Study of Mechanisms Used by Algae to Decrease The Silver Toxicity in Aquatic Environment

Abstract

In the study SEM, EDS, TEM and UV-vis analysis were used to investigate the biosorption, bioaccumulation and bioprecipitation/
bioreduction of silver by freshwater green alga Parachlorella kessleri and to shed light on the reasons of biological silver nanoparticle
production. When dead biomass of P. kessleri was used for silver removal, majority of silver (75%) was removed within
2 min. Biosorption was probably the main mechanisms responsible for Ag+ ions removal from aqueous solutions. However, when
behaviour of living biomass in the presence of silver ions was studied, the decrease of silver concentration was slower (68% within
24 hours) with subsequent increase of silver concentration in the solution and extracellular formation of silver nanoparticles. The
formed AgNPs exhibited a lower toxicity against tested organisms. Algal cells probably used the formation of nanoparticles combined
with rapid biosorption as detoxification mechanisms against silver toxicity. Bioaccumulation inside the cells played only a
minor role in the detoxification process.