ACCESS – Innovative Approaches to undestand Complex microbial Communities for Eco-engineering the degradation of herbicides in Stressed agricultural Soils

FLOCCO, CG; CUADRADO, V; MERINI, LJ; GIULIETTI, AM

Rio de Janeiro - Brasil

Congreso; 2nd Mercosur Congress on Chemical Engineering – 4th Mercosur Congress on Process System Engineering – EMPROMER 2005.; 2005

Current agricultural practices involve the use of different kinds of herbicides and other agrochemicals; therefore this group of compounds is one of the most common and widespread in the environment. Organochlorine herbicides, such as 2,4-D (2,4-dichlorophenoxyacetic acid) and atrazine are widely used in South American agricultural fields. Although their half-life in soil is relatively short, the intensive use of these agrochemicals leads to diffuse contamination of non-target environments. For instance the contamination of groundwater and surface water threatens human health and the environment, due to the toxic properties of these compounds. The primary objective of the ACCESS project is to generate the knowledge base for the eco-engineering of sites polluted with atrazine, 2,4-D, and their derivatives. Such an eco-engineering approach requires focusing mainly on biological means of degradation, which is to study the role of microbial communities, including plant-microbe interactions. For this, microcosms of increasing complexity were designed and used to study the biodegradation of 2,4- D. The parameters assessed were: residual amounts of herbicide; total heterotrophic bacteria and 2,4-D degrading bacteria counts, as well as some physicochemical properties of the soil. We observed a rapid dissipation of the herbicide in all the treatments (total disappearance after 1 day) and the presence of 2,4- DCP (main metabolite), especially in planted microcosms. The total heterotrophic bacteria population in bulk soil was about 10 CFU/gr dry soil in every treatment and an increment of these numbers was observed after 2,4-D addition either for planted or unplanted microcosms (1 order of magnitude after 15 days). Regarding 2,4-D degrading bacteria, there was a 2 orders of magnitude increment in the size of this population after herbicide addition, from time 0 to day 15. This behavior was similar in planted and unplanted microcosms. A preliminary conclusion is that the herbicide addition increases the numbers of 2,4-D degrading and total bacteria counts, and that plants did not influence the degradation of 2,4-D by indigenous microflora. However, a more exhaustive study must be performed in order to correlate the herbicide dissipation with bacterial counts and to explore plant-bacteria interactions. Evaluating the capability of herbicide degradation by soil microbes and the factors that influence on it is a necessary step for future design of bioremediation strategies.