RESUMO
The leaching of herbicides into the soil is essential to control germinating seeds and parts of vegetative weeds. However, herbicide transportation to deeper soil layers can result in groundwater contamination and, consequently, environmental issues. In this research, our objective was to investigate differences in herbicide leaching between commercial formulations and analytical standards using three different soils. Leaching experiments were carried out for diuron, hexazinone, and sulfometuron-methyl herbicides isolated and in binary and ternary mixtures. The herbicide residue quantification was performed by ultra-high-performance liquid chromatography coupled to a mass spectrometer (LC-MS/MS). Diuron had less mobility in soils and was retained in the most superficial layers. Hexazinone and sulfometuron-methyl were more mobile and leached into deeper layers. The leaching process was more intense for hexazinone and sulfometuron-methyl. The additives present in the commercial formulation favored the leaching in soils of diuron, hexazinone, and sulfometuron-methyl herbicides isolated and mixture compared to the analytical standard. This fact highlights the importance of considering these effects for the positioning of herbicides in the field to increase the efficiency of weed control and minimize the potential for environmental contamination.
RESUMO
Sorption and desorption determine the amount of an herbicide in soil solution. Therefore, knowledge of the sorption and desorption coefficients in different soils is an essential factor to estimate the potential for environmental contamination by herbicides. We evaluated the feasibility of multivariate and linear discriminant analyses to predict the sorption and desorption capacity of a soil for diuron, one of the most used herbicides on sugarcane plantations. The adsorptive capacity in twenty-seven Brazilian soil samples was estimated using the sorption constant (Kfs) and desorption constant (Kfd) obtained by the Freundlich isotherms. The regression model was created from the sorbed and nonsorbed concentrations of diuron in soils. Ultra-performance liquid chromatography was applied to quantify the diuron concentrations. The multivariate analysis separated the soils into four groups considering the similarity of the following attributes: pH, organic matter, clay, and base saturation. The groups showed a similar pattern of sorption and desorption for diuron: Lom-Lclay: low sorption (5.9 ± 1.2) and high desorption (10.9 ± 0.6); Lclay: low sorption (7.5 ± 1.1) and high desorption (11.4 ± 1.3); Hom-Hclay: high sorption (11.2 ± 1.2) and low desorption (13.8 ± 1.2); HpH-Hclay: high sorption (10.1 ± 1.1) and medium desorption (11.5 ± 1.4). Linear discriminant analysis of these soil attributes was used to classify other soils described in the literature with adsorption capacity. This analysis was able to identify soils with high and low sorption using the pH, organic matter, clay, and base saturation, demonstrating the enormous potential of the technique to group soils with different contamination risks for subterranean waters. Sugarcane crops in northeastern Brazil showed a higher pollution risk through the leaching of diuron. Multivariate analysis revealed significant diuron-related changes in the soil composition of different Brazilian regions; therefore, this statistical analysis can be used to improve understanding of herbicide behavior in soils.
RESUMO
Knowledge of factors related to the dynamics of herbicides in the environment is of fundamental importance to predicting the behavior of herbicides in soils with different attributes, to select appropriate dosages, as well as to avoid harmful effects on the environment and subsequent crops. The objective of this work was to evaluate the sorption and desorption of ametryn in seven soils with different attributes. Initially, the equilibrium time was determined by the "Batch Equilibrium". Then, it was performed the sorption test with different concentrations (0.5; 1; 2; 4; 8; 16; 24 and 32 mg L-1) of ametryn in 0.01 mol L-1CaCl2. 10 mL of these solutions were added to samples of 2.00 g of each soil, remaining under rotary shaking for 4 hours. After centrifugation and filtration, the ametryn concentration in the supernatant was determined by high-performance liquid chromatography. Desorption was evaluated using the tubes containing 16 mg L-1 prior to sorption testing. The results indicated that the sorption and desorption of ametryn depend on the physicochemical attributes of the soil. Sorption was higher in soils with high organic matter content and high ion exchange capacity, while desorption was inversely proportional to sorption.
O conhecimento dos fatores relacionados à dinâmica de herbicidas no ambiente é de fundamental importância para prever o comportamento de herbicidas em solos com diferentes atributos e para seleção de dosagens adequadas, bem como para evitar efeitos prejudiciais ao ambiente e às culturas subsequentes. O objetivo do trabalho foi avaliar a sorção e dessorção do ametryn em sete solos com diferentes atributos. Inicialmente, foi determinado o tempo de equilíbrio pelo método "Batch Equilibrium". Em seguida foi realizado o ensaio de sorção com diferentes concentrações (0,5; 1; 2; 4; 8; 16; 24 e 32 mg L-1) de ametryn em CaCl2 0,01 mol L-1. Foram adicionadas 10 mL destas soluções a amostras de 2,00 g de cada solo, permanecendo sob agitação rotatória por 4 horas. Após centrifugação e filtração, a concentração do ametryn no sobrenadante foi determinada por cromatografia líquida de alta eficiência. A dessorção foi avaliada utilizando os tubos que continham 16 mg L-1 antes do ensaio de sorção. Os resultados indicaram que a sorção e a dessorção do ametryn depende dos atributos físico-químicos do solo. A sorção foi maior em solos com alto teor matéria orgânica e alta capacidade de troca iônica, enquanto que a dessorção foi inversamente proporcional à sorção.