In this work, an iron/biochar composite was evaluated as a catalyst for 3,6-dichloro-2-methoxybenzoic acid (dicamba) herbicide degradation by heterogeneous Fenton-like process. The biochar was produced from pyrolysis of coffee husks. After FeII adsorption by biochar, the material was submitted to chemical reduction, via borohydride, producing zero-valent iron nanoparticles (BIO-Fe0). The material was characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy and energy dispersive X-ray spectroscopy, Raman scattering spectroscopy, nitrogen adsorption/desorption analysis, among other techniques. The BIO-Fe0 is a heterogeneous material, and the main constituent elements are carbon (C), oxygen (O), silicon (Si), sulfur (S) and iron (Fe). The dicamba degradation was monitored by high-performance liquid chromatography and biological assays using beans (Phaseolus vulgaris) as indicator species. The commercial dicamba (500 mL; 250 mg L 1) was submitted to Fenton-like process (initial pH 3.20; BIO-Fe0: 3 or 5 g; 1.00 mL H2O2 at 3.00 mmol L 1; 1.00 mL Al2(SO4)3 at 1.00 mol L 1; 25 ºC and 5 h of reaction), presenting ca. 100% of degradation. These treated solutions were used in a biological assay. The intoxication levels were less 30%. These results show that BIO-Fe0 has the potential to be used in the dicamba degradation by Fenton-like processes.

Abstract Background: Studies of sorption and desorption of herbicides in soils are essential in predicting their transport, bioavailability, and transformation in the soil profile. These studies are also vital to predict the agronomic efficiency of the herbicides in controlling weeds. Objective: In this study, atrazine’s sorption and desorption kinetics were evaluated in samples composed of single and a mixture of horizons from the Red-Yellow Latosol profile. Methods: This was performed by the Batch equilibrium method, and the quantification was carried out using a High-performance liquid chromatography (HPLC). Results: Freundlich isotherms were adjusted appropriately to describe the atrazine sorption. The Kf values obtained varied between 0.188 and 2.592, and the Koc values ranged between 37.76 and 143.81, which corresponded to horizons C and A, respectively. The desorption was only possible to determine in horizon A. The other substrates presented low sorption, and the desorption of the remaining atrazine was not significant, therefore not adjusting to the Freundlich model. The organic matter (OM) was the main attribute to the atrazine sorption in the soil, presenting a high correlation with Kf and Koc values. In the horizon A samples, the Kfd value obtained in desorption was higher than the Kf obtained in sorption, which indicated a low desorption capacity and, therefore, low potential mobility of the herbicide in this soil horizon. Conclusions: It was concluded that the organic matter present in greater quantity in horizon A of the Red-Yellow Latosol has a crucial role in the dynamics of atrazine in the horizons of this soil.

Durante o ano agrícola 1994/95, foi conduzido ensaio de campo, em Capinópolis, MG, visando avaliar o efeito residua l no solo dos herbicidas imazamox (50 e 100 g/ha) e imazethapyr (100 e 200 g/ha), aplicados à cultura da soja, sobre as culturas de milho e sorgo, cultiva das em sistema de sucessão à soja. Foram realizados, em casa de vegetação, bioensaios utilizando o sorgo como planta - teste, em amostras de solo coletadas nas parcelas onde foram aplicados os herbicidas no campo. As amostras de solo foram coletadas aos 30, 60, 90 e 120 dias após a aplicação (DAA) dos herbicidas. Um dia após a colheita da soja, fez-se também a semeadura, no campo, do milho e do sorgo nas parcelas anteriormente ocupadas com a soja, onde haviam sido feitas as aplicações dos herbicidas. Os resultados obtidos indicam que o imazamox apresentou menor efeito residual, não influenciando no desenvolvimento da planta-teste quando esta foi semeada aos 120 DAA, até mesmo no dobro da dose recomendada. Todavia, o imazethapyr a 200 g/ha (dobro da dose recomendada) apresentou inibição no desenvolvimento das plantas de sorgo quando estas foram semeadas 120 DAA. Em condições de campo, plantas de sorgo semeadas após a colheita da soja em áreas que receberam o dobro da dose recomendada de imazethapyr evidenciaram menor altura de plantas e menor comprimento de panícula do sorgo, não influenciando, entretanto, a produtividade de grãos.

During the 1994/95 growing season, a field assay was conducted in Capinópolis, MG, to evaluate the carryover effect of the herbicides imazamox (50 and 100 g/ha), and imazethapyr (100 and 200 g/ha), applied in soybean, to corn and sorghum crops succeeding soybean. Bioassays using sorghum as test-plant were conducted in greenhouse conditions using soil samples collected from plots sprayed with the herbicides in field. Soil samples were collected at 30, 60, 90 and 120 days after application (DAA) of herbicides. One day after soybean harvest, corn and sorghum were also sowed in the field plots previously used for soybean growth, where the herbicides had been applied. The results obtained denote that imazamox had a shorter residual effect in soil, having no influence on the development of the test-plan t at 120 DAA, even when at double the recommended rate. However, imazethapyr appl ied at 200 g/ha (double the recommended rate), inhibited the development of sorghum plants sowed 120 DAA. Under field conditions, sorghum plants sowed after soybean harvest in areas receiving double the recommended rate of imazethapyr evidenced shorter plant height and shorter plant panicle, although having no effect on grain productivity.