ABSTRACT

This research work focuses on determining the impact of dichiorvos and chiorpyrifos on the microbial diversity of agricultural soil. The soil samples were obtained from an agricultural soil in Michael Okpara University of Agriculture, Umudike. Serial diffusions of the samples resulted in 22 isolates; 10 bacteria, 1 2 fungi. 5 each of both the bacterial and the fungal isolates were used for this study and were identified as Pro teus species, Bacillus species, Kk'bsiella species Psludomonas species, .4clinornyceles species and Fusarium species, Penicilliun species, Asjergillus species, Rhizopus species, Mucor species. The impact of the two pesticides was studied by employing susceptibility test using the disc diffusion method. Pure cultures of the isolates were subjected to 5 different concentrations of the pesticides; lOOtgfml, S0tg/ml, 25Ig/ml, l2.5.Lg/m1, 6.25ig/ml with 0tg/ml as the control concentration. The inhibition zone diameter of each of the isolates was obtained in millimeter. The result showed that the bacterial isolates were more susceptible to the two pesticides than the fungal isolates with the tolerance level order for dichiorvos being Kiebsiella species > Actinornyceles species> Proteus species> Bacillus species .> Pseudo,nona,s' species and that of chiorpyrifos being flue/I/us Species Kiebsiella species and Proteus SCCiCS < Acliiioinyceles species < Pseudonionas species. The order of maximum effect of the two pesticides on the isolates was 1 00igIm1 >50 rig/mI > 25tg/ml > 12.5 ig/ml > 6.25 tg/mI. Also the lowest concentration of the pesticides that inhibited the growth of the isolates was determined. This work revealed that the use of pesticides at higher concentrations could be detrimental to soil microorganisms especially soil bacteria which play essential role in bioremediation and maintenance of soil fertility.