Behavior of Chromium in Soils: V. Fate of Organically Complexed Cr(III) Added to Soil

Abstract

Organically complexed Cr(III) added to soils may remain soluble, whereas the free Cr(III) metal ion would quickly become adsorbed and/or hydrolyzed and precipitated in the absence of soluble, complexing ligands. To separate these two phenomena, a laboratory procedure was developed to simulate the disposal of Cr(III)‐containing organic wastes in soils, and to investigate the solubilities of organic complexes of this heavy metal after addition to soil. The method involves adding Cr(NO3)3 to solutions of organic ligands adjusted to a pH between 3 and 8 to form inorganic hydrolyzed species and organic complexes at each pH. After measuring soluble Cr vs. pH, moist soil is added to bring the pH of each Cr‐ligand system to 6.5–7.0, thereby precipitating nncomplexed, inorganic Cr(III), and labile Cr(III)‐organic complexes. Subtracting Cr(VI) formed from total soluble Cr in the soil suspension gives a relative measure of organically complexed Cr(III) originally present in the aqueous systems at each pH.Citric acid, diethylenetriaminepentaacetic acid (DTPA), fulvic acids, and water‐soluble organic matter from air‐dried soil kept Cr(III) in solution above pH 5.5, and prevented its immediate removal by soil.Added Cr‐citrate remained soluble for at least 1 y in limed samples of an Ultic Hapludalf Ap horizon incubated at field capacity moisture. Because organic acids similar to those studied here may be found in sewage sludge, animal manures, and industrial wastewater, these results should be useful in predicting the fate of Cr(III) added to soils amended with such wastes.

Mycorrhizal Fungi Increase Chromium Uptake by Sunflower Plants: Influence on Tissue Mineral Concentration, Growth, and Gas Exchange

“…This is explained in part because P and Cr are competitive species, as mentioned previously. [23,33,34,36] Tissue P was the same among non-Cr treated AM and Non-AM plants. However, though P concentration was similar (0.30 AE 0.02% vs. 0.26 AE 0.02%) between AM and Non-AM plants it does not necessarily mean that P was not involved in growth enhancement.…”

“…Phosphate (H 2 PO 4 À ) will inhibit CrO 4 2 7 adsorption in equilibrated soil suspensions. [33][34][35][36] Thus, P and Cr are competitive species for surface sites. The utilization of AM to colonize a Cr-hyperaccumulating host plants has obvious advantages.…”

Literature review: Phytoaccumulation of chromium, uranium, and plutonium in plant systems

“…Chromium(III) should be insoluble at the physiological pH, so organic acids must increase the solubility of C r ( Q within the plant, thus enhancing Cr translocation. James and Bartlett (1983a) determined that Cr(III) citrate remains soluble up to pH 7.5. These data suggest that hyperaccumulator plants which translocate more…”

Effect of organic Cr(III) complexes on chromium speciation

“…Free Cr(III) metal ions would quickly become adsorbed or hydrolyzed and precipitated in the absence of soluble complexing ligands. The presence of organic ligands kept Cr(III) in solution and prevented removal of Cr at pH45:5 (James et al, 1983).…”

“…However, a significant percentage of dissolved chromium in river water was found to be non-ionic and probably organically bound (Li et al, 2001). Cr(III) bound to natural organic ligands contributed significantly to total chromium concentrations and was found to be critical in the speciation and solubility of chromium in soils (James et al, 1983;Li et al, 2001). Walsh et al (1996) assessed three chromium speciation methods in relation to possible interferences from Cr(III)-organic complexes.…”