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Aim: To investigate the response of Nitrosomonas and Nitrobacter species to organophosphate and pyrethroid pesticides.
Study Design: This study employs experimental design and statistical analysis of data and interpretation.
Place and Duration of Studies: Soil samples were obtained from University Farm, Rivers State University, Port Harcourt, Nigeria. Samples were transported to the microbiology laboratory of Rivers State University immediately for microbiological and toxicity testing. Pesticides was gotten No.4 Ignatius Ajuru University Road, St. John Campus, Aba Road Port Harcourt. The toxicity testing was done for the period of 28 days at room temperature.
Methodology: Standard microbiological techniques were used: toxicity testing procedures were carried out by preparing a stock culture of the pesticide based on manufactures directions (8 ml into 1000 ml of distilled water) from which the concentrations used for this research work were obtained 0%, 3.125%, 6.25%, 12.5%, 25% and 50% and tested on the soil samples for a period of 28 days. Samples were serially diluted and cultures were incubated at 35°C for 18 to 24 hours. LC50 was determined using SPSS version 2.0.
Results: The results indicate that logarithm mortality of Nitrosomonas and Nitrobacter species increases with increase toxicant concentration and exposure time for pyrethroid pesticide while decreases with increase toxicant concentration and exposure time for organophosphate pesticides. The median lethal concentration LC50 of the pesticides increases in the following order: (Note: the higher the LC50, the lower the toxic effect); pyrethroid pesticide on Nitrosomonas (53.1%) < organophosphate pesticide on Nitrosomona (47.9%), pyrethroid pesticide on Nitrobacter (53.5%) < organophosphate pesticide on Nitrobacter (47.5%).
Conclusion: The results revealed that different concentrations of the toxicants have both negative and positive effect on the survival rate of the test organisms which shows that the organophosphate pesticide can cause more harm to the environment affecting Nitrosomonas and Nitrobacter species that play vital functions in nutrient fixation in the soil environment. While pyrethroid pesticides at appropriate concentrations can stimulate the growth of these organisms there by increasing the rate of nutrient fixation in the soil environment. But also, when these toxicants are misapplied they can cause harm to humans that would consume the crops.