to Soil Components and EFPC Soils

Transcription

1 On the tickiness of Mercury(II) to Soil Components and EFPC Soils Kathryn L. Nagy University of Illinois at Chicago Brett Poulin, Joseph N. Ryan University of Colorado Boulder George R. Aiken USGS Alain Manceau ISTerre, Université Joseph Fourier

2 (Reduced) aqueous sulfides mineral sulfides organo sulfur functionalities [e.g., R SH thiol moeities, which have affinity for Hg(II), Cd(II), Pb(II), Ag(I), Cu(I)]

3 Hg added to peat: binding structures t from EXAFS spectroscopy S reduced Hg S reduced = 1140 to 220 Like a metallothionein metal thiolate cluster = 20 to 10 Hg Linear Hg(Cys)2 type structure S reduced Hg = 4.3 to 0.80 Possible thiolated aromatic structure Nagy et al., 2011, ES&T

4 Questions: Are multinuclear Hg-SR structures from metallothioneins? If so, did added Hg displace other original metals? Is the Hg in the clusters bioavailable? Do the multinuclear Hg-SR structures nucleate HgS minerals? Are there other binding environments still to be discovered?

5 organo sulfur functionalities: let s look again (Waskish Peat Fulvic Acid) ~12 ev variation in energy of the s p electronic transition for different types of functional groups with distinct oxidation states as measured by XANES Gaussian Curve Fitting 6 Gaussians 2 Arctangents Position of reduced S arctangent important Gaussian peak: resonance scattering of ave. binding environment of S Arctangent step function: transition ii of photoelectron to the continuum Manceau & Nagy, in review

6 cystine + S(0) + pyrite + pyrrhotite cysteine 4-Acetamidothiophenol Exocyclic S Heterocyclic S thiophene thiepin Combo Fit Linear combination fitting of 29 reference spectra Retain only spectra with ih positive loadings Then group according to functionality 21: Organo-sulfur compounds 8: mineral sulfates, sulfides, elemental ee e S, Na-sulfite asu

7 Suwannee River Humic Acid % Exocyclic S % Heterocyclic S new methods Xia et al. (1999) Manceau & Nagy, in review

8 When there is a dominant reduced S Species (proteinrich soil OM): Only the Combo Fit method works. 53% Exocyclic; 31% Heterocyclic vs. 83% Exocyclic; 4% Heterocyclic Manceau & Nagy, in review

9 Pony Lake Fulvic Acid Cystine 12% Highest Reduced S of any IHSS OM (65%, excluding sulfate) Less agreement between Exo and Heterocyclic S from two methods e.g., split white line of cystine Exocyclic S combo fit: dibenzyl sulfide, cystine, pyrite, pyrrhotite (py + pyr peaks: ferredoxin?) Manceau & Nagy, in review

10 Mercury release from intact Oak Ridge soils under saturation conditions 10 ID PVC Poulin et al. poster Polyurethane Expanding Foam Teflon Barrier O horizon Intact Soil Core Borosilicate Suction Cups Lower A horizon Borosilicate Glass Base DI Water

11 Hg (ng L 1 ) O Horizon NO 3 Mn +2 Fe +2 SO 4 2 Mercury release from intact Oak Ridge soils under saturation conditions Saturation Event 1 Oxic Saturation Event Time Since Initial Flooding (d) Additional Analyses: [DOC], [DIC], and DOM composition (SUVA and fluorescence) Poulin et al. poster

12 Mercury release from intact Oak Ridge soils under saturation conditions Hg. (ng L 1 ) Hg (ng L 1 ) 400 Saturation Event 1 Oxic Saturation Event O Horizon Time Since Initial Flooding (d) A Horizon Poulin et al. poster

13 from the flooded A horizon: HgL3 edge XANES shows metacinnabar ture absorption spectra metacinnabar Hg rich spot spot m 1 st derivatives

14 Subtraction of SiO 2 XRD patterns leaves only metacinnabar micro diffraction shows metacinnabar XRD lge peak glass scattering sharp peaks qtz

15 from the flooded A horizon: Ca Hg Ca 300 mu Hg on the inside of what appears to be a seed is metacinnabar.

16 from the unflooded O horizon: Hg Si Si 1 metacinnabar 2 Hg OM

17 Hg L 3 edge XANES S K edge XANES Hg rich spot dothiepin metacinnabar Hg rich spot association with heterocyclic S 1 1 st st Hg rich spot deriv. deriv. Hg peat (ES&T) Hg L 3 edge XANES

18 To summarize Hg (and other soft metals ) bind strongly to reduced S. Reduced S species in organic matter are, therefore, important to characterize precisely and accurately. Revision of Gaussian curve fitting approach and use of combo fitting improves accuracy of determined fractional amounts of S functionalities in organic matter. increased precision would be highly useful. S XANES combined with Hg XANES can be used to identify Hgorganic species in soils and sediments. improvements in elemental sensitivity are needed.

19 To summarize and, how strong is the binding of mercury to each organic reduced sulfur species?