Species In Soil Solution Research Articles

Clay mineralogy and its relationship to soil solution composition in soils from different weathering environments of humid Asia: Japan, Thailand and Indonesia

We studied the relationship between the clay mineralogy of subsurface soils from 204 sites and their water extracts in upland soils of humid Asia (Japan, Thailand and Indonesia) to understand their formation. The clay minerals were identified by XRD and the kaolin minerals and gibbsite were quantified with DTA. Their thermodynamic stability was related to the ion activity of soil water extracts. In soils on mica-free andesitic or mafic parent material, kaolin minerals and smectite dominated in all regions. Among mica-containing soils derived from felsic or sedimentary rocks, mineralogical and soil solution compositions indicate that, in Thailand, mica was stable at high pH (5.4–6.5), whereas in soils from Japan and Indonesia mica turned into hydroxy-Al interlayered vermiculite (HIV) or vermiculite at lower pH (4.3–5.5). In Japanese soils, HIV and gibbsite form under high activity of Al–OH species. In contrast, the low activity of Al–OH species in Indonesian soils resulted in the dissolution of Al hydroxides between 2:1 layers and gibbsite and the dominance of kaolin minerals and vermiculite. We conclude that three factors play an important role for the clay mineralogy in humid Asia: the nature of parent material (i.e. presence or absence of mica), soil pH (as affected by precipitation and evapotranspiration) and activity of Al–OH species in soil solution (reflecting soil age).

Characterizing the availability of metals in contaminated soils. II

Abstract. Methods that can be used to determine the distribution of metal species in soil solution are critically reviewed and assessed. They are divided into two groups: those that can provide free ion activity, and those that measure labile species in solution. Ion selective electrodes have long been regarded as a promising technique, but there are practical problems in performing accurate measurements and only the Cu electrode has been used routinely. The Donnan membrane technique is capable of measuring the free ion activity of many metals, but adequate sensitivity can be a problem. Although resin competition methods are versatile, care must be exercised to avoid perturbing the solution excessively. Anodic stripping voltammetry (ASV) measures labile species, so the approximation involved in interpretation as simple inorganic species, from which free ion activities can be derived, should be recognized. Diffusive gradients in thin‐films also measures labile species, but it is applicable to a much wider range of metals than ASV. It requires larger volumes of solution, but it can be used directly on the whole soil where it also measures the metal that can be rapidly supplied to solution. Other techniques such as permeable liquid membranes have yet to be used for measurements on soil solution. All of these methods have strength and weaknesses, and measure different aspects of speciation. Knowledge of the availability of the metals to biota is likely to be best advanced by the critical use of one or more of these speciation methods with a thorough understanding of exactly what is being measured.

Effect of Immobilizing Substances and Salinity on Heavy Metals Availability to Wheat Grown on Sewage Sludge-Contaminated Soil

The objective of the investigation was to evaluate the effect of immobilizing substances and NaCl salinity on the availability of heavy metals: Zn, Cd, Cu, Ni, and Pb to wheat (Triticum aestivum L.). In greenhouse pot experiment, a sewage sludge amended soil was treated with the following immobilizing substances: three clay minerals (Na-bentonite, Ca-bentonite and zeolite), iron oxides (goethite and hematite), and phosphate fertilizers (superphosphate and Novaphos). The pots were planted with wheat and were irrigated either with deionized or saline water containing 1600 mg L−1 NaCl. Wheat was harvested two times for shoot metal concentrations and biomass measurements. Metal species in soil solution were estimated using the software MINEQL+. The addition of metal immobilizing substances to the soil significantly decreased metal availability to wheat. The largest reduction in metal bioavailability was found for bentonites. The irrigation with saline water (1600 mg L−1 NaCl) resulted in a significant increase in metal chloride species (MCl+ and MCl2 0). The highest metal complexation with Cl occurred for Cd, which was about 53% of its total soil solution concentration. The total concentration of Cd (CdT) in soil solution increased by 1.6–2.8-fold due to saline water. The NaCl salinity caused a significant increase in uptake and shoot concentration of Cd for two harvests and small but significant increase in shoot Pb concentration for the second harvest. It was concluded that the use of bentonites is the most promising for the reduction of heavy metal availability to plants. Saline water containing 1600 mg L− 1 NaCl increased the availability of Cd and Pb to wheat and decreased the efficiency of bentonites to immobilize soluble Cd.

Influence of acid mining activity on release of aluminium to the environment

An optimized BCR three-step sequential extraction procedure, several single extractions and the reactive aluminium determination after chelating ion-exchange on Iontosorb Salicyl were used for the fractionation of Al in soil samples from a mining area with sulphidic deposits. The aluminium amounts released by used extraction procedures were valuated and discussed. The new indicative values of fractional Al concentrations in five Chinese certified reference materials (GBW 07103, 07304, 07401, 07405, 07407) were determined after Al fractionation by optimized BCR three-step sequential extraction procedure. The aluminium toxicity indexes calculated for two different soil extracts and plant samples were used for assessment of Al toxicity to plants. It can be concluded that the most sensitive indicator of increasing aluminium toxicity to plants is determination of reactive Al species in soil solution by chelating ion-exchange solid phase extraction. The atomic absorption spectrometry with nitrous oxide-acetylene flame was used for determination of total Al amounts and the Al concentration in different extraction fractions as well.

Salinity and Zinc Application Effects on Phytoavailability of Cadmium and Zinc

Salinity and Zn deficiency in soils are two factors that may change the phytoavailability of Zn and Cd. The aim of this study was to determine the effects of salinity and Zn application on soil Cd and Zn solubility and their concentration in wheat shoots. A greenhouse experiment with wheat (Triticum aestivum L. cv. Rushan) consisting of two levels of Zn (0 and 15 mg Zn kg−1, in the form of ZnSO4), and five salinity levels of irrigation water (0, 60, 120, and 180 mM NaCl, and 120 mM NaNO3) in triplicate was conducted. Wheat was seeded in pots. After 45 d of growth, the shoots were harvested, and Zn and Cd concentrations were determined. After harvesting, electrical conductivity (EC), pH, and concentrations of anions and cations were determined in soil saturation extracts. Concentrations of Cd and Zn species in soil solution were predicted using the speciation program MINTEQA2. Increasing salinity increased total Cd (CdT), Cd2+, CdCl+, CdHCO3+, and CdCl20 concentrations in the soil solution, whereas no such effect was found for the NaNO3 treatment. Higher salinity decreased the total Zn (ZnT) and free Zn2+ concentrations in the soil solution and decreased Zn concentrations in the wheat shoots. With application of Zn fertilizer, shoot Cd concentrations decreased by 11 to 90%, whereas Zn concentration increased by 75 to 103%. Increasing salinity of irrigation water decreased shoot dry matter, especially if no ZnSO4 was applied. Application of Zn had a positive effect on salt tolerance of plant and increased dry matter of shoot.

Phytotoxicity of aluminium to wheat plants in high-pH solutions

Phytotoxicity of aluminium in acid soils is well known. At pH ≥6.3, aluminate [Al(OH)4–] is the principal hydroxo-aluminium species in soil solutions; however, its phytotoxicity has not received much attention. Sodic subsoils in Australia are generally alkaline and have pH above 9. During our survey of 8 subsoils in South Australia, we found aluminate ions at concentrations greater than 0.8 mg/L (29.7 μmol/L of aluminium) in soil solutions when pH was greater than 9, with corresponding high uptake of aluminium by wheat plants. We studied the phytotoxicity of aluminium to wheat plants in solution culture by maintaining the pH of alkaline solutions at 9.2.Relative root lengths of wheat plants, compared with those in reverse-osmosis deionised water, were significantly reduced in alkaline solutions and CO2-free air indicated toxicity of hydroxy, carbonate and bicarbonate ions. Further reduction of root lengths due to aluminate toxicity was also evident. Relative root lengths of wheat plants, when comparing between +aluminium and –aluminium treatments, were reduced up to 50% in alkaline solutions containing as low as 1 mg/L of aluminium. Aluminium accumulated mainly in the roots, thereby reducing their growth. In bicarbonate solutions, aluminium toxicity under alkaline pH was highly significant (P<0.001). However, at the same level of added aluminium in carbonate solutions, relative root length was not reduced. This study concludes that when aluminium species are present at a concentration of about 1 mg/L in soil solutions with pH greater than 9, the growth of wheat plants could be significantly affected.

Acidic deposition: decline in mobilization of toxic aluminium.

The mobilization of aluminium from acidic forest soils is arguably the most ecologically important consequence of acid deposition in the environment because of its adverse effects on soils, forest vegetation and surface water. Here we show that there has been a significant decline in the concentrations of aluminium species in soil solutions at medium-to-high elevations in a northern hardwood forest in the United States in response to decreasing acidic deposition. Streamwater aluminium concentrations have also fallen and, if this rate of recovery persists, will within 10 years no longer pose a threat to fish.

Computer simulation of the distribution of aluminum speciation in soil solutions in equilibrium with the mineral phase imogolite

The speciation of aluminum (Al) is a critical issue when evaluating the environmental and biological significance of elevated Al concentrations in soil solutions caused by acidic precipitation. Numerous studies have revealed that, with increased concentrations of silica acid in soil, the activity of Al species in soil solutions is greatly modified by SiO 4 2−. However, thus far there has been little thorough theoretical modeling of this subject. This paper reports a computer simulation of the distribution of Al speciation in soil solutions in equilibrium with the mineral phase imogolite based on a chemical equilibrium calculation. The unique characteristic associated with imogolite reported by previous researchers can be explained theoretically by the proposed model. The dissolved silica has a remarkable influence on Al speciation: increasing concentrations of silica acid may effectively inhibit the formation of polymeric alumino-hydroxo species, and, furthermore, detoxify Al toxicity to plants.

Flow injection method for iron fractionation by reaction with oxine-derivatised Fractogel

A simple and rapid flow injection analysis (FIA) method is reported for the fractionation of Fe (redox state and lability) associated with humic substances in environmental samples. The fractionation was effected on-line using a pre-concentrating microcolumn containing oxine-derivatised Fractogel. Fe(II) and Fe(III) captured by the gel were subsequently eluted with 0.5 M HCl. Fe(II) was quantified spectrophotometrically as the Fe(II) (1,10-phenanthroline) 3 complex at pH 5.0 and total labile Fe (Fe(II)+Fe(III)) by the same method but with a down-line reduction of Fe(III). The method has a 2 σ detection limit of 42 nM, and a linear working range of 0.2–25 μM Fe, suitable for analysis of Fe species in soil solutions and non-saline waters. The effect of possible interferent species on the Fe(II) signal was quantified, with slight interference being observed for Cu (−13%) and Zn (−9%) when present in solution at the Fe(II) concentration (10 μM). The ability of the oxine-derivatised Fractogel to sequester Fe(II) and Fe(III) bound in organic species was evaluated using both model ligands and a fulvic acid. The developed protocol was used to follow the increases in Fe(II) concentrations that occur as a result of Fe(III) photoreduction in humic water samples.

Effects of pH and Aluminum Concentration on the Form of Aluminum Species in Soil Solution

Effects of pH and Aluminum Concentration on the Form of Aluminum Species in Soil Solution

Effect of straw amendment and plant growth on selenium transfer in a laboratory soil-plant system

Knowledge of the transfers of selenium (Se) in the soil-plant-atmosphere environmental compartments is fundamental in assessing Se cycling through the environment. The purpose of this study was to determine the effects of straw amendments and barley (Hordeum vulgare L.) on Se cycling in soils from Kesterson Reservoir, Merced County, CA (0.68 mg soluble Se kg−1, 6.15 mg total Se kg−1), and to evaluate the feasibility of these agricultural practices as bioremediation strategies. Four treatments were evaluated: soil only, soil + straw, soil + plant, and soil + straw + plant. Straw amendments greatly reduced Se from soil solution (92–97% of initial soluble Se). Selenate [Se(VI)] was the predominant species in soil solution. Phosphate-extractable Se did not account for the decline in soluble Se. Selenium volatilized by microbes represented only 4–5% of the soluble Se removed. Highest Se removal from soil solution and highest Se volatilization rates occurred when both microbial activity and growth were maximal. Selenate microbial reduction to more insoluble Se forms is indicated as being responsible for this removal. Plants did not account for as much Se removal from soil solution as did straw amendments. Total shoot Se corresponded to 1–9% of soluble Se removal. At the end of the experiment, Se in plants represented 0.1–0.7% of total Se in the system, and the Se volatilized accounted for 0.2 to 0.5% of total Se inventory. The results obtained in this study suggest the use of straw amendments as a remediation technique for managing Se contamination at Kesterson Reservoir. Key words: Barley, selenium, soil solution, straw, volatilization

Determination of Arsenic Species in Soil Solution under Flooded Conditions

AbstractGreenhouse experiments were conducted to evaluate the relationships between the species and concentrations of As in the soil solution of flooded soils with other parameters including soil pe, pH, Fe, Mn, and type and amount of As added. Two soils were treated with 0, 5, 15, 25, 35, and 45 mg As kg−1 soil added as either Na‐arsenate or Na‐arsenite and planted with rice (Oryza sativa L.). Soil solution samples were collected during a period of 60 d and analyzed for As. Selective hydride generation was employed to evaluate both type and quantity of As present in the samples. Inorganic As in the form of arsenate and arsenite was found in the soil solution of both soils. The conversion of added arsenite to arsenate occurred within the first 10 d of the experiment when the pe/pH of the soil was not conducive to arsenite stability. Added arsenate was converted to arsenite during the course of the experiment as the pe/pH of the soil declined due to flooding. Arsenate reached a maximum in soil solution at 10 to 20 d after flooding while maximum arsenite concentrations occurred at 20 to 30 d after flooding. The total concentration of As in soil solution generally reached a maximum at 20 to 30 d after flooding, after which time precipitous losses of As from soil solution occurred in all but the highest As treatments. Soil solution As concentrations were not statistically different between planted and unplanted controls.

Plant Uptake and Determination of Arsenic Species in Soil Solution under Flooded Conditions

AbstractPrevious studies have not identified the different As species present in soil systems and determined if effective differences exist between As species with respect to plant parameters such as growth rate and As uptake. This study determined the species and concentrations of As present in soil solution of flooded soils and correlated them to As concentration, P concentration, and growth rate of plants grown in treated soils. Rice (Oryza sativa L.) was grown in two soils treated with 0, 5, 15, 25, 35, and 45 mg As kg−1 soil added as either Na‐arsenate or Na‐arsenite. Soil solution samples and plant samples were collected over a period of 60 d. The As concentration of rice plants best correlated to the mean soil solution arsenate concentration in a Beaumont clay (fine, montmorillonitic, thermic Entic Pelludert) and to the mean soil solution arsenite concentration in a Midland silt loam (fine, montmorillonitic, thermic Typic Ochraqualf). In both soils, plant P concentration was best correlated to the amount of As added to the soil rather than any soil solution As concentration. Plant weight was best correlated to the mean soil solution arsenate concentration in both soils. The rate of As uptake by plants increased as the rate of plant growth increased. Plants grown in soils treated with As had higher rates of As uptake for similar rates of growth when compared with plants in untreated soils. However, growth per unit of As uptake was higher for plants in untreated soils than plants in As treated soils.

Chelate and pH effects on aluminum determined by differential pulse polarography and plant root bioassay

Abstract Aluminum toxicity to plants is related to certain Al species in soil solution, but is alleviated when bound to organics. The objective of this study was to evaluate models for aluminum‐ligand equilibria using differential pulse polarography (DPP) to measure the uncomplexed triva‐lent Al species. Peak height decreased linearly from pH 3.8 to 4.5, but split into two peaks above pH 4.5. Standard curves were linear from 0–15 μM Al. DPP Al followed that predicted by the MINTEQA2 model for nitrilotriacetic acid (NTA), and citrate (CIT). For oxalate (OX) and ethyleneglycol‐bis(2‐aminoethylether)tetraacetic acid (EGTA), the DPP Al followed the same trend as the model but was higher than that predicted. In a nutrient solution experiment with Al, Cu, and NTA, the model and DPP Al concentration followed the same trends, but DPP measured less Al than predicted. In a nutrient solution experiment with four rates of the four chelates, NTA and CIT followed the model well for root lengths.

THE INFLUENCE OF EXTRACTABLE AND SOIL SOLUTION ALUMINUM ON ROOT GROWTH OF WHEAT SEEDLINGS

Short-term bioassay techniques that measure root development of seedlings in soil can be used to evaluate the applicability of chemical methods to predict the Al toxicity of a soil. Wheat (Triticum aestivum cv. Hart) seedlings were grown for 3 d in 20 acidic soil horizons, and root length was related to amounts and forms of Al in soil solution and Al extracted by 0.01 M CaCl2, 1 M KCl, 0.5 M CuCl2, and 0.33 M LaCl3. With the exception of Al extracted by 0.01 M CaCl2, soil extraction methods were not effective in predicting root growth. Root growth was not closely related to total soil solution Al or soil solution Al reacting with 8-hydroxyquinoline, pyrocatechol violet, or aluminon. These colorimetric reagents reacted with nontoxic forms of Al, including organically bound Al, and overestimated the toxic component. Activities of Al species in soil solution were estimated from soil solution composition using the GEOCHEM program. The calculated Al3+ activity ({Al3+}) ranged from 0 to 119 μ M and taken alone was not a good predictor of root growth. It is likely that calculated {Al3+} overestimated actual {Al3+} due to the difficulty of measuring all Al-complexing ligands in soil solution. Root growth in these soils was best described by a multiple regression equation containing soil solution pH, Ca, and Al. The results of this study illustrate the limitations associated with the current methods used to estimate toxic Al levels. New methods are needed to directly measure the toxic Al component or components in soil solution. Until better chemical or instrumental techniques are developed, the short-term bioassay technique should serve as a useful means of assessing the potential Al toxicity of a soil.

Experimental measurements and computer predictions of copper complex formation by soluble soil organic matter

Complexing of metals by organic matter can strongly influence their biological activity in the environment. The extent of copper complex formation by soluble organic matter extracted from an organic soil, a clay, and two sandy loams, was measured under identical conditions using two independent experimental methods. The results in every case fitted equations similar to Langmuir two-surface isotherms, but the values of complexing capacity and complexing strength were not the same for the organic matter from the four soils, and so were unsuitable for use in computer programs intended to predict concentrations of individual copper species in soil solutions. These concentrations can, however, be predicted by an empirical relationship between free and total copper at a constant pH and ionic strength.

CHEMICAL EQUILIBRIA OF SELENIUM IN SOILS

Thermodynamic data were used to develop equilibrium reactions and constants for 83 selenium (Se) minerals and solution species that relate to soils. The solubilities of the metal-selenate minerals are very high in well-aerated soils and are not expected to persist in these systems. The solubilities of 17 metal-selenite minerals studied suggest that MnSeO3(c) is the only selenite mineral that might persist in strongly acid soils. Other selenite minerals appear to be too soluble to form in soils particularly in the alkaline pH range. Metal-selenide minerals, in general, are extremely insoluble in soils under highly reducing conditions. Of the 17 metal selenides studied, Cu2Se(c) is the most stable mineral in acid soils, and both PbSe(c) and SnSe(c) are more stable under neutral and alkaline conditions. Formation of these metal-selenides may prevent the precipitation of elemental Se in soils. The redox (pe+pH) of soils controls Se speciation in solution. Selenate (SeO42-) is the major species in solution at high redox (pe+pH < 15.0). In the medium redox range (pe+pH 7.5–15.0) either SeO32- or HSeO3− species is predominant, depending upon pH. At low redox (pe+pH > 7.5), HSe− is the major species in soil solution. Only in strongly acid soils do H2Se0 species contribute significantly to Se in solution. None of the 27 metal solution complexes studied was found to contribute significantly to total soluble Se in normal cultivated soils. Except for MnSeO3(c), none of the other known selenite or selenate minerals is expected to persist in soils. In moderately to highly oxidized conditions it is possible that an adsorption mechanism may control the distribution of Se between solid surfaces and the solution phase. However, at low redox, either elemental Se or a metalselenide mineral, e.g., Cu2Se(c), PbSe(c) may control Se solubility in soils.

CHEMICAL EQUILIBRIA OF FLUORINE IN SOILS

We selected thermodynamic data for 45 fluorine minerals and solution species that may play important roles in the fluorine chemistry of soils. Equilibrium reactions and stability constants for these minerals and species were calculated and used to develop stability diagrams in soils. Aluminum fluoride is likely to precipitate in strongly acid soils of pH below 4.5. In these soils AlF3(c) in equilibrium with Al(OH)3 (gibbsite) can maintain F− below 10−4M in solution. Fluorite appears to be stable in slightly acid and near-neutral soils. When fluorite is in equilibrium with 10−2.5M Ca2+, it can support 10−3.96M F− in soil solution. Fluorophlogopite mineral is probably stable in alkaline soils. However, it is a complex mineral and its solubility is also affected by the activities of H4SiO40, Al3+, K+, Mg2+, and pH. Fluorapatite is unstable in acid soil, but it is the most stable F mineral in alkaline and calcareous soils. Fluorapatite supports extremely low F− activity (<10−6.5M) in soil solution when it is in equilibrium with hydroxyapatite. Other metal fluorides, e.g., NaF, KF, CuF2, ZnF2, PbF2, CdF2, MgF2, and FeF3 are too soluble to persist in soils. Also, fluorosilicate, fluoroaluminate, and fluoroaluminosilicate minerals, such as Na2SiF6 (malladrite), (NH4)2SiF6 (bararite), K2SiF6 (hieratite), Na3AlF6 (cryolite), and NaCa2Mg4Al3Si6O22F2 (fluorpargasite), are thermodynamically unstable in soils. Solution complexes of aluminum fluorides, e.g., AlF2+, AlF2+, AlF30, and AlF4−, and iron fluorides, e.g., FeF2+, FeF2_, and FeF30, are the major solution species in strongly acid soils below pH 6. Above this pH F− is the predominant species in soil solution. Silicon and lead fluoride complexes, along with KF0, NaF0, CuF+, ZnF20, and HF2− species, are not important in most cultivated soils.