Diapositive 1

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Spatial and Temporal Assessment of high
Resolution Depth profiles Using novel Sampling
Technologies
Mercury analysis (speciation) in porewaters using
the DGT technique
Brussels, September 24, 2004
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Importance of Hg in porewaters

• Hg extremely toxic element
• Toxicity related to the presence of methylated
  forms of Hg
• Monomethylmercury
• Dimethylmercury
• Sediments are the principal sites for the
  methylation of Hg
• Sulfate reducing bacteria are responsible for the
  methylation
• In porewaters methylmercury may account for 90
  of the Hg present

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Hg analysis difficulties

• Routine procedures used for other trace metals
  can often not be applied
• Adsorption on plastic containers
• Low concentrations samples easily contaminated
• Volatile element
• ICPMS problems with memory effects
• Generally specific analytical instrumentation
  (CVAFS, CVAAS) and specific procedures

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Principle of DGT Diffusive Gradient in Thin film

Classical method
Diffusive gel polyacrilamide Resin gel Chelex
Mass of metal accumulated on the gel is dependent
on the exposure time and diffusive thickness (?
g) Diffusive coefficient (D) for the metal must
be determined
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DGT for Hg analysis

• Method developped in University of Brno, Czech
  Republic
• Polyacrylamide gels accumulate Hg! Inadequate as
  diffusive gel
• Better results obtained with agarose gel als
  diffusive gel
• Diffusive coefficient (D) for Hg in agarose gel
  determined
• Direct analysis of the gels in the solid phase
  with the Advanced Mercury Analyser (AMA)
• Comparaison of ion exchange resin (Chelex) and
  resins with thiol groeps (Spherontiol,
  Sumichelate, Dualite, Lewatit) only Spherontiol
  has small particle size)
• Application in field Upper Scheldt, Leie
• Erasmus PhD student Pavel Divis (University of
  Brno)

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Sampling by diving
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(No Transcript)
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Deployment of the DGT probes in the laboratory
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Removing filter and diffusive gel and sectioning
of the resin gel
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Measurements with Advanced Hg Analyser (Lille
Brno)
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Leie Menen

• Agarose diffusive gel
• Resin gels
• Chelex binds labile Hg forms
• Spherontiol binds strongly bound Hg (complexes
  with humic acids, etc and organomercury forms
• Good agreement with total Hg obtained by
  centrifugation of porewater on separate core

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North Sea, Oostende, station 130
In seawater larger fraction of Hg present as
labile Hg due to Cl-complexation In porewaters
large difference between Chelex and Spherontiol
resins Good agreement between Spherontiol and
centrifugation sample Large fraction of Hg
probably present als methylmercury Muddy coastal
sediments are important sources of methylmercury
to the marine environment
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Conclusions DGT Hg

• Due to preconcentration of Hg on the resins it is
  possible to analyse ng/L levels of Hg in
  porewater using the Advanced Hg Analyser (AMA).
  No further sample pretreatment is required
• Using different resins (Chelex, Spherontiol) a
  speciation between the labile and strongly bound
  Hg forms may be made
• Further development is required to determine
  methylmercury with the DGT technique