Environmental Arsenic Speciationdefinitely more than just arsenite and arsenate!
Grand Prismatic Hot Spring, Yellowstone NP
Arsenic the classical poison
Homemade elderberry wine
laced with Arsenic StrychnineArsenic, Strychnine and just a pinch of
CyanideCyanide
Joseph Kesselring, 1939
18401840
1836 M h t t1836 Marsh test
Principle of Marsh´s TestpDetermination of total As by hydride generation
As2O3 + 6Zn + 6H2SO4 → 2AsH3 + 6Zn(SO4)2 + 3H2O
+3 -30 +2+3 -30 +2
As
Arsenic speciesse c spec es
Arsenate As(V)
Arsenate As(V)
Arsenite As(III)
Arsenite As(III)
1970s Species-selective Hydride GenerationSeparating As(III) and As(V)
H3AsIIIO30 / H3AsVO4
0 + NaBH4 AsH3
8090
100H3AsO3H3AsO4As(III)“
0607080 H3AsO4
pK 2.2 pK 9.2
„As(III)
304050
p p
As(III)“
0102030 „As(III)
+ „As(V)“
00 1 2 3 4 5 6 7 8 9 10 11 12
Ion chromatography for speciation of arsenite and arsenate+ detection e g by atomic absorption spectroscopy
1.E+05
+ detection e.g. by atomic absorption spectroscopy
8.E+04
6.E+04
ity [c
ps]
HA O 2
4.E+04
al in
tens HAsO4
2-
arsenate
2.E+04
sign
a
arseniteH3AsO3
0
0.E+000 2 4 6 8 10 12 14 16 18 20 220 2 4 6 8 10 12 14 16 18 20 22
time [minutes]
Modeling arsenite and arsenate distribution
ArsenitepK1, pK2, pK3 (H3AsO3)
t t d+ protonated species H4AsO3
+
A tArsenatepK1, pK2, pK3 (H3AsO4)
link arsenite - arsenate
Traditional Arsenic Speciation
Arsenate07
06
Arsenate
05
04
03
01
03
Arsenite02
01
Gibbon Geyser Basin
Sulfidic environment affects arsenic speciation!
Arsenicup to 5 4 mg/L
Sulfide0 1 5 /L up to 5.4 mg/L0.1-5 mg/L
H2S
Grotto Geyser
Chromatographic separation revealed As species with retention times that did not match those of any commercial standards
1.E+05
times that did not match those of any commercial standards
?
8.E+04?
?
6.E+04
ity [c
ps]
4.E+04
al in
tens arsenate ?
2.E+04
sign
a
arsenite?
0.E+000 2 4 6 8 10 12 14 16 18 20 220 2 4 6 8 10 12 14 16 18 20 22
time [minutes]
Requires a more selective detector:I d ti l l d l t tInductively coupled plasma mass spectrometry
ELAN DRC II ICP-MS, Perkin Elmer
Samplepintroductionca.1 ml/min
aerosolaerosolH2AsO4
-
Plasma 6000-8000°C
atomAs, H, O
ionAs+, H+, O+
Detection of unknown As species
1.E+05sulfate S:As S:As
8.E+04
Arsenic AsO+Sulfur SO+
sulfate S:As0.95 ± 0.1n = 17
S:As2.99 ± 0.22
n = 26
6.E+04y [c
ps]
4 E+04
6.E 04
inte
nsity
arsenatesulfide
S:As1.92 ± 0.14
n = 21 S:As
2 E+04
4.E+04
sign
al
thiosulfateca.4
2.E+04 arsenite
0.E+000 2 4 6 8 10 12 14 16 18 20 22
time [minutes]
Thioarsenates or Thioarsenites?
Thioarsenites
OH SH SH SHOH OH SH SH
As AsAs As
OH OHOH SH
Mono~ Di~ Tri~ Tetra~
OH
OH – As = O
OH
OH – As = O
OH
SH – As = O
SH
SH – As = O
SH
SH – As = SOH As O
SH
OH As O
OH
SH As O
SH
SH As O
SH
SH As S
SH
Thioarsenates retention time match with synthesized standards
Electrospray Ionization MSElectrospray Ionization MSNo prior chromatographic separation!
No atomization of compoundp
• „Soft ionization“, rather transfer from solution to gasg• Solvent evaporation• Formation of desolvated aerosol
H A O ions by Coulombic fission (repellent forces by charged molecules)
H2AsO4-
molecules)
Thioarsenates or Thioarsenites? Identical molecular masses of thioarsenites and thioarsenates on low-resolution
Thioarsenites
mass spectrometry is a problem for electrospray ionization mass spectrometry
OH SH SH SHOH OH SH SH
As AsAs As
OH OHOH SH
Mono~ Di~ Tri~ Tetra~141 157 173
OH
OH – As = O
OH
OH – As = O
OH
SH – As = O
SH
SH – As = O
SH
SH – As = SOH As O
SH
OH As O
OH
SH As O
SH
SH As O
SH
SH As S
SH141 157 173
Thioarsenates retention time match with synthesized standardsm/z: 2 * O (2*16) S (32)
ESI-MS proofs for thioarsenates not thioarsenites
1. ES Q-TRAP MS molecular massesless deviations when assuming thioarsenate m/z ratios
Measured m/z
Thio-arsenate
expected m/z for thio-
rel. dev.
Thio-arsenite
expected m/z for thio-
rel. dev. [ppm]arsenate [ppm] arsenite [ppm]
140.914 H2AsO4- 140.9169 -20.6 H2AsO2S- 140.8991 +105.7
156 891 H AsO S- 156 8941 19 8 H AsOS - 156 8763 +93 7156.891 H2AsO3S 156.8941 -19.8 H2AsOS2 156.8763 +93.7
172.868 H2AsO2S2- 172.8712 -18.5 H2AsS3
- 172.8535 +83.9
188 848 H2AsOS3- 188 8484 -0 53188.848 H2AsOS3 188.8484 0.53
204.825 H2AsS4- 204.8255 -4.88
Wallschläger & Stadey Anal. Chem. 2007, 79, 3873-3880
ESI-MS proofs for thioarsenates not thioarsenites
1. ES Q-TRAP MS molecular masses
OH
less deviations when assuming thioarsenate m/z ratios
OH
SH – As = O2. ES-MS-MS fractionation patterns
(m/z 173 eliminated H2O SH SH
As
SHmust be H2AsO2S2-
H2AsS3- can not eliminate H2O!)
SH
trithio-ESI-MS proofs for thioarsenates not thioarsenites
arsenate
1. ES Q-TRAP MS molecular masses
dithio-arsenate
arsenate
less deviations when assuming thioarsenate m/z ratios
2. ES-MS-MS fractionation patterns(m/z 173 eliminated H2O must be H AsO S2-
monothio-arsenate
must be H2AsO2SH2AsS3
- can not eliminate H2O!)
3 Analysis of IC fractions by ES MStetratharsena
3. Analysis of IC fractions by ES-MS known As:S ratios from IC and molecular mass information from ES-MS
800 1000 1time [s]
S:As 1:1Monothioarsenite (m/z = 141)
Monothioarsenate (m/z = 157)
Thioarsenates predominate arsenic speciationat the geothermal sources
dot size = sum of thioarsenates [%]
Methylated (thio)arsenatesaccounted for all remaining missing species
CH3
CH3 – As = Oaccounted for all remaining missing species CH3 As O
SHSlightly different eluent:0- 3 min 2.5 mM3- 5 min 2.5 20 mM 1.0x104 dimethyl-
arsenitedimethyl-arsenate arsenate
ps]3 5 min 2.5 20 mM
5-10 min 20 mM10-20 min 20 100 mM20 24 i 2 5 M 3
monothio-arsenate
monomethyl-arsenate
monothio-arsenatey
AsO
+ [cp
20-24 min 2.5 mM
No suppressor
1.0x103
monomethyl- monothio- arsenate
arsenate
dithio-arsenatena
l int
ensi
ty
Additional As species: 13-20% DMA
1.0x102
arsenate
sign
13-20% DMA 1% MMA 5% DMMTA 200 400 600 800 1000 120
1.0x101
0.5% MMMTA time [s]
Why were thioarsenates notWhy were thioarsenates not detected in previous studies?p
Preservation of arsenic speciation by acidification90
10012.0
14.0
speciation by acidification
607080
cove
ry [%
]
8.0
10.0
H
304050
arse
nic
rec
4.0
6.0
pH
010
20
0.0
2.0
80
90
100
%]
12.0
14.0
90100
12.0
14.0
50
60
70
80
reco
very
[%
8.0
10.0
pH
607080
ecov
ery
[%]
8.0
10.0H
20
30
40
50ar
seni
c r
4.0
6.0
p
20304050
arse
nic
re
4.0
6.0
p
0
10
20
0.0
2.0
01020
0.0
2.0
Preservation of arsenic speciation by acidificationYellowstone: Trithioarsenate pH >6speciation by acidification
not suitable in sulfidic waters!
Monothioarsenate at all pH conditions
not suitable in sulfidic waters!
flash-freezing
1.2
1.4Monothioarsenate
Dithioarsenate
Trithioarsenate
0.8
1
[mg/
L]
Trithioarsenate
Tetrathioarsenate
0.4
0.6
arse
nic
0
0.2
02 3 4 5 6 7 8 9 10
pH
Analysis of arsenic by hydride generationnot suitable for arsenic speciation in sulfidic waters!
H3AsO30 / H3AsO4
0 + NaBH4 AsH3T t l d ith KI / bi
not suitable for arsenic speciation in sulfidic waters!
8090
100H3AsO3H3AsO4
„As(III)“
Totals: prered. with KI /ascorbicacid in 3.5 M HCl
40506070
pK 2.2 pK 9.2
Speciation: non-std. procedure
• different buffers
10203040 p p
„As(III)“
+ „As(V)“
• final pH 4 to 7
• batch vs. flow injection
Totals: thioarsenates arsenate arsenite
00 1 2 3 4 5 6 7 8 9 10 11 12
(diff. pH of sample / reductant prior to mixing)
Totals: thioarsenates arsenate, arsenite correct (if samples were not acidified for preservation and 1% KI is used as pre-reducing agent; not L-cysteine)
Species: „As(III)“: Arsenite, Di-, Tri-, and Tetrathioarsenate„As(V)“: Arsenate, Monothioarsenate
Traditional Arsenic Speciation
ArsenateImplications of existence
f hi
0706
Arsenate
of thioarsenates…05
04
03
01
03
Arsenite02
01
Gibbon Geyser Basin
Implications for speciation transformations and redox processesp
1.6 1.6
1 2
1.4
1 2
1.4measured byhydride generation
measured by AEC-ICP-MS
1.0
1.2
L]
1.0
1.2
L]
0 6
0.8
seni
c [m
g/L
0 6
0.8
seni
c [m
g/L
0.4
0.6ars
0.4
0.6ars
0 0
0.2
0 0
0.2
0.00 3 6 9 12 15 18 21 24 27 30 33 36
distance from source [m]
0.00 3 6 9 12 15 18 21 24 27 30 33 36
distance from source [m]
„Oxidation“ of thioarsenate to arsenite??1190
1070950
830
720
600
480
360
240
120
0
Thioarsenate / Arsenite ArsenateXX
0
-120
-240
-360
Arsenite + S0 donor Thioarsenate
X
XX
X-480
-600
-720
830
Arsenite + (Sulfide) / S0 donor ThioarsenateXX
-830
-950
intermediate S species determine As speciation
Influence of S-oxidizing microorganisms on arsenic redox transformations…?
• transformation rates are 40-500 times faster (k =
1/min, t1/2 = 0.6 min) than in abiotic control experiments
in the laboratory (k = 0 004/min t1/2 = 170 min)in the laboratory (k 0.004/min, t1/2 170 min)
• arsenate production coincides with the temperature-
dependent occurrence of organisms closely related to
Thermocrinis ruber a known sulfur-oxidizerThermocrinis ruber, a known sulfur oxidizer
Implications for toxicity
1.6 1.6
measured by measured by AEC-ICP-MSLab toxicity tests exposing Vibrio fischeri to thioarsenate standards:
1 2
1.4
1 2
1.4measured by
hydride generation
yto thioarsenate standards:
Exposure time 15 min:
1.0
1.2
L]
1.0
1.2
L]
p
trithioarsenate = arsenite > di >> mono
??
0 6
0.8
seni
c [m
g/L
0 6
0.8
seni
c [m
g/L
Exposure time 60 min:
trithioarsenate > arsenite
??
0.4
0.6ars
0.4
0.6arstrithioarsenate > arsenite
lack of adaptation for thioarsenates?
0 0
0.2
0 0
0.2in the presence of both arsenite and trithioarsenate sig lower toxicity0.0
0 3 6 9 12 15 18 21 24 27 30 33 36distance from source [m]
0.00 3 6 9 12 15 18 21 24 27 30 33 36
distance from source [m]
trithioarsenate sig. lower toxicity
antagonism trithioarsenate - arsenite?
Grenoble, FranceGrenoble, FranceESRF = European Synchrotron Radiation Facility
So what about the thioarsenites …?Synchrothron radiation main advantages: radiation with a large y g gspectrum (IR, VIS, UV, X-Ray), high intensity, sharp focus
844 m
X-ray absorption spectroscopy XAS
monochromator(monochromatic X-rays)
synchrotron radiation source
I0
(high energetic, precise radiation)
incoming beam
sample
absorption
fluorescenceI1
absorption
fluorescence
I2reference (e.g. Au0, As0)
Resulting data: XAS spectra2.5
XANES (E0 ± 50 eV) X ray Absorption Near Edge Spectroscopy
2.0
XANES (E0 ± 50 eV) X-ray Absorption Near-Edge Spectroscopy• oxidation state• local site symmetry and orbital occupancy
1.5
bsor
ptio
n µ absorption edge E0
As 11867 eV
1.0
mal
ized
ab
EXAFS
0.5
nor Extended X-ray Absorption Fine-Structure
50 – 1000 eV above E0, local coordination• bond distances R
0.011650 11850 12050 12250 12450 12650
• coordination number CN • type and number of neighbors
11650 11850 12050 12250 12450 12650
Energy [eV]
Interpretation of coordination number AsS from EXAFS vs. edge position from XANES
As(V)As(III) • First spectra of synthesized thioarsenate standards
upon acidification Thioarsenites?
4
Tetrathioarsenate thioarsenate standards
• First detection of thioarsenates and
2
3
elle
d C
N
Dithioarsenate
As2S3
A S
thioarsenites in the same solution
1
2
mod
e
Monothioarsenate
DithioarsenateAs4S4
011867 11868 11869 11870 11871 11872
Na-ArsenateNa-Arsenite
E0 [eV]
Can the occurrence of thioarsenates and thioarsenites be predicted by thermodynamic models?
Can the occurrence of thioarsenates and thioarsenites be predicted by thermodynamic models?
pH
be predicted by thermodynamic models?
TetrathioarsenateH 9 5 d 12 3
pH 6.3 TetrathioarsenateT ithi it
pH 5.8 Trithio-it
pH 2.3 Trithio-it + A S
1 00E-02
1.00E-012 3 4 5 6 7 8 9 10 11 12
pH pH 9.5 and 12.3Trithioarsenitearsenitearsenite + As2S3
1.00E-03
1.00E 02
H3AsS3As2S3 precipitation
1.00E-04
ion
[mol
/L] H2AsS3-
AsS4-3
AsO4-3
1.00E-06
1.00E-05
conc
entr
at
As tot
1.00E-07
1.00E-08
Projekte• Charakterisierung Thioarsenate/Thioarsenite mit IC-ICP-MS, XAS, RAMAN Elke
DFG Emmy Noether Förderung: Hydrogeochemische Speziierung von As, Au, Cu in Fe-S-Systemen unter Berücksichtigung abiotischer und mikrobiell katalysierter Wechselwirkungen
• Conny: Mikrobiell katalysierte Speziierung in As-Au-S Geothermalsystemen (Yellowstone, Neuseeland) Elke & April (DAAD RISE Praktikantin) As-S + Fe Ulli DA B d t i t diä S S i fü A R d dl tl th l Ulli: DA Bedeutung intermediärer S-Spezies für As-Redoxumwandlungen entlang geothermaler Drainagekanäle in Yellowstone NP (Photometrie vs. ionensensitive Elektrode)
• Abiotische Thioarsen-Speziierung im Fe(II)/Fe(III) System (Probenstabilisierung, Bildung von Fe-As-S Komplexen, Thioarsenat-Sorption/Remobilisierung auf Fe-Hydroxiden und Fe-Sulfiden)p p g y )
• Abiotische Reaktionen von Au- und Cu-Thioarsen-Spezies (Chile, etc.)
DFG Forschergruppe etrap• Identifikation von Polysulfiden und ihre Bedeutung als intermediäre Schwefel-Spezies für
Elektronentransferprozesse in anoxischen Aquiferen Sasan: Derivatisierung Polysulfide, Methoden-Setup RP-IC-ICP-MS Polysulfide als Elektronenshuttle bei indirekter FeOOH Reduktion durch Sulfurospirillum deleyianum Polysulfide als Elektronenshuttle bei indirekter FeOOH-Reduktion durch Sulfurospirillum deleyianum
Postdocs• Sasan: Organo-As-S-Verbindungen, As in Lebensmitteln / Toxikologie…?g g g• Nathaniel Wilson: Thioantimonate, Humboldt-Postdoc-Stipendium beantragt
MSc OS3 Toxizitätstests mit Vibrio fischeri für Thioantimonate
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