Sorption, Desorption and Mobility of Microencapsulated Chlorpyrifos in Two Typical Soils

The sorption, desorption, and mobility of microencapsulated chlorpyrifos (CPF-MC) in two typical soils, namely, silt loam and sandy, were investigated in this study. Sorption/desorption experiments were carried out by using the batch equilibration method. Results showed that the sorption isotherms of CPF-MC and emulsifiable concentrate of chlorpyrifos (CPF-EC) in silt loamy soil were similar. However, a considerable difference was observed in the sorption isotherms of two chlorpyrifos (CPF) formulations in sandy soil. The amounts of CPF desorbed from two soils in four desorption steps decreased sequentially in CPF-EC treatments, while the desorbed amounts remained stable in CPF-MC treatments. Hence, the sorption/desorption processes of CPF-EC were mainly controlled by soil affinity to CPF. However, these processes of CPF-MC were affected by the release rate of CPF from capsules. The mobility of two CPF formulations in soil were estimated in vertical columns packed with soils. Results showed that there was leaching of CPF-EC in silt loam column, whereas CPF-MC was not vertically mobile in silt loam column under the same leaching conditions. However, in column with sandy soil, the percentage of CPF-MC leaching from the column was 86.54%, which was higher than the 73.75% that leached from the column in the treatment with CPF-EC.

Sensing by Molecularly Imprinted Polymer: Evaluation of the Binding Properties with Different Techniques

The possibility of investigating the binding properties of the same molecularly imprinted polymer (MIP), most probably heterogeneous, at various concentration levels by different methods such as batch equilibration and sensing, is examined, considering two kinds of sensors, based respectively on electrochemical and surface plasmon resonance (SPR) transduction. As a proof of principle, the considered MIP was obtained by non-covalent molecular imprinting of 2-furaldehyde (2-FAL). It has been found that different concentration ranges of 2-FAL in aqueous matrices can be measured by the two sensing methods. The SPR sensor responds in a concentration range from 1 × 10−4 M down to about 1 × 10−7 M, while the electrochemical sensor from about 5 × 10−6 M up to about 9 × 10−3 M. The binding isotherms have been fit to the Langmuir adsorption model, in order to evaluate the association constant. Three kinds of sites with different affinity for 2-FAL have been detected. The sites at low affinity are similar to the interaction sites of the corresponding NIP since they have a similar association constant. This is near to the affinity evaluated by batch equilibration too. The same association constant has been evaluated in the same concentration range. The sensing methods have been demonstrated to be very convenient for the characterization of the binding properties of MIP in comparison to the batch equilibration, in terms of reproducibility and low amount of material required for the investigation.

Radiochemical Studies on the Separation of Cesium, Cobalt, and Europium from Aqueous Solutions Using Zirconium Selenomolybdate Sorbent

A procedure for removal and separation of Cs, Eu and activation product of Co using zirconium selenomolybdate was developed. Interactions of134Cs(I),152,154Eu(III), and60Co(II) ions from HNO3acid solutions with zirconium selenomolybdate matrix, dried at 50°C, have been individually investigated by the batch equilibration method. The sorption behavior of the three ions showed a selectivity sequence in the following order: Cs(I) > Eu(III) > Co(II). The breakthrough capacities of zirconium selenomolybdate for Cs(I), Eu(III) and Co(II) were found to be 0.82, 0.45, and 0.18 mmol/g of the sorbent, respectively. A mixture of the three radionuclides (1×10−2 M each) in 140 mL of1×10−2 M HNO3solution was passed through 1 g zirconium selenomolybdate chromatographic column. Thereafter, quantitative elution of the retained Co(II) was achieved with 14 mL of1×10−1 M HNO3acid solution leaving Eu(III) and Cs(I) strongly retained onto the column. Quantitative elution of Eu(III) was achieved by passing 22 mL2.5×10−1 M HNO3. About 89% of the retained Cs(I) was eluted with 32 mL of 2 M NH4Cl solution at a flow rate of 0.5 mL/min.

Adsorption of Chlorimuron-Ethyl on Two Typical Chinese Soils as Affected by Cd

Coexistence of chlorimuron-ethyl and Cd is very common in Chinese soils. Adsorption of chlorimuron-ethyl and Cd on soils strongly affects their mobility. This study was conducted to investigate the effect of Cd on the adsorption of chlorimuron-ethyl on two typical Chinese soils, brown earth (BE) and black soil (BS). Batch equilibration methods were applied. The presence of Cd enhanced the adsorption of chlorimuron-ethyl on BE and BS, which resulted from the decrease of equilibrium solution pH caused by Cd2+ exchange with H+ ions of soil surface. Besides that, chlorimuron-ethyl adsorption possibly takes place on sites where Cd was previously adsorbed and the adsorbed Cd acted as a bridge between the soil and chlorimuron-ethyl. Such results suggested that Cd in field may decrease the mobility and bioavailability of chlorimuron-ethyl and correspondingly decrease its environmental risk.

Hysteretic Characteristics of Atrazine Adsorption-Desorption by a Sharkey Soil

The purpose of this study was to quantify hysteresis during adsorption and desorption of atrazine as a function of incubation time for a Sharkey clay soil. Adsorption was carried out using one day batch equilibration and was followed by incubation periods ranging from 1 to 24 d. Incubation was subsequently followed by six consecutive desorption steps where each step represented 1 d. The Freundlich equation (S = K CNwhere S is the amount of atrazine retained, μg g-1; C is concentration, μg ml-1; K is the distribution coefficient, cm3g-1; and N is a dimensionless parameter) was used to describe batch results. Both adsorption and desorption isotherms were well described by the Freundlich model. Fitted K parameter values for desorption isotherms were consistently higher than those associated with adsorption. The opposite trend was observed for the exponential parameter N. The results revealed that desorption deviated significantly from adsorption data. The deviation, which is commonly referred to as hysteresis, was more pronounced as incubation time increased. Batch equilibration results also indicated that the extent of hysteresis was not influenced by soil sterilization. Attempts to quantify the extent of hysteresis using a simplified approach are presented. We found that, for a given batch data set, hysteresis can be quantified provided that Freundlich N from adsorption and desorption isotherms is known.

Adsorption and Desorption of Atrazine, Hydroxyatrazine, andS-Glutathione Atrazine on Two Soils

Adsorption and desorption isotherms for atrazine and two metabolites, hydroxyatrazine (HA) andS-glutathione atrazine (GSHA), were determined by batch equilibration on Plano and Waukegan silt loam soils at two soil pH levels (Plano, 6.1 and 4.5; Waukegan, 6.1 and 4.0). Freundlich adsorption isotherms were not affected by soil type except for GSHA at pH 4.0 to 4.5. When averaged over both soils, the order of adsorption at pH 6.1 was atrazine (Kf= 3.7) < GSHA (Kf= 7.3) << HA (Kf= 25) and at pH 4.0–4.5 was atrazine (Kf= 6.1) << HA (Kf= 58) ≤ GSHA (Kf: Plano = 35; Waukegan = 78). The average slope of the adsorption isotherms (1/nads) was 0.81. The slopes of all desorption isotherms (1/ndes) were less than their respective 1/nads, indicating hysteresis. Atrazine desorbed into soil solution (1/ndes> 0.0). With the exception of GSHA which desorbed from the pH 6.1 Plano silt loam (1/ndes= 0.15), desorption of HA and GSHA from other treatments was negligible (1/ndes= 0.0). Consequently, leaching of HA and GSHA in these and similar soils is not likely, due to high adsorption and low desorption.