Temporal Changes in Cadmium Speciation in Brazilian Soils Evaluated Using Cd L_III–Edge XANES and Chemical Fractionation

Abstract

Chemical speciation of soil cadmium (Cd) dictates its mobility and potential toxicity in the environment. Our objective was to compare temporal changes in speciation of Cd(II) reacted with samples from six Brazilian soils having varying Cd(II) sorption capacities. Cadmium L-edge X-ray absorption near edge structure (XANES) analysis showed there were short-term changes in speciation after reaction with 4.45 mmol Cd kg for 0.5 and 6 h. Chemical fractionation evaluated changes in Cd extractability after reaction with 89 μmol Cd kg for up to 4 mo. The XANES spectral fits suggested that Cd(II) bound with organic matter was a dominant species in all samples, along with Cd(II) bound with iron and aluminum oxides or montmorillonite. In several samples, CdCl apparently precipitated from aqueous Cd(II) during drying. The XANES spectral fits typically showed <25% change in speciation between 0.5 and 6 h of reaction, and chemical fractionation showed significant ( < 0.05) temporal changes in Cd extractability over time in two samples. Our results suggest that Cd(II) discharged into these soils, such as that occurring as a release into the environment, would bind with soil organic matter and oxide minerals or remain dissolved, with little change in speciation in the months following release.

Respiratory bioaccessibility and solid phase partitioning of potentially harmful elements in urban environmental matrices

“…However, Cd was associated with either the F2, reducible fraction (47PC = 99% and 5AP = 83%) or the F4, residual fraction (35PC = 100%). Colzato et al (2017) observed similar result in a Brazilian Typic Argiudoll which had 75% of Cd extracted by 0.5 mol L -1 NH 2 OH.HCl.…”

Application of Synchrotron Radiation‐based Methods for Environmental Biogeochemistry: Introduction to the Special Section

“…Colzato et al (2017) studied short‐term temporal changes in Cd speciation and long‐term changes in Cd extractability in relation to the properties of highly weathered Brazilian Oxisols and less weathered Mollisols and Entisols. Cadmium L‐edge XANES showed that Cd was mainly sequestered as Cd bound to organic matter and to Fe and Al oxides (or montmorillonite in the smectite‐rich soil sample).…”

“…Their work showed that although the short-term reactions of nanomaterials are dependent on the Cu form and soil chemistry (e.g., pH), in the long term, irrespective of their original form, all of the examined forms of Cu nanoparticles transformed into Cu bound to iron oxyhydroxide or natural organic matter. Colzato et al (2017) studied short-term temporal changes in Cd speciation and long-term changes in Cd extractability in relation to the properties of highly weathered Brazilian Oxisols and less weathered Mollisols and Entisols. Cadmium L-edge XANES showed that Cd was mainly sequestered as Cd bound to organic matter and to Fe and Al oxides (or montmorillonite in the smectite-rich soil sample).…”

Sulfur speciation in a tropical soil under long-term no-till amended with lime and phosphogypsum

“…Fitting was conducted using two approaches. The first was performed as described by Colzato et al (2017) and consisted in fitting all possible combinations of 12 standards with a maximum of four standards per fit in all soil samples selected for XANES analysis. In this procedure no energy shift was used to identify the standards present in the fits with the lowest residual, considered the best fits.…”

“…One of the main concerns on using LCF approach is the selection of the reference compounds to perform LCF. Previous authors used different methods to model S XANES spectra to eliminate the necessity of previous assumptions about the composition of the sample, such as principal component analysis -PCA (Beauchemin et al, 2002) and use of aqueous diluted samples (Almkvist et al, 2010) We used two approaches as described by Colzato et al (2017) and to select the reference compounds to perform the fit. All fits were set to be performed by a combination of a maximum of four reference compounds, and only factions greater than 0.1 (10%) were considered.…”