Kinetics and isotherm analysis of 2,4-dichlorophenoxyl acetic acid adsorption onto soil components under oxic and anoxic conditions

Influence of Organic Matter in Sorption of the Saflufenacil in Ferralsols

The saflufenacil herbicide has been applied in the agricultural areas as an efficient alternative for the control of resistant weeds to glyphosate. However, the environmental risks from the use of saflufenacil, especially in tropical soil, is not yet clearly known. We evaluated if the organic matter addition into the soil influences the sorption of saflufenacil in samples of a sandy and clayey texture soils. The sugarbeet was used as a species indicating the presence of saflufenacil in the solution of the substrates. We estimated the required dose of saflufenacil responsible for causing 50% of sugarbeet intoxication (C₅₀) and the sorption ratio (SR) of this herbicide. The addition of organic matter increased the C₅₀ and SR of saflufenacil in both soils. Here it is demonstrated that the soil organic matter content increases saflufenacil sorption in tropical soils and, consequently influences the dose of this herbicide to be applied in pre-emergence of weeds.

Study of Sorption Kinetics and Sorption-Desorption Models to Assess the Transport Mechanisms of 2,4-Dichlorophenoxyacetic Acid on Volcanic Soils

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 IPD model where 2,4-D sorption kinetics was controlled by external mass transfer and intra organic matter diffusion in Andisols (C1 ≠ 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 IEP, FeDCB, and pH×Silt are important soil descriptors in the 2,4-D sorption in VADS. The Freundlich model accurately represented sorption equilibrium data in all cases (Kf 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 OC content (H close to 0).

Movement and Fate of 2,4-D in Urban Soils: A Potential Environmental Health Concern

The fate and movement of 2,4-dichlorophenoxyacetic acid (2,4-D), in terms of sorption-desorption and leaching potential, were evaluated in urban soils following the batch experimental method. The sorption kinetics of 2,4-D in soils followed both "fast" and "slow" sorption processes that could be well described by a pseudo-second-order kinetics model, suggesting that 2,4-D was partitioned into soil organic matter and clay surfaces, and eventually diffused into soil micropores. The sorption isotherms were linear, following both Langmuir and Freundlich models. Partially decomposed or undecomposed organic matter present in urban soils decreased sorption and increased desorption of 2,4-D. Also, sorption of 2,4-D increased with an increase in the contents of clay and Al and Fe oxides, whereas sand and alkaline pH increased the desorption process. The lower calculated K _d values suggest that 2,4-D is highly mobile in urban soils than in agricultural soils. The calculated values of groundwater ubiquity score, leachability index, and hysteresis index indicated that the herbicide is highly prone to leach out from surface soil to groundwater which might affect the quality of potable water. The present study clearly suggests that 2,4-D must be judiciously applied in the urban areas in order to minimize the potential health and environmental risks.