Mobility of Cd and Zn in polluted and unpolluted Spodosols

Abstract

Leaching of Cd and Zn in polluted acid, well-drained soils is a critical pathway for groundwater pollution. Models predicting future groundwater contamination with these metals have rarely been validated at the field scale. Spodosol profiles (pH 3.2-4.5) were sampled in an unpolluted (reference) field and in a field contaminated with Cd and Zn through atmospheric deposition near a zinc smelter. Average metal concentrations in the upper horizons were 0.2 mg Cd kg À1 and 9 mg Zn kg À1 in the unpolluted field, and 0.8 mg Cd kg À1 and 71 mg Zn kg À1 in the contaminated field. Isotopic dilution was used to measure the labile concentration of Cd and Zn, and the metal transport was modelled using measured sorption parameters that describe the distribution between the labile metal pool (instead of the total metal pool) and the solution phase obtained by centrifugation. Solutions were also collected by wick samplers in two polluted and one unpolluted profile at a depth of 70 cm. Concentrations in these solutions were in the order of 15 mg Cd litre À1 and 0.8 mg Zn litre À1 for the polluted profiles, and 1 mg Cd litre À1 and 0.04 mg Zn litre À1 for the unpolluted profile. The concentrations in these solutions agreed well with those in soil solutions obtained by centrifugation, which supported the use of the local equilibrium assumption (LEA). Present-day Cd profiles in the polluted field were calculated with the LEA, based on the emission history of the nearby smelter and taking spatial variability into account. Observed and predicted depth profiles agreed reasonably well, but total Cd concentrations in the topsoil were generally underestimated by the model. This may be attributed to the presence of non-labile Cd in the atmospheric deposition, which was not accounted for in the retrospective modelling. The large concentrations of nonlabile Zn in the topsoil of the polluted field were also indicative that metals in the atmospheric deposition were (partly) in a sparingly soluble form, and that release of these non-labile metals is a slow process. The presence of non-labile metals should be taken into account when evaluating metal mobility or predicting their transport.

Assessing the variability of the bioavailable fraction of zinc at the global scale using geochemical modeling and soil archetypes

“…A literature review for Zn soil speciation was therefore conducted in order to compare WHAM 6.0 speciation results and experimental speciation data. In total, 40 soils previously sampled around galvanized Zn structures (Lessard 2013) and 248 additional field samples from 18 published studies were listed (Aldrich et al 2002;Catlett et al 2002;Dawson et al 2006;de Groot et al 1998;Degryse and Smolders 2006;Ge 1999;Gooddy et al 1995;Holm et al 1998;Kim and Owens 2009;Kim et al 2010;Lorenz et al 1997;Mallmann et al 2012;Meers et al 2006;Muhammad et al 2012;Nolan et al 2003;Rheinheimer dos Santos et al 2013;van Gestel 2008;Wu et al 2000). The samples provided measurements of soil properties (pH, cation exchange capacity (CEC), texture, OM, and carbonate contents), total Zn and soluble (278), or labile (36) Zn.…”

Pasture Soils Contaminated with Fertilizer-Derived Cadmium and Fluorine: Livestock Effects

“…However, in highly acidic soils, high rates of Cd and F addition can lead to groundwater contamination, especially for coarse-textured soils with shallow water tables. For example, Degryse and Smolders (2006) reported signifi cant quantities of Cd leached below 700 mm depth from several acid [pH (0.01 M CaCl 2 ) 3.2-4.5] sandy Spodosols in Belgium polluted by Cd deposition from a zinc smelter. The mean soil solution Cd concentration at 700 mm in polluted soils (total Cd at 0-100 mm soil depth was 0.82 mg Cd/kg) was 15 µg Cd/L compared to 1 µg Cd/L for unpolluted soils (total Cd at 0-100 mm soil depth was 0.18 mg Cd/kg).…”

Phytosequestration of Metals in Selected Plants Growing on a Contaminated Okhla Industrial Areas, Okhla, New Delhi, India

“…In these experiments, the willow plants were able to accumulate 4.1 mg kg −1 of Cd in stems and 7.3 mg kg −1 of Cd in leaves. Some willow or poplar varieties do not retain elements in roots but transfer them to aboveground plant tissues (Pulford et al 2002;Robinson et al 2006;Degryse and Smolders 2006;Japenga et al 2007). The investigations are accumulation of Pb, Zn, Cu, Cd, Hg, and As by 12 wetland plants species (Deng et al 2004).…”