Information on pesticide degradation and factors influencing are important in predicting the levels of pesticide remaining in soils and allow assessment of potential risk associated with exposure. The present study reports the sorption and degradation of azoxystrobin [methyl (E)-2-{2-(6-(2-cyanophenoxy)pyrimidin-4-yloxy)phenyl}-3-methoxyacrylate] in a sandy loam soil. The fungicide was moderately sorbed, and the Freundlich adsorption parameter K(f) (1/n) values in natural and 5% compost-amended soils were 9.31 and 13.72, respectively. Sorption showed hysteresis with 32.5 and 14.7% of sorbed fungicide desorbed from the natural and 5% compost-amended soils, respectively. Azoxystrobin was more persistent in the aerobic soil than the anaerobic soil with half-life values of 107.47 and 62.69 days, respectively. Amendment of compost (5%) to the soil enhanced the degradation of fungicide, and the respective half-life values in aerobic and anaerobic soils were 73.39 and 38.58 days, respectively. Azoxystrobin acid was recovered as the only metabolite of azoxystrobin degradation in soils. Both sunlight and UV light affected the persistence of azoxystrobin with fungicide degraded at a faster rate in UV light than in sunlight. Soil acts as a screen and slows the fungicide degradation under sunlight and UV light.

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In the quest for identifying low‐cost, locally available and effective adsorbents, pigeon pea (Cajanus cajan L.) residue ash (PRA) and sunflower (Helianthus annuus L.) residue ash (SRA) were evaluated as adsorbents for sequestering a basic dye, methylene blue (MB), from aqueous solution. Effects of contact time, initial solution pH and adsorbent dose on MB adsorption were investigated. MB adsorption onto PRA and SRA was dependent on initial solution pH, with adsorption being greater at higher pH. Percent MB removal increased with increase in adsorbent's dose. Adsorption followed pseudo‐second order kinetics. Intraparticle diffusion was not the sole rate‐controlling step. Both film diffusion and intraparticle diffusion controlled the adsorption process. The equilibrium data fitted well to Langmuir isotherm as compared to Freundlich isotherm, on the basis of coefficient of determination and error analysis. The maximum MB adsorption capacities of PRA and SRA were found as 58.8 and 62.5 mg g−1, respectively. The free energy change and dimensionless equilibrium parameter revealed spontaneous and favorable nature of MB adsorption onto crop residue ashes. Results demonstrate that the PRA and SRA have high adsorptive potential as compared to many previously reported ash based adsorbents, and hence can be used for treating water contaminated with cationic dyes.

This study investigated the technical feasibility of using the tobacco stems biomass (TSB), as a low‐cost novel adsorbent for removal of methylene blue (MB) from water. TSB was characterized by pH zero‐point‐charge (pHZPC) and FTIR analysis. Batch adsorption studies were performed to evaluate process variables, kinetics and equilibrium of MB adsorption. Results showed that MB removal was higher at pH values >pHZPC of adsorbent, and for particle size <0.5 mm. The adsorption kinetics followed pseudo‐second order (k2 = 0.008 to 0.001 g mg−1 min−1), with intraparticle diffusion as one of the rate limiting steps. The Langmuir isotherm with maximum capacity of 169.5 mg g−1 was statistically found a best fit model. A single stage batch adsorber was designed and quantity of TSB required for treating 1000‐10,000 L of stained water was determined. The results imply that the TSB with could be a promising alternative adsorbent for remediation of cationic dye bearing wastewater. © 2017 American Institute of Chemical Engineers Environ Prog, 36: 1005–1012, 2017