Time evolution of Pb(II) speciation in Pampa soil fractions

Abstract

Soil pollution by heavy metals, particularly lead, is an important environmental concern; the bioavailability of such pollutants is strongly dependent on their chemical form. Here, the speciation of Pb(II) in soil fractions as a function of time shortly after its incorporation is studied, using a selective sequential extraction method. The sample came from an Argentinean Pampas region and was extensively characterised, including Rietveld analysis of the silt+clay fraction XRD pattern to find the major mineral components. Experiments were run twice, once in the winter and once in the summer. The results show different speciation time profiles in both cases, showing faster changes in winter due to the higher water content. The summer experiment corresponds to an earlier stage in the speciation profile evolution compared with winter. The soluble/ exchangeable fraction decreases with time in summer but shows a lower and constant value in the winter. A high proportion is found to be adsorbed onto the stable (aluminosilicates+quartz) mineral fraction. The results strongly suggest that, even at a short time following soil pollution with Pb, a high proportion is adsorbed onto the mineral fraction, with only a low fraction being bioavailable. The most stable (mineral incorporated) form is observed to increase with time. Soil water content appears to be more important than temperature in determining the differences between the two.

Evaluation of the impact of organic matter composition on metal speciation in calcareous soil solution: Comparison of Model VI and NICA-Donnan

“…However, partition coefficients are not sufficient to estimate metal bioavailability, and to predict their potential environmental impacts, knowledge of their chemical speciation is necessary. Different approaches are used to evaluate this speciation in the soil like chemical extractions (Malandrino et al 2011;Ferreyroa et al 2014) or in the soil solution like Donnan membrane technique (DMT, Temminghoff et al, 2000;Cancès et al 2003;Weng et al 2002). However free ion concentrations predicted by speciation modelling is often preferred as it is easier to determine.…”

Copper Speciation in Soil: Time Evolution and Effect of Clay Amendment

“…From this homogenized soil mass, the sample employed used in present research was obtained. This soil has been characterized previously (Ferreyroa et al 2014), the main results being presented in Table 1. In short, it was found that this soil is moderately acid with predominance of silt plus clay and an important soil organic matter (SOM) content.…”

“…The modified method of Ma and Uren (Ferreyroa et al 2014) was employed, which is shown in Table 2, where the steps are operationally defined.…”

“…When a soil is polluted by addition of a trace metal in soluble form, the pollutant speciation undergoes an evolution from labile to stable forms, affected by soil water content, temperature, etc. (Ferreyroa et al 2014). In the present study, the time evolution of copper speciation in a Pampas soil was investigated, including the effect of Na-bentonite amendment.…”

“…The speciation of copper is obtained experimentally using a SSE procedure; in a SSE, the different steps beyond the first are expected to selectively dissolve/destroy a particular solid (or groups of solids) fraction, with reactants of increasing strength, releasing the associated metal ions; it is in principle assumed that the metal is mainly incorporated into the solid, however surface-adsorbed species should also be removed in the course of the procedure. One of such methods is the Ma and Uren procedure (Ma and Uren 1998); this method was modified for the purposes of the present work (Ferreyroa et al 2014), giving an operational definition which can be better correlated with bioavailability or functional definition and provides a basis for the application of clays in remediation of contaminated soils.…”