Amending contaminated soils with organic wastes can influence trace element mobility and toxicity. Soluble concentrations of metals and arsenic were measured in pore water and aqueous soil extracts following the amendment of a heavily contaminated mine soil with compost and biochar (10% v:v) in a pot experiment. Speciation modelling and toxicity assays (Vibrio fischeri luminescence inhibition and Lolium perenne germination) were performed to discriminate mechanisms controlling metal mobility and assess toxicity risk thereafter. Biochar reduced free metal concentrations furthest but dissolved organic carbon primarily controlled metal mobility after compost amendment. Individually, both amendments induced considerable solubilisation of arsenic to pore water (>2500 μg l−1) related to pH and soluble phosphate but combining amendments most effectively reduced toxicity due to simultaneous reductions in extractable metals and increases in soluble nutrients (P). Thus the measure–monitor-model approach taken determined that combining the amendments was most effective at mitigating attendant toxicity risk.
Bibliographical noteAcknowledgements: The authors wish to thank Claire Deacon, Ken Cruickshank, Anette Moran, Dave Hadwen and Lenka Maděrová (University of Aberdeen) and Renate Wendler (The James Hutton Institute) for their assistance with analysis of samples. The authors also gratefully acknowledge the support of COST Action TD 1107 ‘Biochar as option for sustainable resource management’ for granting a short term scientific mission (STSM), which assisted the completion of experimental work for this paper.
- soil contamination
- organic amendments
- trace elements
- pore water