Leaching of the herbicide quinclorac in soil columns

The leaching behaviour of quinclorac was elucidated using soil columns. On top of each glass column packed with a rice paddy soil up to the 30 cm height were applied three different treatments of []quinclorac: quincloiac only (T-1), quinclorac adsorbed onto active carbon (T-2), and quinclorac adsorbed onto a mixture of active carbon and (T-3). Half of the columns were planted with rice plants for 17 weeks and half of them unplanted for comparison. Average amounts of -activity percolated from tile soil columns without rice plants in T-1, T-2, and T-3 were 81.1%, 27.8% and 48.0%, respectively, of tile originally applied , whereas those with rice plants grown were 36.8%, 9.6% and 11.0%, respectively, indicating that the leaching of []quinclorac was significantly affected by vegetation and by treatment with the adsorbents. The bioavailability of the herbicide to rice plants in T-1, T-2, and T-3 were 13.6%, 11.0% and 13.9%, respectively. The residue levels of quinclorac in the edible part of rice grains would be far less than the maximum residue limit (MRL, 0.5 ppm). After the leaching, the amounts of remaining in soil in with rice planting T-1, T-2, and T-3 were 36.3%, 73.7%, and 61.8%, whereas those without rice planting were 19.7%, 71.1%, and 52.3%, respectively. The balance sheets indicate that []quinclorac translocated to rice shoots would be lost by volatilization and/or in other ways in T-1 and T-3. The -activity partitioned into the aqueous phase of the leachates collected from all treatments was less than 7% of the total, but it increased gradually with time in the case of rice growing, suggesting tile formation of some polar degradation products.