Phytotoxicity of Soil Trivalent Chromium to Wheat Seedlings Evaluated by Chelating Resin Extraction Method

Abstract

A pot experiment of wheat seedlings with the chelating exchange resin Chelex 100, which is used to extract trivalent chromium (Cr [III]) from the soils, was conducted to examine the phytotoxicity of Cr(III)-spiked soils. Plant height and dry weight of the wheat seedlings were adversely affected by the Cr(III)-spiked acidic soils, whereas growth inhibition of wheat seedlings was not found in alkaline soils with the same quantities of added Cr(III). The concentrations of Cr in plant tissues corresponding to 50% reduction (PT 50 ) of plant height and dry weight were 97.6 and 126.0 mg kg j1 , respectively. The amount of soil resin-extractable Cr(III) increased with the increase of Cr(III) in the Cr(III)-spiked acidic soils. However, no detectable Cr(III) (e0.05 mg kg j1 ) was extractable from the alkaline soils. In addition, the reduction of plant height and dry weight of wheat seedlings and the increase of plant Cr concentration and Cr uptake had a pronounced correlation to the quantity of soil resin-extractable Cr(III) retained by Chelex 100 resin. The correlation between the relative plant height of the wheat seedlings and the amount of soil resinextractable Cr(III) in a logarithmic scale was well fitted to an exponential type of dose-response relation model (r 2 = 0.97). Therefore, the resin extraction method using Chelex 100 could be a reliable method for assessing the phytotoxicity of Cr(III) in Cr-contaminated soils. Based on the dose-response relationship model, the effective concentrations calculated for resin-extractable Cr(III), resulting in 10% and 50% growth inhibition (EC 10 and EC 50 ), were 11.4 and 57.8 mg kg j1 , respectively. (Soil Science 2008;173:638-648)

Assessing the phytotoxicity of chromium in Cr(VI)-spiked soils by Cr speciation using XANES and resin extractable Cr(III) and Cr(VI)

“…After each wetting-drying cycle, the air-dried soils were ground, passed through a 2 mm sieve, and mixed thoroughly for the next wettingdrying cycle. The preparation of Cr(VI)-spiked soils through three wetting-drying cycles, which had been tested in our previous study (Chen et al 2008), could ensure that the Cr(VI) added in each soil sample was homogeneously mixed. After three wetting-drying cycles, the Cr(VI)-spiked soil samples were ground and sieved through a 40 mesh sieve and stored under room temperature until further use.…”

“…Sule and Ingle (1996) suggested that the Chelex 100 resin has high affinity for Cr(III) at pH 4-5 and thus it might be useful for measuring available Cr(III) in acid soils. In a previous study (Chen et al 2008), the amount of extractable soil Cr(III) by Chelex 100 was found to be highly negatively correlated with the plant height of wheat seedlings. A dose-response curve between Chelex-100 resin extractable Cr(III) and the relative plant height suggests that resin-extractable Cr(III) can be used as an index for assessing the phytotoxicity of Cr(III) in soil.…”

“…However, Cr(III) is less toxic and is considered to be the safer state of Cr, and it is essential for humans and animals (Martz 1969). It has been observed that Cr(VI) can be reduced to Cr(III) by soil organic matter in acid soils and that the phytotoxicity of Cr(III) is raised under acid conditions (Han et al 2004;Lee et al 2006;Chen et al 2008). Soil organic matter acts as an electron donor which contributes to Cr(VI) being reduced to Cr(III).…”

Effects of liming on Cr(VI) reduction and Cr phytotoxicity in Cr(VI)-contaminated soils

“…The Chelex 100 resin (with a particle size ranging from 297 to 840 mm) was also washed with 1 M HCl and immersed in deionized water for 2 d. Chelex 100 resin was saturated using 2 M calcium chloride (CaCl 2 ) to convert it into the Ca-saturated form. The calcium (Ca)-saturated Chelex 100 resin was retained in 60 mesh PP bags (Chen et al 2008).…”

“…Therefore, lime application might raise the availability of Cr(VI) in soils and increase the phytotoxicity of Cr in Cr(VI)-contaminated soils by hindering Cr(VI) reduction and enhancing Cr(VI) desorption. On the other hand, liming might reduce the availability of Cr(III) that is formed from Cr(VI) reduction in soils and thus decrease the contribution of Cr(III) to the injury of plants in acid soils (Chen et al 2008). Therefore, the effect of liming on Cr phytotoxicity in acidic Cr(VI)-contaminated soils is worthy of investigation.…”