The tolerance ability of Nitrobacter and Nitrosomonas Sp carbon furan, chloropyrifos and cyahalothrin pesticides was investigated. This study employs experimental design and statistical analysis of data and interpretation. The toxicity testing procedures was carried out for a period of 28days, at room temperature. Standard microbiological techniques were used. Five (5) concentrations 3.125%, 6.25%, 12.5%, 25% and 50% were prepared from chlorpyrifos, carbonfuran and cyahalothrin pesticides. One hundred milliliter(100ml) of each concentration of pesticides were mixed with 1500g of soil inoculated with Nitrosomonas sp and Nitrobacter sp, using a uniform inoculum size of 10ml. The results of the effect of various concentrations of these pesticides on the survival rate of isolates were recorded after 1, 7, 14, 21 and 28days respectively. After day 1, at 50% concentration cyahalothrin had the highest survival rate of Nitrosomonas sp (110±2.0) while at 50% concentration carbonfuran had the lowest survival rate of Nitrosomonas sp (93 ±.0) after day1, Similar results were obtained after 7, 14, and 21days but after 28 days, at 50% concentration chloropyrifos had the lowest survival rate for Nitrosomonas sp.(94±0) Also at 50% cyahalothrin had the highest survival rate of Nitrobacter sp after day1(114±.50 ), while at 50% concentration, CarbonFuran had the lowest survival rate(95±1). cyahalothrin at 50% concentration had the highest survival rate after 7, 14, 21 and 28 days while CarbonFuran had the lowest survival rate after 7, 14, 21 and 28 days. The results revealed that different concentrations of the toxicants have both negative and positive effect on the survival rate of each test organisms. It was also observed that carbon furan pesticide and chloropyrifos were less tolerated by Nitrosomonas and Nitrobacter Species that plays vital roles in nutrient fixation in environment. Cyahalothrin pesticides , if applied at appropriate concentration, can stimulate the growth of these organisms, increasing the rate of nutrient fixation in the environment. However farmers should be alert and informed on the use of this pesticides in order to prevent adverse effect this could have on beneficial microbes. And also beneficial for the safety of foods for consumption.

Keywords: Cyahalothrin, Carbonfuran, pesticide, toxicity, Nitrosomonas and Nitrobacterspp., nitrification, Chloropyrifos