Anjana Srivastava

Adsorption-desorption behaviour of zinc(II) at iron(III) hydroxide-aqueous solution interface as influenced by pH and temperature

Batch studies were carried out to investigate the adsorption of zinc(II) from fresh waters on an iron(III) hydroxide surface maintained at the pH of zero point of charge of hydroxide (ZPC, 6.85) and also on both the acidic (5.5) and alkaline (8.2) sides of pH of ZPC, at 15 and 35 degrees C. Zinc(II) adsorption on iron(III) hydroxide increased with an increase in pH. The rise in temperature from 15 to 35 degrees C increased zinc(II) adsorption at pH 5.5 and 6.85, but decreased it at alkaline pH (8.2). In none of the cases did adsorption attain a maximum adsorption density. The results indicate the presence of heterogeneous sites of varying affinity on the adsorbent. Zinc(II) adsorption followed Langmuir behaviour only at small adsorption densities (less than 10(-2.95) M Zn/kg at pH 5.5) and at higher adsorption densities, the availability of strongest binding sites decreased. Nonspecifically adsorbed zinc(II) (reversible to Ba(II)) decreased with the increase in pH and temperature. Sequential desorption experiments also revealed that desorption of adsorbed zinc(II) decreased with an increase in pH.

Sorption–desorption of fipronil in some soils as influenced by ionic strength, pH and temperature

BACKGROUND The sorption-desorpion of fipronil insecticide is influenced by soil properties and variables such as pH, ionic strength, temperature, etc. A better understanding of soil properties and these variables in sorption-desorption processes by quantification of fipronil using liquid chromatography may help to optimise suitable soil management to reduce contamination of surface and groundwaters. In the present investigation, the sorption-desorption of fipronil was studied in some soils at varying concentrations, ionic strengths, temperatures and pH values, and IR specta of fipronil sorbed onto soils were studied. RESULT The sorption of fipronil onto soils conformed to the Freundlich isotherm model. The sorption-desorption of fipronil varied with ionic strength in each of the soils. Sorption decreased but desorption increased with temperature. Sorption did not change with increasing pH, but for desorption there was no correlation. The cumulative desorption of fipronil from soil was significantly and inversely related to soil organic carbon content. IR spectra of sorbed fipronil showed the involvement of amino, nitrile, sulfone, chloro and fluoro groups and the pyrazole nucleus of the fipronil molecule. CONCLUSION The sorption of fipronil onto soils appeared to be a physical process with the involvement of hydrogen bonding. An increase in soil organic carbon may help to reduce desorption of fipronil. High-temperature regimes are more conducive to the desorption.

Degradation of AM Nitrification Inhibitor in Soil of Subtropical Region

ABSTRACT The aim of the study was to evaluate the degradation and persistence of 2-amino 4-chloro 6-methyl pyrimidine (AM), nitrification inhibitor at 1 and 2 µg g−1 application rates in soil. The extraction of AM was done by QuEChER’s (Quick, Easy. Cheap. Rugged and Safe) method and the quantitative analysis by high-performance liquid chromatography (HPLC). AM decreased with time at both the levels of application with the decline being faster in the beginning up to 7 d. Dissipation of AM occurred in a single phase with the persistence data fitting well to the first-order kinetics. Half-lives of AM were determined to be 14.33 and 16.7 d at 1 and 2 µg g–1 levels application rates. Since AM remains effective for an adequate period of time, it can be used for increasing efficiency of nitrogenous fertilizers in rice–wheat cropping systems as well as a safeguard for controlling environmental pollution in subtropical soils.

Effect of Sunlight and Ultraviolet Light on Dissipation of Fipronil Insecticide in Two Soils and Effect of pH on its Persistence in Aqueous Medium

In a laboratory investigation, the effect of natural sunlight and UV light exposure on dissipation of fipronil insecticide from two soils (clay loam and sandy clay loam) and the effect of pH on the persistence of fipronil in aqueous medium were studied. Dissipation of fipronil insecticide under sunlight followed biphasic first order kinetics in both soils. The half-life of the insecticide in sandy clay loam type soil was found to be 5.71 days for the first faster phase and 23.88 days for the second slower phase, whereas, in clay loam soil, the corresponding half-lives were 4.02 and 8.38 days, respectively. Under the UV light exposure, the dissipation of fipronil followed a single phase first order kinetics in both the soils with a half-life of 3.77 days in clay loam and 5.37 days in sandy clay loam, respectively. Residues of fipronil dissipated faster in clay loam than in sandy clay loam under both sunlight and UV lamp light. As compared to sunlight, dissipation was found to be faster under UV lamp light. Persistence of fipronil in aqueous medium under different pH conditions revealed that fipronil residues were below the limit of detection (LOD), <0.05 μg g−1, after 40 days of sampling at all the three pH. The dissipation of fipronil from aqueous medium increased with increasing pH from 5.0 to 9.0; the corresponding half-lives were 14.12, 9.83, and 6.76 days at pH 5.0, 7.0, and 9.0, respectively.

Effect of farmyard manure and conjoint application of farmyard manure and microbial consortium on lindane residues in soil, drainage water, and crops in lysimeters

The efficacies of farmyard manure (FYM) application alone and the conjoint use of FYM and microbial consortiums (Gordonia sp.) were evaluated for reducing lindane residues in soil, plants and percolated water in lysimeters cropped with maize and rice. At the normal application rate of lindane (0.6 kg ha−1), the concentration of lindane residues in drainage water was well above the United States EPA limit for drinking water (0.2 µg L−1); however, no detectable residues of lindane were observed in plant samples of both maize and rice crops. The residue level of lindane in the percolated water under rice was higher than under maize crop. Application of FYM at 5 t ha−1 decreased the pesticide residues both in percolated water and soil. The conjoint use of FYM at 5 t ha−1 and scheduled application of a microbial consortium of Gordonia sp. soon after the pest control was more effective than the application of FYM alone in reducing the level of lindane residues in soil and percolated water.

Kinetics and Adsorption-Desorption Behavior of AM Nitrification Inhibitor in Mollisols

ABSTRACT Kinetics and adsorption-desorption behavior of a potent nitrification inhibitor, 2-amino 4-chloro 6-methyl pyrimidine (AM), was examined in Mollisol samples of different depths. Adsorption of AM was better accounted by pseudo-second order kinetics. Adsorption and desorption data of AM onto soil samples of different depths conformed to single surface Freundlich isotherm model. The values of ln K varied from −0.1515 (0–15 cm) to 1.5171 (45–60 cm) and of 1/n from 0.9961 (45–60 cm) to 1.3237 (30–45 cm). Computed values of desorption capacity (ln K’) varied from 3.4734 (0–15 cm) to 4.0674 (45–60 cm) while that of 1/n´ from 0.0017 (45–60 cm) to 0.0367 (0–15 cm). Intensity of desorption (1/n´) had significant positive correlation with soil electrical conductance and clay content. The values of desorption index (n´/n) varied from 14.60 (0–15 cm) to 472.33 (30–45 cm) indicating high degree of irreversibility of adsorbed AM and hence poor leaching from these soils.