Bioremediation of oxamyl in sandy soil using animal manures

The bioremediation of the nematicide oxamyl, applied at the recommended rate of 6 l ha−1 in sandy soil cultivated with tomato and amended with different animal manures at the recommended dose of 2.5 tons ha−1, was investigated. The experiment was conducted in a controlled environmental chamber under a 16-h photoperiod, with a light intensity of 300 μ Em−2 s−1 at 25 °C and relative humidity of 70 ± 5%. The remaining amount of oxamyl in soil was extracted after different time intervals based on the solid phase extraction (SPE) with methanol and then analyzed by HPLC. Only the peak corresponding to oxamyl was observed in the chromatogram and no intermediate could be detected. By the end of the experiment (28 days), the dissipation percentage of oxamyl reached about 99% in the case of bovine manure-amended soil. This rate of disappearance was 1.76 times higher than in unamended-soil, while poultry and sheep manures enhanced the dissipation rate by 1.52 and 1.44 times, respectively. The disappearance rate constants and half-life values of the compound were obtained from the exponential decay equations. The decomposition of oxamyl in the control followed the first order kinetics with t1/2 of about 26 days. On the other hand, a biphasic model was assumed to explore the disappearance of oxamyl in soil amended with different animal manures where the rate of disappearance in the first phase was faster than the second phase. This is clearly reflected in the half-life (t1/2) values for the first and second phases, where the t1/2 values of oxamyl ranged from 3.19 to 5.41 and 9.76 to 43.31 days, respectively. The results demonstrated that animal manures may offer an efficient, cheap, safe, and friendly bioremediator for pesticide-polluted soil.