Ecotoxicological assessment of doxycycline in aged pig manure using multispecies soil systems

This paper assesses the ecotoxicity of the antibiotic doxycycline in aged spiked pig manure using a multispecies soil system (MS 3) covering plants, earthworms and soil microorganisms. The study reproduced realistic exposure conditions, as well as higher exposure doses covering the uncertainty factors typically employed for covering interspecies variability. MS 3, consisting of columns of natural sieved soil assembled with earthworms and seeds from three plant species, were employed. Pig manure was spiked with doxycycline (75 or 7500 μg/ml), aged for 15 days under aerobic/anaerobic conditions and added on top of the soil columns (120 ml/column, equivalent to 220 kg N/ha). Water and doxycycline free manure were used as negative controls. Doxycycline (7500 μg/ml) solution was used as a positive control. No effects on plants or earthworms were observed. Significant effects on soil phosphatase activity, indicating effects on soil microorganisms, were observed at the highest exposure dose, affecting all soil layers in the doxycycline-solution-treated MS 3 (positive control) but only the top layer in the spiked pig manure system. Chemical analysis confirmed the different behavior of doxycycline in both systems (with and without manure) and those effects were observed in soil with measured concentrations over 1 mg/kg soil. The detection of doxycycline in leachates revealed a potential mobility. Leachate concentrations were similar for doxycycline solution and spiked manure treatments.