Persistence, mobility and degradation of hexazinone in forest silt loam soils

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Abstract
This study reports the persistence, degradation, vertical leaching and lateral movement of hexazinone, 3‐cyclohexyl‐6‐(di‐methylamino)‐1‐methyl‐1,3,5‐triazine‐2,4(1H,3H)‐dione, in a white spruce plantation treated at 4.3 kg active ingredient (ai)/ha by a helicopter equipped with a MICROFOIL boom. Soils were monitored for 104 days after treatment for residues of hexazinone and its metabolites A, 3‐(4‐hydroxycyclohexyl)‐6‐(dimethylamino)‐1‐methyl‐1,3,5‐triazine‐2,4(1H,3H)‐dione and B, 3‐cyclohexyl‐6‐(methylamino) ‐1‐methyl‐1,3,5‐triazine‐2,4(1H,3H)‐dione. Soil at 3 depths, including a surface organic, and 0–15 cm and 15–30 cm mineral layers, were collected and analysed before and at 9, 23, 55, 104 days after application. Sixty six percent (66?) of hexazinone was degraded and dissipated at the end of 104‐day monitoring, decreasing from 7.12 ug/g (9 days) to 2.09 ug/g (104 days). The higher amount of metabolite‐? (30–50? of hexazinone detected) compared to metabolite‐B (0–12?) indicated higher hydroxylation than demethyl‐ation activity in the silt loam soil. Leaching of hexazinone and its metabolites from the surface organic to the underlying 0–15 cm mineral soil layer was found only in the 55‐day sample. No residues of hexazinone and its metabolites were detected at deeper (15–30 cm) soil horizons. The lateral movement was not detected at distances of 20 m and 40 m outside of the treated block on a 5–10? slope.