Biodegradation of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA) in contaminated soil

Degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA) was investigated in inoculated non-contaminated and contaminated soil. In 28 days three bacterial isolates (Xanthomonas maltophilia SB5, Pseudomonas sp, SB9 and Rhodococcus globerulus SA(2)) degraded an average of 91% 2,4-D and 99% MCPA in a spiked non:contaminated soil in comparison with 48% of 2,4-D (SB5) and 61% of MCPA (SB5) in the contaminated soil. The addition of a combined NPK fertilizer significantly increased degradation of both herbicides in inoculated (2,4-D 79% vs. 48%; MCPA 81% vs. 61%) and non-inoculated (2,4-D 75% vs. 34%; MCPA 84% vs. 70%) soil. In contrast, the addition of lime,to raise the soil pH (from 6.7 to 7.5) to the optimum for SE, activity, inhibited degradation of 2,4-D and MCPA in both inoculated (2,4-D 24% vs. 48%; MCPA 41% vs. 61%) and non-inoculated (24-D 29% vs. 34%; MCPA 45% vs. 70%) soil. By 8 weeks, ja significant increase in herbicide degradation, in both inoculated and non-inoculated soil, was measured in soils amended with nitrogen only (NH4NO3:2,4-D 48%; MCPA 32%) or phosphorus only (NaHPO4 2H(2)O: 2,4-D 48%; MCPA 37%). However, there was no significant difference in the amount of herbicide degraded in potassium-amended (K2CO3: 2,4-D 25%; MCPA 14%) and the non-amended (2,4-D 23%; MCPA 15%) soils.