Adsorption thermodynamics of carbofuran on antimony (V) silicate cation exchanger

The adsorption thermodynamics of carbofuran has been studied on antimony (V) silicate cation exchanger at 30 and 50 degrees C. The adsorption isotherms of carbofuran have been found to follow the Freundlich adsorption model and yield "S" class isotherms. The order of adsorption of carbofuran is in accordance with the partial molal free-energy changes in the exchanger. The thermodynamic equilibrium constant (K0), standard free energy (delta G degrees), enthalpy (delta H degrees), and entropy (delta S degrees) changes have also been calculated for predicting the nature of adsorption.     

Adsorption thermodynamics of carbofuran on acid and base saturated soils

The adsorption of carbofuran on hydrogen, sodium, and calcium saturated soils has been studied at 25 and 50 degrees C. The adsorption data for all types of soils is in close agreement with Freundlich isotherms and yielded S-class isotherms. The maximum adsorption was observed in acid saturated soil. Therefore, it has been in accordance with the partial molal free energy changes (F) and Kd values. The adsorption has been lower at higher temperatures. The thermodynamic constant (KO), standard free energies (delta G degree), enthalpies (delta H degree), and entropy changes (delta S degree) have been calculated for predicting the nature of adsorption.     

Movement of carbofuran (nematicide) in soil columns

Adsorption and movement of carbofuran (a systemic nematicide) were studied using two Indian soils (clay loam and silt loam) of alluvial origin. Equilibrium adsorption coefficient (K) values measured using a batch-slurry technique follows the order clay loam greater than silt loam soil. The distribution coefficients (Kd) for both the soils in batch adsorption as well as in columns were also calculated. Carbofuran movement in soil columns during water infiltration in both air-dried and water-saturated columns was estimated. The order was as anticipated from K and Kd values. A larger amount of water was needed for leaching the carbofuran to 152 cm in clay loam soil than in silt loam soil. Carbofuran appears to increase in drier soils and in finer textured soils.     

Degradation and persistence of cotton pesticides in sandy loam soils from Punjab, Pakistan

The present study evaluated the influence of temperature, moisture, and microbial activity on the degradation and persistence of commonly used cotton pesticides, i.e., carbosulfan, carbofuran, lambda-cyhalothrin, endosulfan, and monocrotophos, with the help of laboratory incubation and lysimeter studies on sandy loam soil (Typic Ustocurepts) in Pakistan. Drainage from the lysimeters was sampled on days 49, 52, 59, 73, 100, 113, and 119 against the pesticide application on days 37, 63, 82, 108, and 137 after the sowing of cotton. Carbofuran, monocrotophos, and nitrate were detected in the drainage samples, with an average value, respectively, of 2.34, 2.6 microg/L, and 15.6 mg/L for no-tillage and 2.16, 2.3 microg/L, and 13.4 mg/L for tillage. In the laboratory, pesticide disappearance kinetics were measured with sterile and nonsterile soils from 0 to 10 cm in depth at 15, 25, and 35 degrees C and 50% and 90% field water capacities. Monocrotophos and carbosulfan dissipation followed first-order kinetics while others followed second-order kinetics. The results of incubation studies showed that temperature and moisture contents significantly reduced the t(1/2) (half-life) values of pesticides in sterile and nonsterile soil, but the effect of microbial activity was nearly significant that might be due to less organic carbon (0.3%). The presence of carbofuran and monocrotophos in the soil profile (0-10, 10-30, 30-60, 60-90, 90-150 cm) and the higher concentrations of endosulfan and lambda-cyhalothrin in the top layer (0-10 cm) showed the persistence of the pesticides. The detection of endosulfan and lambda-cyhalothrin in the 10-30 cm soil layer might be due to preferential flow. The data generated from this study could be helpful for risk assessment studies of pesticides and for validating pesticide transport models for sandy loam soils in cotton-growing areas of Pakistan.     

Solubilities and surface activities of phthalates investigated by surface tension measurements

Aqueous solutions of DEP (di-ethyl), DnBP (di-n-butyl), DnH(6)P (di-n-hexyl), and DEHP (di-[2-ethyl-hexyl]) phthalates have been investigated by use of surface tension measurements at temperatures between 10 and 35 degrees C. A tensiometric approach allows for the determination of unimeric solubilities and delta G degree, which is the standard Gibbs free energy change, for the dissolution of phthalates in water. The unimeric solubility of the phthalates increase with decreasing temperature. The delta G degree shows a linear increase with increasing phthalate alkyl chain length. The contribution of enthalpy (delta H degree) and entropy (delta S degree) to delta G degree were calculated from the temperature-dependent solubilities. The contributions of both delta H degree and delta S degree are negative and increase in magnitude with increasing alkyl chain length, suggesting hydrophobic interactions between phthalates and water. The ability of different phthalates to lower the surface tension decreases with increasing alkyl chain length, whereas the relative affinity for adsorption in the air-water interface increases drastically for long-chain phthalates. Despite the low surface activity of phthalates compared with that of common surfactants, they show significant affinity for adsorption in air-water interfaces of natural surface waters. This property, combined with their low solubilities, may affect the fate of these compounds within the natural environment, because they form emulsions above unimeric saturation in aqueous media.     

Assessment of the Insecticide Carbofuran''s Potential to Contaminate Groundwater through Soils in the Subtropics

The possible contamination of groundwater by the insecticide carbofuran was assessed with the behavior assessment model (BAM) and groundwater pollution-potential model (GWP). Dissipation coefficients of this insecticide in two subtropical soils at different moisture contents and soil temperatures were studied by determining the degradation and adsorption of the herbicide in soils. Movement of carbofuran was studied by leaching the insecticide in a soil column in the laboratory. Under 40% field capacity and at 25°C, more than 80% of carbofuran residue was found in both Luchu clay and Yuanlin silty clay loam after incubation for 63 days. The results indicate that the higher the moisture content in the soil, the less the carbofuran residue under the soil moisture below the field capacity. Carbofuran tends to dissipate more easily in Yuanlin soil than in Luchu soil. The distribution coefficient (K_d) withr²of 0.69 and 0.92 for Luchu and Yuanlin soils, respectively, was found using the first-order kinetics law. In leaching experiment, carbofuran exhibited easier movement in Luchu than in Yuanlin soil.     

Persistence and retention of active ingredients in four granular cholinesterase-inhibiting insecticides in agricultural soils of the lower Fraser River valley, British Columbia, Canada, with implications for wildlife poisoning

The persistence and retention of active ingredients in granules of Thimet 15G (phorate 15% by weight), Dyfonate 10G (fonofos 10% by weight), Counter 15G (terbufos 15% by weight), and Furadan 10G (carbofuran 10% by weight) were determined in silt loam and organic muck agricultural soils typical of the lower Fraser River valley (BC, Canada). In June 1995, treatment bags made of polyester cloth (7.5 x 7.5 cm) containing granules of a single insecticide, either alone or with soil, were placed during spring planting in the bottom of the furrow and retrieved periodically until April 1996. The parent component of each insecticide declined monotonically except for carbofuran (logistic decline). In the silt loam (organic muck) soil, the average June-to-October first-order rate constants and half-lives were 0.009 (0.010)/d and 80 (71) d for fonofos, 0.012 (0.009)/d and 58 (82) d for phorate, and 0.032 (0.015)/d and 21 (47) d for terbufos; the half-life of carbofuran was 129 (97) d. By December, the average amounts of fonofos and phorate in silt loam (organic muck) were 26% (range: 17-40%; 14% [range: 3.4-21%]) and 21% (range: 15-30%; 10% [range: 5.0-24%]) of the initial amounts of active ingredients measured at time zero, respectively. By April, the percentages dropped to 16% (range: 7.8-24%; 2.3% [range: 0-7.7%]) and 7.3% (range: 1.9-25%; 0.6% [range: 0-1.9%]). During this period, about 95% of the active ingredients were granule bound, the rest remaining in the bag. Only low levels of terbufos and carbofuran persisted in both soils from December to April of the following year. Results indicate an enhanced probability for poisoning of waterfowl and raptors because of the high levels of active ingredients retained on granules of all four insecticides in both soils in the fall. The risk of acute poisoning by phorate and fonofos continued though the winter.     

Protein interaction: concepts from thermodynamic measurements

Proteins are biological molecules par excellence. They have evolved as elements of structure, catalysis and control. The conflict between the requirement of structural stability and the requirement of functional specificity and efficiency, under varying environmental conditions in which they are often called upon to function, has been evolutionarily solved by a process of thermodynamic compensation. In the simplest form of thermodynamic compensation the Gibb's free energy change (delta G) of a process occurring under different environmental conditions is kept constant (linear compensation) or allowed to vary slightly (non linear compensation) by compensating a large change in enthalpy (delta H) by an equally (or nearly 80) large change in entropy, delta S. In processes like protein adsorption to surfaces the number of various types of interactions involved is so large that compensatory or augmenting changes in the same type of thermodynamic parameter may occur and complicate the picture. Published data do, however, suggested the occurrence of thermodynamic compensation in protein adsorption. It is pointed out that the simultaneous measurement of two thermodynamic parameters, namely, enthalpy change (delta H), and heat capacity change (delta Cp), under appropriate conditions could often lead to an understanding of the dominant types of forces involved in adsorption.     

Sorption Behaviour of Forchlorfenuron in Soil

Adsorption of forchlorfenuron on three Indian soils reached equilibrium within 48 h with rate of adsorption being highest on sandy-loam followed by clay and silty-clay soils. The relative adsorptivity of the test soils could be attributed to the different organic matter and clay contents. Desorption rate followed the reverse trend. The rate constants for adsorption and desorption at 298 and 308 K were determined from Lindstrom model, which simultaneously evaluated adsorption and desorption kinetics. The data for rate constants, activation energies, enthalpy of activation, entropy of activation and free energy indicated chemical adsorption of forchlorfenuron on soil. A good fit to the linear and Freundlich isotherms was observed with correlation coefficients >0.97. The groundwater ubiquity score for different soils varied between 1.6 and 2.2, on the basis of which forchlorfenuron could be categorised as a chemical with low to medium leaching category.     

Carbofuran transfer and persistence in drained agricultural soils related to their structure and adsorption properties

Carbofuran (Curater 5G) behavior was studied in two drained cornfield soils, clay and loamy-clay, for 2 successive years. Different dissipations were observed in each soil for the same time period (8 weeks in 1985, 9 weeks in 1986). The authors found drained water from organic mater-rich soil to possess a higher carbofuran content, with 7.1-13.7 and 2.5-5.0% of the applied dose for clay and loamy-clay soils, respectively. The major part of these percentages arose from the drained waters associated with rainfall occurring during the first 2-3 weeks after application. Laboratory experiments confirmed the influence of the soil structure and its properties on carbofuran adsorption, and consequently on carbofuran leaching under field conditions.     

Ammonium removal from aqueous solutions by clinoptilolite: determination of isotherm and thermodynamic parameters and comparison of kinetics by the double exponential model and conventional kinetic models

The adsorption isotherm, the adsorption kinetics, and the thermodynamic parameters of ammonium removal from aqueous solution by using clinoptilolite in aqueous solution was investigated in this study. Experimental data obtained from batch equilibrium tests have been analyzed by four two-parameter (Freundlich, Langmuir, Tempkin and Dubinin-Radushkevich (D-R)) and four three-parameter (Redlich-Peterson (R-P), Sips, Toth and Khan) isotherm models. D-R and R-P isotherms were the models that best fitted to experimental data over the other two- and three-parameter models applied. The adsorption energy (E) from the D-R isotherm was found to be approximately 7 kJ/mol for the ammonium-clinoptilolite system, thereby indicating that ammonium is adsorbed on clinoptilolite by physisorption. Kinetic parameters were determined by analyzing the nth-order kinetic model, the modified second-order model and the double exponential model, and each model resulted in a coefficient of determination (R(2)) of above 0.989 with an average relative error lower than 5%. A Double Exponential Model (DEM) showed that the adsorption process develops in two stages as rapid and slow phase. Changes in standard free energy (?G°), enthalpy (?H°) and entropy (?S°) of ammonium-clinoptilolite system were estimated by using the thermodynamic equilibrium coefficients.     

Sorption of selected organic pollutants in Danish soils

The sorption of benzoic acid, nitrobenzene, 4-nitrophenol, 2,4-dichlorophenoxyacetic acid (2,4-D), and naphthalene was determined for 10 Danish soils in laboratory studies. Measured equilibrium isotherms were of nonlinear Freundlich type for nearly all combinations of soil-test compounds. Adsorption was significantly correlated with the organic carbon content of the soils tested. No significant correlations with pH and cation-exchange capacity were observed. The adsorption of benzoic acid was found to be reversible and the sorption of naphthalene was reversible in 4 of 10 soils. A desorption-resistant fraction of adsorbed 2,4-D was estimated from interdependent adsorption and desorption isotherms.     

Sorption of linear alkylbenzene sulfonate to soil components and effects on microbial iron reduction

When sewage sludge is applied to arable land, linear alkylbenzene sulfonate (LAS) is released into the environment. In soils, LAS has been shown to impede microbial processes, such as bacterial iron reduction. The aim of the present study was to quantify LAS adsorption and desorption to agricultural soils and iron oxides and relate this to the inhibition of microbial iron reduction. Two agricultural soils were used, namely, Askov (coarse sandy loam soil) and Lundgaard (coarse sandy soil). In both soils, LAS inhibited microbial iron reduction even at low LAS concentrations with 10% effect concentrations of 6 to 7 and 26 to 32 mg LAS/kg dry-weight soil for Lundgaard and Askov soil, respectively. The sorption isotherms showed that sorption of LAS to iron oxides was 10 to 100 times stronger than sorption to the agricultural soils. Also, it appeared that at low LAS concentrations (< 10 mg/kg dry-wt soil), Lundgaard soil adsorbed approximately 10 times more LAS than Askov soil. Thus, the inhibitory effect of LAS on microbial iron reduction was highest in the Lundgaard soil, which exhibited both the strongest sorption and the lowest desorption of the two soils. A possible hypothesis to explain this correlation was that LAS toxicity toward bacterial iron reduction was, at least partly, caused by LAS adsorbed to iron oxides, which could interfere with transfer of electrons between the bacteria and their respiratory electron acceptor.     

Effect of fungicide iprodione on soil bacterial community

The effect of the fungicide iprodione on soil bacterial communities was studied by treating two kinds of soils with different concentrations of iprodione. Degradation rates of iprodione in sterile and unsterile soils were also investigated. Residues of iprodione were measured by using high-performance liquid chromatography (HPLC) and a change of bacterial communities was performed with denaturing gradient gel electrophoresis (DGGE) by counting the 16S rDNA band on DGGE patterns. The degradation rate of iprodione was slower in sterile soil than in unsterile soil in both Da-Hu sandy loam and Kuan-Shi loam. After treatment with fungicide, soil bacterial communities were changed and recovered rapidly to the original status when incubated at a lower temperature (15 degrees C) and a lower iprodione concentration (5 microg/g). At the same temperature but with more iprodione (50 microg/g) added, the soil bacterial community increases slowly and regains the original status slowly. However, when incubated at the higher temperature (30 degrees C), the soil bacterial community is more complex than that at the lower temperature. The response of the soil bacterial community to the iprodione is faster at the higher than at the lower temperature. At 30 degrees C and with 50 microg/g iprodione, the amounts of soil bacterial communities increased quickly but cannot be reduced to the original status after incubation for 23 days.     

The Dissipation of Carbofuran in Two Soils with Different Pesticide Application Histories within Nzoia River Drainage Basin,Kenya

The dissipation of carbofuran from soils within the Nzoia River Drainage Basin in Kenya was studied under real field conditions for 112 days. Results showed significantly enhanced dissipation of carbofuran with half life (DT₅₀) values of 8 days (p = 0.038) in soils with prior exposure to carbofuran compared to 19 days in soils with no application history. At the end of the experiment, residues of 2.57 % and 9.36 % of the initial carbofuran applied were recorded in the two types of soil, respectively. Carbofuran metabolites identified in the study were 3-keto carbofuran and carbofuran phenol with 5.84 % and 15.0 % remaining in soils with prior exposure, respectively. Soils with no application history recorded 16.05 % and 12.82 % of 3-keto carbofuran and carbofuran phenol metabolites, respectively.     

The adsorption of cyanobacterial hepatoxins as a function of soil properties

Cyanobacterial hepatotoxins present a risk to public health when present in drinking water supplies. Existing removal strategies, although efficient, are not economically viable or practical for remote Australian communities and developing nations. Bank filtration is a natural process and a potential low cost, toxin removal strategy. Batch studies were conducted in 12 texturally diverse soils to examine the soil properties influencing the adsorption of the cyanobacterial hepatotoxins, microcystin-LR and nodularin. Sorption isotherms were measured. Freundlich and linear isotherms were observed for both toxins with adsorption coefficients not exceeding 2.751 kg(-1) for nodularin and 3.81 kg(-1) for microcystin. Significant positive correlations were identified between hepatotoxin sorption and clay and silt contents of the soils. Desorption of toxins was also measured in three different soils. Pure nodularin and microcystin-LR readily desorbed from all soils.     

Enhancing the attenuation of explosives in surface soils at military facilities: sorption-desorption isotherms

The primary objective of the present study was to develop inexpensive soil amendments that can be applied to enhance the adsorption of energetic compounds on military training ranges, thus limiting the potential for these compounds to migrate to groundwater. Adsorption and desorption isotherms were determined for 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine with a wide variety of natural and man-made adsorbents, including wheat straw, sawdust, peat moss, ground rubber tires, and clays. Among the various adsorbents tested, peat moss proved to be the most effective sorbent for the three explosives. The adsorption coefficients (Kd(s)) for TNT and RDX with peat (310 and 87 L/kg, respectively) were at least two orders of magnitude higher than that determined for adsorption of these energetics with two surface soils. The adsorption-desorption isotherms for the explosives showed considerable hysteresis (Kd(s) < Kd(d)) with some of the solid adsorbents, suggesting that the sorption process is not readily reversible but, rather, that some fraction of the adsorbed contaminant is either irreversibly bound or present as a slowly desorbed fraction. The data indicate that the application of specific adsorbents to soils at military impact ranges may significantly improve the protection of local groundwater resources.     

Potential of the insecticides acephate and methamidophos to contaminate groundwater

The possible contamination of groundwater by the insecticides acephate and methamidophos was assessed using the behavior assessment model (BAM) and the groundwater pollution-potential model (GWP). The dissipation coefficients of the two insecticides in two soils (Annei silt loam and Pingchen silt clay loam) at different moisture contents (50 and 100% field capacity) and soil temperatures (20 and 30 degrees C) were studied by determining the degradation and adsorption of each insecticide in the soil. The movement of acephate and methamidophos was studied by leaching each insecticide in a soil column in the laboratory. The absorption coefficient of methamidophos was much higher than that of acephate in both types of soil. In the leaching test, methamidophos more easily leached out from the Pingchen soil column than from the Annei soil column. Methamidophos was rapidly degraded, with a half-life of 1.11 to 1.61 days in the Annei soil and 7.50 to 13.20 days in the Pingchen soil at different temperatures and soil water contents. Acephate was found to have a longer half-life than methamidophos in soil; however, the mobility of methamidophos in both soils was slower than that of acephate. The mobility of acephate in soil is somewhat faster than that of methamidophos, and thus acephate may lead to the contamination of groundwater much more easily than methamidophos under normal conditions.     

Adsorption of arsenic on flyash

Studies on removal of AS(III) by adsorption on flyash and activated carbon powder have been carried out at room temperature (30 +/- 1 degrees C). The adsorption isotherm of AS(III) on flyash and activated carbon powder was obtained in a batch reactor. Various parameters such as pH, initial concentraction of adsorbate and absorbent dose were studied. The experimental adsorption data fitted reasonably well to the Langmuir and Freunlich isotherms for both the adsorbents. Activated carbon has been observed to have greater adsorptive capacity than flyash.     

Adsorption of Cd on Soils with Various Particle Sizes from an Abandoned Non-ferrous Smelting Site: Characteristics and Mechanism

Soil particle size could intensively impact the Cd adsorption in soils. The adsorption characteristics of Cd on miscellaneous fill (MF) and weathered slate (WS), collected from a zinc smelting site, were studied by batch experiments under conditions of different initial Cd concentrations and soil particle sizes. The results showed that the adsorption kinetics of Cd for soil particles from MF and WS were well fitted with the pseudo-first-order model, and the Cd adsorption isotherms well conformed to the Freundlich model. Soil particle size had an inconspicuous influence on adsorption rate, while the adsorption capacity decreased with particle size increase. The Cd adsorption on soil particles could be due to the exchange with Fe/Al, and -OH/C=O sites were the predominant adsorption sites. The MF may cause secondary pollution risk due to its low adsorption ability for Cd in smelting sites.