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
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ABSTRACT: The validity of the soil quality standard for copper (Cu) established by the Spanish legislation (Spanish Royal Decree 9/2005) is evaluated in representative agricultural Mediterranean soils under an accumulator crop (Lactuca sativa L. var. Romaine cv. Long Green), considering both the effect of the metal on crop growth (biomass production) and its accumulation in the edible part of the plant. For saline soils, such a soil quality standard seems not to be valid taking into account both of the aspects evaluated. For non-saline soils, the soil quality standard also seems not to be valid since, considering the metal accumulation in the edible part of the plant, the soil quality standard should be above such standard; but considering the productivity function of soil (biomass production), the standard should be much below, meaning that this function is being greatly affected by the presence of high concentrations of Cu. The soil quality standard for each soil considered should correspond to a value between its respective EC50 and EC10 values (effective concentrations of added Cu causing 50% and 10% inhibition on the biomass production), depending on the politicians and/or farmers' compromise with yield production and, therefore, with soil productivity. These threshold values were greater for the soil having more organic matter and clay content, showing that Cu toxicity also depends on these properties. Further research in other agricultural areas of the region would improve the basis for proposing adequate soil quality standards as highlighted by the European Thematic Strategy for Soil Protection.Water Air and Soil Pollution 01/2012; 223(4). · 1.75 Impact Factor
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ABSTRACT: Purpose With the rapid development of nanotechnology, hydroxyapatite-based nanoparticles have been applied in wastewater and soil remediation. However, limited studies have been conducted on the remediation of heavy metal-contaminated soils by microhydroxyapatite (MHA) and nanohydroxyapatite (NHA). Thus, we investigated the effects of MHA and NHA on soil pH values and fractions of copper (Cu) and cadmium (Cd). The changes of soil enzymes with application of MHA and NHA were also evaluated. Materials and methods Pots contained 200 g of the soil with MHA and NHA ranging from 1 % to 5 % incubated for 60 days under greenhouse condition, and maintained at 60 % of soil water holding capacity by adding deionized water. Soil pH, catalase, urease, and acid phosphatase were analyzed at incubation times of 7, 14, 30, and 60 days by chemical assays. The fractions of Cu and Cd were analyzed after 60 days by a sequential extraction procedure. Results and discussion Application of MHA and NHA sig-nificantly increased soil pH values. Especially, we found for the first time that soil pH values with 3 % (pH>7.90) and 5 % (pH>8.83) application rates of MHA were larger than that of MHA itself (pH=7.71). MHA was more effective than NHA in immobilizing Cu and Cd by significantly decreasing exchangeable fractions of Cu and Cd and trans-forming them from active to inactive fractions. Soil catalase and urease significantly increased, but acid phosphatase apparently decreased with increasing application rates of MHA. However, three enzymes activities changed slightly for NHA treatments. Conclusions MHA was more effective than NHA in immo-bilizing Cu and Cd. MHA had a more positive effect on soil catalase and urease activities than NHA. Furthermore, Pear-son's correlation coefficients showed that soil pH value was a key factor to influence the bioavailability of Cu and Cd and the activity of soil enzymes. The results of this study provided an efficient method for the remediation of heavy metal-contaminated soils.
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ABSTRACT: Purpose Sugarcane waste products (boiler ash, filter cake, and vinasse) from an ethanol production plant were used as soil amendments by adding 3 % (w/w) in single and/or in combination, with a research focus towards stabilization of cadmium (Cd) and zinc (Zn) in contaminated soils. The objective of this laboratory study was to evaluate the effects of adding these sugarcane waste products on bioavailability of Cd and Zn over time (aging) in Cd- and Zn-contaminated agricultural soils of Thailand. Materials and methods Two agricultural contaminated soils of low (<3 mg kg−1) and high (10–15 mg kg−1) Cd concentrations were collected from Tak Province, Northwest Thailand. Fourteen treatments were sampled at 2-week intervals for 84 days for metal bioavailability using BCR extraction procedures (proposed by The Standards, Measurements and Testing Programme of the European Union, SM&T) that determined exchangeable (BCR1), reducible (BCR2), oxidizable (BCR3), and residual (BCR4) fractions, and total concentration was determined using aqua regia digestion and microwave digestion. Results and discussion Cd was potentially bioavailable, predominantly in exchangeable (BCR1) and reducible (BCR2) fractions, while the higher contribution of Zn was more prevalent in refractory fractions (BCR2 and BCR4). Aging had an influence on fractionation of Cd and Zn, most notably in the first two fractions (BCR1 and BCR2) of BCR sequential extraction, which resulted in reduction of exchangeable Cd during the first few weeks of incubation (T = 0 to 28 days). At the end of pot experiment, the exchangeable Cd fraction in the low Cd (LCdS) soil was reduced from 2.3 to 4.7 % and 9.4 to 39.9 % in low and high Cd (HCdS)-contaminated soils, respectively, as compared to nonamended soils. Conclusions The observed reduction in exchangeable Cd (BCR1) in the amended soils at the 3 % (w/w) application rate, the low total metal concentrations, and the significant amount of essential plant nutrients (N, P, and K) within these waste products highlight the benefits of amending metal-rich soils with them.Journal of Soils and Sediments 13(6). · 1.97 Impact Factor