arsenic speciation - year 4/5
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Arsenic Speciation - Year 4/5. Bernine Khan University of Miami Dept. of Civil, Architectural & Environmental Engineering July 9th, 2001. Speciation. Definition: Various species of an element which make up the total concentration of that element - PowerPoint PPT PresentationTRANSCRIPT
Arsenic Speciation - Year 4/5
Bernine KhanUniversity of Miami
Dept. of Civil, Architectural & Environmental EngineeringJuly 9th, 2001
Definition:Various species of an element which make up the total concentration of that element
• different oxidation states (e.g. arsenic +3, +5, -3)
• inorganic - many contain sulfur• organic - contains carbon/hydrogen groups
Speciation
• All soluble arsenic compounds are considered poisonous to humans
• Arsenic & its compounds - widely distributed in nature primarily in two oxidation states – As III - arsenite (+3) & As V - arsenate (+5)
• As III (+3) - more soluble in water & body fluids & not excreted as readily
• Toxicity - a function of magnitude of exposure (concentration accumulated over time.)
Why Are We Interested in Speciation?
Toxicity of Arsenic Species Dependent on chemical form
• AsH3 - arsine (gas) – formed under very reduced conditions eg. landfills
• As(III) - arsenite• As(V) - arsenate • MMA - monomethylarsonic acid• DMA - dimethylarsinic acid• TMAO - trimethylarsine oxide• AsB - arsenobetaine (marine) *• AsC - arsenocholine (marine) *
Toxicity of Arsenic Species Dependent on chemical form
• AsH3 - arsine (gas) • As(III) - arsenite – inorganic (more toxic)• As(V) - arsenate – inorganic - CCA• MMA - monomethylarsonic acid• DMA - dimethylarsinic acid• TMAO - trimethylarsine oxide• AsB - arsenobetaine (marine) *• AsC - arsenocholine (marine) *
Toxicity of Arsenic Species Dependent on chemical form
• AsH3 - arsine (gas) • As(III) - arsenite – inorganic• As(V) - arsenate – inorganic• MMA - monomethylarsonic acid• DMA - dimethylarsinic acid• TMAO - trimethylarsine oxide• AsB - arsenobetaine (marine) *• AsC - arsenocholine (marine) *
bacteria
Toxicity of Arsenic Species Dependent on chemical form
• AsH3 - arsine (gas) • As(III) - arsenite – inorganic• As(V) - arsenate – inorganic• MMA - monomethylarsonic acid• DMA - dimethylarsinic acid• TMAO - trimethylarsine oxide• AsB - arsenobetaine (marine) *• AsC - arsenocholine (marine) *
Oxidizing Condition • Measure of
system state (O2/no O2)
• Soluble As increases with decreasing Eh & increasing pH
Arsenic Mobility Eh-pH diagram
0 2 4 6 8 10 12 14 pH
Eh (volts)
0.75
0.50
0.25
0
-
0.25
-
0.50
-
0.75
Reducing Condition
As(V)+5
As(III)+3
As(III)-3
AsH3 (aq)
AsS+3
As
Oxidising Condition
Arsenic Mobility Eh-pH diagram
0 2 4 6 8 10 12 14 pH
Eh (volts)
0.75
0.50
0.25
0
-
0.25
-
0.50
-
0.75
Reducing Condition
As(V)+5
As(III)+3
As(III)-3
AsH3 (aq)
AsS+3
As
Most surface watersMost ground waters
Predicted Landfills
Field Sampling MethodsSamples collected :
– background & detection wells – purged for 20 minutes– Temperature, pH & ORP– stored on ice– refrigerated <4oC– analysed within 48 hrs for As speciation– analysed for particulate
& total As
• Collect and analyse groundwater & leachate samples from MSW & C&D landfill
• Three step analysis:– Step 1 – Dissolved phase– Step 2 – Particulate phase– Step 3 - Total phase
• Analysis by HPLC-HG-AFS – Speciation
Current Research Study
ICP-MS – Total Arsenic
Step 1 – Dissolved Phase
Filtrate (dissolved phase)Analysed for As species by HPLC-HG-AFS*
Sample filtered through 0.45 m PVDF filter
Sample
* HPLC-HG-AFS - High Performance Liquid Chromatography- Hydride Generation-Atomic Fluorescence Spectrometry
Speciation by HPLC-HG-AFS• HPLC- Separates the arsenic species• HG- Converts species to a hydride (gas)• AFS – Detects each specie. DL = ~1 g/L• Only detects hydride-forming arsenic
As(III)
MMADMA
As(V)
0 5 10 15Retention time (secs)
Filter – Particulate phase
Analysed for Total As by ICP-MS *(EPA Method 6020)
Microwave digestion with nitric acid (HNO3)(EPA Method 3051)
* Inductively Coupled Plasma-Mass Spectrometry
Step 2 – Particulate Phase
Unfiltered sampleAnalysed for Total As by ICP-MS
Analysed for Total As by ICP-MS* (EPA Method 6020)
Microwave digestion with nitric acid (HNO3)(EPA Method 3051)
* Inductively Coupled Plasma-Mass Spectrometry
Step 3 – Total Arsenic
Total & Particulate Arsenicby ICP-MS
• Sample dispersed in stream of argon gas• ICP- converts sample to ions• MS – separate ions by to mass & counted• Detection limit = ~0.1 g/L• Detects all arsenic
GW Speciation ResultsHPLC-HG-AFS
MSW
As(III)g/L)
As(V)g/L)
MMAg/L)
DMAg/L)
<1--
<1
-3.3<1-
----
----
FacilityTotalg/L)
<13.3<1<1
• Most GW samples analysed contained no detectable arsenic
Leachate Results
MSW
C&D
As(III) As(V) MMA DMA0.5-
5.74.33<1
3.653.31.6<13.3<1--
<1
8.216.213.37.8<19.93.410.2<15.3-
3.3<1-
------
<16.5------
------
2.2<1------
Facility
AFSTot. Diss.8.7
16.219
12.13<2
13.55<9.9<19.3
<28.6<13.3<1<1
ICP-MSDiss.+Part.35.23
43.4897.24
NA36.5039.28128.8
992.956.80227.535.2915.54
6.7822.372
g/L)
0
20
40
60
80
100
120
140
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
HST-T
Leachate Results
140120100806040200
1 2 3 4 5 6 7 8 910
11
12
15
13
14
Conc.(g/L)
Landfills
Diss. by HPLC-HG-AFS(readily forming hydride arsenic)
Diss.+Part. by ICP-MS(all arsenic)
Particulate phasein leachate very small
HG-AFS vs ICP-MS
MSW
MSW
AFSTot. Diss.
16.2
13.3
Facility
ICP-MSTot. Diss.
34.33
22.18
ICP-MSDiss.+Part.
41.05
32.92
ICP-MSTot. Part.
1.18
1.68
++
hydride forming
arsenic in diss.
all units = g/L)
all arsenicIn diss.
all arsenicIn part.
all arsenic
In sample
HG-AFS vs ICP-MS
MSW 1
MSW 2
AFSTot. Diss.
16.2
13.3
Facility
ICP-MSTot. Diss.
34.33
22.18
ICP-MSDiss.+Part.
41.05
32.92
ICP-MSTot. Part.
1.18
1.68
++
hydride forming
arsenic in diss.
all units = g/L)
all arsenicIn diss.
all arsenicIn part.
all arsenic
In sample
50
40
30
20
10
0
HG-AFS vs ICP-MS
MSW
1
g/LT
D-ICP
D-AFS
TD-ICP
D-AFS
MSW
2Not all arsenic readily converted to hydrides (non-labile) – not detectable by HG-AFS
hidden
arsenic
Matrix Interference by HPLC-HG-AFS
71421
As(III)
As(V)
MMA
DMA
g/Lspike
909391
104
150
100
129136100
96113103
• Good recoverability for As III & As V• Indicates – HPLC-HG-AFS capable of
detecting arsenic once it can be converted to a hydride (labile)
Conclusion of Results• Samples from GW and leachate mostly
in the inorganic form (As III & AsV)• Inorganic arsenic (As III & As V) are
much more toxic than organic arsenic• Speciation of samples show low conc.
of arsenic (2-20 g/L), total analysis show considerable more As present (2-130 g/L)
• Indicates most of the As is tied up (non-labile) & cannot form hydrides easily & therefore are not detectable by HG-AFS
• Further analysis is required
Conclusion of Results• Samples from GW and leachate mostly
in the inorganic form (As III & AsV)• Inorganic arsenic (As III & As V) are
much more toxic than organic arsenic• Speciation of samples show low conc.
of arsenic (2-20 g/L), total analysis show considerable more As present (2-130 g/L)
• Indicates most of the As is tied up (non-labile) & cannot form hydrides easily & therefore are not detectable by HG-AFS
• Further analysis is required
Conclusion of Results• Samples from GW and leachate mostly
in the inorganic form (As III & AsV)• Inorganic arsenic (As III & As V) are
much more toxic than organic arsenic• Speciation of samples show low conc.
of arsenic (2-20 g/L), total analysis show considerable more As present (2-130 g/L)
• Indicates most of the As is tied up (non-labile) & cannot form hydrides easily & therefore are not detectable by HG-AFS
• Further analysis is required
Conclusion of Results• Samples from GW and leachate mostly
in the inorganic form (As III & AsV)• Inorganic arsenic (As III & As V) are
much more toxic than organic arsenic• Speciation of samples show low conc.
of arsenic (2-20 g/L), total analysis show considerable more As present (2-130 g/L)
• Indicates most of the As is tied up (non-labile) & cannot form hydrides easily & therefore are not detectable by HG-AFS
• Further analysis is required
Conclusion of Results• Samples from GW and leachate mostly
in the inorganic form (As III & AsV)• Inorganic arsenic (As III & As V) are
much more toxic than organic arsenic• Speciation of samples show low conc.
of arsenic (2-20 g/L), total analysis show considerable more As present (2-130 g/L)
• Indicates most of the As is tied up (non-labile) & cannot form hydrides easily & therefore are not detectable by HG-AFS
• Further analysis is required
Current Work • Environmental Experiment:
Continue quantification of arsenic species from C&D landfills (Florida):– Groundwater samples– Leachate samples
• Laboratory Experiment: Analyze leachate from lysimeters designed to simulate C&D landfill conditions – filled with treated and untreated wood waste
• Subject unburned wood & wood ash to the TCLP & SPLP
Current Work • Environmental Experiment:
Continue quantification of arsenic species from C&D landfills (Florida):– Groundwater samples– Leachate samples
• Laboratory Experiment: Analyze leachate from lysimeters designed to simulate C&D landfill conditions – filled with treated and untreated wood waste
• Subject unburned wood & wood ash to the TCLP & SPLP
Current Work • Environmental Experiment:
Continue quantification of arsenic species from C&D landfills (Florida):– Groundwater samples– Leachate samples
• Laboratory Experiment: Analyze leachate from lysimeters designed to simulate C&D landfill conditions – filled with treated and untreated wood waste
• Subject unburned wood & wood ash to the TCLP & SPLP
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