Pseudo toxicity abatement effect of norfloxacin and copper combined exposure on Caenorhabditis elegans

The coexistence of antibiotics and heavy metals may result in complex ecotoxicological effects on living or-ganisms. In this work, the combined toxic effects of norfloxacin (NOR) and copper (Cu) on Caenorhabditis elegans (C. elegans) were investigated due to the highly possible co-pollution tendency. The results indicated that locomotion behaviors (frequency of head thrash and body bend) of C. elegans were more sensitive as the exposure time of NOR or Cu prolonged. Meanwhile, the physiological indexes (locomotion behaviors, body length) of C. elegans were more sensitive to the combined pollution that with lower Cu dosage (0.0125 mu M), in prolonged exposure experiments. In addition, the toxic effects of NOR-Cu on physiological indexes of C. elegans seemed to be alleviated during prolonged exposure when Cu was 1.25 mu M. Similarly, the ROS production and apoptosis level almost unchanged with the addition of NOR compared with Cu (1.25 mu M) exposure groups, but both significantly higher than the control groups. Furthermore, compared with Cu (0.0125 mu M and 1.25 mu M) exposure experiments, the addition of NOR had resulted in the genetic expression decrease of hsp-16.1, hsp-16.2, hsp-16.48, and the oxidative stress in C. elegans seems to be alleviated. However, the significantly decreased of ape-1 and sod-3 expression indicated the disruption of ROS defense mechanism. The irregular change in ace-1 and ace-2