Bacteria nanoparticle toxicity testing : toward the use of original methods and complex matrices
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The development and use of engineered nanoparticles (NPs) has continuously expanded over the last two decades. Despite clear beneficial aspects of NPs, their extensive use and hardly regulated dissemination has raised concern regarding their potential adverse effects. Reports on the environmental release of NPs in wastes, waters, and wastewaters have emerged as well as ecotoxicity related information to a diverse range of model microorganisms (e.g. crustaceans, worms, algae, bacteria). However, in spite of growing knowledge in nanoecotoxicology there is limited evidence to draw conclusive statements about the toxicity and fate of NPs, especially in real matrices, in part due to a lack of appropriate methodologies. In this context, this work aimed to investigate the ecotoxicity of widely used and potentially antimicrobial inorganic NPs (Ag, ZnO, CuO, TiO2) to environmentally relevant bacteria (Pseudomonas putida) in various matrices (microbiological growth medium, artificial wastewater, real crude and final wastewaters). Complementary planktonic (i.e. using a luminescent switch-off bioreporter in a microtitre plate format) and biofilm (i.e. using mono and multi-species structures in flow-cell reactors) based assays were used. In addition, the implementation of microcantilever (μCT) and surface plasmon resonance imaging (SPRi) biosensor technologies were piloted. Toxicity of NPs was discussed across approaches (when applicable) in light of their physico-chemical characterisation (using dynamic light scattering, atomic absorption spectroscopy, and ultraviolet-visible spectrophotometry) in used matrices of exposure. This work provides both practical and fundamental insights about water/wastewater related ecotoxicology of NPs using bacteria. Overall outputs highlighted the suitability of original methods for testing of NPs in or with complex (i.e. real) materials and emphasised further the possible limited impact of NPs below the mg L-1 level to bacteria (as planktonic or biofilms) in the environment, especially with ageing of NPs (as reported with the Ag NPs), or considering the potential of recovery of bacterial structures (as shown with the biofilms). In addition, the workability of SPRi for testing of NPs was reported for the first time with bacteria, offering new opportunities of further real-time and high throughput biosensor based applications in nanoecotoxicology.