The aim of this research is to determine the tolerance of Pseudomonas species and Bacillus species to Chloropyrifos and Cyahalothrin pesticides. The study area was the Rivers State University school farm, Faculty of Agriculture, Rivers State, Nigeria. The University farm is a large area of land that specializes in fish farming, livestock farming, poultry farming and all types of agricultural product farming. The university farm has also been used by students for research purposes. Standard microbiological procedures were used; Nutrient agar was prepared by weighing 28g of nutrient agar into 1000ml of distilled water in Erlenmeyer flask. The medium was sterilized at 121ºC  for 15 minutes using the autoclave at 15psi. centrimide agar was prepared by weighing 45.3g of the agar and measuring 10ml of glycerol in 990ml of distilled water. The medium was heated with frequent agitation and boiled to completely dissolve the medium before autoclaving at 121ºC for 15 minutes. Toxicity testing procedures were carried out by preparing a stock culture of the pesticide based on directions (8ml into 1000ml of distilled water) from which the concentrations used for this research was obtained 0%, 3.125%, 6.25%, 12.5%, 25% and 50% and tested on the soil sample for a period of 28 days. Samples were serially diluted and cultures were incubated at 35⁰C for 18 to 24 hours. LC₅₀ was determined using SPSS version 2.0. Acute toxicity analysis was carried on pesticides (Chlorpyrifos and Cyahalothrin) in soil using Bacillus and Pseudomonas species as bio indicators. The toxicity results obtained in this study revealed that the pesticides (Chloropyrifos and Cyahalothrin) were toxic to the microorganisms. The results of median lethal concentration (LC₅₀) of the pesticides to the bio indicators (Pseudomonas and Bacillus species) which were determined by subtracting the value of the highest concentration used (50%) from the sum of concentration difference, multiplied by mean percentage mortality and divided by the control (100). Results showed that Cyahalothrin exposed to Pseudomonas species for 28 days had 30.99%, Chlorpyrifos exposed to Pseudomonas species had 12.83 %, Cyahalothrin exposed to Bacillus species had 12.77%, Chloropyrifos exposed to Bacillus species had 10.77 % (Tables 4.2b to 4.5b and Figure 4.5.). This indicated that Chlorpyrifos exposed to Bacillus species had the lowest median lethal concentration (10.77%) and the highest toxic effect while Cyahalothrin exposed to Pseudomonas species had the highest median lethal concentration (LC₅₀) and the lowest toxic effect according to the report of Williams and Dilosi (2018); Kpormon and Douglas (2018). The results obtained in this research work revealed that pesticides (Chlorpyrifos and Cyahalothrin) have the ability to inhibit biological processes that are mediated by key environmental microorganisms such as Bacillus and Pseudomonas species etc in soil. Due to the   effect observed on the survival rate of these organisms in this study, it indicates that these pesticides are capable of causing serious environmental pollution which will not only affect the microorganisms and their functions but also the abiotic components of the environment.

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