Thifensulfuron-Methyl 75%WDG weedicide sulfonylurea herbicide

                                                                                             Thifensulfuron

Thifensulfuron is an N-sulfonylurea in which the sulfur atom is attached to a 2-carboxythiophen-3-yl group and in which the non-sulfonated

nitrogen is substituted by a 4-methoxy-6-methyl-1,3,5-triazin-2-yl group. The corresponding methyl ester, known as thifensulfuron-methyl, is

used as a post-emergence herbicide for the control of grass and broad-leaved weeds. It has a role as a herbicide and an agrochemical. It is a N-

sulfonylurea, a member of 1,3,5-triazines and a thiophenecarboxylic acid.

Sulfonylurea herbicides are applied at relatively low rates (3 to 40 g ha−1) to control weeds in a variety of crops across the Canadian prairies.

Because of their high phytotoxicity and the likelihood of their transport in surface runoff, there is concern about their possible impact to aquatic

ecosystems. Little is known, however, about their persistence and behavior in aquatic ecosystems. To assess persistence in aquatic ecosystems,

three prairie farm dugouts (ponds) were fortified with either thifensulfuron‐methyl {methyl 3‐[[[[(4‐methoxy‐6‐methyl‐1,3,5‐triazin‐2

‐yl)amino]carbonyl]amino]sulfonyl]‐2‐thiophenecarboxylate}, ethametsulfuron‐methyl {methyl 2‐[[[[[4‐ethoxy‐6‐(methylamino)‐1,3,5‐triazin‐2

‐yl]amino]carbonyl]amino]sulfonyl]benzoate} or metsulfuron‐methyl {methyl 2‐[[[[(4‐methoxy‐6‐methyl‐1,3,5

‐triazinyl)amino]carbonyl]amino]sulfonyl]benzoate}. The decreasing order of persistence of environmentally relevant concentrations (1 to 4.6 μg

L−1) of these herbicides in dugout water over the June to October period was metsulfuron‐methyl>ethametsulfuron‐methyl>thifensulfuron‐methyl.

The corresponding dissipation half‐lives (DT50) of 84, 30, and 16 d, respectively, are in the same relative order as the recropping intervals for

these herbicides. Thifensulfuron‐methyl showed a biphasic dissipation with slower dissipation during the winter months. In contrast, the

dissipation of metsulfuron‐methyl, the sulfonylurea herbicide with the longest DT50, was somewhat enhanced under winter conditions. One of the

major routes of sulfonylurea herbicide dissipation was removal from the water column when dugout water was lost during hydrological discharge.

The relatively long persistence of these herbicides in water indicates that partitioning into sediments was minimal, the sulfonylurea and methyl

ester linkages in these compounds were resistant to hydrolysis in weakly alkaline waters, and that microbial and photolytic degradation in dugout

waters were slow.