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Investigation of the toxic effects of herbicides on some selected microbial populations from soil

The toxic effect of herbicide on some selected microbial populations from soil was investigated. Soil samples were collected from two unpolluted designated fields of Chukwuemeka Odumegwu Ojukwu University and later polluted with herbicides at different application rates (0.1 %, 0.2 %, 0.5 %, 1 % and 5 %) and periods using spraying method. Standard chemical processes were used for determining physico-chemical parameters of the soil while isolation, enumerating the population of the microorganisms and identification of the isolates were determined using standard microbiological methods. The result revealed that the soil samples are slightly acidic, sandy clay loam type, lower organic carbon content, higher total nitrogen and phosphorus contents and moderate water holding capacity. The isolates Pseudomonas aeruginosa, Bacillus vallismottis, Aeromonas hydrophila and Enterobacter clocea were selected using selective media and identified. Pseudomonas aeruginosa and Bacillus vallismottis had the least (zero CFU/g) and maximum population counts (10 x 107 CFU/g) during glyphosate exposure while Pseudomonas aeruginosa and Enterobacter clocea had the least (zero CFU/g) and maximum population counts (2.50 x 107 CFU/g) during 2, 4 - D amine exposure for 15 days, respectively. Thus, the application of glyphosate and 2, 4 - D amine herbicides on the soil have resulted into lower counts of the selected microbial groups. The inhibitions of their growths are dependent on concentration and exposure period, although 2, 4 - D amine had more inhibition than the glyphosate herbicide.