HEXAZINONE AND ITS METABOLITES IN BOREAL FOREST VEGETATION

Concentrations of hexazinone and two metabolites in vegetation were de termined for 2 yr after broadcast application of a 10% granular formul ation of hexazinone at 2 and 4 kg ai ha-1 rates in August 1986 in a bo real forest. Prewinter concentrations of hexazinone in stems of trembl ing aspen, Saskatoon berry, and willow ranged from 0.02 to 0.05 mug-1 dry wt at 64 d after treatment (DAT). Absorption of hexazinone acceler ated during spring thaw (1987), and residues in foliage of several woo dy and herbaceous species peaked during May to July. Patterns of accum ulation of hexazinone and its metabolites varied with the species. Fol iar concentrations diminished significantly by the end of the first gr owing season in 1987 (372 DAT) and were undetectable or extremely low at the end of the second growing season in 1988 (707 DAT). Based on th e highest residue concentrations detected in several plant species, it is estimated that wildlife would ingest a maximum of 16, 28, and 24 m g of hexazinone, metabolite A, and metabolite B, respectively, for eve ry kg of dry matter consumed. Reported LD50 values suggest that applic ation of hexazinone at the 4 kg ai ha-1 rate or less poses no toxicolo gical threat to wildlife.