|Conn, Jeffery - FORMER USDA-ARS|
|Werdin, Nancy - FORMER USDA-ARS|
|Graham, J - ALASKA DIV FORESTRY|
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 30, 1996
Publication Date: N/A
Interpretive Summary: Long herbicide persistence in the high latitudes of the subarctic is due to cold soils. As herbicide persistence increases, the potential for herbicide leaching also increased. Experiments were conducted under subarctic conditions to determine the leaching of the herbicide metribuzin and its major breakdown products in two Alaska soils. Degradation of metribuzin appeared to proceed rapidly in the two subarctic soils and it did not readily leach downward. It also appears that breakdown products of metribuzin do not leach in appreciable quantity. The question remains, however, as to whether the bound residues will be slowly available in the future. Additional research is needed or long-term bioavailability of bound residues.
Technical Abstract: Persistence and leaching of **14C-metribuzin and metabolites were determined in Tanana and Beales silt loam soils under irrigated and non-irrigated conditions in the subarctic. Overall, dissipation of total **14C (metribuzin and metabolites) was slower in Tanana than Beales soil over the first 105 d, but by 468 d, the **14C remaining (51% of applied) did not differ between soils. Initial degradation of metribuzin was rapid in both soils. At 35 d after application 24% of applied metribuzin remained. At the end of the study, 5.0% of the applied metribuzin was still present. Metribuzin degraded less rapidly in Beales than Tanana soil. Unextractable residues accounted for the greatest amount of **14C remaining in the soils. Of the extractable metabolites, greater amounts of desamino-metribuzin were found in both soils than diketo-metribuzin or desamino-diketo-metribuzin. More water moved through the irrigated than non-irrigated soil as evidenced by bromide movement. Also, more **14C moved to 15-22.5 cm depth in the irrigated than in the non-irrigated soil, but less than 1% of applied **14C was detected below 22.5 cm for both soils and irrigation treatments. Rapid metribuzin degradation in combination with sorption processes minimized leaching of total metribuzin residues through these subarctic surface soils.