Activities per year
We investigated the interaction of soil Zn with calcium carbonate granules secreted by the earthworm Lumbricus terrestris. Earthworms were kept in agricultural soil amended with ZnSO4 to give Zn concentrations up to 750 mg / kg and in two former mine site soils containing 500 and 120 mg Zn / kg. After 21-42 days the earthworms accumulated 260-470 mg Zn / kg. Granule production was 0.027 - 2.11 mg CaCO3 / earthworm / day and was positively correlated with soil and soil solution pH (r = 0.66 and 0.85 respectively, p < 0.01). Granule Zn concentration was 34 -163 mg / kg. Granules collected from Zn-free control soil and left in Zn-bearing soil for 28 days contained 49-60 mg Zn / kg suggesting that the majority of Zn associates with granules after their secretion. However, synchrotron X-ray fluorescence indicates some incorporation of Zn into granules during their formation. X-ray diffraction and X-ray absorption spectroscopy indicate that the granules are predominantly calcite and the spectroscopy suggests that the Zn is either adsorbed to, or incorporated into, the calcite lattice. X-ray diffraction of the outer c. 35 micron of the granules supports incorporation of Zn into the calcite lattice. The low granule production rates in the mine site soils and the granule Zn concentrations suggest that earthworm secreted calcium carbonate is unlikely to impact significantly on Zn mobility in soils.
Bibliographical noteCopyright © 2014 Elsevier Ltd.
- calcium carbonate