1 / 32

Arsenic Speciation - Year 4/5

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

sienna
Download Presentation

Arsenic Speciation - Year 4/5

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Arsenic Speciation - Year 4/5 Bernine Khan University of Miami Dept. of Civil, Architectural & Environmental Engineering July 9th, 2001

  2. Speciation 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

  3. Why Are We Interested in 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.)

  4. 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) *

  5. 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) *

  6. 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

  7. 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) *

  8. Arsenic Mobility Eh-pH diagram 0.75 0.50 0.25 0 -0.25 -0.50 -0.75 Oxidizing Condition As(V) +5 As(III) +3 • Measure of system state (O2/no O2) • Soluble As increases with decreasing Eh & increasing pH Eh (volts) AsS +3 As(III) -3 AsH3 (aq) As Reducing Condition 0 2 4 6 8 10 12 14 pH

  9. Arsenic Mobility Eh-pH diagram 0.75 0.50 0.25 0 -0.25 -0.50 -0.75 Oxidising Condition As(V) +5 Most surface waters As(III) +3 Most ground waters Eh (volts) AsS +3 Predicted Landfills As(III) -3 AsH3 (aq) As Reducing Condition 0 2 4 6 8 10 12 14 pH

  10. Field Sampling Methods • Samples 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

  11. Current Research Study • 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 ICP-MS – Total Arsenic

  12. Step 1 – Dissolved Phase Sample Sample filtered through 0.45 mm PVDF filter Filtrate (dissolved phase) Analysed for As species by HPLC-HG-AFS* * HPLC-HG-AFS - High Performance Liquid Chromatography- Hydride Generation-Atomic Fluorescence Spectrometry

  13. Speciation by HPLC-HG-AFS • HPLC- Separates the arsenic species • HG- Converts species to a hydride (gas) • AFS – Detects each specie. DL = ~1 mg/L • Only detects hydride-forming arsenic As(III) DMA MMA As(V) 0 5 10 15 Retention time (secs)

  14. Step 2 – Particulate Phase Filter – Particulate phase Microwave digestion with nitric acid (HNO3) (EPA Method 3051) Analysed for Total As by ICP-MS * (EPA Method 6020) * Inductively Coupled Plasma-Mass Spectrometry

  15. Step 3 – Total Arsenic Unfiltered sample Analysed for Total As by ICP-MS Microwave digestion with nitric acid (HNO3) (EPA Method 3051) Analysed for Total As by ICP-MS* (EPA Method 6020) * Inductively Coupled Plasma-Mass Spectrometry

  16. 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 mg/L • Detects all arsenic

  17. GW Speciation ResultsHPLC-HG-AFS MMA (mg/L) As(V) (mg/L) As(III) (mg/L) DMA (mg/L) Total (mg/L) Facility <1 - - <1 - 3.3 <1 - - - - - <1 3.3 <1 <1 - - - - MSW • Most GW samples analysed contained no detectable arsenic

  18. Leachate Results ICP-MS Diss.+Part. AFS Tot. Diss. As(V) As(III) MMA Facility (mg/L) DMA MSW C&D 0.5 - 5.7 4.33 <1 3.65 3.3 1.6 <1 3.3 <1 - - <1 8.2 16.2 13.3 7.8 <1 9.9 3.4 10.2 <1 5.3 - 3.3 <1 - 8.7 16.2 19 12.13 <2 13.55 <9.9 <19.3 <2 8.6 <1 3.3 <1 <1 35.23 43.48 97.24 NA 36.50 39.28 128.89 92.95 6.802 27.53 5.291 5.54 6.782 2.372 - - - - - - <1 6.5 - - - - - - - - - - - - 2.2 <1 - - - - - -

  19. Leachate Results Conc. (mg/L) 140 120 100 80 60 40 20 0 Diss. by HPLC-HG-AFS (readily forming hydride arsenic) Diss.+Part. by ICP-MS (all arsenic) Particulate phase in leachate very small 4 5 8 9 10 11 12 13 14 15 3 1 2 6 7 Landfills

  20. HG-AFS vs ICP-MS all units = mg/L) hydride forming arsenic in diss. all arsenic In diss. all arsenic In part. all arsenic In sample AFS Tot. Diss. ICP-MS Tot. Part. ICP-MS Diss.+Part. ICP-MS Tot. Diss. Facility 41.05 32.92 1.18 1.68 MSW MSW 16.2 13.3 34.33 22.18 + +

  21. HG-AFS vs ICP-MS all units = mg/L) hydride forming arsenic in diss. all arsenic In diss. all arsenic In part. all arsenic In sample AFS Tot. Diss. ICP-MS Tot. Part. ICP-MS Diss.+Part. ICP-MS Tot. Diss. Facility 41.05 32.92 1.18 1.68 MSW 1 MSW 2 16.2 13.3 34.33 22.18 + +

  22. HG-AFS vs ICP-MS 50 40 30 20 10 0 T D-ICP T D-ICP mg/L D-AFS hidden arsenic D-AFS MSW 1 MSW 2 Not all arsenic readily converted to hydrides (non-labile) – not detectable by HG-AFS

  23. Matrix Interference by HPLC-HG-AFS • Good recoverability for As III & As V • Indicates – HPLC-HG-AFS capable of detecting arsenic once it can be converted to a hydride (labile) MMA % As(V) % As(III) % DMA % mg/L spike 7 14 21 90 93 91 104 150 100 129 136 100 96 113 103

  24. 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 mg/L), total analysis show considerable more As present (2-130 mg/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

  25. 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 mg/L), total analysis show considerable more As present (2-130 mg/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

  26. 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 mg/L), total analysis show considerable more As present (2-130 mg/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

  27. 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 mg/L), total analysis show considerable more As present (2-130 mg/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

  28. 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 mg/L), total analysis show considerable more As present (2-130 mg/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

  29. 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

  30. 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

  31. 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

  32. Questions ? ? Questions Questions Questions Questions

More Related