Department of Applied Chemistry and Physics

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Remediation of lead-contaminated soils -
challenges and options
Helinä Hartikainen, Mirva Levonmäki
and Salla Hartikainen

• Department of Applied Chemistry and Physics

Faculty of Agriculture and forestry
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Pb as a soil pollutant in Finland

• Use in gasoline ended in 1994
• still high concentrations on roadsides
• Use in pellets and shots
• forbidden in hunting of aquatic birds
• allowed in other type of hunting
• allowed on shooting ranges

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Shooting ranges - a special problem 1/2

• 2000-2500 open-air ranges
• 60 of them in active use
• Often very heavily polluted
• about 1/3 of the ranges can threaten groundwater
• 4 may cause an immediate health risk
• Uneven distribution of Pb load
• hot spots

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Shooting ranges - a special problem 2/2

• Very complex environments
• Pb is continuously released from shots and
  pellets of different age
• ? large diversity of Pb species and compounds
• Abandoned ranges often
• remain as forested fallow areas used for
  recreation or colonization
• are a risk to biota and humans
• Remediation measures are needed

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Theoretical background of the study

• Detrimental effect of Pb to biota depends on its
  species
• free Pb2 cations are more toxic than the
  complexed forms
• Bioavailability of Pb is limited by
• a high tendency to be retained in soil (several
  mechanisms)
• low permeability of plant cells to Pb
• Harmful effects of Pb may also be latent
• interference with ecosystem functions

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Remediation options 1/2

• Phytoextraction
• Efficiency of depends on the translocation of Pb
  within plant
• translocation to above-ground parts is a
  prerequisite
• Pb may have detrimental effects on plant
  metabolism
• Are trees naturally present in shooting range
  areas able to stabilize Pb?
• Is their growth affected by Pb?
• Can phytoextraction be enhanced by peat-derived
  soluble complexing agents?

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Remediation options 2/2

• Chemical treatment
• Can tailing material from apatite mine be used as
  a sorbent for free Pb cations?
• contains several components contributing to Pb
  retention

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Soil material

• Hälvälä shooting range soil
• 260-530 pellets in 100-g samples from the surface
  humic layer
• total acid soluble Pb 2 000- 43 000 mg/kg (after
  removing the pellets)
• ? 50 in exchangeable form potentially
  bioavailable
• complexation capacity of the humic soil layer
  seemed to be exceeded

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Microcosm experiment

• The aim was to study
• the uptake and allocation of Pb in pine (Pinus
  sylvestris L.)
• the impact of Pb on the photosynthesis and
  transfer of carbon to different plant parts
• to indicate the impact of Pb on plant growth
• if peat is able to promote the transport of Pb to
  roots

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Microcosms

• Uncontaminated coarse-textured mineral soil in
  the root zone
• Humic soil layer from heavily contaminated sector
  (acid soluble Pb 21 000 mg kg-1)
• pellets were not removed
• Uppermost layer peat cover of different
  thickness
• One plant per one experimental unit
• 
  
  
  Peat
• Humic soil
• Mineral soil

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Analyses

• 14CO2 fixation was measured at the end of the
  experiment
• 14C activity of different plant parts was
  determined
• Pb in various plant parts was determined

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Plant responses to Pb

• Biomass was not affected by Pb during 11-week
  growing period
• Mycorrhizas appeared in the rhizosphere in all
  units
• roots were active
• No Pb tocixity symptoms were seen

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Table 1. Total Pb (mg) in various plant parts of
the pine seedlings in different treatments

• Main part of Pb was allocated in roots
• Peat addition
• tended to enhance the Pb allocation in the roots
• reduced the Pb translocation to needles and stems

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• Transfer of 14C to the roots was
• - reduced by high Pb in the needles
• - enhanced by peat addition
  

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Conclusions

• Pb allocated in roots hardy was taken into the
  root cells
• maybe present as extracellular complexes
• Less than 0.1 of acid soluble Pb was
  bioaccessible
• acid soluble Pb cannot be used as a measure for
  the bioavailable Pb or immediate environmental
  risk of Pb
• Peat can be used to stabilize Pb in roots but not
  to enhance the phytoextraction to above-ground
  parts

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Chemical treatment

• Immobilisation of Pb by
• Biotite
• previously a mineral name used to designate the
  whole mineral series (annite-phlogopite)
• refers here to mixture of minerals processed from
  tailings produced in apatite ore enrichment
• main components
• phlogopite (75)
• carbonate minerals (16)
• other minerals (e.g. apatite) (3)

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Chemical properties of Biotite

• Al- and Fe-rich silicate mineral
• ?Al- and Fe(oxy)hydroxides are
• sorbents for heavy metals
• Carbonates function as Pb sorbents and promote
  the retention through
• precipitation or through increase in soil pH
• Apatite is likely to form poorly soluble Pb
  compounds

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Siilinjärvi apatite pitThe largest phosphate
mine in Western Europe produces - apatite
about 800 000 t/a - biotite 70 000 t/a
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Laboratory study

• The aim was to examine
• the ability of Biotite to retain Pb from aqueous
  solution
• the impact of articificial weathering and
  particle size of the mineral on its retention
  capacity
• the effect of reaction time on Pb retention by
  Biotite

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IMMOBILIZATION OF Pb BY UNTREATED BIOTITE WITHIN
24 H
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IMMOBILIZATION OF Pb BY ACID-TREATED BIOTITE
WITHIN 24 H
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Conclusions

• Untreated Biotite efficiently immobilises Pb from
  aqueous solution, the shape of the isotherm
  indicating precipitation
• Small particles retain Pb more than the coarse
  ones
• Weathering increases the Pb sorption capacity
• ?retention mechanisms presumably differed
  from
• those functioning in the untreated
  material
• Reaction time has little or no effect on the
  retention

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Thank you!