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Mechanisms of Adsorption of Phenoxyalkanoic Herbicides on Fulvic and Humic Acids

Authors: Tadeusz Paszko,Joanna Matysiak,Claudio A. Spadotto,Patrycja Boguta,Kamil Skic
Publisher: MDPI AG
Publish date: 2024-11-26
ISSN: 1422-0067 DOI: 10.3390/ijms252312699
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This study exhibits significant methodological and analytical shortcomings that undermine its scientific credibility. The adsorption experiments lack adequate confirmation of equilibrium conditions, and the assumptions of isotherm models, such as Langmuir or Freundlich, are not rigorously tested. Furthermore, the reported thermodynamic parameters, including ∆H⁰ values, appear inconsistent with the observed adsorption behaviors, suggesting possible calculation errors or overlooked system variations.

Critical deficiencies in the experimental design include the absence of detailed controls, such as ensuring uniform humic and fulvic acid preparation or verifying the stability of Al³⁺ species under varying pH conditions. The study’s reliance on single-replicate measurements for key FTIR and thermodynamic analyses raises concerns about reproducibility and the validity of statistical inferences.

The interpretation of pH-dependent adsorption mechanisms, particularly for anionic herbicides, is flawed by a lack of supporting kinetic data. The proposed roles of hydrophobic interactions, H-bonding, and π–π stacking are speculative, as no molecular evidence (e.g., docking simulations) corroborates these claims. Moreover, discrepancies between adsorption trends reported for humic acids and fulvic acids at neutral and alkaline pH remain unexplained, questioning the internal consistency of the findings.

The study’s statistical framework is inadequate, with no mention of error propagation or sensitivity analyses to address variability in thermodynamic measurements. Additionally, the cited references are not adequately contextualized or critically examined; several key claims regarding adsorption efficiency and environmental implications contradict findings from cited works. For instance, the comparison of KₒC values across different studies overlooks soil heterogeneity, which significantly influences adsorption coefficients.

Key design limitations include insufficient randomization, lack of replication across different soil matrices, and inadequate exploration of confounding factors such as ionic strength or competing ions. Together, these flaws cast serious doubt on the study’s reliability, limiting its applicability and raising concerns about the robustness of its conclusions.

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