Biodegradation of methyl parathion in the presence of goethite: The effect of Pseudomonas sp. Z1 adhesion

• We studied the biodegradation of methyl parathion in the presence of goethite.
• The interactions of degrading bacteria and the pesticide with goethite were analyzed.
• Degradation of methyl parathion was stimulated at low concentration but inhibited at higher concentration of goethite.
• Goethite attached on the outer surface of bacteria influenced the biodegradation process.

In this research, the influence of goethite on biodegradation kinetic of methyl parathion was investigated in the presence of Pseudomonas sp. Z1. Semipermeable membrane experiments were performed to demonstrate the role of adhesion of degrading bacteria to surface of goethite in biodegradation of methyl parathion. Sorption of methyl parathion and bacteria onto goethite particles were also measured to assess the distribution of methyl parathion and bacteria between water and goethite surface. The first-order degradation rate constant of methyl parathion in different concentrations of goethite was in the order of 0.1 g L−1 > 0.01 g L−1 > 0 g L−1 > 1 g L−1 > 20 g L−1, suggesting the presence of low concentrations of goethite accelerated the biodegradation of methyl parathion and high concentrations of goethite inhibited this biodegradation process. According to the result of semipermeable membrane experiment, when no bacterial attachment occurred in the system, the promotive effect of 0.1 g L−1 goethite for microbial degradation was disappeared and the inhibition effect of 20 g L−1 goethite increased. The results clearly demonstrated that the adhesion of bacteria to goethite was beneficial to the biodegradation of methyl parathion. The information obtained is of fundamental significance for the understanding of microbial degradation of organic pollution in soil.