Abstract
The sorption behavior of 2,4-dichlorophenoxyacetic acid (2,4-D) in the abundant agricultural volcanic ash-derived soils (VADS) is not well understood despite being widely used throughout the world, causing effects to the environment and human health. The environmental behavior and risk assessment of groundwater pollution by pesticides can be evaluated through kinetic models. This study evaluated the sorption kinetics and 2,4-D sorption–desorption in ten VADS through batch sorption experiments. Differences in the sorption extent for the fast and slow phases was observed through the model where 2,4-D sorption kinetics was controlled by external mass transfer and intra organic matter diffusion in Andisols ( ≠ 0). We confirmed from the spectroscopic analysis that the carboxylate group directly drives the interaction of 2,4-D on Andisol soil. The MLR model showed that , , and are important soil descriptors in the 2,4-D sorption in VADS. The Freundlich model accurately represented sorption equilibrium data in all cases ( values between 1.1 and 24.1 µg1−1/n mL1/ng−1) with comparatively higher sorption capacity on Andisols, where the highest hysteresis was observed in soils that presented the highest and lowest content ( close to 0).
Highlights
The Blake method was used to determine the cation exchange capacity (CEC) [26]. pH was measured in soil suspensions with a soil to water ratio of 1:2.5 (w/v)
The soils studied presented acidic pH (4.1–5.7, Table 4). 2,4-D is a phenoxyacetic acid with ionic equilibrium constants related to the acidic carboxyl group
All soils presented a negative net charge (IEP value lower than its pHH2 O ) (Table 4)
Summary
Herbicide contamination of surface and groundwater is a major concern due to the widespread use of these chemicals in agricultural and urban areas and the decline in biodiversity [1]. 2,4-Dichlorophenoxyacetic acid (2,4-D) is a selective, post-emergence ionizable herbicide developed by the Dow company, corresponding to a formulation broadly used widely around the world to control annual and perennial herbs in pastures, fruits, cereals, hay, wheat, maize, barley cultivation, sorghum, sugar cane, and rice [2,3,4]. The relative persistence and mobility of the said herbicide are of global public concern over the potential of 2,4-D and its primary metabolites to contaminate groundwater [4] and the effects at the ecosystem level because rice production relies heavily on ample water.
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