Streamwater Contamination After Aerial Application of a Pelletized Herbicide
Concentrations of hexazinone and its metabolites were monitored in a Piedmont stream for 8 months after aerial application of a pelletized formulation (Velpar® Gridball™). Downstream water-users and fish are probably safe from toxic exposure if treatment areas have only small streams (less than 50 cm average channel width) and if labeled rates are not exceeded. Hexazinone concentrations were highest 30 minutes after application at 2.4 ppm, declining to less than half at 1 hour, 1.1 ppm, and half again at 2 hours, .49 ppm. No contamination was evident after the Sthday sampling. Stream contamination from pellets was as much as 100 times the concentrations reported for foliar sprays, aerially applied over brush-covered streams at similar rates.