Sequential extraction of heavy metals in soils irrigated with wastewater

Abstract

Different chemical forms of cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), lead (Pb), nickel (Ni), and zinc (Zn) were determined in agricultural soils cultivated with lettuce and celery. These soils have been irrigated for several decades with nontreated wastewaters. The chemical forms of the metals were characterized by sequential extraction analysis in five steps, the extracting solutions of which contained 200 mg L -1 nitrilotriacetic acid (NTA). The results showed that Cd, Pb, and Cu exhibited the highest values of extracted metal, and Cr exhibited the lowest value. Almost all of the metals in these soils are bound to iron oxides, followed by the metal complexed to organic matter. The form bound to manganese oxides is equally important to Co. Cadmium is the most mobile metal and its available forms account for 40% of the total extracted. When these metals were determined in plants, both shoots and roots, a greater concentration of Cr, Zn, and Cu was found in celery, and Cu, Ni, and Zn in lettuce, most of the metals being in roots. Only Cd and Co are similarly distributed in shoots and in roots. The relation between the metal contents in plants and the different fractions of the metal in soil was evaluated through linear correlations. Different results were obtained, the forms accounting for the metal in celery are those of the metal bound to iron oxides, while the metal content in lettuce would be related to the exchangeable, bound to manganese oxide, and carbonate forms.

Assessment of heavy metal speciation in soils impacted with crude oil in the Niger Delta, Nigeria

“…A high MF value for heavy metal in soil has been interpreted as evidence of relatively high reactivity and biological availability (Karczewska 1996;Ma and Rao, 1997;Ahumada et al, 1999;Kabala and Singh, 2001). The MF values (Table 2) for the metals at all sites and depths follows the order Cd4Zn4Pb4Ni4Mn4Cu4Cr and the factor decreased with depths except for Cu in few sites (e.g.…”

Pollution, fractionation, and mobility of Pb, Cd, Cu, and Zn in garden and paddy soils from a Pb/Zn mining area

“…It is undoubtedly important to know the total metal concentrations for the purpose of evaluating the level of soil contamination. However, many previous studies have shown that the toxicity and mobility of these pollutants depend strongly on their specific forms or binding state (Ahumada et al 1999;Cornelis 2002;Moćko and Waclawek 2004;Abul Kashem et al 2007). For this reason, the chemical speciation analysis of heavy metals in soil is increasingly important and attracting more attention.…”

“…The relative index of metal mobility was calculated as a "mobility factor (MF)" (Kabala and Singh 2001;Olajire et al 2003), and the high MF values have been interpreted as symptoms of relatively high lability and biological availability of heavy metals in soils (Ma and Rao 1997;Ahumada et al 1999). The MF value was calculated using the following equation:…”

“…In some research work, consistent correlations between specific metal fractions and plant metal contents were found. Similarly, heavy metals in the water/acid soluble and exchangeable fractions are considered to be the most mobile and available forms present in the soils, followed by the carbonate phase (Tessier et al 1979;Ahumada et al 1999;Howari and Banat 2001). The iron and manganese oxide fractions are relatively stable under normal conditions, which are otherwise reduced in acidic conditions (Tessier et al 1979;Banat et al 2005).…”

Depth-wise distribution, mobility and naturally occurring glutathione based phytoaccumulation of cadmium and zinc in sewage-irrigated soil profiles

“…Distribution of heavy metal keeps on continuously changing in soils due to both anthropogenic activities and the natural turn over in rock-soil-plant system below to the depth of 60 m through the soil profile. These metals are associated with various soil components in different ways and these associations influence both their mobility and distribution in the soil profile (Ahumada et al 1999;Adelekan and Alawode 2011).…”