Fractionation of copper and cadmium and their binding with soil organic matter in a contaminated soil amended with organic materials

Abstract

Purpose The contamination of agricultural soils by heavy metals is a worldwide problem. Organic amendments can be used for the immobilization and binding of heavy metal ions in soils by complexation, adsorption, and precipitation. A field trial was carried out to evaluate the influence of some low-cost organic materials such as rice straw (RS), green manure (GM), and pig manure (PM) on the distribution of Cu and Cd and the retention of these metals by organic matter fractions in heavy metal-polluted soils. Materials and methods The experiment was conducted in Miaoyunao Village, Daye County, Hubei province, China. PM, GM (peanut plants), and RS were obtained from a farm close to the village. Sixteen treatments with three replicates were designed. Soil chemical properties such as soil pH, electrical conductivity (EC), organic matter (OM), and available P were measured by standard methods. Soluble/ exchangeable, organic-bound, inorganic precipitates and residual Cu and Cd in the soil were sequentially extracted and analyzed. The amounts of Cu and Cd bound with soil particulate organic matter (POM) fractions and humic substances were also determined. Results and discussionThe addition of organic amendments declined significantly the concentrations of soluble/ exchangeable Cu and Cd, but increased the amounts of these metals in organic-bound and inorganic precipitate forms in the soil. RS was more effective than GM and PM in diminishing the solubility of Cu and Cd. The largest retention for Cu and Cd by humic substances and POM was noticed in RS treatments, whereas the lowest was found in PM treatments. Humic substances showed higher potential in the fixation of Cu and Cd than POM fractions. The conversion of soluble/exchangeable Cu and Cd to other insoluble forms after the application of organic amendments may be ascribed to the increases of soil OM, pH, EC, and available P contents. The highest binding of Cu and Cd with POM fractions and humic substances after the incorporation of RS mainly resulted from the greatest increase of soil OM contents. Conclusions RS, GM, and PM can be employed as good and cheap substances for the immobilization of Cu and Cd in heavy metal-polluted soils. RS was the best amendment in decreasing the solubility of Cu and Cd, and also in enhancing the retention of these metals by humic substances and POM fractions in the soil. Futures studies should focus on the influence of these organic amendments or their mixtures on the phytotoxicity of Cu and Cd for different plants in heavy metal-contaminated soils.

Achilles heel of environmental risk from recycling of sludge to soil as amendment: A summary in recent ten years (2007–2016)

“…Mohamed et al (2010) found that amendment of sludge significantly decreased the concentrations of exchangeable Cd and Cu but increased the amounts in the organic-bound and precipitate forms. However, left a little regret, they were unable to determine which components of the sludge were involved in altering the heavy metal bioactivities in the soil.…”

Residual effects of biosolids and farm manure on speciation and plant uptake of heavy metals in a calcareous soil

“…Perez et al (2007) explained the increase of Cu concentration in the organic soil fraction mainly due to the fixation of Cu by organic matter in BSamended soils. Mohamed et al (2010) also showed the highest increase of Cu in the organically bound fraction after application of some low-cost organic materials such as rice straw, green manure, and pig manure. The residual fraction was the major form of Ni with approximately 65 % of total Ni in both control and amended soils (Table 5).…”

Total nitrogen and pH-controlled chemical speciation, bioavailability and ecological risk from Cd, Cr, Cu, Pb and Zn in the water level-fluctuating zone sediments of the Three Gorges Reservoir

“…The reducible fraction (F 2 ) of Cd and Cr could be transformed to an acid soluble fraction (F 1 ) due to submerged conditions and higher organic matter inputs into the tributaries [28,46]. The organic matter could be gradually degraded into small-molecule organic acids, resulting in the dissociation of a reducible fraction of heavy metals [47].…”