Remobilization of bound residues of herbicides in soils cultivated with sugar cane with vinasse application, straw and filter cake and identification of metabolites

Author(s)

Marcela Lembi Viti

• Document type: Master's Dissertation
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Centro de Energia Nuclear na Agricultura (CENA/STB)
• Defense date: 2014-09-19

Examining board members

Valdemar Luiz Tornisielo; Alex Vladimir Krusche; Rafael Marques Pereira Leal

• Advisor: Valdemar Luiz Tornisielo

Abstract

The environmental significance of the presence of bound residues of herbicides and their metabolites in the soil are fundamental to new methods of herbicide application, considering the transition of these residues to following crops, their effect on the biota of terrestrial and aquatic systems, the potential transfer to the food chain, the potential for contamination of groundwater, and their long term effects on the quality and fertility of soils. The application of vinasse for fertigation, straw and filter cake in sugar cane fields is often used, but it is unknown if such practice causes mineralization and remobilization of bound residues of herbicides, which may provide benefits for the degradation of the herbicides by soil microorganisms, or affect the quality of the soil, leaching to groundwater. The aim of this project is to evaluate, under laboratory conditions, the remobilization and degradation/mineralization of bound residues of 14C-diuron, 14C - hexazinone, 14C - diuron + hexazinone e 14C - metribuzin in two soils for growing sugar cane, where were used known quantities of these herbicides radiolabeled with application of treatments vinasse, filter cake and straw and identify the metabolites formed from the remobilization. The experiment was performed in Bartha flasks collecting solutions of NaOH at 7, 14, 21, 28, 35, 42, 49, 56, 63 and 70 days after the beginning of the experiment and conducted the reading on the Liquid Scintillation Spectrometer to determine the mineralization of herbicides. After 70 days of incubation, the soils were extracted and the extracts were read in Liquid Scintillation Spectrometer and concentrated. Application was made on TLC plates and read on Radio scanner. After extraction, the soils were oxidized in Biological Oxidizer and the radioactivity was determined by Liquid Scintillation Spectrometer. The metabolites of the herbicides were identified by Ultra Performance Liquid Chromatography coupled to quadruple time-of-flight mass spectrometer. The analysis time was 9 minutes with Acquity UPLC® BEH C-18 column (1.7 ?m, 2.1 mm d.i. x 100 mm) and temperature of 40 ºC. The metribuzin was the least remobilized, with an average of 74.98% of product that remained bound to the soil and the herbicide hexazinone was the most remobilized (14CO2 evolution averaging 23.78%) in both soils and treatments. Through the masses, molecular formulas and isotopic characteristics, were identified the metabolite DCPMU (1-(3,4-dichlorophenyl)-1-methylurea), belongs to diuron, the metabolite B (3-cyclohexyl-6-(methylamino)-1-methyl-1,3,5-triazine-2,4-(1H,3H)-dione), belongs to hexazinone, and the metabolites DA (Desamino-metribuzin), DK (Diketo-metribuzin), and DADK (Desamino-diketo-metribuzin), belongs to metribuzin (AU)

• FAPESP's process: 11/15677-0 - Remobilization of bound residues of herbicides in soils cultivated with sugar cane with vinasse application, straw and filter cake
• Grantee: Marcela Lembi Viti
• Support Opportunities: Scholarships in Brazil - Master