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Incorporation of lead into calcium carbonate granules secreted by earthworms living in lead contaminated soils

DOI: 10.1016/j.gca.2011.02.015 DOI Help

Authors: A. Fraser (University of Reading) , D. C. Lambkin (University of Reading) , M. R. Lee (University of Glasgow) , P. F. Schofield (Natural History Museum) , J. F. W. Mosselmans (Diamond Light Source) , M. E. Hodson (University of Reading)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Geochimica Et Cosmochimica Acta

State: Published (Approved)
Published: February 2011
Diamond Proposal Number(s): 1115

Abstract: The influence of soil organisms on metal mobility and bioavailability in soils is not currently fully understood. We conducted experiments to determine whether calcium carbonate granules secreted by the earthworm Lumbricus terrestris could incorporate and immobilise lead in lead- and calcium- amended artificial soils. Soil lead concentrations were up to 2000 mg kg-1 and lead:calcium ratios by mass were 0.5-8. Average granule production rates of 0.39 + 0.04 mgcalcite earthworm-1 day-1 did not vary with soil lead concentration. The lead:calcium ratio in granules increased significantly with that of the soil (r2 = 0.81, p = 0.015) with lead concentrations in granules reaching 1577 mg kg-1. X-ray diffraction detected calcite and aragonite in the granules with indications that lead was incorporated into the calcite at the surface of the granules. In addition to the presence of calcite and aragonite X-ray absorption spectroscopy indicated that lead was present in the granules mainly as complexes sorbed to the surface but with traces of lead-bearing calcite and cerussite. The impact that lead-incorporation into earthworm calcite granules has on lead mobility at lead-contaminated sites will depend on the fraction of total soil lead that would be otherwise mobile.

Journal Keywords: Calcite; Earthworms; Lead; Adsorption; XAS; Biominerals; Calcium carbonate; Cerussite

Subject Areas: Environment

Instruments: I18-Microfocus Spectroscopy