Effects of Moisture, Temperature, and Biological Activity on the Degradation of Isoxaflutole in Soil

Abstract

The effects of several environmental factors on the dissipation, transformation, and mineralization of isoxaflutole were investigated in laboratory incubations. In the soil, isoxaflutole hydrolyzed to a diketonitrile derivative, which is the active form of the herbicide. The diketonitrile was then metabolized to an inactive benzoic acid derivative and later into two unknown products, which were found only in small quantities. Degradation of isoxaflutole was faster in soil maintained at -100 or -1500 kPa compared to that in air-dry soil. At 25 °C, the half-lives for isoxaflutole were 9.6, 2.4, and 1.5 days in air-dry, -1500 kPa, and -100 kPa moisture regimes, respectively. A simple Arrhenius expression described the response of isoxaflutole transformation (mineralization and transformation) to temperature in the range of 5 to 35 °C. An activation energy value (E a ) of 67 kJ/mol for isoxaflutole suggested the transformation of the herbicide to the diketonitrile derivative was primarily a chemical reaction. Moreover, biological activity had little effect on the hydrolysis of isoxaflutole, with half-lives of 1.8 and 1.4 days in sterile and nonsterile soil, respectively. However, the transformation of diketonitrile to benzoic acid and the production of the unknown products were greatly reduced in the sterile soil, suggesting one or more biologically mediated processes.

Microbial degradation of sulfentrazone in a Brazilian rhodic hapludox soil

“…Researchers have demonstrated that the rate of herbicide degradation can be strongly influenced by the soil moisture content and temperature, due to interference of these parameters on the soil microorganisms (18,27,36,43). Weber & Weed (45) reported that higher soil temperatures and moisture contents enhanced the degradation of triazine, and degradation has been reported to be faster in moist soil than in dry soil (44).…”

Efeito residual de isoxaflutole após diferentes períodos de seca

“…A persistência aumenta em solos secos, e sua meia-vida passa de 1,5 dia (umidade de 100 Kpa) para 9,6 dias (solo seco ao ar) (Taylor-Lovell et al, 2002). Segundo Vidal & Merotto Jr. (2001), a meia-vida do IFT foi de 20 horas em solo com 30% da capacidade de campo e de 60 horas em solo com 15%.…”

“…A conversão de IFT em DKN é rápida no solo, na água e nas plantas (Mitra et al, 1999(Mitra et al, , 2000; no caso do solo, quanto maior a umidade, mais rápida a conversão. A meiavida diminui de 74 para 38 horas quando a umidade do solo passa de 10 para 40%; se o solo estiver seco, essa reação não ocorre ou acontece muito lentamente (Taylor-Lovell et al, 2002).…”

“…O metabólito DKN é mais solúvel, mais estável e mais persistente que o IFT. Taylor-Lovell et al (2002) relatam meiavida maior que 56 dias em solo com pH 7,0 e 2,5% de carbono orgânico para o DKN, comparado à meia-vida menor que dois dias para o IFT no mesmo solo.…”

Tolerância de híbridos de milho ao herbicida isoxaflutole

“…Segundo Rouchaud et al (1998), a dissipação do isoxaflutole em diquetonitrila é mais rápida em pH 7,2 do que em pH 5,5. O metabólito diquetonitrila é mais solúvel, estável e persistente que o isoxaflutole e apresenta solubilidade em água de 326 mg L -1 (Mitra et al, 2000;Taylor-Lovell et al, 2000, 2002. Taylor-Lovell et al (2002) relatam meia-vida maior que 56 dias em solo com pH 7,0 e 2,5% de carbono orgânico para o diquetonitrila, comparado à meia-vida menor que dois dias para o isoxaflutole no mesmo solo.…”