Chemical speciation and solubility of arsenic, cadmium and lead in
contaminated soil from abandoned mine tailing in Toyama prefecture,
Japan
Abstract
Heavy metals such as lead, zinc, copper, arsenic, and cadmium are
usually found in surface soils affected by mining or smelting
activities, agricultural practices, and industrial areas. The total
amount of trace metals in soils is generally not sufficient to assess
the environmental impacts of metal contamination. Therefore, chemical
forms and binding types of metals enable evaluation of their behavior
and bioavailability in the soil environment. Thirty-two soil samples
were analyzed, determining the chemical fractionation of As, Pb and Cd
using by the six-step sequential extraction (SEP), X-ray absorption fine
structure (XAFS), X-ray diffractometer (XRD) and scanning electron
microscopy. The results of SEP showed that most of the Pb were
associated with non-residual fractions, mainly in crystalline (hydrous)
iron oxides (goethite). The Cd appeared mainly associated with adsorbed
fraction in the roots of the dried plants in the soils. The XAFS spectra
of the samples showed that Pb in the soil is adsorption form into
Fe-(hydr)oxides surface. Results of XAFS analysis showed Cd in the
samples were adsorbed on clay minerals. Arsenic appeared mainly
associated with the amorphous and crystalline iron oxides. Heavy metals
are associated with adsorbed fraction, amorphous and crystalline iron
oxides, thus being potentially more mobile to the environment if
conditions were more acidic or reducing. Keywords: Heavy metals, soil,
chemical speciation, sequential extraction