Introduction Ghent University Arsenic Speciation Inorganic - - PDF document

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Ghent University Faculty of Bioscience Engineering Department of Applied Analytical and Physical Chemistry Laboratory of Analytical Chemistry and Applied Ecochemistry

Arsenic and Arsenic Speciation

Pradeep Alava Promoter: Filip Tack, Tom van de Wiele Co-Promoter: Gijs Du Laing

Contact mail: Pradeep.alava@UGent.be

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Introduction

Arsenic = Toxic Regulatory limits EPA – RfD - 0.3 µg/kg/day ATSDR – MRL – 0.3 µg/kg/day (chronic exposure) WHO – 10 µg/l drinking water

OSHA – Workplace air 0.5 mg/m3

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Introduction Arsenic Speciation

Inorganic

• Pentavalent (AsV)
• Trivalent (As III)

Organic

Methylated

• Pentavalent (DMA V, MMA

V etc)

• Trivalent (DMA III, MMAIII)

Thiolated (MMTA, DMDTA etc)

• Inorganic forms are more toxic than pentavalent methylated species
• Trivalent methylated species are more toxic than inorganic species
• Speciation studies are very important to assess the toxicity.

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Objective

To assess the physical, chemical and microbial effect

• n

biotransformation of As species in human gastrointestinal tract. Development of a analytical method to identify and quantify different As species. Incubation experiments using SHIME, where we can mimic human gut environment to study microbial affect. Assess the Physical and chemical factors effecting biotransformation of arsenic species

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Method Development

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Method Development

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• mimicks physicochemical, enzymatic

and microbiological processes of the human intestine

• validated against in vivo data

concerning

– microbial community composition – microorganism-associated enzymatic activities

• long-term-stability of the microbial

community composition

Molly et al. (1993) Appl Microbiol Biotechnol, 39, 254-258. Molly et al. (1994) Microbial Ecol Health Disease, 7, 191-200 Possiemiers et al. (2004) Fems Microbiol Ecol, 49, 495-507

Incubation Experiment ( SHIME)

stomach small intestine colon ascendending transverse descendending stomach

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Sample Preparation

0.5g sample 50 mL polypropylene tubes 10 ml MilliQ water Microwave Digestion At 80oC Made up to 25 mL Total Analysis 0.5g sample 50 mL polypropylene tubes 10 ml MilliQ water Microwave Digestion At 80oC Speciation Analysis Incubated sample Centrifuged Supernatant and pellet collected Freeze Thawed before analysis Total analysis on pellet, Speciation analysis on supernatant

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Analytical Setup

Nebulizer Torch Mass analyzer Detector

Total Analysis of Arsenic

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Analytical Setup

nebulizer & spray chamber gas controller ICP torch turbo molecular pump Q-pole mass filter Ar gas rotary pump turbo molecular pump liquid chromatograph

Speciation Analysis of Arsenic

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Results

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Results

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Results

• HPLC-ICP-MS hyphenated method developed to identify and

quantify seven different arsenic species.

• Biotransformation to trivalent methylated species and

thiolated species took place after incubating rice samples in SHIME.

• No thiolation or methylation obesrved in autoclaved SHIME

incubations.

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Conclusions

• Currently able to detect and quantify total

amount of arsenic and different arsenic species even at non equimolar ratios in water, environment samples, food samples etc.

• Future perspective : Assessment of Physical

and chemical factors affecting transformation

• f As species within the gastrointestinal tract.

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