Department of Applied Chemistry and Physics Faculty of Agriculture and forestry Remediation of lead-contaminated soils - challenges and options Helinä Hartikainen, Mirva Levonmäki and Salla Hartikainen

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

Shooting ranges - a special problem 1/ 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

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

Theoretical background of the study Detrimental effect of Pb to biota depends on its species free Pb 2+ 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

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 1. Are trees naturally present in shooting range areas able to stabilize Pb? 2. Is their growth affected by Pb? 3. Can phytoextraction be enhanced by peat-derived soluble complexing agents?

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

Soil material Hälvälä shooting range soil pellets in 100-g samples from the surface humic layer total acid soluble Pb mg/kg (after removing the pellets )  50% in exchangeable form potentially bioavailable complexation capacity of the humic soil layer seemed to be exceeded

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

Microcosms Uncontaminated coarse-textured mineral soil in the root zone Humic soil layer from heavily contaminated sector (acid soluble Pb ~ 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

Analyses 14 CO 2 fixation was measured at the end of the experiment 14 C activity of different plant parts was determined Pb in various plant parts was determined

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

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

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

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

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%)

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

Siilinjärvi apatite pit The largest phosphate mine in Western Europe produces - apatite about t/a - biotite t/a

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

IMMOBILIZATION OF Pb BY UNTREATED BIOTITE WITHIN 24 H

IMMOBILIZATION OF Pb BY ACID-TREATED BIOTITE WITHIN 24 H

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 R eaction time has little or no effect on the retention

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