Metal extractability patterns to evaluate (potentially) mobile fractions in periurban calcareous agricultural soils in the Mediterranean area—analytical and mineralogical approaches

Abstract

A set of periurban calcareous agricultural Mediterranean soils was spiked with a mixture of Cd, Cu, Pb and Zn at two levels within the limit values proposed by current European legislation, incubated for up to 12 months, and subjected to various one-step extraction procedures to estimate mobile (neutral salts) and potentially mobile metal fractions (complexing and acidic extraction methods). The results obtained were used to study metal extractability patterns according to the soil characteristics. The analytical data were coupled with mineralogical investigations and speciation modelling using the Visual Minteq model. The formation of soluble metal-complexes in the complexing extracts (predicted by the Visual Minteq calculations) led to the highest extraction efficiency with complexing extractants. Metal extractability patterns were related to both content and composition of carbonate, organic matter, Fe oxide and clay fractions. Potentially mobile metal fractions were mainly affected by the finest soil fractions (recalcitrant organic matter, active lime and clay minerals). In the case of Pb, scarce correlations between extractable Pb and soil constituents were obtained which was attributed to high Pb retention due to the formation of 4PbCO3·3PbO (corroborated by X-ray diffraction). In summary, the high metal proportion extracted with complexing agents highlighted the high but finite capacity to store potentially mobilizable metals and the possible vulnerability of these soils against environmental impact from metal accumulation.

Improving the relationship between soil characteristics and metal bioavailability by using reactive fractions of soil parameters in calcareous soils

“…Soil pH CaCl2 values were generally 0.6 units lower than pH H2O , between –0.4 pH units (soils 2 and 10) and –0.9 pH units (soil 4). The proportion of the active lime represented between 20% and 67% of the equivalent CaCO 3 content, with active lime and equivalent CaCO 3 negatively correlated ( r = –0.655, p < 0.05), indicating a different composition of the carbonate fraction in the soil samples, as previously reported . Such diverging linking between the gradients of the total contents and reactive fractions or pools of soil parameters was also observed for organic, oxide, and metal fractions.…”

“…Climate conditions are typical Mediterranean conditions: an average annual temperature of approximately 13 °C with low interannual variability, average rainfall of 400 mm y −1 , and a potential evaporation of approximately 760 mm y −1 . Soil sampling and characteristics are described elsewhere . Briefly, soil samples were collected from different experimental plots at the El Encín Agricultural Research Station (40°31′23′′N, 03°17′23′′W, 588 m altitude).…”

“…In addition to electrical conductivity and clay content, occurring in both datasets, we selected the relative proportions of crystalline and amorphous Fe and Mn oxides, the pH CaCl2 illustrating the soil base‐saturation degree, and diethylene‐triamine‐pentaacetic acid (DTPA) relative metal extractability (% extractable metal vs total metal content) as the usual parameters chosen for calcareous soils . Moreover, the total equivalent CaCO 3 content was replaced by the proportion of active lime, which has been noted to give a better insight into metal availability . This parameter provides an indication of the carbonate particles in the clay and the fine silt fractions .…”

Copper in soil fractions and runoff in a vineyard catchment: Insights from copper stable isotopes

“…Fernández-Calviño, 2008a, 2008bEl Azzi et al, 2013), Fe oxide (de Santiago-Martín et al, 2013;Sayen et al, 2009) as well as clay minerals and organo-clay complexes (Besnard et al, 2001;Sipos et al, 2008) control the Cu sorption and accumulation in soils. Cu sorption to SOM (Δ 65 Cu SOM-Cu(II)aq = 0.15 to 0.37‰) (Bigalke et al, 2010b), Fe oxy (hydr)oxides (Δ 65 Cu Fe oxy(hydr)oxides-Cu(II)aq = 0.24 to 0.98‰) (Balistrieri et al, 2008;Pokrovsky et al, 2008) is expected to enrich bound Cu in 65 Cu.…”

Health Risk Assessment in Calcareous Agricultural Soils Contaminated by Metallic Mining Activity Under Mediterranean Climate

“…Health risk assessment studies were mainly conducted on acidic environments but they are rare in carbonated ones. In carbonated environment, low transfer of metals from soil solution to plants is expected because of the low metal mobility due to precipitation and adsorption on soil particles, favored by the high pH values controlled by the carbonates minerals . Hence, in alkaline environments, metals bind with hydroxyl ions and carbonates to form non dissoluble mineral phases becoming unavailable to plants .…”