Speciation, reactivity, and cycling of Fe and Pb in a meromictic lake (original) (raw)
Related papers
Speciation Of Pb In Industrially Polluted Soils
Water, Air, and Soil Pollution, 2006
This study was aimed at elucidating the importance of original Pb-speciation versus soilcharacteristics to mobility and distribution of Pb in industrially polluted soils. Ten industrially polluted Danish surface soils were characterized and Pb speciation was evaluated through SEM-EDX studies, examination of pH-dependent desorption, distribution in grain-size fractions and sequential extraction. Our results show that the first factors determining the speciation of Pb in soil are: (1) the stability of the original speciation and (2) the contamination level, while soil characteristics are of secondary importance. In nine of ten soils Pb was concentrated strongly in the soil fines (<0.063 mm). In all soils, particles with a highly concentrated Pb-content were observed during SEM-EDX. In eight of the soils, the particles contained various Pb-species with aluminum/iron, phosphate, sulfate and various metals (in solder and other alloys) as important associates. In the one soil, where Pb was not concentrated in the soil fines, Pb was precipitated solely as PbCrO 4 , while pure (metallic) Pb was repeatedly observed in the last soil. Pb was bound strongly to the soils with >50% extracted in step III (oxidizing) and IV (residual) of sequential extraction for all soils but one. A significant amount of exchangeable Pb existed only in severely contaminated soils, where the bonding capacity of organic matter and oxides was exceeded. Among soil constituents, Pb was observed to adsorb preferentially to feldspars and organic matter while presence of phosphate increased the strength of the Pb-bonding in phosphate-rich soils.
Part 3: The Pb2+ + OH–, Cl–, CO32–, SO42–, and
2015
Complex formation between Pb II and the common environmental inorganic ligands, Cl-, OH-, CO 3 2-, SO 4 2-, and PO 4 3-, can be significant in natural waters with low concentrations of organic matter. Numerical modeling of the speciation of Pb II amongst these inorganic ligands requires reliable values for the relevant stability (formation) constants. This paper provides a critical review of such constants and related thermodynamic data. It recommends values of log 10 β p,q,r°v alid at I m = 0 mol kg-1 and 25 °C (298.15 K), along with the equations and empirical coefficients required to calculate log 10 β p,q,r values at higher ionic strengths using the Brønsted-Guggenheim-Scatchard specific ion interaction theory (SIT). Some values for reaction enthalpies, Δ r H, are also reported. In weakly acidic fresh water systems (-log 10 {[H + ]/c°} < 6), the speciation of Pb II is similar to that of Cu II. In the absence of organic ligands, Pb II speciation is dominated by Pb 2+ (aq), with PbSO 4 (aq) as a minor species. In weakly alkaline solutions, 8.0 <-log 10 {[H + ]/c°} < 9.0, the speciation is dominated by the carbonato species PbCO 3 (aq) and Pb(CO 3) 2 2-. In weakly acidic saline systems (-log 10 {[H + ]/c°} < 6), the speciation is dominated by PbCl n (2-n)+ complexes, (n = 0-3), with Pb 2+ (aq) as a minor species. In this medium (and in seawater), the speciation contrasts with that of Cu II because of the higher stability of the Pb 2+-chlorido-complexes. In seawater at-log 10 {[H + ]/c°} = 8.2, the calculated speciation is less well defined, although it is clearly dominated by the uncharged species PbCO 3 (aq) (41 % of [Pb] T) with a significant contribution (16 %) from Pb(CO 3)Cland minor contributions (5-10 %) from PbCl n (2-n)+ , (n = 0-3) and Pb(CO 3) 2 2-. The uncertainty in calculations of Pb II speciation in seawater arises from (a) the large uncertainty in the stability constant for the apparently dominant species PbCO 3 (aq), (b) the reliance on statistical predictions for stability constants of the ternary species Pb(CO 3)Cland Pb(CO 3)OH-, and (c) the uncertainty in the stability constant for PbCl 4 2-, the available value being considered *Sponsoring body: IUPAC Analytical Chemistry Division: see more details on p. 2453.
Geochimica et Cosmochimica Acta, 1995
The geochemical processes controlling the behavior of stable Pb, ""Pb, and ""PO in seasonally anoxic Lake Sammamish, Washington were identified from water column distributions and box model calculations. Total (sum of dissolved and particulate) inventories of stable Pb, "?b, and *"'PO increased in the whole lake during the latter part of the oxic stage of the lake and were attributed to diffusion from sediments. Large decreases in the total inventories of these elements occurred during the transition from oxic to anoxic conditions, and the lowest inventories were observed during the sulfidic stage of stratification. The cycling of stable Pb and ""Pb during oxic periods appeared to be linked to Fe cycling while ""PO cycling was more closely linked to the cycling of Mn. The behavior of stable and radioactive Pb and, possibly, *"'PO during anoxia was influenced by sulfur cycling. Thermodynamic calculations indicated that dissolved Pb concentrations might be controlled by PbS precipitation during anoxia.
210 Pb (210 Po) speciation of aquatic deposits: Refinement and utility
Journal of Radioanalytical and Nuclear Chemistry, 1990
A refined chemical procedure for speciation studies of sediments has been thoroughly examined. The suggested method, although only tested on 210 Pb (210 Po), could be applied to other chemical species, especially heavy metals and radioactive nuclides. Successive dissolutions using dilute HC1 (1–2.5%) and NaOH (0.5–1%) proved that the geochemistry of fulvic, humic, and mineral compounds plays an important role in the mobility, transport, and accumulation of 210 Pb in various aquatic systems. This work ...
Geochimica Et Cosmochimica Acta, 2011
Dissolved organic matter (DOM) from the treated effluent of a wastewater treatment plant and from the river Seine under high human pressure has been separated into three fractions: hydrophobic (containing humic and fulvic substances), transphilic and hydrophilic using a two column array of XAD-8 and XAD-4 resins. The acid base properties and the binding characteristics with respect to Pb ions (using the new electroanalytical technique AGNES, Absence of Gradients and Nernstian Equilibrium Stripping) have been studied and fitted to NICA (Non-Ideal Competitive Isotherm). We evaluated the binding potential of each DOM fraction in order to better predict the speciation of Pb and, later, its bioavailability in the river. The total binding capacity of the different fractions to Pb, as well as the total titratable charge, reaches its maximum value at the most hydrophilic fraction from the treated effluent. Specific properties of the distribution of the complexing sites within each DOM fraction have been exposed by plotting the conditional affinity spectrum (CAS). The addition of these distributions, weighted according to the respective abundance of each organic fraction, allows for a full description of the Pb binding properties of the whole DOM of a sampling site. Despite its weak aromaticity, the hydrophilic fraction from the wastewater treatment plant effluent exhibits a high lead binding affinity, so that at typical environmental pH and free Pb levels (0.1 lg L À1 ), Pb is mainly bound to the most hydrophilic fraction of the treated effluent (49% of bound Pb at pH 7). This feature may greatly enhance the transport of Pb and highlights that Pb speciation should also consider other fractions apart from humic and/or fulvic acids when studying surface waters under high human pressure.
Determining speciation of Pb in phosphate-amended soils: Method limitations
Science of The Total Environment, 2005
Determining the effectiveness of in situ immobilization for P-amended, Pb-contaminated soils has typically relied on nonspectroscopic methods. However in recent years, these methods have come under scrutiny due to technical and unforeseen error issues. In this study, we analyzed 18 soil samples via X-ray diffraction (XRD), selective sequential extraction (SSE), and a physiologically based extraction test (PBET). The data were compared against each other and to previous data collected for the soil samples employing X-ray absorption fine structure spectroscopy coupled with linear combination fitting (XAFS-LCF), which spectroscopically speciates and quantifies the major Pb species in the samples. It was observed that XRD was incapable of detecting pyromorphite, the hopeful endpoint of the immobilization strategy for reduced Pb bioavailability in our studies. Further, the SSE and PBET extraction methods demonstrated an increase of recalcitrant Pb forms in comparison to the XAFS-LCF results suggesting that SSE and PBET methods induced the precipitation of pyromorphite during the extraction procedures. The theme of this paper illustrates the experimental concerns of several commonly employed methods to investigate immobilization strategies of amended, metal-contaminated systems which may not be in true equilibrium. We conclude that appropriate application of spectroscopic methods provides more conclusive and accurate results in environmental systems (i.e., Pb, Zn, Cd, etc.) examining P-induced immobilization. D
Mobility of Pb in salt marshes recorded by total content and stable isotopic signature
Total lead and its stable isotopes were analysed in sediment cores, leaves, stem and roots of Sacorconia fruticosa and Spartina maritima sampled from Tagus (contaminated site) and Guadiana (low anthropogenic pressure) salt marshes. Lead concentration in vegetated sediments from the Tagus marsh largely exceeded the levels in non-vegetated sediments. Depth profiles of 206Pb/207Pb and 206Pb/208Pb showed a decrease towards the surface (206Pb/207Pb=1.160–1.167) as a result of a higher proportion of pollutant Pb components. In contrast, sediments from Guadiana marsh exhibited low Pb concentrations and an uniform isotopic signature (206Pb/207Pb=1.172±0.003) with depth. This suggests a homogeneous mixing of mine-derived particles and pre-industrial sediments with minor inputs of anthropogenic Pb. Lead concentrations in roots of plants from the two marshes were higher than in leaves and stems, indicating limited transfer of Pb to aerial parts. A similar Pb isotopic signature was found in roots and in vegetated sediments, indicating that Pb uptake by plants reflects the input in sediments as determined by a significant anthropogenic contribution of Pb at Tagus and by mineralogical Pb phases at Guadiana. The accumulation in roots from Tagus marsh (max. 2870 μg g− 1 in S. fruticosa and max. 1755 μg g− 1 in S. maritima) clearly points to the dominant role of belowground biomass in the cycling of anthropogenic Pb. The fraction of anthropogenic Pb in belowground biomass was estimated based on the signature of anthropogenic Pb components in sediments (206Pb/207Pb=1.154). Since no differences exist between Pb signature in roots and upper sediments, the background and anthropogenic levels of Pb in roots were estimated. Interestingly, both background and anthropogenic Pb in roots exhibited a maximum at the same depth, although the proportion of anthropogenic Pb was relatively constant with depth (83±4% for S. fruticosa and 74±8% for S. maritima).
The solubility of Pb in coastal marine rainwaters: pH-dependent relationships
Atmospheric Environment, 2000
Data on the particulate dissolved speciation of total Pb ( Pb) in 175 rainwater samples from a variety of coastal marine environments have been used to construct a composite &pH}% Pb solubility' plot which covers the pH range found in natural rainwaters. The % Pb solubility values of the samples display large variations, ranging from '90 to (10%. The &pH}% Pb solubility' relationship is constrained by a relatively sharp classical pH-edge, extending from pH&5.0 at the high solubility end to pH &5.8 at the low solubility end. At pH values greater than that of this &limiting' pH-edge, the % Pb solubility is (&10% at any solution pH. The composite plot therefore con"rms that pH-mediated adsorption/desorption reactions play a dominant role in controlling the solubility of the Pb in precipitation. However, the plot shows a wide range of Pb solubilities at pH values to the more acidic side of the &limiting' pH-edge. Lead in the dissolved state has the most signi"cant e!ect on aquatic systems, and the major environmental consequence of the variation in Pb solubilities at pH values less than that of the &limiting' pH-edge is that even in urban regions, where the scavenged aerosol has relatively high concentrations of Pb in a potentially soluble form, the actual % Pb solubility in rainwater can have large variations ( (&10 to '&90% of the Pb) over a narrow pH range.
Pb isotopes and Pb concentrations were measured in two sediment cores sampled in Lake Geneva (i) at the center of the basin (central plain) and (ii) in an area which receives the effluents of the wastewater treatment plant of Lausanne as well as runoff inputs. The presence of an anthropogenic contribution is observed over all the sampled period (150 years), even at the center of the lake. At both sites, the maximum contamination of Pb occurred in the late 1970s, and has declined to present. The site close to Lausanne received much more Pb than the one at the center of the lake. Surprisingly, the Pb isotopes show that gasoline-derived Pb has had a minor influence, at least over the last 20 years. Instead, deposition of Pb from industrial (and domestic) activities predominates. This study demonstrates that one of the major limitations of the isotopic method is the poor (or partial) knowledge of how the isotopic compositions of potential sources have evolved through the past. A simple method of sample dissolution, based on HNO3 leaching assisted by microwave, is also presented. We believe that this sample preparation can be extensively used because it provides a reliable estimate of Pb having an anthropogenic origin.
Sources, lability and solubility of Pb in alluvial soils of the River Trent catchment, U.K
Science of The Total Environment, 2012
Alluvial soils are reservoirs of metal contaminants such as Pb that originate from many different sources and are integrated temporally and spatially through erosional and depositional processes. In this study the source, lability and solubility of Pb was examined in a range of alluvial soils from the middle and lower River Trent and its tributary the River Dove using Pb isotope apportionment and isotopic dilution. All samples were collected within 10 m of the river bank to represent the soil that is most likely to be remobilised during bank erosion. Paired samples were taken from the topsoil (0-15 cm) and subsoil (35-50 cm) to assess differences with depth. Lead concentrations in soil ranged from 43 to 1282 mg/kg. The lability of soil Pb varied between 9-56% of total metal concentration whilst Pb concentrations in pore water varied between 0.2 and 6.5 µg/L. There was little difference in the % Pb lability between paired top and sub soils, possibly because soil characteristics such as pH, iron oxides and clay content were generally similar; a result of the recycling of eroded and deposited soils within the river system. Soil pH was found to be negatively correlated with % Pb lability. Source apportionment using 206 Pb /207 Pb and 208 Pb /207 Pb ratios showed that the isotopic ratios of Pb in the total, labile and solution pools fitted along a mixing line between Broken Hill Type ('BHT') Pb, used as an additive in UK petrol, and the local coal/Sourthern Pennine ore Pb. Various anomalies were found in the Pb isotopes of the bankside alluvial soils which were explained by point source pollution. Statistically significant differences were found between (i) the isotopic composition of Pb in the total soil pool and the labile/solution pools and (ii) the isotopic composition of Pb in the labile and solution pools, suggesting an enrichment of recent non-Pennine sources of Pb entering the soils in the labile and solution pools.