Soil properties and metal accumulation by earthworms in the Siena urban area (Italy)

This paper reports the results of a study focused on the metal (Cd, Co, Cr, Cu, Ni, Pb, Sb, U and Zn) distri-bution in soils and uptake and accumulation by earthworms Nicodrilus caliginosus (Savigny) from urban,peri-urban, green-urban and non-urban zones of Siena municipality (central Italy). The main goal wasto define the influence of soil properties and metal soil contents on the uptake of these contaminantsby earthworms. Data indicated that Cd, Cu, Pb, Sb and Zn soil contents increased in the following order:non-urban < green-urban < peri-urban < urban soils, suggesting that vehicular traffic affects the distribu-tion of these metals. Pb and Sb were the main soil contaminants and their highest enrichments werefound in urban sites where stop-and-go traffic occurs. Concentrations of these traffic-related metals inearthworms showed a distribution pattern similar to that in soil, suggesting that soil contamination influ-enced the uptake of Cd, Cu, Pb, Sb and Zn by N. caliginosus. There were significant positive correlationsbetween Cd, Pb and Sb earthworm concentrations and their soil contents. The lack of correlation for Cuand Zn could be due to the physiological regulation of these elements by earthworms. Statistical analysispointed out that the uptake and accumulation of Cd, Cu, Pb, Sb and Zn by earthworms were affected bysome soil physicochemical properties such as the organic carbon and carbonate contents that are able torule the bioavailability of metals in soils.