Captación de malatión en sedimentos artificiales y su efecto tóxico sobre Limnodrilus hoffmeisteri

The damage caused by xenobiotics on aquatic ecosystems depends on their biodisponibility and persistence as well as on the uptake capacity of the organisms. In this study the toxicity and bioconcentration factor of malathion (MA) spiked in artificial sediments of Limnodrilus hoffmeisteri were evaluated, in order to demonstrate the utility of this organism in biorremediation studies. All the studies were done in a water-artificial sediments system (sand, kaolinite and organic matter) contaminated with the insecticide. The lethal concentration fifty (LC₅₀) of MA at 96 hours was determined in the worm. For the sublethal toxicity and bioconcentration studies the tubifficids were intoxicated with LC₅₀/10 of the agrochemical. After 0, 6, 12, 24, 48, and 72 hours of exposure, the MA concentration was determined in sediment and worm by gas chromatography. In the organism also damaged biomarkers were measured: acetycholinesterase activity (AChA), lipid peroxidation level as well as protein and lipid concentration. The results showed that the system constituted by oligochaetes and sediment presented high MA uptake capacity due that its half lives (t_1/2) were of 121 and 29 hours respectively. MA had effect on AChA activity (96% of inhibition), lipid peroxidation level (increase of 88.2%), protein concentration (decrease until 95%) and lipids (decrease until 35.2%), at pesticide levels considered safe for agricultural products and food. However, we could observe that during the 6-24 h exposure, the maximum uptake of MA by the organism was of 83%. It is suggested that worm exposure to insecticide should not be longer than this time, since its bioconcentration capacity could be reduced. By the results obtained we conclude, that Limnodrilus hoffmeisteri is a good candidate to be used in biorremediation processes of aquatic systems polluted with MA.