The role of size and protein shells in the toxicity to algal photosynthesis induced by ionic silver delivered from silver nanoparticles

• Published in: The Science of the total environment Vol. 692; pp. 233 - 239
• Main Authors: Salas, Patricia, Odzak, Niksa, Echegoyen, Yolanda, Kägi, Ralf, Sancho, M. Carmen, Navarro, Enrique
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 20.11.2019
• Subjects: Algal photosynthesis; Bioavailability; Biological Availability; Casein; Chlamydomonas reinhardtii - drug effects; Chlamydomonas reinhardtii - metabolism; Cysteine - administration & dosage; Dose-Response Relationship, Drug; Ionic silver; Ions - adverse effects; Metal Nanoparticles - adverse effects; Photosynthesis - drug effects; Protective Agents - administration & dosage; Protein shell; Silver - adverse effects; Silver nanoparticles; Bioavailability; Protein shell; Casein; Algal photosynthesis; Silver nanoparticles; Ionic silver
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2019.07.237

Because of their biocide properties, silver nanoparticles (AgNPs) are present in numerous consumer products. The biocidal properties of AgNPs are due to both the interactions between AgNP and cell membranes and the release of dissolved silver (Ag+). Recent studies emphasized the role of different nanoparticle coatings in complexing and storing Ag+. In this study, the availability of dissolved silver in the presence of algae was assessed for three AgNPs with different silver contents (59%, 34% and 7% of total Ag), silver core sizes and casein shell thicknesses. The impact of ionic silver on the photosynthetic yield of Chlamydomonas reinhardtii was used as a proxy to estimate the amount of ionic silver toxically active during in vivo assays. The results showed that cysteine, a strong silver ligand, mitigated the toxicity of AgNPs in all cases, demonstrating the key role of Ag+ in this toxicity. The results showed that the AgNPs presenting an intermediate level of silver (34%) were 10 times more effective in terms of total mass (EC50 ten times smaller) than those presenting more (59%) or less (7%) silver. The higher toxicity was due to the higher release of Ag+ under biotic conditions due to the high surface/mass ratio of the nanoparticle silver core. Protein shells played a minor role in altering the availability of Ag+, probably acting as intermediate reservoirs. This study highlighted the utility of a very sensitive biological endpoint (i.e., algal photosynthesis) for the optimization of ionic silver delivery by nanomaterials. [Display omitted] •The Ag soluble is the main responsible for the biocidal activity of AgNPs.•There is difficult to assess the Ag bioavailable from AgNPs at biological interfaces.•Algal photosynthesis may be used a as a sensible bioavailable-Ag sensor.•The protein shells and the surface of AgNPs determine the amount of bioavailable Ag.