Laboratory Experiments to Study Radiocaesium Interaction in Organic Soils

Abstract

The total concentration of a pollutant in a given environmental compartment is often used for risk assessment. However, the real impact of the pollutant also depends on its toxicity and mobility. In soils, pollutant mobility is strongly related to its interaction with the different sites. The mechanisms and dynamics of this interaction may be studied by adsorption and desorption approaches. Adsorption experiments based on the measurement of the pollutant solid-liquid distribution coefficient (K_D) determine the interaction capacity of the soil and identify the nature of the sites involved. Desorption experiments based on single, sequential or consecutive extractions show the reversibility of the adsorption process (soil fixation capacity) and how it might be affected by changes in field conditions. They also predict changes in reversibility over time. In this work, the study of radiocaesium interaction in organic soils is used to illustrate these statements. In this study, the combined use of adsorption and desorption experiments shows that, even in highly organic soils, the specific sites of clay materials may govern radiocaesium behaviour.     

Study of Sorption Processes of Selected Pesticides on Soils and Ceramic Porous Cups used For Soil Solution Sampling

Abstract

Soil sorption constants of four organochlorine (lindane, dicofol, chlorfenson and tetradifon) and three organophos-phorus pesticides (dimethoate, fenitrothion and methidathion) were measured using two different soils at six concentrations.

Soil samples were collected at depths of 0-20 cm and around 100 cm from an experimental citrus crop field. Effects of soil properties (organic matter, moisture content, pH and texture) on the sorption processes were also investigated.

Partitioning of pesticides between soil and solution was investigated after batch equilibration, using pesticide concentrations ranging from 10 to 200 μg1^?1. The equilibration time was estimated in 2 h for organochlorine, and 72 h for organophosphorus pesticides. Data fitted to Freundlich types adsorption isotherms.

Analytical determinations were carried out by gas chromatography with ECD and NPD detectors, after liquid-liquid extraction with dichloromethane of the water supernatant.

Moreover, a validation of the use of suction samplers used to collect soil solution samples from the vadose zone, based on a short term study in the laboratory was determined.     

Pollution Potential of Some Triazole Pesticides

Abstract

The widespread occurrence of pesticides, especially in the groundwater has stimulated research into the behavior of these agrochemicals in the environment. In this work a simple model to describe the fate of the two triazole fungicides Flutriafol and Flusilazol in a silt soil is presented. For this purpose we constructed mini-columns of soil, on which we applied the two fungicides, the percolation waters and the soils were collected at different times and the pesticides quantified in these samples. In the first part, these experiments were carried out outdoors during a period of 6 months on the silt soil and in a second part, we did similar indoor experiments with the same soil and with two others. To complete our work, we studied the adsorption of these two compounds on these three types of soil with batch equilibrium experiments. The results demonstrate that the fungicide Flusilazol is an immobile compound in soil, being strongly adsorbed whatever the nature of the soil. The Flutriafol is slightly to moderately mobile in the different soils, being less adsorbed.     

Effect of Different Salt Leachates on the movement of some Carbamoyl Groups Containing Pesticides in Soils using Thin-Layer Chromatography

Abstract

The influence of pH, leachates of alkaline and saline salts, inorganic fertilizers and surfactants on the mobility of five carbamoyl group containing pesticides, viz. aldicarb, bavistin, carbofuran, dimecron and oxamyl has been studied using soil thin layer chromatographic technique. The variation in the movement of pesticides under different solvent amendments expressed in terms of Rf, RB and RM values and explained on the basis of adsorption and leachability.     

A Review of Analytical Methods for Sulfonylurea Herbicides in Soil

Abstract

The sulfonylurea herbicides are a group of about twenty compounds used for the control of broad-leaved weeds and some grasses in cereal crops. These herbicides are non-volatile, and their water solubilities are pH dependent being greater in alkaline than in acidic solutions. Their soil adsorption is generally low, with leaching potential in alkaline field soils. Sulfonylurea herbicides are degraded in soils by both chemical and biochemical mechanisms. Chemical degradation is particularly important in acidic soils where herbicide degradation is considerably more rapid that in soils of pH > 7. Application rates in the order of 10 g ha^?1 necessitate analytical techniques capable of quantifying soil based residues in the sub μ kg^?1 levels. Analytical methodologies based on plant bioassays, and chemical extraction followed by gas chromatographic (GC), high performance liquid chromatographic (HPLC), and enzyme immunoassay techniques are described and discussed.     

Study of the behaviour of azinphos-methyl in a clay mineral by batch and column leaching

Research efforts dealing with the processes affecting the transport of pesticides in soils are needed in order to prevent further damage of surface and groundwater reserves. Although organic matter has been recognised as the most important contributor to the adsorption of non-ionic organic pesticides in soils, in some cases clay minerals may have an important role in the retention of these compounds. The present study was designed to improve the knowledge of the behaviour of azinphos-methyl in soils. Coefficients from adsorption isotherms and HPLC analysis of soil column leachates were used in this work for predicting pesticide mobility in soils. The studied clay mineral was a Spanish bentonite with a predominant montmorillonite fraction. The results showed that azinphos-methyl was adsorbed on the clay mineral and demonstrated the catalytic effect of bentonite on the hydrolysis of the pesticide.     

Adsorption and Desorption of the Herbicide Thiazafluron as A Function of Soil Properties

Abstract

The effect of soil composition on the adsorption and desorption of the herbicide thiazafluron [1.3-dimethyl-1-(5-trifluoromethyl-1,2,3-thiadiazol-2-yl) urea] by 20 soil samples of 13 selected soil profiles of southern Spain has been studied. The adsorption curves conformed the Freundlich equation and the values of the constants, Kf and nf, ranged from 0.13 to 4.64 and from 0.14 to 1.30, respectively. The simple and multiple regression analysis between Kf and soil properties revealed soil clay content, illite content and CEC as fundamental factors determining thiazafluron adsorption by soils. Unlike other substituted ureas, non significant correlation was found with soil organic matter. Desorption of thiazafluron was hysteretic in all cases, showing and values much lower than those for adsorption. Desorption kinetic indicated that this hysteresis is essentially due to irreversible adsorption, although some degradation seems also to occur. The Freundlich desorption Kfd values were closely related to the same factors as Kf: clay and illite contents and also montmorillonite content, suggesting that most of the hysteresis was due to thiazafluron irreversibly bound to soil clay mineral components.     

Microwave-assisted extraction through an aqueous medium and simultaneous cleanup by partition on hexane for determining pesticides in agricultural soils by gas chromatography: a critical study

A simple microwave-assisted extraction and partitioning method (MAEP) using water-acetonitrile and n-hexane for desorption and simultaneous partitioning, respectively, together with gas chromatography (GC) was studied to determine representative pesticides (trifluralin, metolachlor, chlorpyriphos and triadimefon) with a broad range of physico-chemical properties in agricultural soils. Three points were considered crucial in this study: instrumental and sample-associated factors affecting extraction of the target compounds were studied through experimental design; the spiking procedure at trace levels was carried out to reproduce the solute-soil sorption taking place in the environment as closely as possible; and results were analyzed taking into account the adsorption behaviour of the compounds on different kinds of soils. The complete analytical procedure proposed consisted of the MAEP of pesticides from 1.0 g of soil with 1 mL of 1:1 water/acetonitrile mixture, and 5 mL of hexane for trapping. The microwave heating program applied was 2 min at 250 W and 10 min at 900 W, and 130 °C maximum temperature. After extraction, the hexane layer was evaporated to dryness; the residue was re-dissolved and directly analyzed by gas chromatography electron capture detection (GC-ECD). Clean chromatograms were obtained without any additional cleanup step. Besides the four pesticides used to optimise MAEP, the method was applied to determine an additional group of pesticides (triallate, acetochlor, alachlor, endosulphan I and II, endrin, methoxychlor and tetradifon) in different soils. Most of the compounds studied were recovered in good yields with relative standard deviations (R.S.D.s) below 9% and detection limits ranged from 0.004 to 0.036 μg g⁻¹. The described method is efficient and fast to determine hydrophobic pesticides at ng g⁻¹ level in soil with different clay-to-organic matter ratios.     

Model study of acid rain effect on adsorption of trace elements on soils using a multitracer

Using a radioactive multitracer and model acid rain (HCl or H₂SO₄ solution), batch experiments were performed to examine the pH effect on the adsorption-desorption equilibrium of 16 elements on soils as a model study of an acid rain effect. Kaolin, black soil (original and with organic matter almost removed) and Kureha soil (original and with organic matter almost removed) were used as adsorbents. Characteristic dependence on the pH value of the suspension was observed for the adsorption of the elements on kaolin and the soils. The results of this model study indicate that acid rain decreases the retention of cations, while it increases or does not change the adsorption of anions on soils. Organic matter in soils has a positive effect on the extent of adsorption of most elements investigated.     

Studies of 85Sr adsorption on grain fractions of soil

Summary The adsorption of ⁸⁵Sr on grain fractions isolated from four different types of soil was studied. The influence of pH, concentration and presence of calcium ions on the process was investigated. The adsorption process depends mainly on pH, grain size of the solidandthe type of soil. Ca²⁺in the system is lowering the adsorption of ⁸⁵Sr.     

Mechanisms of Tebuconazole Adsorption in Profiles of Mineral Soils

The study attempted to identify the soil components and the principal adsorption mechanisms that bind tebuconazole in mineral soils. The K_F values of the Freundlich isotherm determined in 18 soils from six soil profiles in batch experiments after 96 h of shaking ranged from 1.11 to 16.85 μg^1−1/n (mL)^1/n g⁻¹, and the exponent 1/n values from 0.74 to 1.04. The adsorption of tebuconazole was inversely correlated with the soil pH. Both neutral and protonated forms of this organic base were adsorbed mainly on the fraction of humins. The adsorption of the protonated form increased in the presence of hydrogen cations adsorbed in the soil sorption sites. Fourier transform infrared spectroscopy coupled with the molecular modeling studies and partial least squares regression analysis indicated that the tebuconazole molecule is bound in the organic matter through the formation of hydrogen bonds as well as hydrophobic and π–π interactions. Ion exchange was one of the adsorption mechanisms of the protonated form of this fungicide. The created mathematical model, assuming that both forms of tebuconazole are adsorbed on the organic matter and adsorption of the protonated form is affected by the potential acidity, described its adsorption in soils well.     

Leaching of Triazine Pesticides in Loamy Soil and their Determination by Reversed Phase HPLC

Abstract

The separation and identification of triazine pesticides (ametryn, atrazine, cyanazine and simazine) was carried out on Nova Pak C₁₈ column (150 × 3.9mm). The mobile phase used was acetonitrile-water (65:35, v/v) adjusted to pH 4.5 with acetic acid. The flow rate of the mobile phase used was 1.0mL/min. The detection of the pesticides was carried out at 250 nm. The values of the separation factor (α) were in the range of 1.49–5.32 and the values of the resolution factors (R _s) were ranged from 1.18 to 2.99 for the separated pesticides. The developed HPLC method was used to determine the concentrations of the reported pesticides in the loamy soil samples. The recovery of the pesticides from soil samples was found to be about 50%. The relative standard deviation and limit of detection were in the range of 0.01–0.02 and 0.5–1.0 μg/mL respectively.     

Adsorption and desorption of copper and zinc in the surface layer of acid soils

The environmental and health effects of the contamination of soils by heavy metals depend on the ability of the soils to immobilize these contaminants. In this work, the adsorption and desorption of Cu and Zn in the surface layers of 27 acid soils were studied. Adsorption of Cu(II) from 157-3148 mumol L(-1) solutions was much greater than adsorption of Zn(II) from solutions at the same concentration. For both Cu and Zn, the adsorption data were fitted better by the Freundlich equation than by the Langmuir equation. Multiple regression analyses suggest that Cu and Zn adsorption depends to a significant extent on pH and CEC: for both metals these variables accounted for more than 80% of the variance in the Freundlich pre-exponential parameter K(F), and pH also accounted for 57% of the variance in 1/n for Zn and, together with carbon content, for 41% of the variance in 1/n for Cu. The percentage of adsorbed metal susceptible to desorption into 0.01 M NaNO3 was greater for Zn than for Cu, but in both cases depended significantly on pH, decreasing as pH increased. In turn, both pH(H2O) and pH(KCl) are significantly correlated with cation exchange capacity. Desorption of metal adsorbed from solutions at relatively low concentration (787 mumol L(-1)) exhibited power-law dependence on Kd, the quotient expressing distribution between soil and soil solution in the corresponding adsorption experiment, decreasing as increasing Kd reflected increasing affinity of the soil for the metal. The absence of a similarly clear relationship when metal had been adsorbed from solutions at relatively high concentration (2361 mumol L(-1)) is attributed to the scant between-soil variability of Kd at these higher concentrations. In general, adsorption was greater and subsequent desorption less in cultivated soils than in woodland soils.     

Determination of I-129 and I-127 in soil and tracer experiments on the adsorption of iodine on soil

Neutron activation analysis of¹²⁹I and¹²⁷I in soil has been studied. The limit of detection for¹²⁹I in soil was about 0.05 mBq/kg or 1×10^–9 as¹²⁹I/¹²⁷I atom ratio. The range of¹²⁹I concentration in surface soils collected around Tokaimura (Ibaraki Prefecture) was 0.9–41 mBq/kg.Tracer experiments on the adsorption of iodine were also carried out, in order to obtain information on the behaviour of iodine in soil-water systems. Different adsorption patterns of iodide and iodate on soil were found. It was supposed that iodide was adsorbed by the soil fraction which became unstable at about 200° C and iodate by the fraction which was relatively stable to heating.     

The effect of sorption properties of soil minerals on the vertical migration rate of cesium in soil

The vertical distribution of¹³⁷Cs is shown for two types of soil: silly loamy “supposed” soil and silly lessive one, slightly eroded, occuring in the vicinity of Lublin (Eastern Poland). Based on the distribution data the vertical migration rates of¹³⁷Cs are calculated for both soils. These rates are found to be 0.045 and 0.3 cm/year respectively. The percent contribution of¹³⁷Cs originating from the damaged reactor in Chernobyl is also calculated. The kinetics of cesium adsorption and its adsorption isotherms on minerals separated from the tested soils are also studied. The sorption of Cs on soil minerals markedly affects the migration rate of¹³⁷Cs in soil. The experimental results indicate that, among the extracted mineral fractions, the largest adsorption takes place on marls from the silly loamy soil. This work is supplemented by results of a physicochemical analysis of the studied soils.     

Retention of Metamitron by Model and Natural Particulate Matter

Abstract

Adsorption isotherms of metamitron on model soil colloidal components: kaolinite, illite, montmorillonite, iron oxide and humic acid, and their binary associations were obtained using a batch equilibration procedure. Sorption parameters, K_f and n_f, were calculated by fitting the sorption data to the Freundlich equation and results obtained for binary associations were compared with those obtained for the individual model components. The sorption efficiency of the humic acids and their binary associations was measured as Koc. The adsorption behaviour of the < 2 μm fraction of two soils from Southern Spain was also studied as natural particulate matter. Montmorillonite and humic acids were found to be the most important components responsible for metamitron retention by the model adsorbents studied. On the contrary, metamitron showed little interaction with kaolinite, illite or iron oxide. These individual adsorption behaviours were reproduced in the montmorillonite-iron oxide-humic acid binary systems, but with differences suggesting changes on the surface properties upon association. Differences in Koc values of isolated humic acids and their associations indicate that the interaction transforms the humic acid surfaces and suggest different types of bonding between colloids and metamitron. The results obtained with model adsorbents and their associations were in agreement with the highest adsorption of metamitron found for the natural clay fraction of two soils which displayed the largest adsorption in that with the highest content in montmorillonite and organic carbon. The importance of organic matter and montmorillonite in metamitron adsorption by colloidal components was also shown by the decrease in K_f and the increase in Koc observed after removal of organic matter from the soil clay fraction with the highest organic carbon content.     

Investigation of 85Sr adsorption in the presence of Na+, K+ and Cs+ on selected soils from different horizons</p> </p>

Summary Results of studies of Na⁺, K⁺ and Cs⁺ influence on the adsorption of ⁸⁵Sr on soil samples of the different types of successive horizons are presented. It was proved that the adsorption isotherms in log-log coordinates are of straight-line type and may be described by the Freundlich equation. Monovalent cations influence the coverage degree of the soil surface by ⁸⁵Sr (most often lowering it) in the following order K⁺3Na⁺3Cs⁺. The investigation of pH influence proved its essential meaning in the process. The plateau of surface coverage degree versus pH lies above pH 5.5 or 6.5 depending on the soil type. Generally, in the studied system, the size of ⁸⁵Sr adsorption depends on the concentration of the isotope, pH of the solution, type of monovalent cation, and on the soil properties.</p> </p>     

Approach to the Dynamic of Carbamazepine and its Main Metabolites in Soil Contamination through the Reuse of Wastewater and Sewage Sludge

The release of pharmaceutically active compounds to the soils through the application of sewage sludge and the irrigation with wastewater, or even with surface water, is constant. The adsorption of these compounds onto the soil is one of the key factors affecting their fate in the environment and their potential environmental risks. In this work, the adsorption of carbamazepine (CBZ) and its metabolites, 3-hydroxy-carbamazepine (3OH-CBZ), carbamazepine-10,11-dihydro-10,11-epoxide (EP-CBZ), and 10,11-dihydro-10-hydroxycarbamazepine (10OH-CBZ), in three Mediterranean soils was evaluated using single-solute and four-solute experiments. The highest adsorptions were measured for 3OH-CBZ, followed by CBZ, EP-CBZ, and 10OH-CBZ, in that order. A high influence of the physicochemical characteristics of the compounds, pH, and soil characteristics in the adsorption of the studied compounds was observed and corroborated by the statistical analysis of the results. Moreover, a good fit was observed in the three isotherm models evaluated (linear, Freundlich, and Langmuir) in single-solute experiments (R² > 0.90). However, a decrease of the measured adsorptions and a worse fit to the isotherm models were observed in the case of multiple-solute experiments. This could be mainly due to the competition established between the studied compounds for the active sites of the soils.     

pH-dependence of pesticide adsorption by wheat-residue-derived black carbon

The potential of black carbon as an adsorbent for pesticides in soils may be strongly influenced by the properties of the adsorbent and pesticides and by the environmental conditions. This study evaluated the effect of pH on the adsorption of diuron, bromoxynil, and ametryne by a wheat (Triticum aestivum L.) residue derived black carbon (WC) as compared to a commercial activated carbon (AC). The pH drift method indicated that WC had a point of zero charge of 4.2, much lower than that of 7.8 for AC. The density of oxygen-containing surface functional groups, measured by the Boehm titration, on WC was 5.4 times higher than that on AC, resulting in a pesticide adsorption by WC being 30-50% of that by AC, due to the blockage of WC surface by the waters associated with the functional groups. A small decrease (5.5%/unit pH) in diuron adsorption by WC with increase in pH resulted from increased deprotonation of surface functional groups at higher pH values. A much larger decrease (14-21%/unit pH) in bromoxynil adsorption by WC with increase in pH resulted from the deprotonation of both the adsorbate and surface functional groups of the adsorbent. The deprotonation reduced the adsorptive interaction between bromoxynil and the neutral carbon surface and increased the electrical repulsion between the negatively charged WC surface and bromoxynil anions. Deprotonation of ametryne with increase in pH over the low pH range increased its fraction of molecular form and thus adsorption on WC by 15%/unit pH. Further increase in pH resulted in a 20%/unit pH decrease in ametryne adsorption by WC due primarily to the development of a negative charge on the surface of WC. The pH-dependent adsorption of pesticides by black carbon may significantly influence their environmental fate in soils.     

Surface Adsorption and Photo-Reactivity of Sulfonylurea Herbicides

Photodegradation of two sulfonylurea herbicides, triasulfuron and thifensulfuron-methyl adsorbed on Preveza or Nea Malgara soils (Greece) was studied in outdoor and laboratory experiments. Herbicides on adsorbed phase and kept in the dark were characterised by a high reactivity, giving depletion curves that can be all described by a first order equation. In the irradiation experiments the kinetic behaviour of photodegradation was complex and characterised by a double step photoreaction. After a first period varying from 8 to 24 h the rate of reaction was reduced to 7-31% of the initial rate. The kinetic constant related to the degradation of triasulfuron practically showed the same values of those obtained for thifensulfuron-methyl. The half-lives obtained on Nea Malgara soil were generally higher than those obtained using Preveza soil. The observed behaviour is explained considering the photochemical properties of the herbicides, and the organic matter content of the soils.