Potential Impact of Cypermethrin on Selected Groups of Soil Microorganisms

Document Type : Original Article

Authors

1 Department of Microbiology, University of Lagos, Lagos, Nigeria

2 Discipline of Microbiology, School of Life Sciences, University of Kwa-Zulu-Natal, Pietermaritzburg, 3201, South Africa

Abstract

Application
of cypermethrin as insecticide during agricultural practices is a global
concern due to its toxicity and potential accumulation of its metabolites in
the aquatic environment. A mesocosm plot of agricultural land (500 m2)
was demarcated and deliberately contaminated with cypermethrin to study its
impact on the autochthonous microorganisms. Potential effects of
3-phenoxybenzoic acid (3-PBA), a known suicide metabolite of cypermethrin, on
hydrolytic activities were also investigated by using fluorescein diacetate assay
(FDA). A significant increase in the abundance of total heterotrophic bacteria
from 3.55 x 106cfu g-1to 1.30 x 108cfu g-1in
12 weeks as against the control was induced by the insecticide in the mesocosm.
The number of starch hydrolysing bacteria increased after the second
insecticide treatment from 6.25 x 106cfu g-1to 2.70 x 107
cfu g-1in three weeks. However, there was no significant
increase in the microbial count of fungi, presumptive actinomycetes and
nitrogen fixing bacteria during the twelve weeks of experiment. The hydrolytic
activity of soil microorganisms was apparently inhibited insoil treated with different
concentration of 3-PBAthan in untreated soil. These results suggest that the
application of a commercial cypermethrin formulation increased the abundance of
selected soil microorganisms while3-PBA reduced the soil microbial hydrolytic
activity

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