Solid-phase speciation and phytoavailability of copper in representative soils of Italy

Abstract

A study was conducted to determine the solid phase distribution of copper in representative soils of Italy with wide differences in the chemical and physicochemical properties. Sites selected varied in location as well in current vegetation and land use. Samples with a high load of Cu, 133.2 -252.9 mg kg À 1 from a vineyard cultivation area were also included to study the effect of contamination on the distribution of Cu amongst solid-phases. The solid-phase fractionation of Cu in the soils was determined using a nine-step selective sequential extraction method. The results indicated that copper was dominantly associated with organic binding sites, 62.6 -74.8%. The relative importance of the solidphase fractions in assessing the Cu phytoavailability by durum wheat in a greenhouse setting and the effectiveness of two soil tests, the DTPA -TEA and NH 4 Cl extraction methods, for predicting the phytoavailable Cu was studied. Most of Cu was retained by roots with very limited translocation to the upper plant parts of wheat. Both soil tests correlated well with the Cu content in the durum wheat (Triticum turgidum var. durum L.) plant (r 2 =0.99; P=0.0001). A significant correlation (r=0.960, P= 0.0001) was found between the plant Cu content and the Cu associated with metal -fulvic complexes, indicating that copper was mainly available through the metal -fulvic complexes. The contaminated soils (soils nos. 9 and 10) had a significantly higher proportion (77%) of Cu associated with organic binding sites, in comparison to that of uncontaminated soil (soil no. 8) (21.3%), resulting in higher proportion of phytoavailable Cu.

Mobility and Bioavailability of Heavy Metals and Metalloids in Soil Environments

“…The bioavailability of heavy metals and metalloids, their biological uptake, and their eco-toxicological effects on the soil biota can be better understood in terms of their chemical speciation. The mobility and bioavailability, and hence potential toxicity of metal in the soil depend on its concentration in soil solution, the nature of its association with other soluble species, and soil ability to release the metal from the solid phase to replenish that removed from soil solution by the plants (Krishnamurti and Naidu, 2002;Huang and Gobran, 2005;Krishnamurti et al, 2007).…”

Transformation of Lead Solid Fraction in the Rhizosphere of Elsholtzia splendens: The Importance of Organic Matter

“…This was most likely due to the accumulation of root exudates in the rhizospheric region. Therefore, root exudates play an important part in the enhanced amount of organic matter in the rhizosphere and increase the Pb-fulvic complexes, thus enhancing its phytoavailability because metal-fulvic complexes, such as Cu, Zn, and Cd, show a close relationship to their phytoavailability (Krishnamurti and Naidu 2002;Krishnamurti et al 2004;Krishnamurti et al 2007). Microorganisms, as a major component of organic matter in the rhizosphere, are also widely recognized as important contributors to the biogeochemical cycle of trace elements in terrestrial environments through several microbially mediated processes such as biosorption, complexation, dissolution, and redox reactions, thus affecting the bioavailability of metals (CloutierHurteau et al 2008).…”

“…The organically bound fractions are relatively stable under normal soil conditions and generally considered to have low phytoavailability. However, recent research work shows fulvic complexes of heavy metals have a close relationship with their phytoavailability (Krishnamurti and Naidu 2002;Krishnamurti et al 2007). Therefore, any alteration of this fraction of Pb-fulvic complexes in the rhizosphere deserves close attention.…”

“…The two methods both defined speciation of heavy metals released in the oxidizable step as "organic-bound fractions," and this fraction is thought to be associated with stable high molecular weight humic substances with a low bioavailability (Filgueiras et al 2002). However, more and more evidence indicates organic-bound metals have a close relationship to metal bioavailabilty (Romkens et al 1999;Parker et al 2001;Cattani et al 2006;Krishnamurti et al 2007), and exogenous humic substances enhanced the potential phytoavailability and uptake of heavy metals (e.g., Pb, Cd) by plants (Halim et al 2003;Khan et al 2006). Furthermore, the organic-bound fraction of heavy metals shows significant differences between the rhizosphere soil and non-rhizosphere soil of different plants.…”

“…Moreover, Krishnamurti et al (1995) proposed a modified sequential extraction fractionation scheme for Cd, which defined the fractions as exchangeable, specifically adsorbed, bound to metalorganic complexes, easily reducible metal oxides, organics, amorphous mineral colloids, and crystalline Fe oxides, and detrital (bound to mineral lattices). The scheme was modified by Krishnamurti and Naidu (2002), who showed the great importance of heavy metals associated with metal-fulvic complex binding sites on metal phytoavailability in natural and contaminated soils (Krishnamurti and Naidu 2000;Krishnamurti and Naidu 2002;Krishnamurti et al 2007). This SSE method provides an alternative approach for investigating the transformation of heavy metal fractions, especially different organically bound fractions, in soil of the rhizosphere.…”