OCCURRENCE AND PERSISTENCE OF PICLORAM IN GRASSLAND WATER SOURCES

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Abstract
Summary. At 2 weeks following application, concentrations of picloram in surface runoff water collected adjacent to a South Texas grassland treated with 1·1 kg/ha ranged from 0·055 to 0·184 ppm as detected by gas chromatography. Picloram in surface runoff water diminished with time and amount of rainfall as a decay function. Picloram was not detectable in a flowing stream 0·8 km below a 32‐ha area treated with 1·1 kg/ha. Residual picloram was not detected in domestic water wells at any time up to 2 years following treatment of adjacent areas with 1·1 kg/ha.Dissipation of picloram from treated livestock‐watering ponds was concentration‐dependent, with the final losses resulting largely from dilution. Initial loss rates in the ponds ranged from 14 to 18%/day but decreased to less than 1%/day at 100 days following treatment. After 100 days, when the concentrations were less than 0·005 ppm, the primary changes in picloram content appeared to be due to dilution from rainfall or to concentration by runoff from adjacent treated areas.