Pesticide microbial degradation in periurban horticultural soil.

GISELLE QUEREJETA; ENRIQUE HUGHES; ANITA ZALTS; DIANA VULLO; JAVIER MONTSERRAT

Mar del Plata

Congreso; Congreso de la Sociedad Argentina de Microbiología General; 2012

Small agricultural activities surrounding cities (periurban agriculture) may have environmentally relevant impacts either in soil or biodiversity because of the use of pesticides. It has been observed in previous works that during the application of pesticides, up to a 50% of the product ends on soils. The objective of this work was to compare the degradative capacity of horticultural soils versus a non- productive soil and to study the influence of autochthonous microbial population on the fate of applied pesticides.Soil samples were taken from horticultural production units in Moreno district, Buenos Aires, Argentina, where the main crops are lettuce, broccoli, cauliflower and strawberries. As no significant differences were found in the biological and physico-chemical analysis of different sections of the field, a composite called “huerta” was made with samples from each productive section. Non-productive soil samples were chosen from an eucalyptus forest, situated near the field.About 50g of each sample were placed in pots (microcosms). Five pots were prepared for each of different exposure times: three replicas for pesticide degradation tests and the other two to check biological activity (microbial respiration) in presence or absence of pesticide. The products applied were: Trigermin 0.044% v/v (trifluralin), Sumilex 0.040%p/v (procymidone) and Lorsban 0.0062v/v (chlorpyrifos). Microcosms were incubated for 40 days at room temperature in the dark, following different parameters from T0 (0h: before product addition) to T9 (768 h.). Pesticide quantification was carried out by GC-ECD after extraction with ciclohexane:acetone (1:1). Total heterotrophs were evaluated by CFU/g soil determination after 48h at 32ºC. In parallel, an enrichment and isolation of pesticide degraders was performed in M9 medium (g/L: K2HPO4 7.3, KH2PO4 3.0, NH4Cl 1.0, MgSO4 0.1202, CaCl2.2H2O 0.55) supplemented with 1% v/v of commercial products.Nine isolates were preliminary characterized by biochemical tests resulting of the Pseudomonas genus.A high degradative capacity of productive soil was found as an exponential decrease of pesticide concentrations with time, while the initial pesticide amount remained constant in the non-productive soil.  These results were consistent with two facts: 1. the CFU/g decreased with time in the non-productive soil, compared to the constant CFU/g counts obtained in the productive soil and 2. almost all isolates came from the horticultural soil. This result evidenced that microbial population of the horticultural soil is adapted to pesticide treatments. Deeper studies will be performed in future to optimize pesticide degradation in productive soils as an initial way to their restoration, taking into account that these periurban areas have a long time on pesticide utilization.