Analysis of metsulfuron-methyl residues in wheat field soil: a comparison of HPLC and bioassay techniques

Metsulfuron-methyl is a low-application-rate sulfonylurea herbicide that is widely used to control broad-leaved weeds in wheat. Owing to its persistent nature, its residues may be present at phytotoxic levels for the next crop in rotation. Therefore, a comparative evaluation of HPLC and bioassay techniques was made for the analysis of this herbicide in wheat field soil.

Metsulfuron-methyl was applied to wheat crop at different rates (4, 8 and 12 AI ha(-1)) at 28 days after sowing as a post-emergence application, and the soil was analysed for metsulfuron-methyl residues by HPLC and lentil seed bioassay techniques. The bioassay was found to be the more sensitive technique. At the recommended rate of application, 4 g AI ha(-1), the bioassay technique could detect the residue up to 30 days in surface soil, while, with HPLC, residues were not detectable on the 15th day. The half-lives of metsulfuron-methyl by HPLC and bioassay were calculated as 6.3-7.8 and 17.5 days respectively. Under field conditions, residues of metsulfuron-methyl were also detected in subsurface soil by the bioassay technique at trace levels, but were not detected by the solvent extraction/HPLC method.

Lentil seed bioassay is a more sensitive technique than HPLC. Traces of residues detected in subsurface soil indicated the mobility of metsulfuron-methyl into lower layers.