Sabry M. Shaheen

A review of the distribution coefficients of trace elements in soils: influence of sorption system, element characteristics, and soil colloidal properties.

Knowledge about the behavior and reactions of separate soil components with trace elements (TEs) and their distribution coefficients (Kds) in soils is a key issue in assessing the mobility and retention of TEs. Thus, the fate of TEs and the toxic risk they pose depend crucially on their Kd in soil. This article reviews the Kd of TEs in soils as affected by the sorption system, element characteristics, and soil colloidal properties. The sorption mechanism, determining factors, favorable conditions, and competitive ions on the sorption and Kd of TEs are also discussed here. This review demonstrates that the Kd value of TEs does not only depend on inorganic and organic soil constituents, but also on the nature and characteristics of the elements involved as well as on their competition for sorption sites. The Kd value of TEs is mainly affected by individual or competitive sorption systems. Generally, the sorption in competitive systems is lower than in mono-metal sorption systems. More strongly sorbed elements, such as Pb and Cu, are less affected by competition than mobile elements, such as Cd, Ni, and Zn. The sorption preference exhibited by soils for elements over others may be due to: (i) the hydrolysis constant, (ii) the atomic weight, (iii) the ionic radius, and subsequently the hydrated radius, and (iv) its Misono softness value. Moreover, element concentrations in the test solution mainly affect the Kd values. Mostly, values of Kd decrease as the concentration of the included cation increases in the test solution. Additionally, the Kd of TEs is controlled by the sorption characteristics of soils, such as pH, clay minerals, soil organic matter, Fe and Mn oxides, and calcium carbonate. However, more research is required to verify the practical utilization of studying Kd of TEs in soils as a reliable indicator for assessing the remediation process of toxic metals in soils and waters.

Amendment of biochar reduces the release of toxic elements under dynamic redox conditions in a contaminated floodplain soil

Biochar (BC) can be used to remediate soils contaminated with potential toxic elements (PTEs). However, the efficiency of BC to immobilize PTEs in highly contaminated floodplain soils under dynamic redox conditions has not been studied up to date. Thus, we have (i) quantified the impact of pre-definite redox conditions on the release dynamics of dissolved aluminum (Al), arsenic (As), cadmium (Cd), copper (Cu), nickel (Ni), and zinc (Zn) in a highly contaminated soil (CS) (non-treated) and in the same soil treated with 10 g kg(-1) biochar based material (CS+BC), and (ii) assessed the efficacy of the material to reduce the concentrations of PTEs in soil solution under dynamic redox conditions using an automated biogeochemical microcosm apparatus. The impact of redox potential (EH), pH, dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), iron (Fe), manganese (Mn), and sulfate (SO4(2-)) on dynamics of PTEs was also determined. The EH was lowered to +68 mV and afterwards increased stepwise to +535 mV. Significant negative correlation between EH and pH in CS and CS+BC was detected. The systematic increase of EH along with decrease of pH favors the mobilization of PTEs in CS and CS+BC. The material addition seems to have little effect on redox processes because pattern of EH/pH and release dynamics of PTEs was basically similar in CS and CS+BC. However, concentrations of dissolved PTEs were considerably lower in CS+BC than in CS which demonstrates that BC is able to decrease concentrations of dissolved PTEs even under dynamic redox conditions.

Opportunities and challenges in the use of coal fly ash for soil improvements – A review

Coal fly ash (CFA), a by-product of coal combustion has been regarded as a problematic solid waste, mainly due to its potentially toxic trace elements, PTEs (e.g. Cd, Cr, Ni, Pb) and organic compounds (e.g. PCBs, PAHs) content. However, CFA is a useful source of essential plant nutrients (e.g. Ca, Mg, K, P, S, B, Fe, Cu and Zn). Uncontrolled land disposal of CFA is likely to cause undesirable changes in soil conditions, including contamination with PTEs, PAHs and PCBs. Prudent CFA land application offers considerable opportunities, particularly for nutrient supplementation, pH correction and ameliorating soil physical conditions (soil compaction, water retention and drainage). Since CFA contains little or no N and organic carbon, and CFA-borne P is not readily plant available, a mixture of CFA and manure or sewage sludge (SS) is better suited than CFA alone. Additionally, land application of such a mixture can mitigate the mobility of SS-borne PTEs, which is known to increase following cessation of SS application. Research analysis further shows that application of alkaline CFA with or without other amendments can help remediate at least marginally metal contaminated soils by immobilisation of mobile metal forms. CFA land application with SS or other source of organic carbon, N and P can help effectively reclaim/restore mining-affected lands. Given the variability in the nature and composition of CFA (pH, macro- and micro-nutrients) and that of soil (pH, texture and fertility), the choice of CFA (acidic or alkaline and its application rate) needs to consider the properties and problems of the soil. CFA can also be used as a low cost sorbent for the removal of organic and inorganic contaminants from wastewater streams; the disposal of spent CFA however can pose further challenges. Problems in CFA use as a soil amendment occur when it results in undesirable change in soil pH, imbalance in nutrient supply, boron toxicity in plants, excess supply of sulphate and PTEs. These problems, however, are usually associated with excess or inappropriate CFA applications. The levels of PAHs and PCBs in CFA are generally low; their effects on soil biota, uptake by plants and soil persistence, however, need to be assessed. In spite of this, co-application of CFA with manure or SS to land enhances its effectiveness in soil improvements.

Temporal dynamics of pore water concentrations of Cd, Co, Cu, Ni, and Zn and their controlling factors in a contaminated floodplain soil assessed by undisturbed groundwater lysimeters

We aimed to assess the dynamics of pore water concentrations of Cd, Co, Cu, Ni, Zn and their controlling factors (EH, pH, DOC, Fe, Mn, and SO4(2-)) in a contaminated floodplain soil under different flood-dry-cycles. Two parallel undisturbed groundwater lysimeters (mean values presented) were used for long term (LT; 94 days) and short term (ST; 21 days) flood-dry-cycles. Reducing conditions under LT lead to low EH and pH, while DOC, Co, Fe, Mn, and Ni increased. Cadmium, Cu, Zn, and SO4(2-) increased under oxidizing conditions during ST. Cobalt and Ni revealed a similar behavior which seem to governed by EH/pH, Mn, Fe, and DOC. Cadmium, Cu, and Zn reveal a similar fate; their dynamics were affected by EH/pH, DOC, and SO4(2-). Our findings suggest that a release of Cd, Cu, Co, Fe, Mn, Ni, and Zn under different flood-dry-cycles can assumed what might create potential environmental risks in using metal-enriched floodplain soils.

Removal of Heavy Metals from Aqueous Solution by Zeolite in Competitive Sorption System

In this study, the sorption behaviour of natural (clinoptilolite) zeolites with respect to cadmium (Cd), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn) has been studied in order to consider its application to purity metal finishing wastewaters. The batch method has been employed, using competitive sorption system with metal concentrations in solution ranging from 50 to 300 mg/l. The percentage sorption and distribution coefficients (Kd) were determined for the sorption system as a function of metal concentration. In addition lability of the sorbed metals was estimated by DTPA extraction following their sorption. The results showed that Freundlich model described satisfactorily sorption of all metals. Zeolite sorbed around 32, 75, 28, 99, and 59 % of the added Cd, Cu, Ni, Pb and Zn metal concentrations respectively. According to the percentage sorption and distribution coefficients values, the selectivity sequence of studied metals by zeolite can be given as Pb > Cu > Zn > Cd > Ni. About 57, 47, 78, 22, and 29 % from the total sorbed Cd, Cu, Ni, Pb and Zn recovered by DTPA indicating that lability of the adsorbed Ni was higher than, Cd, Cu, Zn, and Pb respectively. These results show that natural zeolites hold great potential to remove cationic heavy metal species from industrial wastewater.

Redox effects on release kinetics of arsenic, cadmium, cobalt, and vanadium in Wax Lake Deltaic freshwater marsh soils.

The impact of redox potential (EH), pH, iron (Fe), manganese (Mn), chloride (Cl(-)), aliphatic and aromatic dissolved organic carbon (DOC), and sulfate ( [Formula: see text] ) on the release of dissolved arsenic (As), cadmium (Cd), cobalt (Co), and vanadium (V) were studied in Louisiana freshwater marsh Wax Lake Delta soil (Mississippi River) using an automated biogeochemical microcosm apparatus. The experiment was conducted from reducing (-60 mV) to stepwise oxidizing (+491 mV) conditions. The initial pH was 7.4 and decreased under reducing conditions to 4.9, and remained constant during the increase of EH. Concentrations of As (1.3-120.5 μg L(-1)), V (0.9-48.6 μg L(-1)), Fe, DOC, and the specific UV absorbance increased under reducing conditions and decreased with rising EH. Release of As and V appeared to be related to changes of EH/pH, co-precipitation with Fe oxides, and the release of dissolved aromatic carbon compounds. Concentrations of soluble Cd (4.8-11.2 μg L(-1)), Mn, [Formula: see text] , and Cl(-) increased under oxidizing conditions. Release of Co (166.6-258.2 μg L(-1)) was related to the chemistry of Fe, Mn and DOC. Phospholipid fatty acids analysis indicated the potential for the microbial community to be involved in biogeochemical processes such as the formation of sulfides, oxidation and reduction of compounds, and the bio-methylation of elements such as As. Overall, we measured a release of As and V under anoxic conditions, while oxic conditions favored the release of Cd. These results outline concern on the potential risk of mobilization of toxic elements in temporary waterlogged soils for agricultural purposes in deltaic ecosystems.

Distribution Coefficient of Copper in Different Soils from Egypt and Greece

Distribution coefficient (Kd ) indicates the capability of a soil to retain a solute and consequently its distribution between solid and liquid phase. The purpose of this study was to determine copper (Cu) Kd values of different soils to evaluate their ability to retain it and control its mobility and therefore availability. Eleven surface soil samples varying widely in their origin and properties were selected from Egypt and Greece for this study. Four of them were from Egypt representing the main soil orders: Entisols (developed on fluvial, lacustrine, and sandy marine deposits) and Aridisols (calcareous deposits). The other seven soils were from Greece belonging to the orders Entisols, Alfisols, Vertisols, Mollisols, and Histisols. Copper (Cu) distribution coefficient values were obtained by batch equilibrium experiments from which adsorption isotherms were prepared. The results showed that the Freundlich model satisfactorily described Cu sorption. Clayey and alkaline soils exhibited much greater Cu sorption capacity than the sandy and acid soils. Copper distribution coefficients values differed significantly between the studied soil orders and ranged from 80.9 l kg−1 in the acid Greek Alfisol to 7502.4 l kg−1 in the Egyptian lacustrine Entisol and were significantly correlated with clay content, cation exchange capacity, organic matter, total free silica, and amorphous iron (Fe), aluminum (Al), silicon (Si), and manganese (Mn) oxides. Adsorption of Cu in the studied variable charge red soils was pH dependent. Values of Kd decreased clearly as the concentration of the included cation increased in the test solution.

Exploiting biogeochemical and spectroscopic techniques to assess the geochemical distribution and release dynamics of chromium and lead in a contaminated floodplain soil.

Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX) combined with a seven steps sequential extraction technique were used to assess the geochemical distribution of chromium (Cr) and lead (Pb) in a contaminated floodplain soil. Total contents of Cr and Pb were 490.3 and 402.1 mg kg(-1), respectively. The residual fraction was 59.5 and 56.3% of total Cr and Pb. The crystalline iron (Fe) oxide was the dominant non-residual fraction of Cr (35.9% of total Cr). Considerable amounts of Pb were found in the organic fraction (35.4%). Using (13)C nuclear magnetic resonance spectroscopy, the soil organic matter was identified as 48.9% aromatic carbon, which indicated that a certain portion of Pb and Cr might be associated with aromatic compounds. The SEM-EDX images demonstrate a concomitant occurrence of Pb, manganese (Mn), Fe, and aluminum (Al) as well as a coexistence of Cr and Fe. The release dynamics of dissolved Cr and Pb as affected by redox potential (EH), pH, Fe, Mn, dissolved organic carbon, and sulfate was quantified using an automated biogeochemical microcosm apparatus. Soil pH decreased under oxic conditions. The release of Cr, Pb, Fe, and Mn increased under acidic oxic (pH = 3.7, EH = 521 mV) conditions due to the associated decrease of pH (7.1-3.7). The mobilization of Cr and Pb was affected by the Fe and Mn. In conclusion, our multi-technique approach identified the geochemical distribution of Cr and Pb and verified major factors that explain mobilization of Cr and Pb in floodplain soils.

Phytoextraction of potentially toxic elements by Indian mustard, rapeseed, and sunflower from a contaminated riparian soil

The objective of this study was to quantify the phytoextraction of the potentially toxic elements Al, As, Cd, Co, Cr, Cu, Mo, Ni, Pb, Se, V, and Zn by Indian mustard, rapeseed, and sunflower from a contaminated riparian soil. To achieve this goal, a greenhouse pot experiment was established using a highly contaminated grassland soil collected at the Wupper River (Germany). The impact of ethylene-diamine-tetra-acetic acid (EDTA), humate (HK), and phosphate potassium (PK) on the mobility and uptake of the elements by rapeseed also was investigated. Indian mustard showed the highest efficiency for phytoextraction of Al, Cr, Mo, Se, and V; sunflower for Cd, Ni, Pb, and Zn, and rapeseed for Cu. The bioconcentration ratios were higher than 1 for the elements (except As and Cu), indicating the suitability of the studied plants for phytoextraction. Application of EDTA to the soil increased significantly the solubility of Cd, Co, Cr, Ni, and Pb and decreased the solubility of Al, As, Se, V, and Mo. Humate potassium decreased significantly the concentrations of Al and As in rapeseed but increased the concentrations of Cu, Se, and Zn. We may conclude that HK can be used for immobilization of Al and As, while it can be used for enhancing the phytoextraction of Cu, Se, and Zn by rapeseed. Phosphate potassium immobilized Al, Cd, Pb, and Zn, but enhanced phytoextraction of As, Cr, Mo, and Se by rapeseed.

Miscellaneous additives can enhance plant uptake and affect geochemical fractions of copper in a heavily polluted riparian grassland soil

The problem of copper (Cu) pollution in riverine ecosystems is world-wide and has significant environmental, eco-toxicological, and agricultural relevance. We assessed the suitability and effectiveness of application rate of 1% of activated charcoal, bentonite, biochar, cement kiln dust, chitosan, coal fly ash, limestone, nano-hydroxyapatite, organo-clay, sugar beet factory lime, and zeolite as soil amendments together with rapeseed as bioenergy crop as a possible remediation option for a heavily Cu polluted floodplain soil (total Cu=3041.9mgkg(-1)) that has a very high proportion of sorbed/carbonate fraction (484.6mgkg(-1)) and potential mobile fraction of Cu (1611.9mgkg(-1)). Application changed distribution of Cu among geochemical fractions: alkaline materials lead to increased carbonate bounded fraction and the acid rhizosphere zone might cause release of this Cu. Thus, mobilization of Cu and uptake of Cu by rapeseed were increased compared to the control (except for organo-clay) under the prevailing conditions.