Speciation Of Chromium In Soils Research Articles

Speciation of chromium in soils near Sheba Leather Industry, Wukro Ethiopia

A study on speciation of chromium in soils near Sheba Leather Industry was performed by Flame Atomic Absorption (FAAS) after selective extraction of Cr(VI) using the EPA 3060A method, and oxidizing the Cr(III) residue in the soils with HNO3 and H2O2. The extraction method was evaluated using the spiking method with satisfactory results (recoveries>95% and RSDs<5%). The limit of detection (LOD) for Cr(VI) based on three times the standard deviations of the blank (for n=5) was 0.56µgg−1.Statistical evaluation indicated that the comparison of the sum of the concentrations of chromium species to that of the total concentration of chromium do not show any difference at 95% level of confidence. Besides, no statistically significant difference at 95% confidence level was observed between the UV–vis spectrophotometry and FAAS results for Cr(VI). However, it is observed that selective extraction of Cr(VI) using EPA 3060A and subsequent determination by FAAS is simple and faster compared to the other method. Furthermore, for comparison and as control two soil samples collected from a distance of about 2km from the main Industry and effluent stream. The results indicate that higher total chromium content was observed in soils collected from the target area. Nevertheless, the maximum concentrations of Cr(VI) found in soil samples collected around Sheba Leather Industry was 9.9µgg−1 and are within the acceptable level of 10µgg−1 in accordance with the WHO.

Soil Pollution Investigation of Chromium Slag Contaminated Site

In this paper, a chemical plant of chromium salt was selected as the typical chromium slag contaminated site. The range and level of chromium in soil were tested by way of digestion and leaching in order to investigate the pollution of chromium slag. Speciation of chromium in soil was simultaneously analyzed by way of Tessier. The results showed that soil around the residue piling yard was polluted by Cr. Concentrations of Cr (VI) and total chromium in soil were both higher than the background value. Speciation analysis indicated that Cr in contaminated soil was mainly in the residual fraction. The data of investigation display chromium slag diffusion rule in horizontal direction is accord with particulate matter non-point source diffusion model.

Speciation of Chromium in Soil and Sludge in the Surrounding Tannery Region, Ranipet, Tamil Nadu

The distribution and mobility of chromium in the soils and sludge surrounding a tannery waste dumping area was investigated to evaluate its vertical and lateral movement of operational speciation which was determined in six steps to fractionate the material in the soil and sludge into (i) water soluble, (ii) exchangeable, (iii) carbonate bound, (iv) reducible, (v) oxidizable, and (vi) residual phases. The present study shows that about 63.7% of total chromium is mobilisable, and 36.3% of total chromium is nonbioavailable in soil, whereas about 30.2% of total chromium is mobilisable, and 69.8% of total chromium is non-bioavailable in sludge. In contaminated sites the concentration of chromium was found to be higher in the reducible phase in soils (31.3%) and oxidisable phases in sludge (56.3%) which act as the scavenger of chromium in polluted soils. These results also indicate that iron and manganese rich soil can hold chromium that will be bioavailable to plants and biota. Thus, results of this study can indicate the status of bioavailable of chromium in this area, using sequential extraction technique. So a suitable and proper management of handling tannery sludge in the said area will be urgently needed to the surrounding environment as well as ecosystems.

Speciation of chromium in soil inoculated with Cr(VI)-reducing strain, Bacillus sp. XW-4

Cr(VI)-amended soil was inoculated with Cr(VI)-reducing strain, Bacillus sp. XW-4 and incubated at 28 °C in an incubator. Cr(VI) reduction, available Cr and Cr fraction in soils were studied. The results show that addition of Bacillus sp. XW-4 can promote Cr(VI) reduction, but inoculation of this strain has a negative effect on the decrease of available Cr content in soil. In controls (without this strain) amended with 100 and 200 mg/kg of Cr(VI), Cr(VI) contents decrease to about 41 and 92 mg/kg respectively after incubation of 4 d, while in soil inoculated with XW-4, Cr(VI) contents decrease to about 18 and 60 mg/kg, respectively. The content of available Cr in soils with inoculation of XW-4 is higher than that in controls. Chromium is partitioned into water soluble Cr, exchangeable Cr, precipitated Cr, Cr bound to organics and residual Cr. The highest content of Cr is observed in residual form and water soluble Cr is not detected for all treatments after 42 d, but the soils inoculated with Bacillus sp. XW-4 contain higher content of exchangeable Cr and lower content of precipitated Cr than the soil without the inoculum. Inoculation of Bacillus sp. XW-4 can increase chromium activity in soils.

Interactions of soil components and their effects on speciation of chromium in soils

For evaluation of real risks of soil contaminated with chromium it is important to identify and understand the reactions of Cr species with main soils components. In this research reactions of Cr(III) and Cr(VI) with Fe(OH) 3, MnO 2, CaCO 3, kaolinite and natural organic matter (NOM) were examined in batch experiments. Since the batches were compositions of soil component mixtures the experimental design was carried out by applying Simplex algorithm and the results of the experimental domain were interpreted by partial least squares (PLS). The research confirmed the significance of studying all the soil components simultaneously instead of studying only the effects of one component at a time. The ability of pure components to change the speciation of Cr(III) and Cr(VI) in liquid phase was different to that in mixtures, which indicated that the soil components interacted with each other. The order of pure components to convert Cr(III) by adsorption, precipitation or oxidation was Fe(OH) 3=kaolinite=CaCO 3>NOM>MnO 2, while in mixtures the order was: Fe(OH) 3>CaCO 3>kaolinite>MnO 2>NOM. This means that in mixtures with the highest amount of Fe(OH) 3 the conversion of Cr(III) was highest. In mixtures with the highest amount of NOM the changes in speciation of dissolved Cr(III) were the lowest. The order for the pure components to change the speciation of Cr(VI) was: Fe(OH) 3>NOM>kaolinite>CaCO 3>MnO 2 and in mixtures the order was: NOM>Fe(OH) 3>kaolinite>MnO 2>CaCO 3. The reactions between different soil components also affected the oxidation/reduction ability of soils. As separate component MnO 2 oxidized Cr(III) to Cr(VI). However, in mixtures with NOM or Fe(OH) 3 the oxidation was hindered. The effect of pH on speciation of Cr in mixtures was also examined and is discussed.