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Mobile herbicides have a high potential for groundwater contamination. An alternative to decrease the mobility of herbicides is to apply materials with high sorbent capacity to the soil, such as biochars. The objective of this research was to evaluate the effect of eucalyptus, rice hull, and native bamboo biochar amendments on sorption and desorption of hexazinone, metribuzin, and quinclorac in a tropical soil. The sorption-desorption was evaluated using the batch equilibrium method at five concentrations of hexazinone, metribuzin, and quinclorac. Soil was amended with eucalyptus, rice hull, and native bamboo biochar at a rate of 0 (control-unamended) and 1% (w w -1 ), corresponding to 0 and 12 t ha -1 , respectively. The amount of sorbed herbicides in the unamended soil followed the decreasing order: quinclorac (65.9%) > metribuzin (21.4%) > hexazinone (16.0%). Native bamboo biochar provided the highest sorption compared to rice hull and eucalyptus biochar-amended soils for the three herbicides. The amount of desorbed herbicides in the unamended soil followed the decreasing order: metribuzin (18.35%) > hexazinone (15.9%) > quinclorac (15.1%). Addition of native bamboo biochar provided the lowest desorption among the biochar amendments for the three herbicides. In conclusion, the biochars differently affect the sorption and desorption of hexazinone, metribuzin, and quinclorac mobile herbicides in a tropical soil. The addition of eucalyptus, rice hull, and native bamboo biochars is a good alternative to increase the sorption of hexazinone, metribuzin, and quinclorac, thus, reducing mobility and availability of these herbicides to nontarget organisms in soil., (© 2024. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

Herbicide mixtures have often been used to control weeds in crops worldwide, but the behavior of these mixtures in the environment is still poorly understood. Laboratory and greenhouse tests have been conducted to study the interaction of the herbicides diuron, hexazinone, and sulfometuron-methyl which have been applied alone and in binary and ternary mixtures in the processes of sorption, desorption, half-life, and leaching in the soil. A new index of the risk of leaching of these herbicides has also been proposed. The sorption and desorption study has been carried out by the batch equilibrium method. The dissipation of the herbicides has been evaluated for 180 days to determine the half-life (t 1/2 ). The leaching tests have been carried out on soil columns. The herbicides isolated and in mixtures have been quantified using ultra-high performance liquid chromatography coupled to the mass spectrometer. Diuron, hexazinone, and sulfometuron-methyl in binary and ternary mixtures have less sorption capacity and greater desorption when compared to these isolated herbicides. Dissipation of diuron alone is slower, with a half-life (t 1/2 ) = 101 days compared to mixtures (t 1/2 between 44 and 66 days). For hexazinone and sulfometuron-methyl, the dissipation rate is lower in mixtures (t 1/2 over 26 and 16 days), with a more pronounced effect in mixtures with the presence of diuron (t 1/2 = 47 and 56 and 17 and 22 days). The binary and ternary mixtures of diuron, hexazinone, and sulfometuron-methyl promoted more significant transport in depth (with the three herbicides quantified to depth P4, P7, and P7, respectively) compared to the application of these isolated herbicides (quantified to depth P2, P4, and P5). Considering the herbicides' desorption and solubility, the new index proposed to estimate the leaching potential allowed a more rigorous assessment concerning the risk of leaching these pesticides, with hexazinone and sulfometuron-methyl presenting a higher risk of contamination of groundwater., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Weed control efficiency and the environmental contamination potential of herbicides depend on soil sorption and desorption. Among the indexes that evaluate the soil adsorption processes, the coefficients sorption (Kf s ) and desorption (Kf d ) obtained by Freundlich isotherms can provide accurate information about the behavior of an herbicide in the soil. The values of Kf s and Kf d of an herbicide vary according to the physicochemical characteristics of the soil, so it is possible to estimate these coefficients with high precision if good predictive mathematical models are constructed. Therefore, our objective aimed to evaluate the use of multiple regression models (MLR) associated with multivariate techniques to estimate the coefficient Kf s and Kf d for the hexazinone based on the chemical and physical attributes of soils. The correlation analyses, principal components, and clustering analysis allowed the multiple linear regression technique to generate models with higher adjustment coefficient (R 2 ) for Kf s (0.73 to 0.99) and Kf d (0.94 to 0.99), and lower root mean squared error (RMSE) for Kf s (0.003 to 0.065) and Kf d (0.018 to 0.120). Regression models created from groups of soils showed greater prediction performance for Kf s and Kf d . The organic matter followed by the cation exchange capacity was the most important attributes of soils in sorption and desorption processes of hexazinone.