Fractionation of copper and cadmium and their binding with soil organic matter in a contaminated soil amended with organic materials
ABSTRACT PurposeThe 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 methodsThe 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.
ConclusionsRS, 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.
KeywordsFractionation-Heavy metal-Humic substances-Organic amendments-POM
- SourceAvailable from: Zueng-Sang Chen[show abstract] [hide abstract]
ABSTRACT: Two rural soils contaminated by cadmium (Cd) and lead (Pb) were used to evaluate the effect of different chemical treatments on changes in speciation and extractability of Cd and Pb, and in phytoavailability to wheat. Triplicates of seven chemical treatments were tested to compare and evaluate the remediation techniques for contaminated soils using pot experiments. Treatments applied were calcium carbonate, a high quantity of phosphate salt, hog composts, iron oxide, manganese oxide, zeolite, and unamended control. Wheat (Triticum aestivum) was planted in the different amended soils for a further one month to evaluate the effectiveness of treatments on uptake of Cd and Pb by the wheat shoots. Results indicated that addition of calcium carbonate, manganese oxide, or zeolite reduces the extractability of Cd or Pb in both soils, and significantly reduce the uptake of Cd and Pb by wheat shoots. Changes in the extractability and metal sequential fractionations indicate that the exchangeable (or available) form of Cd and Pb in two soils can be transformed into unavailable forms after these amendments.Chemosphere 08/2000; 41(1-2):235-42. · 3.14 Impact Factor
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ABSTRACT: The Mezquital Valley in Central Mexico has received wastewater from Mexico City for nearly 100 years. Wastewater brings in organic matter and nutrients but also trace metals. Humic substances, the main components of organic soil matter, are responsible for retaining and regulating the mobility of trace metals in soils. In this study, humic substances were extracted from the soil and separated into distinct fractions (humic acids, fulvic acids and humins). The particle induced X-ray emission (PIXE) technique was applied to determine the metal content in bulk soil as well as in humic acids and fulvic acids not soluble in H3PO4. In order to assess whether the long-term input of organic matter and metals modifies the metal association with these humic substances, parcels irrigated for three time periods (5, 47 and 89 years) were selected for this study. It was observed that metals such as Zn and Cu are mainly associated with the humic acids. Fulvic acids retain mainly Cr while Pb is distributed among humic and fulvic acids. It was also observed that in general, metal retention by humic substances increases with irrigation time. Depth also affects metal association with the humic substances.Microchemical Journal - MICROCHEM J. 01/2009; 91(1):129-132.
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ABSTRACT: There is a gradual decline in availability of fresh water to be used for irrigation in India. As a consequence, the use of sewage and other industrial effluents for irrigating agricultural lands is on the rise particularly in peri-urban areas of developing countries. On the other hand, there is increasing concern regarding the exceedance of statutory and advisory food standards for trace metals throughout the world. Hence, a case study was undertaken to assess the long-term effect of sewage irrigation on heavy metal content in soils, plants and groundwater. For this purpose, peri-urban agricultural lands under Keshopur Effluent Irrigation Scheme (KEIS) of Delhi, India were selected where various cereals, millets, vegetable and fodder crops have successfully been grown. Sewage effluents, ground water, soil and plant samples were collected and analysed mainly for metal contents. Results indicated that sewage effluents contained much higher amount of P, K, S, Zn, Cu, Fe, Mn and Ni compared to groundwater. While, there was no significant variation in Pb and Cd concentrations in these two sources of irrigation water and metal content were within the permissible limits for its use as irrigation water. There was an increase in organic carbon content ranging from 38 to 79% in sewage-irrigated soils as compared to tubewell water-irrigated ones. On an average, the soil pH dropped by 0.4 unit as a result of sewage irrigation. Sewage irrigation for 20 years resulted into significant build-up of DTPA-extractable Zn (208%), Cu (170%), Fe (170%), Ni (63%) and Pb (29%) in sewage-irrigated soils over adjacent tubewell water-irrigated soils, whereas Mn was depleted by 31%. Soils receiving sewage irrigation for 10 years exhibited significant increase in Zn, Fe, Ni and Pb, while only Fe in soils was positively affected by sewage irrigation for 5 years. Among these metals, only Zn in some samples exceeded the phytotoxicity limit. Fractionation study indicated relatively higher build-up of Zn, Cu, Fe and Mn in bioavailable pools of sewage-irrigated soils. By and large, tissue metal concentrations in all the crops were below the generalized critical levels of phytotoxicity. Based on the soil to plant transfer ratio (transfer factor) of metals, relative efficiency of some cereals, millet and vegetable crops to absorb metals from sewage and tubewell water-irrigated soils was worked out. Risk assessment in respect of metal contents in some vegetable crops grown on these sewage-irrigated soils indicated that these vegetables can be consumed safely by human.Agriculture, Ecosystems & Environment. 09/2005;