Mineralization of Parathion in the Rice Rhizosphere

We studied CO(2) evolution from ring-labeled [2,6-C]parathion (O,O-diethyl-O-p-nitrophenyl phosphorothioate) in the rhizosphere of rice seedlings. The soil samples (nonflooded [60% water-holding capacity] and flooded) were treated first with technical parathion (20 mug/g) and then after 10 days with ring-labeled [C]parathion. In unplanted soil, less than 5.5% of the C in the parathion was evolved as CO(2) in 15 days under both flooded and nonflooded conditions. In soil planted with rice, 9.2% of the radiocarbon was evolved as CO(2) under nonflooded conditions, and 22.6% was evolved under flooded conditions. These results suggest that soil planted with rice permits significant ring cleavage, especially under flooded conditions.