Response of Soil Microflora to Pesticides - Pesticides: Evaluation of Environmental Pollution - page 251

and 12 mg/kg soil (Hua et al. 2009). Values of the average well color development (AWCD)
were significantly lower in comparison with the control, only within the first 2 weeks of
incubation and recovered till the end of the experiment (35 days), reaching the same or
extended values of AWCD as in the control. Also, no significant changes were observed for
all the values of the diversity index (H') (Hua et al. 2009).
An alteration of the catabolic profiles of the soil bacterial communities was also observed
in the soils exposed to the fungicide vinclozolin (Lupwayi et al. 2009b). The authors also
observed that combined fungicide and insecticide treatment had a different bacterial com-
munity structure compared with the control and single pesticide application. Analysis
of the Biolog data revealed that some substrates were utilized more extensively as com-
pared with others. The authors underlined that the measured bacterial functional poten-
tial showed shifts caused by fungicide and insecticide application that were not observed
by estimating such parameters as bacterial diversity or microbial biomass. Moreover, these
shifts can lead to successions in the microbial communities that could have long-term
effects on soil activity (Lupwayi et al. 2009b).
8.7 Conclusions
The varied results on the impact of pesticides on microbial number, activity, and diversity
indicated that it is difficult to precisely assess the overall influence of pesticides on soil
systems and microbe-mediated processes. Interactions between pesticides, soil, and soil
microorganisms are complex as many biotic and abiotic factors influence the final value of
the measured parameters. The impact of the applied pesticides on the microbial activity is
strongly correlated with the soil characteristics, pesticide type and its dose, exposure time,
and interactions between these factors. The field-rate pesticide dosages do not usually
have long-term adverse effects on the microbial activity. These effects are usually transient
and detected immediately after pesticide application. However, higher doses of pesticides
very often display a negative effect on the microbial activity, resulting in the alteration of
the biological balance of the soil processes.
Due to the high complexity and biodiversity of soil ecosystem, single-process tests do
not provide adequate data to predict the overall potential environmental hazards of the
pesticides. It seems that polyphasic approaches including measurements of numerous
parameters reflecting the functional and structural status of both culturable and noncul-
turable fractions of the microbial community should be used to assess the response of the
soil microorganisms to the pesticides.
References
Abd El-Mongy, M. and Abd El-Ghany, T. M. 2009. Field and laboratory studies for evaluating the
toxicity of the insecticide Reldan on soil fungi. Int. Biodeterior. Biodegradation 63: 383-388.
Abdell-Malek, A. Y., Moharram, A. M., Abder-Kader, M. I., and Omar, S. A. 1994. Effect of soil treat-
ment with the organophosphorus insecticide Profenofos on the fungal flora and some microbial
activities. Microbiol. Res. 149: 167-171.