A human cell panel for evaluating safe application of nano-ZrO2/polymer composite in water remediation.

Nanomaterials, such as ZrO2 nanoparticles (ZrO2 NPs), are very effective in water remediation. However, the safety issues related to nanoparticle release and toxicity to humans remain to be resolved. Here we evaluated the cytotoxicity of ZrO2 NPs and their adducts with pollutants using a human cell panel containing stomach, intestine, liver and kidney cells. We found that different pollutants or ZrO2NP/pollutant adducts targeted cells from different organs, suggesting the necessity of a cell panel to model oral exposures. The cooperation of ZrO2 NPs and pollutants was quite complex, consisting of synergistic, antagonistic, or additive effects. For example, ZrO2 NPs enhanced the cytotoxicity of Pb2+ in GES-1 cells and of Pb2+, Cd2+ in FHC cells, while alleviating the toxicity of Pb2+ and As (III) in HepG2 and Hek293 cells. Our results also indicated that even concentrations of pollutants that meet the national standard, the ZrO2 NPs concentration should be kept below 17 µg/mL to avoid ZrO2 NP/pollutant adduct synergistic toxicity.

Sulfadiazine/ciprofloxacin promote opportunistic pathogens occurrence in bulk water of drinking water distribution systems.

Effects of sulfadiazine and ciprofloxacin on the occurrence of free-living and particle-associated opportunistic pathogens in bulk water of simulated drinking water distribution systems (DWDSs) were investigated. It was found that sulfadiazine and ciprofloxacin greatly promoted the occurrence of opportunistic pathogens including Pseudomonas aeruginosa, Legionella pneumophila, Mycobacterium avium and its broader genus Mycobacterium spp., as well as the amoebae Acanthamoeba spp. and Hartmanella vermiformis, in bulk water of DWDSs. Moreover, sulfadiazine and ciprofloxacin exhibited much stronger combined effects on the increase of these opportunistic pathogens. Based on the analysis of the antibiotic resistance genes (ARGs) and extracellular polymeric substances (EPS), it was verified that EPS production was increased by the antibiotic resistant bacteria arising from the effects of sulfadiazine/ciprofloxacin. The combined effects of sulfadiazine and ciprofloxacin induced the greatest increase of EPS production in DWDSs. Furthermore, the increased EPS with higher contents of proteins and secondary structure ß-sheet led to greater bacterial aggregation and adsorption. Meanwhile, large numbers of suspended particles were formed, increasing the chlorine-resistance capability, which was responsible for the enhancement of the particle-associated opportunistic pathogens in bulk water of DWDSs with sulfadiazine/ciprofloxacin. Therefore, sulfadiazine and ciprofloxacin promoted the occurrence of particle-associated opportunistic pathogens in bulk water of DWDSs due to the role of EPS produced by the bacteria with ARGs.