Leaching and half-life of the herbicide tebuthiuron on a recharge area of Guarany aquifer in sugarcane fields in Brazil

Abstract

This study was undertaken to evaluate the degradation and mobility of the herbicide tebuthiuron (N-[5-(1,1-dimethylethyl)-1,3,4-thiadiazol-2-yl]-N,N'-dimethylurea) in soil under field conditions, and its potential for leaching and groundwater contamination. A watershed, Espraiado, located over a recharge area in Brazil, was chosen for soil and water studies. At Espraiado, water samples were collected from seven wells at intervals of three months from March 2004 to June 2006 and analyzed for tebuthiuron. Other samples were taken from city wells located outside of the recharge area. To assess the potential movement to the aquifer, tebuthiuron was also applied to trial plots at the recommended label rate of 1.0 kg/ha a.i. in May of 2004, with and without sugarcane coverage, on sandy soil. Soil samples were collected during the years of 2004 and 2005, at depths intervals of 20 cm from soil surface down to 120 cm and analyzed for tebuthiuron at zero, 3, 30, 60, 90, 120, 150, 180, 240, and 300 days after application. There was no clear effect of sugarcane coverage on the tebuthiuron degradation in soils, but it moved faster into the soil where there was no cover. After 180 days there were no measurable residues in the soil, and tebuthiuron was not found below 40 cm depth in any time. Tebuthiuron had a half-life of 20 days under those conditions. No tebuthiuron residue was found in ground water samples at any sampling time.

Comportamento do tebuthiuron em solo de cultivo de cana-de-açúcar utilizando lisímetro de drenagem modificado

“…Os resultados ainda estão de acordo com aqueles observados por Boeira & Dornelas de Souza (2005), em que o movimento desse herbicida não ultrapassou 20 e 10 cm de profundidade, respectivamente, em solos de textura média e argilosa. Os resultados também confirmam aqueles verificados por Cerdeira et al (2006), que coletaram amostras de solo (textura média e argilosa) em diferentes profundidades e não encontraram resíduos de tebuthiuron abaixo de 40 cm.…”

Herbicide distribution in soils of a riparian forest and neighboring sugar cane field

“…Standards of diuron (98.7% pure) and hexazinone (98.5% pure) were donated by DUPONT and tebuthiuron (97.7% pure) from DowAgroSciences. The extraction was conducted as described previously (Matallo et al, 2003(Matallo et al, , 2005Negrisoli et al, 2005;Cerdeira et al, 2007). The following validation parameters were obtained: limit of quantification (LQ) 0.02 mg kg − 1 and limit of detection (LD) of method 0.01 mg kg − 1 ; linearity from 0.050 to 5.00 mg L − 1 (r 2 N 0.999) and recoveries from 90 to 103%.…”

Controle de três espécies de Euphorbia por herbicidas aplicados em pré-emergência sobre a palhada de cana-de-açúcar

“…They concluded that the more contact time of the herbicide with the straw, the less its transposition to the soil, regardless of the simulated rain quantity, reducing by about 30% the total leached product when this remained exposed for 28 days after application. The active principle of this herbicide (tebuthiuron) presents long half-life, about a year in soils with high carbon content and little rain (Chang and Strizke, 1977;Helling, 2005;Gomes et al, 2006); it may have its half-life reduced up to 20 days under specific soil conditions (moisture, organic matter concentration, microbial community) and climate (temperature, radiation) (Cerdeira et al, 2007). In this study, tebuthiuron was not effective in controlling after 45 days without rain, indicating that the product may have been volatilized and/or photodegraded during this period.…”