Arsenic Speciation - Year 4/5 Bernine Khan University of Miami Dept. of Civil, Architectural & Environmental Engineering July 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 AsH 3 - 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 AsH 3 - 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 AsH 3 - 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 AsH 3 - 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 (O 2 /no O 2 ) Soluble As increases with decreasing Eh & increasing pH Arsenic Mobility Eh-pH diagram pH Eh (volts) Reducing Condition As(V) +5 As(III) +3 As(III) -3 AsH 3 (aq) AsS +3 As

Oxidising Condition Arsenic Mobility Eh-pH diagram pH Eh (volts) Reducing Condition As(V) +5 As(III) +3 As(III) -3 AsH 3 (aq) AsS +3 As Most surface waters Most ground waters Predicted Landfills

Field Sampling Methods Samples collected : –background & detection wells –purged for 20 minutes –Temperature, pH & ORP –stored on ice –refrigerated <4 o C –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) MMA DMA As(V) Retention time (secs)

Filter – Particulate phase Analysed for Total As by ICP-MS * (EPA Method 6020) Microwave digestion with nitric acid (HNO 3 ) (EPA Method 3051) * Inductively Coupled Plasma-Mass Spectrometry Step 2 – Particulate Phase

Unfiltered sample Analysed for Total As by ICP-MS Analysed for Total As by ICP-MS* (EPA Method 6020) Microwave digestion with nitric acid (HNO 3 ) (EPA Method 3051) * Inductively Coupled Plasma-Mass Spectrometry Step 3 – Total Arsenic

Total & Particulate Arsenic by 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 Results HPLC-HG-AFS MSW As(III)  g/L) As(V)  g/L) MMA  g/L) DMA  g/L) <1 - < < Facility Total  g/L) <1 3.3 <1 Most GW samples analysed contained no detectable arsenic

Leachate Results MSW C&D As(III) As(V) MMA DMA < <1 3.3 <1 - < < < <1 - < <1 - Facility AFS Tot. Diss < <9.9 <19.3 <2 8.6 <1 3.3 <1 ICP-MS Diss.+Part NA  g/L)

Leachate Results Conc. (  g/L) Landfills Diss. by HPLC-HG-AFS (readily forming hydride arsenic) Diss.+Part. by ICP- MS (all arsenic) Particulate phase in leachate very small

HG-AFS vs ICP-MS MSW AFS Tot. Diss Facility ICP-MS Tot. Diss ICP-MS Diss.+Part ICP-MS Tot. Part hydride forming arsenic in diss. all units =  g/L) all arsenic In diss. all arsenic In part. all arsenic In sample

HG-AFS vs ICP-MS MSW 1 MSW 2 AFS Tot. Diss Facility ICP-MS Tot. Diss ICP-MS Diss.+Part ICP-MS Tot. Part hydride forming arsenic in diss. all units =  g/L) all arsenic In diss. all arsenic In part. all arsenic In sample

HG-AFS vs ICP-MS MSW 1  g/L T D-ICP D-AFS T D-ICP D-AFS MSW 2 Not all arsenic readily converted to hydrides (non- labile) – not detectable by HG-AFS hidden arsenic

Matrix Interference by HPLC-HG-AFS As(III)  As(V)  MMA  DMA   g/L spike 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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