Partitioning of Zn, Cd, Pb, and Cu in organic-rich soil profiles in the vicinity of a zinc smelter

Abstract

A five-step sequential extraction procedure was applied to organic-rich soil samples from five soil profiles situated 1 -8 km from a zinc smelter. The partitioning of Zn, Cd, Pb, and Cu into five operationally defined fractions (exchangeable, ''carbonate''-bound, reducible, oxidizable, and residual) was studied at different soil depths down to 35 cm. In the surface soil (0 -1 cm) a major part of Pb and Cu was extracted in the oxidizable fraction, whereas for Zn and Cd slightly more was extracted in the ''carbonate''-fraction than in the other four fractions. Extracted metal proportions in the oxidizable fraction were respectively of the order of 30%, 20%, 50%, and 80% for Zn, Cd, Pb, and Cu in the surface soil for all sites, but these proportions decreased with soil depth. In the surface soil less than 20% of all the elements were extracted in the residual fraction, but the proportions associated with this fraction generally increased with soil depth. In the C-horizon, differences in extracted proportions of Pb and Cu in the residual fraction were probably due to geochemical factors, whereas for Zn the low extracted proportion at a highly contaminated site (20%) may be due to Zn migration to the C-horizon at this site. For Cd the extracted proportions in the C-horizon were lower than for the other elements, generally below 20%, presumably because Cd is weaker in terms of its adsorption to the soil than the other elements studied. Total concentrations of the metals decreased strongly with increasing distance from the smelter, but less systematic differences were observed for their distributions among fractions. Potentially bioavailable metal proportions (exchangeable þ ''carbonate''-bound fraction) in the surface soil were about 50%, 60%, 20%, and 10% for Zn, Cd, Pb, and Cu, respectively. In C-horizon soil the mobility sequence Cd4Zn!Pb ¼ Cu was generally observed. The present results indicate that the concentrations and chemical fractionation of Zn, Pb, and Cd in these soils represent a considerable risk to natural terrestrial food chains.

Impact of Abattoir Wastes on Trace Metal Accumulation, Speciation, and Human Health–Related Problems in Soils Within Southern Nigeria

“…The trends for the several fractions of Zn in the studied soils and control site are OX > RED > AEX > RES and RES >> RED > AEX > OX, respectively. Cu also existed principally in the oxidizable fraction which is in agreement with the results by Svendsen et al 102 and Ebong et al 103 This could be the consequence of the high tendency of OM in forming stable complexes with organic substances in soil. 104,105 Nevertheless, Cu existed mostly in the residual fraction in the control site.…”

An Ex-Situ Immobilization Experiment with Zn, Pb, and Cu in Dredged Marine Sediments from Bohai Bay, China

“…Trace metals of Zn, Pb, and Cu in each fraction were analyzed by a volt-ampere spectrometer (797 VA Computrace, Metrohm, Herisaucity, Switzerland). The mobility factor (MF%) has been defined as the percentage of metals in the acid exchangeable fraction in the cumulative total extracted amount of the metal, which was used to express the immobilization effect of different immobilizing agents [48,49]. Among the four fractions, which were extracted in sequential extraction, the first fraction (acid exchangeable fraction) contains the metals with the highest mobility and is readily available to organisms, thus having the most severe toxicity and ecological risk [50].…”

Metal Mobility in Afforested Sites of an Abandoned Zn-Pb Ore Mining Area

“…The chemical forms of metals (Figure 6) are related to the properties of the particular element rather than to the position of the profile within each heap. The average acid values of the extractable fraction indicate that Zn and Pb follow the highest potential mobility of Cd, reflecting a well-known regularity for these elements [3,[39][40][41]. The mobility of the elements is also generally weakly affected by depth.…”