Metals distribution in the organic and inorganic fractions of soil: a case study on soils from Sicily

Abstract

The content of Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn, has been determined in the organic and inorganic fraction of eight soil samples from Sicily. A modified type-Tessier sequential extraction procedure has been used to recognize metals in five different fractions categorised as follows: (a) exchangeable metals, (b) metals bound to carbonates, (c) metals bound to iron and manganese oxides, (d) metals bound to organic matter, and (e) metals in residual fraction. The mineralogical composition of soils samples was characterized by X-ray diffraction. Humic substances were extracted by means of an alkaline extraction procedure. It has been found that both the mineralogical composition and the different content of humic fraction of organic matter in the soils investigated are responsible for the observed trace metal distribution. The obtained data show that a significant amount of trace metals is bound to the organic fraction where different binding sites are present simultaneously. In particular, Pb and Cu seem to be the elements more tightly linked to the organic fraction of soils, whilst cadmium is mostly concentrated into the iron and manganese oxides fraction. The presence of clay minerals in soil is significant for metal distribution, playing a fundamental role in binding metal ions. Besides, it has been observed that the calcophile metal mobility is strongly dependent on the presence of sulfide phases. Applying the Risk Assessment Code to the analyzed soils, it appears that they contain, generally, less than 30% of metals in the exchangeable and carbonate fractions. Calcic brown soil from Piano Zucchi exhibits a medium up to very high risk for Pb, Cd, Co, Zn and Mn. It also been recognized the elevated presence of Cd in the exchangeable and carbonate fractions of andic brown soil on volcanites from Pachino.

Potential use of sicilian landraces in biofortification of modern durum wheat varieties: Evaluation of caryopsis micronutrient concentrations

“…On average, Sicilian landraces showed grain-Fe concentration increased by 32%, grain-Zn by 21%, grain-Mn varied of 38% compared to modern cultivars (Cu was the only element showing significant reduction). Such microelement concentrations are in line or in greater degree, at varying of element bioavailability in soil (Giacalone et al 2005), with those available in literature. A comparative work on Fe and Zn concentrations in Iranian landraces and commercial varieties (Heidari et al 2016) shows Fe concentration in landraces ranging from 24.9 to 66.5 (mg kg -1 ) and Zn concentration from 18.7 to 38.7, while in commercial cultivars Fe varied between 38.9 and 54.9 mg kg -1 while Zn ranged from 12.4 to 27.2 mg kg -1 .…”

Metal (Loid)s in Farmland Soils and Strategies to Reduce Bioavailability

“…On the contrary, Pb and Cu seemed to be more tightly bound to the organic fraction while cadmium was mostly bound to the Fe/Mn oxides fraction in contaminated soils from Sicily; though a signifi cant amount of all HMs (Cd, Pb, Cu, Co, Cr, Fe, Mn, Ni, Zn) were bound to the organic fraction [46]. The oxidic fraction usually has more affi nity for Pb than Cd, so this may be due to high concentration and strong negative charges on organic fraction of the soil.…”

Forest Humus Type Governs Heavy Metal Accumulation in Specific Organic Matter Fractions

“…The higher content of these fractions, the higher the accumulation of the mentioned metals, which would indicate the considerable importance of these fractions in metal binding. The geochemical mobility of toxic metals in soils depends on how and which soil phase they are bound to and their chemical form (Giacalone et al 2005). In mineral horizons of the tested humus types, all heavy metals exhibited a clear positive association with the amount of C oLF , whereas the strongest relationship with C MAF was shown by the concentration of Cd, Co, Mn, and Zn.…”