higher than frequently reported Tl contents in contaminated soils (few to few tens of mg/kg) and the Tl/Mn ratio of 0.03 would correspond to at least 70 000 mg/ kg Tl associated with MnO2 and may thus exceed the capacity of birnessite for oxidative Tl sequestration. Tl uptake by Mn-oxides, however, may be more relevant in contaminated soils with lower contents of Tl than studied here. For example, chemical fractionation data for Tl in smelter-impacted soils from Silesia (Poland) with Tl contents of 0.2−30 mg/kg suggest that Tl uptake by Mn oxides may account for a significant fraction (16− 47%) of total Tl.13 Furthermore, in a study with two soils spiked with 5 mg/kg Tl(I), addition of 0.5% w/w K-birnessite, corresponding to a Tl loading of the birnessite of ∼1000 mg/ kg in case of complete Tl sequestration, was found to effectively reduce the exchangeable Tl fraction and Tl uptake by Sinapis alba, whereas addition of illite (1.5% w/w) had only limited effects.20 Considering that the topsoil samples contained 2.6−4.1% organic carbon (SI Table S2) and that the soils exhibited high contents of oxalate-extractable Fe (as an estimate for amorphous and poorly crystalline Fe(III)-(hydr)oxides), it is worthwhile noting that our μ-XRF and spectroscopic data did not point to significant fractions of Tl associated with organic carbon or Fe(III)-minerals (apart from Tl(I)-jarosite), in line with the reported low affinity of Tl(I) for sorption to ferrihydrite2,19 and humic acids.36 Also the large variations in carbonate content from the topsoils to the subsoils (as reflected in the Ca data in Table 1) did not detectably affect Tl speciation, suggesting that interactions of Tl with carbonate minerals were negligible. Extractability of Tl in Relation to Tl Speciation. In a subset of the soil samples studied by XAS, the extractability of Tl and other elements was determined in 0.2 M NH4-oxalate (pH 3.25), 1 M NH4-acetate (pH 7.0) and 10 mM CaCl2 (results for Tl in Table 1, complete results in SI Tables S3−S5). Acid oxalate extraction is commonly assumed to target poorly crystalline Fe and Mn phases (and associated elements). We found that the fractions of oxalate-extractable Tl increased with the LCFderived Tl(III)-fraction (Figure 5a). Whereas only ∼10% of total Tl was oxalate-extractable in samples without Tl(III) where Tl(I)-illite was the dominant Tl-phase, probably due to cation
indicates the presence of a yet unidentified Tl(III) species in this sample. The spectra of the topsoil samples (and major fractions in several subsoil samples) were perfectly reproduced by the Tl(I)illite reference, indicating that Tl was dominantly sequestered by illite. The spectrum of topsoil from profile P1 spiked with an additional 1000 mg/kg Tl (P1 00−30 +1000) also closely matched the Tl(I)-illite reference, showing that illite-type clay minerals could still sequester additional Tl. Source of Tl in Erzmatt Soil and Sequestration by Secondary Tl-Bearing Minerals. The exclusive contamination with very high levels of Tl and As and the high Fe contents in the Erzmatt soil suggest that Tl and As originated from a Tl−As−Fesulfide mineralization resembling Tl- and As-rich metal sulfide mineralizations reported for Alsar (Macedonia),10 Jas Roux (France),32 Lanmuchang (China),11 or Lengenbach (Switzerland),33,34 and in line with the hydrothermal origin of As proposed by Truninger.25 Excluding the two deepest samples from profile P3, the remaining samples had an average molar Tl/ As ratio of 0.13 ± 0.02 (SI Table S1, n = 14), which may reflect the average Tl/As ratio in the original deposit. Tl(I)- and As(V)substituted jarosite and avicennite identified in thin sections and bulk samples (and goethite observed by XRD) were interpreted as secondary Tl-bearing minerals formed by the weathering of Tl−As−Fe-sulfide minerals. Formation of Tl(I)-jarosite is well documented in hydrometallurgy, and nearly ideal solid solutions between K- and Tl(I)-jarosite can be synthesized.35 Dorallcharite, the Tl(I)-endmember, has been described as an early weathering product of a Tl-sulfide and Tl−As-sulfosalts,22 and avicennite has been shown to form from carlinite (Tl2S) in the oxidation zone of Tl-rich metal sulfide deposits.21 Pedogenic Tl Species. Both Tl(III) associated with Mnoxides and Tl(I) associated with illite were identified as pedogenic Tl species that can also be expected to form in soils receiving inputs of Tl released from other sources than weathering of Tl-bearing sulfide minerals (e.g., emissions from cement plants15 or acid mine drainage2). Importantly, the XAS results showed that Tl uptake by illite dominated over Tl sequestration by Mn-oxides in the topsoil samples. Although oxalate-extractable Mn fractions of the topsoils indicated that most Mn was contained in Mn-oxides (SI Table S3), Tl uptake by Mn-oxides may have been limited by the high total molar Tl/ G
DOI: 10.1021/acs.est.5b00629 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Article
Environmental Science & Technology
Environmental Implications. This study provided first spectroscopic insight into the speciation of Tl in a geogenically Tl-rich soil that may serve as a natural analogue for heavily Tlcontaminated soils. The results show that Tl(I)-substituted jarosite and Tl2O3 are important secondary host phases for Tl in soils contaminated with Tl(I)-bearing metal sulfides. Tl(I) sorbed to illite and Tl(III) bound to Mn-oxides represent pedogenic Tl species that may also be found in soils contaminated from other sources as for example cement plants. A more detailed quantitative and mechanistic understanding of Tl sorption to clay minerals and Mn oxides is therefore essential for the assessment of the mobility and bioavailability of Tl in soils.
exchange of Tl+ by NH4+ and protons, ∼75% oxalate-extractable Tl was estimated by extrapolation of the data in Figure 5a to 100% Tl(III). The effective extraction of Tl(III) by oxalate may be due to Tl(III) complexation with oxalate in the TlC2O4+ complex followed by its redox transformation into Tl+ and 2CO2,37 combined with limited readsorption of the released Tl(I) in the presence of 0.2 M NH4+. The fractions of NH4-acetate-extractable Tl revealed no clear trends with soil depth or between profiles (Table 1, Figure 4). On average, 4.9% ± 2.4% of the total Tl and 0.6% ± 0.2% of the total K (n = 14) in the soil samples were NH4-acetate-extractable (results for individual soils in SI Table S4). The almost 10-times lower fractions of NH4-acetate-extractable K than Tl may reflect the partial association of K with rock-forming minerals and predominant uptake of Tl in illite and illite/smectite. Only 5.2% ± 1.7% of the total Tl was NH4-acetate-extractable from the six samples with LCF-derived Tl(I)-illite fractions >80% (P1 00−20, P1 20−40, P2 00−20, P2 60−80, P2, 95−115, P3 00−20). We assume that Tl+ fixed in the interlayer and Tl+ bound to frayed edge sites of illite exhibit similar coordination geometries and hence similar XAS spectra. Hence, low NH4acetate-extractable Tl fractions in combination with high LCFderived Tl(I)-illite fractions most probably indicate that a substantial fraction of the total Tl in these samples was fixed in the interlayers of illite and illite/smectite. Considering that illite accounts for 10−20% of the topsoil mass (based on XRD results for samples P1 00−20 and P3 00− 20; SI Table S6), its Tl loading in samples with ∼1000 mg/kg Tl that are dominated by Tl(I)-illite (e.g., P1 00−30 +1000, P3 00− 20; Figure 4) reached at least ∼5000 mg/kg or 25 mmol/kg. This Tl loading clearly exceeds the concentration of high-affinity frayed edge sites on illite (∼0.5 mmol/kg30), again suggesting that a significant fraction of the Tl associated with illite was fixed in the interlayer space. Similar fractions of the total Tl (0.05% ± 0.07%) and K (0.06% ± 0.02%) were mobilized in the dilute 10 mM CaCl2-extract (Table 1 for Tl, SI Table S5 for K). Combined with the much higher fractions of NH4-acetate-extractable Tl than K, the CaCl2extraction results suggested that exchangeable Tl was more strongly bound than exchangeable K, similar to the higher affinity of Cs than K for sorption to illite.30 The log-transformed concentration of Tl in the CaCl2-extracts (TlCaCl2), which serve as a proxy for the concentrations of Tl in soil pore water, correlated with the log-transformed total soil Tl contents (Tltot) and extract (“soil”) pH:
■
ASSOCIATED CONTENT
S Supporting Information *
Distribution maps for topsoil Tl and As on the Erzmatt, soil profile pictures, acid-extractable element contents in profile samples, total element contents in samples studied by extractions, NH4-oxalate-, NH4-acetate- and CaCl2-extractable element contents, X-ray diffraction results, Tl L3-edge XANES and EXAFS LCF results, and Tl L3-edge XANES and EXAFS spectra of reference materials and selected soil samples, microXRD pattern of avicennite in thin section. This material is available free of charge via the Internet at http://pubs.acs.org.
■
AUTHOR INFORMATION
Corresponding Author
*Phone: +41 58 765 54 70; fax: +41 58 765 52 10; e-mail:
[email protected]. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS We kindly thank Daniel Schmutz, Ivan Fankhauser, and Céline Girod (Amt für Umweltschutz und Energie, Kanton BaselLandschaft, Switzerland) for offering access to soil profiles and for sharing data on acid-extractable Tl and As in topsoils and acid-extractable element contents and pH in soil profiles, local farmers for access to the Erzmatt, Suzanne Beauchemin (Natural Resources Canada) and Caroline Peacock (University of Leeds, UK) for Tl L3-edge XANES reference spectra of Tl(I)-jarosite and Tl(III)-HX-birnessite, respectively, Atsushi Kyono (University of Tsukuba, Japan) for synthetic Tl-feldspar, Stefan Graeser (University of Basel, Switzerland) for a lorandite specimen, Scott Johnston (Southern Cross University, Australia) for EXAFS spectra of Fe and As in K-jarosite, Ruben Kretzschmar (ETH Zurich, Switzerland) for access to laboratory μ-XRF, Ralf Kaegi (Eawag) for help with sample collection, Irene Brunner and laboratory technician apprentices (Eawag) for support in the laboratory, and Bas Vriens (Eawag) and Miguel Gomez (National Museum of Natural Sciences, Madrid, Spain) for help during XAS measurements. The Angströmquelle Karlsruhe (ANKA, Germany) is acknowledged for the allocation of synchrotron beamtime. Five anonymous reviewers are thanked for their constructive comments that helped to improve the clarity of the manuscript.
log(Tl CaCl 2/(μg/L))( ±0.22) = 0.52( ±0.71) + 1.16(± 0.13)log(Tl tot/(mg/kg)) − 0.29(± 0.08)pH 2
r = 0.91 (1)
Over about 2 orders of magnitude in dissolved and total soil Tl, dissolved Tl concentrations calculated with eq 1 relatively closely matched experimental values (Figure 5b), except for one sample (PII 60 Y with 65% Tl(I)-illite) that was excluded from the regression. Deviations between calculated and measured values seemed not to depend on the LCF-derived Tl(I)-illite fraction (Figure 5b). The nearly linear dependence of log-transformed dissolved Tl on log-transformed total soil Tl (1.16 ± 0.13) and the relatively weak pH-dependence (−0.29 ± 0.08) pointed to cation exchange reactions on clay minerals as dominant process controlling dissolved Tl in most samples.
■
REFERENCES
(1) Thallium in the Environment; Nriagu, J. O., Ed.; John Wiley & Sons: New York, 1998. (2) Casiot, C.; Egal, M.; Bruneel, O.; Verma, N.; Parmentier, M.; ElbazPoulichet, F. Predominance of aqueous Tl(I) species in the river system H
DOI: 10.1021/acs.est.5b00629 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Article
Environmental Science & Technology
phytoavailability of thallium - A synthetic soil experiment. J. Hazard. Mater. 2013, 250−251, 265−271. (25) Truninger, E. Arsen als natürliches Bodengift in einem schweizerischen KulturbodenDer Boden der Erzmatt bei Buus (Baselland). Landwirtsch. Jahrb. Schweiz 1922, 36, 1015−1030. (26) Ravel, B.; Newville, M. ATHENA, ARTEMIS, HEPHAESTUS: Data analysis for X-ray absorption spectroscopy using IFEFFIT. J. Synchrotron Radiat. 2005, 12, 537−541. (27) Marcus, M. A.; Macdowell, A. A.; Celestre, R. S.; Manceau, A.; Miller, T.; Padmore, H. A.; Sublett, R. E. Beamline 10.3.2 at ALS: A hard X-ray microprobe for environmental and materials sciences. J. Synchrotron Radiat. 2004, 11, 239−247. (28) Dutrizac, J. E.; Chen, T. T.; Beauchemin, S. The behaviour of thallium(III) during jarosite precipitation. Hydrometallurgy 2005, 79, 138−153. (29) Costanzo, P. M. Baseline studies of the Clay Minerals Society source clays: Introduction. Clays Clay Miner. 2001, 49 (5), 372−373. (30) Poinssot, C.; Baeyens, B.; Bradbury, M. H. Experimental and modelling studies of caesium sorption on illite. Geochim. Cosmochim. Acta 1999, 63 (19/20), 3217−3227. (31) Kyono, A.; Kimata, M. The crystal structure of synthetic TlAlSi3O8: Influence of the inert-pair effect of thallium on the feldspar structure. Eur. J. Mineral. 2001, 13, 849−856. (32) Johan, Z.; Mantienne, J. Thallium-rich mineralization at Jas Roux, Hautes-Alpes, France: A complex epithermal sediment-hosted, oreforming system. J. Czech Geol. Soc. 2000, 45 (1−2), 63−77. (33) Graeser, S. Ein Vorkommen von Lorandit (TlAsS2) in der Schweiz. Contrib. Mineral. Petrol. 1967, 16, 45−50. (34) Hettmann, K.; Kreissig, K.; Rehkämper, M.; Wenzel, T.; MertzKraus, R.; Markl, G. Thallium geochemistry in the metamorphic Lengenbach sulfide depost, Switzerland: Thallium-isotope fractionation in a sulfide melt. Am. Mineral. 2014, 99, 793−803. (35) Dutrizac, J. The behavior of thallium during jarosite precipitation. Metall. Mater. Trans. B 1997, 28B, 765−776. (36) Liu, J.; Lippold, H.; Wang, J.; Lippmann-Pipke, J.; Chen, Y. Sorption of thallium(I) onto geological materials: Influence of pH and humic matter. Chemosphere 2011, 82, 866−871. (37) Mønsted, L. B.; Mønsted, O.; Nord, G. Reaction kinetic and equilibrium studies of the oxidation of oxalic acid by thallium(III) in aqueous perchlorate solutions. Trans. Faraday Soc. 1970, 66, 936−942. (38) Manceau, A.; Marcus, M. A.; Tamura, N., Quantitative speciation of heavy metals in soils and sediments by synchrotron X-ray techniques. In Rev. Min. Geochem.; Fenter, P. A., Rivers, M. L., Sturchio, N. C.; Sutton, S. R., Eds.; Mineralogical Society of America: Washington, DC, 2002; Vol. 49, pp 341−428.
downstream from the abandoned Carnoulès mine (Southern France). Environ. Sci. Technol. 2011, 45, 2056−2064. (3) Karlsson, U.; Karlsson, S.; Düker, A. The effect of light and iron(II)/iron(III) on the distribution of Tl(I)/Tl(III) in fresh water systems. J. Environ. Monit. 2006, 8, 634−640. (4) Twining, B. S.; Twiss, M. R.; Fisher, N. S. Oxidation of thallium by freshwater plankton communities. Environ. Sci. Technol. 2003, 37, 2720−2726. (5) Lin, T.-S.; Nriagu, J. Thallium speciation in the Great Lakes. Environ. Sci. Technol. 1999, 33, 3394−3397. (6) Peacock, C. L.; Moon, E. M. Oxidative scavenging of thallium by birnessite: Explanation for thallium enrichment and stable isotope fractionation in marine ferromanganese precipitates. Geochim. Cosmochim. Acta 2012, 84, 297−313. (7) Salminen, R., Ed. Geochemical Atlas of Europe. Part 1: Background Information, Methodology and Maps; Geological Survey of Finland: Espoo, 2005. (8) Tremel, A.; Masson, P.; Sterckeman, T.; Baize, D.; Mench, M. Thallium in French agrosystemsI. Thallium contents in arable soils. Environ. Pollut. 1997, 95 (3), 293−302. (9) Vanĕk, A.; Chrastný, V.; Mihaljevic, M.; Drahota, P.; Grygar, T.; Komárek, M. Lithogenic thallium behavior in soils with different land use. J. Geochem. Explor. 2009, 102, 7−12. (10) Bačeva, K.; Stafilov, T.; Šajn, R.; Tănăselia, C.; Makreski, P. Distribution of chemical elements in soils and stream sediments in the area of abandoned Sb-As-Tl Allchar mine, Republic of Macedonia. Environ. Res. 2014, 133, 77−89. (11) Xiao, T.; Guha, J.; Boyle, D.; Liu, C.-Q.; Zheng, B.; Wilson, G. C.; Rouleau, A.; Chen, J. Naturally occurring thallium: A hidden geoenvironmental health hazard? Environ. Int. 2004, 30, 501−507. (12) Lis, J.; Pasieczna, A.; Karbowska, B.; Zembrzuski, W.; Lukaszewski, Z. Thallium in soils and stream sediments of a Zn-Pb mining and smelting area. Environ. Sci. Technol. 2003, 37, 4569−4572. (13) Vanĕk, A.; Chrastný, V.; Komárek, M.; Penížek, V.; Teper, L.; Cabala, J.; Drábek, O. Geochemical position of thallium in soils from a smelter-impacted area. J. Geochem. Explor. 2013, 124, 176−182. (14) Cheam, V.; Garbai, G.; Lechner, J.; Rajkumar, J. Local impacts of coal mines and power plants across Canada. I. Thallium in waters and sediments. Water Quality Res. J. Can. 2000, 35 (4), 581−607. (15) Kersten, M.; Xiao, T.; Kreissig, K.; Brett, A.; Coles, B. J.; Rehkämper, M. Tracing anthropogenic thallium in soil using stable isotope compositions. Environ. Sci. Technol. 2014, 48, 9030−9036. (16) Pacyna, J. M.; Pacyna, E. G. An assessment of global and regional emissions of trace metals to the atmosphere from anthropogenic sources worldwide. Environ. Rev. 2001, 9, 269−298. (17) Environmental Health Criteria 182 - Thallium; World Health Organization: Geneva, 1996. (18) Mineral Commodity Summaries; U.S. Geological Survey: Reston, VA, 2015. (19) Jacobson, A. R.; McBride, M. B.; Baveye, P.; Steenhuis, T. S. Environmental factors determining the trace-level sorption of silver and thallium to soils. Sci. Total Environ. 2005, 345, 191−205. (20) Vanĕk, A.; Komárek, M.; Vokurková, P.; Mihaljevic, M.; Šebek, O.; Panušková, G.; Chrastný, V.; Drábek, O. Effect of illite and birnessite on thallium retention and bioavailability in contaminated soils. J. Hazard Mater. 2011, 191, 170−176. (21) Radtke, A. S.; Dickson, F. W.; Slack, J. F. Occurrence and formation of avicennite, Tl2O3, as a secondary mineral at the Carlin gold deposit, Nevada. J. Res. U.S. Geol. Surv. 1978, 6 (2), 241−246. (22) Balič Ž unić, T.; Moëlo, Y.; Lončar, Ž .; Micheelsen, H. Dorallcharite, Tl0.8K0.2Fe3(SO4)2(OH)6, a new member of the jarosite-alunite family. Eur. J. Mineral. 1994, 6, 255−263. (23) Tremel, A.; Masson, P.; Garraud, H.; Donard, O. F. X.; Baize, D.; Mench, M. Thallium in French agrosystemsII. Concentration of thallium in field-grown rape and some other plant species. Environ. Pollut. 1997, 97 (1−2), 161−168. (24) Vanĕk, A.; Mihaljevic, M.; Galušková, I.; Chrastný, V.; Komárek, M.; Peníže k, V.; Zádorová, T.; Dráb ek, O. Phase-dependent I
DOI: 10.1021/acs.est.5b00629 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
