Fate of terbutryn in macrophyte‐free and macrophyte‐containing farm ponds

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Abstract
Summary: Terbutryn (2‐ethylamino‐4‐(tert‐butylamino)‐6‐methylthio‐s‐triazine) was applied in June 1978, to two farm ponds (A and C) near Winnipeg. Canada, to give 100 μg/l water concentrations. The persistence of the herbicide and its degradation products was monitored over a 61‐week period following application. The half‐life of terbutryn m the water column ranged from 3 weeks in Pond C, which contained heavy growths of cattails (Typha sp.) and duckweed (Lemna sp.), to 30 days in Pond A. which was free from aquatic macrophytes, Terbutryn residues m sediment reached a maximum of 1.4 μg/g (dry wt) in Pond A and 0.5 μg/g in C. Maximum concentrations of N‐deethylated terbutryn (2amino‐4‐(tert‐butylamino)‐6‐methylthio‐s‐tria‐zine)(DET) were 14.4 μg/l in Pond A water after 61 weeks and 0.14 μg/g in Pond C sediment after 30 weeks. The maximum concentration of hydroxy‐terbutryn (2‐hydroxy‐4‐ethyl‐amino‐6‐(tert‐butylamino)‐s‐triazine) (HT) observed in pond water was 6.4 μg/l in Pond C after 7 weeks. HT was not detected in sediment (Typha ranged from 0.3 μg/g (dry wt) in the shoot to 3.3 μg/g in the roots. After 12 weeks, terbutryn residues in plants (Pond C) were estimated to account for 1 to 4% of the herbicide in the pond.

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