Mobility Of Cd In Soils Research Articles

Relationship between Cadmium Fractions Obtained by Sequential Extraction of Soil and the Soil Properties in Contaminated and Uncontaminated Paddy Soils

The method for the sequential extraction of cadmium from soil was adapted to investigate the relationship between different chemical forms of cadmium in soils and the soil properties of Cd-contaminated and uncontaminated paddy soils. Air-dried soil samples from each field site were sequentially fractionated into five forms: exchangeable Cd, inorganically bound Cd, organically bound Cd, oxide-occluded fraction, and residual Cd. The average and range of soil properties such as pH, total C, total N, CEC, exchangeable Ca, Mg, K, base saturation, available phosphate, particle size distribution, free iron oxide, oxalate extractable Al, and Fe were somewhat similar between uncontaminated and contaminated soils. The average total Cd in uncontaminated and contaminated soils was 0.26 and 0.65 mg kg−1, respectively. The proportions of soil Cd fractions did not differ between the uncontaminated and contaminated soils, although the Cd concentration of several fractions in contaminated soils was statistically higher than those in uncontaminated soils except for residual fraction. The proportion of exchangeable Cd was correlated with the CEC and phosphate absorption coefficient in contaminated soil but not in uncontaminated soil. Thus, soil properties appear to affect the proportions of soil Cd fractions in contaminated soil and should be considered when evaluating soil Cd mobility.

Application of Biochar for Enhancing Cadmium and Zinc Phytostabilization in Vigna radiata L. Cultivation

Cadmium (Cd) is a toxic and nonessential element. Because of its toxicity, Cd soil contamination is a major environmental risk to living organisms. Several studies have reported on the successful use of biochar to immobilize Cd in soil as it reduces Cd accumulation in plant parts. This research reports on the contrasting effect of biochar on enhancing Cd uptake by plants. A cassava stem biochar produced through low-temperature pyrolysis was applied to natural Cd-contaminated soil that also had a high zinc (Zn) concentration. Vigna radiata L. (a green bean) was grown in treatments receiving three biochar rates, i.e., 5, 10, and 15 %, respectively. The results showed that the 10 % biochar-amended soil had a positive effect on promoting plant growth and seed yield. Unfortunately, 15 % biochar-amended soil caused an adverse effect to plant growth. Cadmium uptake by plants increased with increasing biochar application rate. Zinc uptake by plants tended to decrease with biochar application. Cadmium and Zn bioavailability in soil was significantly reduced with an increasing biochar application rate. The results also showed that the biochar-amended soil could be an alternative and cost-effective method to promote plant growth and decrease Cd mobility in soil. The ratio of Cd concentration in plant root to soil was higher than 1, while the translocation factor from root to shoot was less than 1. These results indicate that the cultivation of V. radiata L. coupled with biochar application is an appropriate method to enhance Cd phytostabilization efficiency of V. radiata L. in Cd-polluted sites.

Growth and Cd Accumulation of Orychophragmus violaceus as Affected by Inoculation of Cd-Tolerant Bacterial Strains

Beneficial interactions between microorganisms and plants, particularly in the rhizosphere, are a research area of global interest. Four cadmium (Cd)-tolerant bacterial strains were isolated from heavy metal-contaminated sludge and their effects on Cd mobility in soil and the root elongation and Cd accumulation of Orychophragmus violaceus were explored to identify the capability of metal-resistant rhizobacteria for promoting the growth of O. violaceus roots on Cd-contaminated soils. The isolated strains, namely, Bacillus subtilis, B. cereus, B. megaterium, and Pseudomonas aeruginosa, significantly enhanced the plant Cd accumulation. The Cd concentrations in the roots and shoots were increased by up to 2.29- and 2.86-fold, respectively, by inoculation of B. megaterium, as compared with the uninoculated control. The bacterial strains displayed different effects on the shoot biomass. Compared with the uninoculated plants, the shoot biomass of the inoculated plants was slightly increased by B. megaterium and significantly decreased by the other strains. B. megaterium was identified as the best candidate for enhancing Cd accumulation in O. violaceus. Thus, this study provides novel insight into the development of plant-microbe systems for phytoremediation.

Fate of Cd during Microbial Fe(III) Mineral Reduction by a Novel and Cd-Tolerant Geobacter Species

Fe(III) (oxyhydr)oxides affect the mobility of contaminants in the environment by providing reactive surfaces for sorption. This includes the toxic metal cadmium (Cd), which prevails in agricultural soils and is taken up by crops. Fe(III)-reducing bacteria can mobilize such contaminants by Fe(III) mineral dissolution or immobilize them by sorption to or coprecipitation with secondary Fe minerals. To date, not much is known about the fate of Fe(III) mineral-associated Cd during microbial Fe(III) reduction. Here, we describe the isolation of a new Geobacter sp. strain Cd1 from a Cd-contaminated field site, where the strain accounts for 10(4) cells g(-1) dry soil. Strain Cd1 reduces the poorly crystalline Fe(III) oxyhydroxide ferrihydrite in the presence of at least up to 112 mg Cd L(-1). During initial microbial reduction of Cd-loaded ferrihydrite, sorbed Cd was mobilized. However, during continuous microbial Fe(III) reduction, Cd was immobilized by sorption to and/or coprecipitation within newly formed secondary minerals that contained Ca, Fe, and carbonate, implying the formation of an otavite-siderite-calcite (CdCO3-FeCO3-CaCO3) mixed mineral phase. Our data shows that microbially mediated turnover of Fe minerals affects the mobility of Cd in soils, potentially altering the dynamics of Cd uptake into food or phyto-remediating plants.

Cadmium Sorption and Desorption in Soils: A Review

Cadmium (Cd) is an environmental pollutant that can be readily taken up by plants and may enter the food chain, causing risk to human health. It can also affect soil quality and, if easily leached, has the potential to pollute surface and ground waters. Sorption and desorption are critical processes controlling the phytoavailability and mobility of Cd in soils. The authors present the present knowledge on the mechanisms and hysteresis of Cd sorption and desorption in soils and factors such as pH, ionic strength, index cation, other heavy metal cations, inorganic anions, organic ligands, Cd loading rate, and the type and amounts of organic matter and inorganic colloids influencing these processes. The methods used to determine the nature and magnitude of Cd sorption and desorption are also critically reviewed.

Modelling the complexation of Cd in soil solution at different temperatures using the UV-absorbance of dissolved organic matter

It is well established that the soil temperature impacts on the mobility of Cd in soil but the role of dissolved organic matter (DOM) quality in this process is still unclear. During a 42-day period, soil solutions were sampled from a Cd-contaminated soil incubated at 10, 20 or 30 °C. The quantity and the quality of DOM were monitored over time as well as the concentration and the speciation of dissolved Cd. The fraction of Cd complexed by ligands ( f CdL) increased over time and with the rise in soil temperature and exhibited a significant correlation with the absorbance of DOM at 254 nm. In contrast, the quantity of DOM did not much vary between soil solutions. These results suggest that, during incubation, the composition of DOM shifted to more aromatic compounds, assimilated to humic substances (HS), with higher Cd affinity. The kinetics of DOM aromatization and Cd complexation were described using thermal time. A first order model adequately fitted all the experimental data, suggesting that similar microbial processes responsible for the aromatization of DOM occurred at 10, 20 and 30 °C. The fraction of Cd complexed by ligands was predicted by Visual MINTEQ using the solution properties measured at 140 day-degrees and the specific UV-absorbance of DOM ( SUVA) monitored over thermal time. SUVA values were used to adjust the reactivity ratio of DOM ( R). The model predictions were highly correlated with the measured values but they overestimated f CdL. It is concluded that the aromaticity of DOM should be taken into account to predict the impact of soil temperature on the complexation of Cd in rewetted soils. The relation between SUVA values and the HS fraction of DOM still needs, however, to be worked out.

Energia livre da reação de adsorção de cádmio em latossolos ácricos

O cádmio é um metal pesado que pode ser adicionado ao solo por meio do lixo urbano ou industrial, lodo de esgoto e fertilizantes fosfatados. É facilmente absorvido e translocado pelas plantas, tendo potencial de entrar na cadeia alimentar humana. A persistência e a mobilidade do cádmio no solo é determinada pela intensidade da adsorção pelos colóides do solo. A avaliação da energia livre de adsorção de um elemento ao solo pode servir como medida da força da reação. Estudou-se a energia livre da reação de adsorção de cádmio em amostras superficiais (0-0,2m) e subsuperficiais (na maior expressão do horizonte B) de um Nitossolo Vermelho eutroférrico, um Latossolo Vermelho acriférrico e um Latossolo Amarelo ácrico, após a adição de 5, 10, 15, 25, 50, 75, 100, 125, 150, 175 e 200mg L-1 de cádmio. A adsorção de cádmio pelos solos foi espontânea, pois a energia livre apresentou valores negativos em todas as concentrações estudadas. Os valores de energia livre diminuíram com o aumento da dose de cádmio adicionada. O Nitossolo apresentou maior energia livre do que os Latossolos, sobretudo na camada superficial. Os horizontes superficiais apresentaram maior energia livre para as reações de adsorção de cádmio dos que os subsuperficiais, provavelmente devido ao efeito da matéria orgânica, que apresenta alta afinidade pelo elemento.

Solubility, sorption and desorption of native and added cadmium in relation to properties of soils in New Zealand

SummarySolution cadmium (Cd) concentrations and sorption and desorption of native and added Cd were studied in a range of New Zealand soils. The concentration of Cd in solution and the concentrations and patterns of native soil Cd desorbed and added Cd sorbed and desorbed varied greatly between the 29 soils studied. Correlation analysis revealed that pH was the most dominant soil variable affecting solution Cd concentration and sorption and desorption of native and added Cd in these soils. However, organic matter, cation exchange capacity (CEC) and total soil Cd were also found to be important. Multiple regression analysis showed that the log concentration of Cd in solution was strongly related to soil pH, organic matter and total Cd, which in combination explained 76% of the variation between soils. When data from the present study were combined into a single multiple regression with soil data from a previously published study, the equation generated could explain 81% of the variation in log Cd solution concentration. This reinforces the importance of pH, organic matter and total Cd in controlling solution Cd concentrations. Simple linear regression analysis could at best explain 53% of the total variation in Cd sorption or desorption for the soils studied. Multiple regression analysis showed that native Cd desorption was related to pH, organic matter and total Cd, which in combination explained 85% of the variation between soils. For sorption of Cd (from 2 μg Cd g–1 soil added), pH and organic matter in combination explained 75% of the variation between soils. However, for added Cd desorption (%), pH and CEC explained 77%. It is clear that the combined effects of a range of soil properties control the concentration of Cd in solution, and of sorption and desorption of Cd in soils. The fraction of potentially desorbable added Cd in soils could also be predicted from a soil’s Kd value. This could have value for assessing both the mobility of Cd in soil and its likely availability to plants.

Effect of soil solution composition on cadmium transport through variable charge soils

Cadmium (Cd) is of no known essential biological function and is toxic to plants and animals. Leaching of Cd through soil profiles has implications for both its accumulation in subsoil or contamination of ground-water. We measured adsorption and transport of Cd in the presence of Ca and Na salts of varying ionic strengths using batch and miscible displacement techniques. Two variable charge soils, an Oxisol and an Alfisol, were used in this study. The Alfisol, despite its lower clay content, showed an adsorption coefficient ( K) that was four times higher than the clay-rich Oxisol. Such a difference in adsorption was attributed to the presence of 2 : 1 layer silicate minerals in the Alfisol and the consequent high surface negative charge density. In column experiments, a marked effect of ionic strength on the breakthrough curves (BTCs) of Cd was observed when the concentrations of NaNO 3 were increased from 0.03 M to 0.15 M in the background solutions. This increase caused nearly four times faster movement of Cd through the Oxisol soil column. The effect of increasing Ca(NO 3) 2 concentration on Cd adsorption and transport was relatively less pronounced than that recorded for the NaNO 3 solution. In the Alfisol, the increase in Ca(NO 3) 2 ionic strength from 0.05 M to 0.25 M resulted in four-fold smaller adsorption coefficient. For both soils, the movement of Cd at a constant ionic strength was, however, an order of magnitude faster in the presence of Ca(NO 3) 2 than that in the presence of NaNO 3. To describe the combined effect of ionic strength and pH, we used the K values calculated from the BTCs with CXTFIT model to develop a simple theoretical relationship between Cd adsorption and [H +], [Ca 2+] and [Cd 2+] in solution. The relation was found to be consistent with other published studies. The study demonstrated that Cd mobility in soils is strongly affected by the soil solution composition (ionic strength and type of cations).

An EXAFS Investigation of the Mechanism of Cd Attenuation on Fe and Mn (Oxyhydr)Oxide Minerals

The structure of aqueous cadmium sorption complexes on the iron oxyhydroxide minerals goethite (~-FeOOH), lepidocrocite (?-FeOOH), a k a g a n e i t e ( ~ F e O O H ) , s c h w e r t m a n n i t e (FesOs(OH)6SO4), and cryptomelane (KMn8OI6) have been determined in situ (in the presence of water) using Extended X-Ray Adsorption Fine Structure (EXAFS) spectroscopy. Sorption on these minerals may limit the mobility of Cd in soils and groundwater.

Évaluation par des extractions sélectives de l'immobilisation du Cd après l'apport de matériaux inorganiques dans deux terres polluées

Two soils, contaminated by sludge application or by smelter activities, have been amended with : lime (CaO), lime + Al-pillared smectites (CaO + Sm), phosphate basic slags (SCO), manganese oxide (HMO), iron oxide (HFO) and steel shot (GA). Four single soil extractions (water, 0.1 M Ca(NO 3) 2 0.05 M ED TA-NH 4 and acetic acid (0.43 M HAc)) and the two plant cultures (tobacco and ryegrass) were used to evaluate the effect of these inorganic additives on the mobility and plant-availability of cadmium in the soils. The Cd extracted by the different solutions was compared to the concentration of Cd in the shoots of ryegrass and tobacco. The effect of treatments on Cd mobility in soil was easily discriminated by the use of either water or Ca(NO 3) 2. The addition of HMO and GA reduced both the mobility and the phyto-availability of Cd in the two soils. Conversely, the alkaline additives and HFO decreased the Cd mobility, but not the Cd plant availability. Single soil extractions using either water or Ca(NO 3) 2 are a useful tool for estimating Cd immobilization, but not sufficient for assessing Cd plant availability ; a validation by plant tests must be conducted.

Adsorption and Mobility of Cadmium in Natural, Uncultivated Soils

AbstractThe influence of soil properties on the adsorption and mobility of Cd was studied in 22 natural, uncultivated soils from Salamanca province to understand the environmental characteristics of Cd as a pollutant. Cadmium adsorption was studied by means of adsorption isotherms, using low Cd concentrations that were similar to those potentially found in polluted soils, and Cd mobility was investigated by using soil thin layer chromatography. The Freundlich adsorption constant (K) was not found to be related to any soil properties studied. In contrast, the distribution coefficients (Kd) at 15 and 30 µg L−1 equilibrium concentrations were found to be related to the cation exchange capacity (CEC) of the soil (r = 0.43 and r = 0.44, respectively, p < 0.05). The adsorption (Q), amount adsorbed at high concentrations (Ci = 1000/µg L−1), was found to be significantly related to the CEC, the exchangeable Ca2+ content and the sum of bases. In addition, Rf values, which are indicative of the Cd mobility in soil, bore a highly significant (p < 0.001) negative correlation with some soil parameters such as pH, the exchangeable Ca2+ and Mg2+ contents and the sum of bases, as well as a less significant (p < 0.05), negative correlation with the CEC and clay content of the soil, but no correlation whatsoever with the adsorption constants. The type of organic matter present in the soil must be more influential on Cd mobility than was its content. The above results confirm that a CEC of a soil is highly influential on Cd adsorption and mobility.