Degradation of Four Commonly Used Pesticides in Malaysian Agricultural Soils

Abstract

First-order kinetics were observed for the degradation of 2,4-D, lindane, paraquat, and glyphosate in sandy loam and muck soils, with the exception of glyphosate degradation in an anaerobic muck. Short half-lives were observed for 2,4-D in aerobic (3.4 days) and anaerobic (9.3 days) muck soils, while longer half-lives were found for glyphosate (19.2 days) and 2,4-D (35.9 days) in the sandy loam. Long half-lives were observed for lindane (1.0−1.7 years) and paraquat (1.4−7.2 years) in the soils. The results of the laboratory studies on the degradation of the pesticides in the Malaysian soils showed little difference from the results reported in soils from other parts of the world. Keywords: 2,4-D; lindane; paraquat; glyphosate; degradation

Influence of repeated applications of glyphosate on its persistence and soil bioactivity

“…The amounts of 14 C-non-extractable residues, which are the slow released residues because they depend on the microbial attack on the soil fraction where they are bound, varied from 19% (four applications, two months) to 29.5% (three applications, two months). Finally, the balance of total radiocarbon recovered from 14 C-glyphosate varied from 80% to 103% (Figure 3), which is in agreement with Cheah et al (1998).…”

“…The amount of 14 CO 2 varied from approximately 47% (one application) to 33.5% (four applications), two months after treatments. These values are higher than those detected by Cheah et al (1998). Araújo et al (2003) found higher production of carbon dioxide from soils treated six years with glyphosate than from soils treated only one time.…”

“…On the other hand, the half-lives of total mineralization increased with the number of 14 C-glyphosate applications, i.e., 2.2, 3.0, 3.1 and 3.4 months, respectively after 1, 2, 3 and 4 applications. These values are higher than the Feng and Thompson's (1990) and Cheah's et al (1998) values, and these differences can be attributed to the higher amount of organic matter of their soils, since it is known that soil microbial activity is highly dependent of the soil organic matter content. Thus, the higher amount of the herbicide itself or its metabolites in the soil, the lesser metabolism would be expected.…”

“…Feng & Thompson (1990) and Cheah et al (1998) had also detected initially rapid, followed by slower, degradation of glyphosate in soil and attributed, respectively, to the initial action of microorganisms on the free glyphosate and subsequent attack to the herbicide adsorbed in the soil. The 14 C-glyphosate utilized is radiolabelled in the phosphonomethyl carbon, which is also present in the aminomethyl phosphoric acid (AMPA) molecule, that is the main metabolite of glyphosate.…”

Comportamento do glifosato no solo e deslocamento miscível de atrazina

“…de até 22,7 anos para solos vulcânicos, com elevado grau de sorção (Nomura & Hilton, 1977) e t 1/2 em torno de 19 dias (Cheah et al, 1998) para a maioria dos solos. Apesar do glifosato ser uma molécula bastante rica em energia, e constituída de C, H, O, P e N, o que a torna altamente biodegradável em meio líquido sem adsorventes.…”