Abstract: Biodegradation of parathion methyl by Pseudomonas sp.(DLL-1)and its influencing factors in solution were studied in the laboratory.Results showed that when the population of DLL-1 bacteria was 10 ⁵ ml ^-1 in the solution,high rated biodegradation occurred.It reached 88.5% in 3 h.But the concentration of parathion methyl did not change much in the contrast test.The half time of degradation of parathion methyl was 2.84,0.685 and 1.43 h in the solutions with pH at 5.0, 7.0 and 9.0,respectively.Mechanism of the degradation of parathion methyl by DLL-1 bacteria was also studied.With the aid of GC-MS,IC and Ion Chromatography,intermediate products and final products of the degradation were determined. p Nitro phenol was the main intermediate product and could be further degraded into NO ₂ ^- and NO ₃ ^- .

Key words: pesticide, biodegradation in solution, Pseudomonas sp.(DLL-1)