Abstract:

To evaluate the safety of oxadiargyl in paddy field, a field experiment was conducted to study the residues and degradation dynamics of oxadiargyl in rice and environment. The residues of rice shell samples were extracted with dichloromethane, and paddy water, soil, rice plant and brown rice samples were extracted with acetonitrile, the samples were cleaned up by glass chromatographic column and determined by GC-ECD. The results showed that when the concentration of oxadiargyl in paddy water, soil, rice plant, rice shell and brown rice samples ranged from 0.01 to 1.0 mg/kg, the average recovery was 82.4%-99.6%, with the variation coefficient of 1.62%-7.56%, the minimum detectable mass fraction (LOQs) was 0.01 mg/kg. Degradation of oxadiargyl in paddy water, soil and rice plant conformed to chemical kinetic equation C_t=C_oe^kt, with the half-life of 2.4-5.4, 10.0-12.7 and 2.4-5.8 days, respectively. Oxadiargyl was applied at the dosage of 112.5 and 168.75 g a.i./hm², each for once, the final residue of oxadiargyl in soil, rice plant, rice shell and brown rice were all below the detection limits. The results reveal that the residue of oxadiargyl in brown rice is less than the MRL set by China and EU.

Key words: oxadiargyl, residue, dissipation, rice, rice field, GC