Aim of this study was to describe the toxicity of a set of different commercially available silver nanoparticles (AgNPs) to the gram-negative bacterium Pseudomonas putida (growth inhibition assay according to ISO 10712) in order to contribute to their environmental hazard assessment. Different AgNP sizes and coatings were selected in order to analyze whether those characteristics are determinants of nanoparticle toxicity. Silver nitrate was tested for comparison. In general Pseudomonas putida reacted very sensitive towards the exposure to silver, with an EC 10 value of 0.058 μg/L for AgNO 3 and between 0.15 and 4.93 µg/L for the different AgNPs (EC 50 values 0.16 µg/L for AgNO3, resp. between 0.25 and 13.5 μg/L for AgNPs). The results indicate that the toxicity is driven by the Ag + ions, implying that an environmental hazard assessment for microorganisms based on total silver concentration and the assumption that AgNPs dissolve is sufficiently protective. The characterization of particle behavior as well as the total and dissolved silver content in the medium during the exposures was not possible due to the high sensitivity of Pseudomonas (test concentrations were well below detection limits), indicating the need for further development in the analytical domain.
Characterization of multiple biomarker responses using flow cytometry to improve environmental hazard assessment with the green microalgae Raphidocelis subcapitata
