Accumulation and Fractionation of Iron and Copper in Urban and Rural Soil from Brazilian City

Iron (Fe) and copper (Cu) are essential elements and naturally present in soils. However, these metals content can be altered by natural phenomena and/or anthropic actions, causing changes in the ecological balance. The anthropic actions effects on soil contamination with respect to Fe and Cu accumulation were evaluated through procedures to determine the pseudo-total concentration and fractionation by sequential extraction procedure in soils from a rural and urban area collected in different depths, which the fractions were experimentally defined as exchangeable, carbonate-, reducible (Fe-Mn oxide-), oxidizable (organic matter and sulfites-bound) and residual. Results showed that pseudototal Cu concentrations were 13.7 and 10.5 times and Fe concentrations were 2.8 and 1.5 times higher in the urban area at depths of 5 and 15 cm, respectively, than rural area. The fractionation evidenced the anthropic effects in the different elemental species. In general, the Cu and Fe distribution into the various solid phases showed similar patterns for each sample, which followed order: residual > bound to organic matter > bound to Fe-Mn oxides > bound to carbonates > exchangeable. Nevertheless, the Cu concentration in the fractions exchangeable and bound to carbonates in the rural soil collected at the depth of 15 cm were significantly higher in relation to the depth of 5 cm, while there was no significant difference between Cu concentrations in other fractions at both depths evaluated. On the other hand, unlike that observed in the rural area, in the urban area the fractions of Cu exchangeable (fraction 1) and bound to carbonates (fraction 2) decreased significantly with increasing depth from 5 to 10 cm. In addition, it was observed that significant Cu and Fe amounts were associated with the residual fraction in the soil from both regions, ranging from 20% (Cu: rural, 15 cm) to 91% (Fe: urban, 15 cm) in relation to the pseudo-total concentration. (AU)