Estudo da biodegradação do acido 2,4-diclorofenoxiacetico em formulações de liberação controlada

AUTOR(ES)
DATA DE PUBLICAÇÃO

1999

RESUMO

Technical grade 2,4-D (2,4-dichlorophenoxyacetic acid, i.e., free 2,4-D), and the herbicide retained in lignin-based controlled release formulations (2,4-D/CRF), were submitted to biodegradation. For this purpose, Pseudomona putida bacteria, Phanerochaete chrysosporium fungus and soil microflora were utilized. Different degradation rates were observed in accordance with different initial herbicide concentrations in the medium. In the initial free 2,4-D concentrations of 5, 10 and 20 mg/L, P. chrysosporium degraded 12, 45 and 56% of the herbicide, respectively. For 40, 60 and 80 mg/L of 2,4-D, 35% degradation was observed, and for 100 mg/L, 25%. For the CRF, 20, 43, 46 and 42% degradation for 10, 20, 40 and 60 mg/L was observed, respectively. Experiments with P.putida and free 2,4-D presented 19% degradation in a concentration of 10 mg/L. In concentrations greater than 10 mg/L, no degradation was observed. Comparatively, for CRF of 10 and 100 mg/L of 2,4-D, 29 and 12% degradation was observed, respectively. Experiments in soil were carried out at a constant 2,4-D concentration of 9.4 Kg/ha. In soil not stimulated by growth of microorganisms, free 2,4-D presented between 7-10% degradation, and stimulated soil, 44.5 4.5% degradation. In comparison, the CRF 2,4-D presented 17 3% degradation and no degradation for soils with and without stimulation of the initial growth of the microorganisms, respectively. The absence of metabolites of the 2,4-D degradation via was determined by gas chromatography coupled with mass spectrometry, and demonstrated that the conditions utilized in the degradation experiments favored the mineralization of the herbicide. A CRF porosity increase after degradation by fungus and bacteria was observed by means of scanning electronic microscopy, and demonstrated that the formulation had undergone physical and chemical modifications after the degradation process. The hydrolysis of the ester group between the 2,4-D and lignin was observed by FTIR analysis of the CRF. These physical and chemical modifications resulted in a herbicide release rate increase in the CRF. Apparent 2,4-D diffusion constants of the CRF went from 9 days to 17, and from 12 days to 16 days after treatment with fungus and bacteria, respectively. The CRF acted as a barrier to biodegradation of the active ingredient present in the formulation. However, greater ar smaller degradation rates of the active ingredient depended on the initial concentration provided by the controlled release system.

ASSUNTO(S)

herbicida lignina

ACESSO AO ARTIGO

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