Abstract
The objective of this study was to evaluate the capability of the bacteria Bacillus safensis strain FO-36bT isolated from pesticide-polluted soil in degrading fenthion and temphos in mineral salt media (MSM). Fenthion and temphos were incubated with the isolated bacteria. Samples were drawn at 0, 3, 7, 14, and 30 days to analyze residual fenthion and temphos content with gas chromatography (GC) and high-performance liquid chromatography (HPLC), respectively. The loss of the initial pesticide concentration (400 mg/L) over time was determined and used to compute the half-lives using a biphasic model. Gas chromatography-mass spectrometry (GC-MS) was used to identify the major metabolites as well as to re-confirm the identity of starting material (fenthion). The results showed that the bacterium was still viable at the end of each incubation period. The biodegradation of fenthion and temphos followed a biphasic model. The half-lives of fenthion in the first and in the second phase were 0.29 and 3.69 days, respectively, whereas the corresponding values for temphos were 0.11 and 1.15 days. Only one metabolite "iso-fenthion" (O, S-dimethyl O-[3-methyl-4-(methylthio)phenyl] phosphorothioate) was detected in fenthion culture, while no metabolites were detected in temphos culture. Based on the half-lives, this bacterium was able to degrade temphos at a faster rate than fenthion. Key words: Biodegradation, fenthion, temphos, bacteria, pesticides-contaminated soil, Sudan.
Highlights
Fenthion and temphos are organophosphorus insecticides used as larvicides in fresh and polluted waters, under urban malaria schemes (UMS)
Pesticides polluted soil in Sudan was studied under mineral salt medium (MSM)
The bacteria reduced the half-life of fenthion to 0.29 days in the first phase (t1/2) and 3.69 days in the second phase (t1/2) while for temphos it was reduced to 0.11 days in the first and 1.15 days in the second phase
Summary
Fenthion and temphos are organophosphorus insecticides used as larvicides in fresh and polluted waters, under urban malaria schemes (UMS). The use of the same larvicide for a long-time may, cause resistance in mosquito larvae (Mittal et al, 1999). The frequent and extensive field use of temphos has caused the development of resistance in Chironomus yoshimatsui in the Kanda River, Tokyo (Ohno and Okamoto, 1980). Based on its high toxicity to birds, fenthion is used in various parts of the world for weaver bird control as well as for the control of pigeons around public buildings. It has contact action and it is readily absorbed through skin. Fenthion is classified by the U.S Environmental Protection Agency (EPA) as a Restricted Use Pesticide (RUP) due to the special handling warranted by its toxicity (VanDrieshe, 1985)
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