Tolerance of Nitrosomonas spp to Carbofuran and Cyhalothrin Pesticides in the Soil of Teaching and Research Farm Gidan Kwano Minna, Niger State

Abstract

The tolerance of Nitrosomonas spp to Carbofuran and Cyahalothrin Pesticides was investigated by collecting soil samples from a portion of the Teaching and Research farm of the Federal University of Technology, Minna where there was no history of pesticide application. The Soil collected was taken to Soil Science and Land Management Microbiology laboratory and subjected to toxicity testing for a period of 21 days, at room temperature. Pesticide concentration of 0.00%, 3.125%, 6.25%, 12.5%, 25% and 50% were prepared by transferring 0.00ml, 3.125ml, 6.25ml, 12.5ml, 25ml and 50ml of stock solution into 100ml, 96.8ml, 93.75ml, 87.5ml, 75ml and 50ml of sterile distilled water respectively. Part of the soil was sterilized at 121oC for 15minutes with the autoclave followed by the filling of the pots with 1.5 kg of sterilized soil, and watering before inoculating with 10mls of nitrosomonas per pot and incubating for 1, 7, 14 and 21 days at 28oC. From the treated pots and at every incubation interval, 1g of soil was taken and diluted serially to achieve 10-3 dilution level. From 10-3dilution, 1ml was plated and incubated for 4 days at 28oC. Result obtained were interpreted using Pollution/toxicity biomonitoring evaluation chart and it indicated that logarithm mortality of nitrosomonas species increased with increase in toxicant concentration and exposure time to cyahalothrin pesticide while decrease in nitrosomonas population was observed with increased toxicant concentration and exposure time to carbofuran pesticide. The median lethal concentration (LC50) of cyahalothrin pesticide on nitrosomonas was 100% indicating that effect of cyahalothrin on nitrosomonas was mild. Conversely, the median lethal concentration (LC50) of carbofuran pesticide on nitrosomonas was 16% implying that its effect on nitrosomonas was toxic.