Soil Chemical Analysis

The rhizosphere is the zone of soil immediately surrounding plant roots that is modified by root activity In this critical zone, plants perceive and respond to their environment As a consequence of normal growth and development, a large range of organic and inorganic substances are exchanged between the root and soil, which inevitably leads to changes in the biochemical and physical properties of the rhizosphere Plants also modify their rhizosphere in response to certain environmental signals and stresses Organic anions are commonly detected in this region, and their exudation from plant roots has now been associated with nutrient deficiencies and inorganic ion stresses This review summarizes recent developments in the understanding of the function, mechanism, and regulation of organic anion exudation from roots The benefits that plants derive from the presence of organic anions in the rhizosphere are described and the potential for biotechnology to increase organic anion exudation is highlighted

Function and mechanism of organic anion exudation from plant roots

Chelate assisted phytoextraction of heavy metals from soil. Effect, mechanism, toxicity, and fate of chelating agents.

In a field experiment we investigated the efficiency of two hyperaccumulating species, four agricultural crop plants, and one woody crop, at phytoextraction of Zn, Cd, and Cu from a polluted calcareous soil. In addition, we examined the possibility to enhance the phytoextraction of these metals by application of nitrilotriacetate (NTA) and elemental sulfur (S8) to the soil. Metal uptake by hyperaccumulating species was higher than that by crop species but was generally low in all treatments compared to results reported in the literature, maybe as a result of lower total and available soil metal concentrations. Soil amended with either S8 or NTA increased the solubility (NaNO3-extraction) of Zn, Cd, and Cu ions by factors of 21, 58, and 9, respectively, but plant accumulation of these metals was only increased by a factor of 2−3. As a result, even the highest metal removal rates achieved in this study were still far from what would be required to make this technique practicable for the remediation of the D...

Enhancement of phytoextraction of Zn, Cd, and Cu from calcareous soil: The use of NTA and sulfur amendments

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EDTA-enhanced phytoremediation of heavy metal contaminated soil with Indian mustard and associated potential leaching risk

Various weak organic acids and/or their salts were tested for the remediation of a loam and a sandy clay loam naturally polluted by heavy metals for over three years against two strong synthetic chelating agents (EDTA and DTPA). Among 7 weak organic acids and/or their salts, citrate, tartarate and oxalate were found to effectively remove Cd, Cu, Pb and Zn from the two soils in double extractions, at a wide range of pH. Citrate removed 80 to 99.9% of all four metals within 24 h at pH from 2.3 to 7.5. Tartarate removed 84 to 99.9% of all metals from both soils within 24 h at pH from 2.1 to 6.7. Oxalate alone is not effective in removing metals particularly Pb but with ammonium citrate (1:1 ratio) removed effectively 82, 70, 99.9, and 99.9% for Cd, Pb, Cu and Zn, respectively at pH from 2.6 to 5.8. Zinc met the Quebec A level soil clean-up criteria after two extractions whereas Cu and Pb reached the B level. Probably, two more extractions with these weak organic acids and/or their salts are required to meet ...

Remediation of Soils Polluted by Heavy Metals using Salts of Organic Acids and Chelating Agents

Weak organic acids have the capabilities ofwashing heavy metals without seriously deteriorating the soil properties. A clay loam naturally contaminated by heavy metals was characterized physically and analyzed for its content in Cr, Hg, Mn, and Pb. At various pH, concentration, and reaction time, several weak organic acids and their salts were used to leach out heavy metals. The optimum pH ranged from 5 to 7 for citrate and 2 to 3 for tartarate in the case of Cr, Hg, and Mn and 2 to 7 in the case ofPb. More than 85% ofPb was removed with both citrate and tartarate at a concentration of 0.12 and 0.2 M, respectively, within 24 h. From 86 to 99% ofHg was removed by tartarate and citrate, whereas up to 60% ofCr was removed. EDTA and DTPA were found to be quite effective in removing Pb but not the other metals. Four citrate or tartarate extractions were required to remediate the experimental soil to a category A except for Hg. For Hg, remediation criteria are so strict that only the C criteria were met after two extractions, with citrate and tartarate, that left levels of32 and 62 mglkg, respectively, when a category A soil requires no more than 0.5 mglkg.

S. A. Wasay

Papers

Remediation of Soils Polluted by Heavy Metals using Salts of Organic Acids and Chelating Agents

Organic acids to remediate a clay loam polluted by heavy metals