Aerobic Metabolism of Flupropacil in Sandy Loam Soil

The aerobic soil metabolism of [14C]flupropacil (isopropyl 2‐chloro‐5‐(1,2,3,6‐tetrahydro‐3‐methyl‐2,6‐dioxo‐4‐trifluoromethylpyrimidin‐1‐yl)benzoate) was determined in microbially active, sieved (2‐mm) sandy loam soil with a soil moisture content of 75% at 1/3 bar. The soil was treated with [14C]flupropacil at 0·5 mg kg−1 (twice the field use rate) and placed in incubation flasks connected to a series of traps (50 g litre−1 NaOH, 0·5M H2SO4, ethylene glycol) and incubated at 25(±1)°C. Soil was sampled at 0, 3, 9, 20, 30, 48, 76, 120, 181 and 238 days of aerobic incubation. Volatiles were collected once every two weeks and on the day of soil sampling. Flupropacil metabolized with a half‐life of 79 days under aerobic conditions. The major metabolite was flupropacil acid which accounted for up to 69·1% of the initially applied radioactivity at Day 238. Each of the two minor metabolites detected at the end of the study accounted for less than 0·5%. One of the minor metabolites was identified as C4242 acid (2‐chloro‐5‐(1,2,3,6‐tetrahydro‐2,6‐dioxo‐4‐trifluoromethylpyrimidin‐1‐yl)benzoic acid). Only a negligible portion (less than 0·3%) of the applied flupropacil was mineralized to [14C]carbon dioxide. Extractable radioactivity ranged from 78·9% to 95·5%, with bound residues accounting for 3·2%–23·4%. The material balance ranged from 91·6% to 104·4%.