Journal article

Publication year: 2022

Pages: 311-319

Journal: Gondwana Research

Volume number: 105

ISSN: 1342-937X

eISSN: 1878-0571

DOI Link: https://doi.org/10.1016/j.gr.2021.09.013

Publisher: Elsevier

Abstract: 

Soils are highly heterogeneous dynamic mixtures with unique properties. The general properties of each type of soil affect its contaminants sorption; thus, obtaining sorption information about any regional soil may require actual sorption experiments. Hence, two soil types (alfisol-AFL and oxisol-OXL) were sampled and used for ivermectin sorption in order to obtain data on sub-Saharan soils for this new emerging contaminant from agriculture. Environmental parameters such as sorption time, ambient solution pH, ivermectin concentration, temperature and desorption were studied, while data were evaluated using two adsorption isotherm models, four kinetic models and the thermodynamics. The soils were neutral, typical of neutral West African soils and having slightly acidic pHpzc with similar particle size description and medium-to-low CECeff and SOM. Ivermectin sorption equilibrium was fast at 180 min for both soils. The rate constant k for sorption on AFL soil was slightly faster than for the OXL. Solution pH has some degree of influence on the sorption process which exhibited two sorption optimum peaks; one around pH 3 and the other around pH 9.5. Ivermectin sorption was concentration dependent; there was higher sorption as initial concentration increased, while sorption increased significantly with ambient temperature from 19.5 to 29.5 degrees C (approximate to 55%) but there was slight reduction on further temperature increase to 39.5 degrees C compared to sorption at 29.5 degrees C (<= 1%). The magnitude of the estimated energetics signaled a non-spontaneous and increasingly random process, with small size of the Delta H degrees values which were compatible with low energy interactive sorption forces and the overall process was exothermic. The ivermectin sorption process was controlled by external mass transfer (which was concentration dependent), with approximately 81.6% of sorption occurring on the soil surfaces, while 18.4% was within the pores or soil phases. The better fits of the sorption data to both the Freundlich adsorption isotherm model and the homogeneous fractal pseudo-second order model are complementary, and confirms that ivermectin sorption process on both soils involves complex interactions on heterogeneous sorption surfaces which include electrostatic interactions, multi-layer adsorption probably facilitated by it-it interactions between surface sorbed ivermectin molecules and those in solution, possibly trapping of ivermectin molecules within the soil pores, and various van der Waals attractive forces. Though ivermectin was rapidly dissipated on these soils, the hysteresis was high; irrespective of the soil, the amount of ivermectin leached per soil was small, in fact less than 6% of the initial amount sorbed. Our study has vital implications in predicting the fate of specific contaminants in the environment. (C) 2021 International Association for Gondwana Research.

Harvard Citation style: Olu-Owolabi, B., Diagboya, P., Mtunzi, F., Adebowale, K. and Düring, R. (2022) Empirical aspects of an emerging agricultural pesticide contaminant retention on two sub-Saharan soils, Gondwana Research, 105, pp. 311-319. https://doi.org/10.1016/j.gr.2021.09.013

APA Citation style: Olu-Owolabi, B., Diagboya, P., Mtunzi, F., Adebowale, K., & Düring, R. (2022). Empirical aspects of an emerging agricultural pesticide contaminant retention on two sub-Saharan soils. Gondwana Research. 105, 311-319. https://doi.org/10.1016/j.gr.2021.09.013