Environmental availability of trace elements (Pb, Cd, Zn, Cu) in soil from urban, suburban, rural and mining areas of Attica, Hellas

The environmental availability of trace elements (Pb, Cd, Zn, Cu) in soil samples from the urban area of Athens and Piraeus is compared to that from samples of suburban, uncontaminated rural and the nearby historical mining area of Lavrion in Attica. These trace elements had been previously shown to be related to anthropogenic activities in the urban chemical environment of Athens. Trace element environmental availability is determined by using three single stage chemical extractions of (i) nitric acid (HNO3), (ii) ethylenediaminetetraacetic acid (EDTA) and (iii) acetic acid (CH3COOH), and the respective extractabilities are calculated as ratios relative to total element concentrations. All elements showed the same decreasing concentration trend in the order mining > urban > suburban ≈ rural soil categories. Median concentration, based on aqua regia dissolution, are 185, 173, 86, 0.4 mg/kg and 2.26% for Pb, Zn, Cu, Cd and Fe, respectively, for the urban soil samples. Whereas, the corresponding median concentrations of Pb, Zn and Cd in Lavrion soil are over ten times higher. The ratios of the extractable concentrations of Pb, Zn and Cd, relative to the aqua regia extractable content in soil, are also higher for the mining soil category. Extractable concentrations for all the studied elements are highly dependent on their respective aqua regia extractable values in all land use categories; extractability ratios are also controlled by HNO3 extractable Fe in soil. For the two toxic elements, Pb and Cd, the data of this study suggest that environmental availability has to be assessed on a site-specific basis as local conditions, and in particular the mineralogical composition of soil, may influence their relative extractability.