Influência dos antimicrobianos oxitetraciclina e imazalil sobre a decomposição da macrófita aquática Egeria najas Planch
Abstract
The pharmaceutical compounds residues, especially antibiotics, are among the most
worrying emerging environmental contaminants. These residues potentially cause
negative effects on microorganisms that play an important role in the ecosystems
processes, dynamics and stability. The objective of this study was to evaluate the
oxytetracycline (OTC) (against bacterium) and imazalil (IMZ) (against fungus) action on
the aquatic macrophyte Egeria najas Planch decomposition in laboratory bioassays.
Microcosm experiments were performed in borosilicate flasks, in triplicate, containing
fragments of E. najas and water collected in Beija-Flor Reservoir, Jataí Ecological
Station, Luiz Antônio, São Paulo, Brazil. The experiments were performed as follows:
water and macrophyte; water with OTC and macrophyte; water with IMZ and
macrophyte; water with a mixture of OTC and IMZ and the macrophyte. The OTC decay
in water was also analyzed in microcosm without plant detritus addition. The experiments
were kept in the dark, at 21 °C, in two experimental conditions: aerobic and anaerobic.
Water pH and electrical conductivity of the systems were measured at the sampling times
(1, 3, 5, 15, 35 and 65 days after the onset of the experiments). Dissolved organic carbon
(DOC), total nitrogen (TN) and OTC were analyzed in the dissolved fraction. Bacterial
diversity was evaluated by Denaturing Gradient Gel Electrophoresis (DGGE) and
bacterial cell number counted by epifluorescence microscopy in the aqueous portion. A
first-order kinetic model was adopted to describe and compare macrophyte
decomposition at different treatments. The results showed that the refractory fraction
decomposition and the DOC mineralization were lower in experiments containing
antimicrobial OTC than in control experiments in aerobic conditions. Changes in
decomposition rates were not observed in anaerobic conditions. The OTC action was not
effective due to its adsorption to particulate plant material (between 61 and 65%).
According to the DGGE profiles obtained for the Bacteria Domain, the bacterial
community in bioassays has been modified throughout the experiment time and according
to the treatment. From these results, it was concluded that antimicrobial agents can alter
the rate of decomposition of detrital plant material in water, depending on environmental
conditions.