Hexazinone Residues in Surface and Groundwater at Two Sites Within Agassiz Provincial Forest, Manitoba, Canada

Studies were undertaken to determine the fate and effect of Velpar L (hexazinone) on aquatic systems following application to reforestation plantations. Surface water and groundwater were monitored for hexazinone residues. Conventional flask and microplate algal bioassays were conducted using Selanastrum capricornutum Printz, a Microtox bioassay was undertaken using Photobacterium phosphoreum and a S.O.S. chromotest was undertaken using Escherichia coli. Both lateral off-site migration and vertical migration of hexazinone were observed within the surficial aquifer at the study sites. Lateral movement was limited to the extent that less than 10 µg/L were detected in groundwater samples within 5 m of the application site. Hexazinone residues were detected in test wells for a period of approximately 1000 days following application. Hexazinone appeared to move downward in a relatively narrow band at a rate that was artificially enhanced during the process of groundwater sample extraction. Hexazinone residues were detected within ephemeral pools that formed on treated soils for a period of approximately 1000 days following application. Algal bioassay studies indicated inhibition of primary productivity would occur at relatively low hexazinone concentrations (22.5 µg/L). Velpar L was not mutagenic as evidenced by the S.O.S. chromotest and was relatively non-toxic as indicated by the Microtox bioassay.