The growing industrial, health care, pharmaceutical and water purification application of nanomaterials (NMs) has upraised concerns about their effect on the human health and environment. Whether the NM remains stable, dissolves with the release of ions, or forms larger aggregates, is crucial in finding out its possible fate. Herein, the stability of tannic acid/sodium citrate-stabilized Ag (nAg) and Silicon-Graphite flakes produced within the European FP7 project FutureNanoNeeds was investigated at various pH values, ionic strengths (IS) and in natural reservoir water. Furthermore, the effect of these NMs in deionised and reservoir water was assessed on the soil bacterium Pseudomonas putida. Three methods were applied in order to determine stability and behaviour of the NMs, namely differential centrifugal sedimentation analysis, UV-Vis spectrophotometry and zeta potential analysis. The kinetics of ion release and/or particle agglomeration was strongly pH- and IS- dependent which resulted in change of UV-Vis spectra, particle size distribution and particle zeta potential. Low pH caused fast dissolution of nAg whereas no significant effect was observed at high pH. In contrary, high pH strongly influenced the stability of Silicon-Graphite flakes. Moreover, it was found that the organic matter and ions present in the reservoir water significantly influenced both NMs causing their rapid agglomeration and/or dissolution. P. putida was affected by both NMs at concentration of 50 mg/L after 6h of exposure. Concentrations up to 10 mg/l of Silicon-Graphite did not cause any harm to P. putida in both deionised and reservoir water. Interestingly, the negative effect of nAg disappeared in deionised water after 24h and prevailed in reservoir water.Keywords: Stability; nanoparticle; nAg; Silicon-Graphite; environmental fate; Pseudomonas putida
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