Degradation Mechanism, Kinetics and Toxicity Studies of Dicamba: Theory Combined with Toxicity Assay

Abstract

Dicamba (DA) is herbicide with ecological and human health risks. The study utilizes quantum chemical calculations combined with toxicity tests to explore DA degradation mechanisms and its potential environmental risks in water and on soil particle models (SixOy(OH)z)) at varying pH levels. The findings reveal H-abstraction as the dominant degradation pathway for DA across all pH conditions (0-14), with a decreasing branching ratio at higher pH. Reaction rate constants increase with pH, suggesting faster degradation under alkaline conditions. The presence of soil particle clusters significantly accelerates DA degradation compared to homogeneous environments. While H-abstraction remains the primary pathway in both contexts, the resulting byproducts generally exhibit lower ecotoxicity, except for 3,6-dichloro-2-hydroxybenzoic acid and its cytotoxicity was significantly higher than that of dicamba as measured by MTT assay. In addition, the hepatotoxicity and thyrotoxicity of the degradation products were higher than that of DA itself.

Keywords: Dicamba, Reaction mechanism, Kinetics, Non-homogeneous reaction, Ecotoxicity, MTT assay