Fate of metsulfuron-methyl in soils in relation to pedo-climatic conditions

Abstract

The dependence of the behaviour of metsulfuron-methyl on soil pH was conÐrmed during incubations under controlled laboratory conditions with two French soils used for wheat cropping. The fate of [14C] residues from [triazine-14C]metsulfuron-methyl was studied by combining di †erent experimental conditions : soil pH (8É1 and 5É2), temperature (28 and 10¡C), soil moisture (90 and 50% of soil water holding capacity) and microbial activity (sterile and nonsterile conditions). Metsulfuron-methyl degradation was mainly inÑuenced by soil pH and temperature. The metsulfuron-methyl half-life varied from Ðve days in the acidic soil to 69 days in the alkaline soil. Under sterile conditions, the half-life increased in alkaline soil to 139 days but was not changed in the acidic soil. Metsulfuron-methyl degradation mainly resulted in the formation of the amino-triazine. In the acidic soil, degradation was characterised by rapid hydrolysis giving two speciÐc unidentiÐed metabolites, not detected during incubations in the alkaline soil. Bound residues formation and metsulfuron-methyl mineralisation were highly correlated. The extent of bound residue formation increased when soil water content decreased and was maximal [48 (^4)% of the applied metsulfuron-methyl after 98 incubation days] in the acidic soil at 50% of the water holding capacity and 28¡C. Otherwise, bound residues represented between 13 and 32% of the initial radioactivity.1998 SCI ( Pestic. Sci., 53, 311È323 (1998)

Kinetic Distribution of 14C‐Metsulfuron‐methyl Residues in Paddy Soils under Different Moisture Conditions

“…Although metabolites were not identified in the present study, several metsulfuron‐methyl metabolites have been reported in previous studies. Pons and Barriuso (1998) found that hydroxyl‐metsulfuron‐methyl and amino‐triazine, referred to as methyl‐2‐(4‐hydroxy‐6‐methyl‐1,3,5‐triazine‐2‐yl carbamoylsulfamoyl) benzoate, and 4‐hydroxy‐6‐methoxy‐2‐amino‐1,3,5‐triazine, respectively, were the main intermediates from the two metabolic pathways involved in the degradation of metsulfuron‐methyl: O ‐demethylation and cleavage of sulfonylurea bridge of the methoxy‐triazine moiety. Sarmah et al (2000) noted that 2‐[( N ‐acetylcarbamoyl)carbamoylcarbamoylsulfamoyl] benzoic acid was the hydrolysis product with opened triazine ring for metsulfuron‐methyl.…”

“…Sarmah et al (2000) noted that 2‐[( N ‐acetylcarbamoyl)carbamoylcarbamoylsulfamoyl] benzoic acid was the hydrolysis product with opened triazine ring for metsulfuron‐methyl. However, the complete degradation of triazine amine went slower than that of metsulfuron‐methyl in soil (Pons and Barriuso, 1998; Bossi et al, 1999), which may constitute an ever‐present and cumulative risk of metabolites to the environment and, eventually, to non‐target organisms. Despite this, the adverse effects caused by the metabolites of metsulfuron‐methyl along with the parent compound in soil have been presented (Boldt and Jacobsen, 1998; Li et al, 2005; Hollaway et al, 2006).…”

“…Metsulfuron‐methyl has been shown to persist in the environment for many months (Pons and Barriuso, 1998; Wang et al, 2001; Hollaway et al, 2006). Occasionally, even extremely low concentrations of metsulfuron‐methyl residues remaining in soil caused phytotoxicity (Moyer, 1995; Yao et al, 1997; Ye et al, 2003; Li et al, 2005; Hollaway et al, 2006).…”

“…The principal degradation pathways of metsulfuron‐methyl in soil include chemical hydrolysis and microbial degradation (Brown, 1990; Sarmah and Sabadie, 2002). The half‐lives and the sorption distribution coefficients of metsulfuron‐methyl are variable and are dependent on soil properties and environmental factors (Pons and Barriuso, 1998; Wang et al, 2001; Oliveira et al, 2001; Berglöf et al, 2003; Kah and Brown, 2007). It has been reported that pH seems to be the most important soil property controlling metsulfuron‐methyl behavior.…”

“…It has been reported that pH seems to be the most important soil property controlling metsulfuron‐methyl behavior. It influences the ionization state, which in turn can affect the herbicide's residual form, sorption, and chemical degradation (Brown, 1990; Pons and Barriuso, 1998; Wang et al, 2001; Sarmah and Sabadie, 2002). In the cereal‐growing area of southeastern China, the pH of paddy soils ranges from 5 to 9 in the top 20‐cm layer.…”