Intracellular Silver Accumulation inChlamydomonas reinhardtiiupon Exposure to Carbonate Coated Silver Nanoparticles and Silver Nitrate

Abstract

The intracellular silver accumulation ({Ag}(in)) upon exposure to carbonate coated silver nanoparticles (AgNP, 0.5-10 μM, average diameter 29 nm) and silver nitrate (20-500 nM) was examined in the wild type and in the cell wall free mutant of the green alga Chlamydomonas reinhardtii at pH 7.5. The {Ag}(in) was measured over time up to 1 h after a wash procedure to remove silver ions (Ag(+)) and AgNP from the algal cell surface. The {Ag}(in) increased with increasing exposure time and with increasing AgNP and AgNO(3) concentrations in the exposure media, reaching steady-state concentrations between 10(-5) and 10(-3) mol L(cell)(-1). According to estimated kinetic parameters, high Ag(+) bioconcentration factors were calculated (>10(3) L L(cell)(-1)). Higher accumulation rate constants were assessed in the cell wall free mutant, indicating a protective role of the cell wall in limiting Ag(+) uptake. The bioavailability of AgNP was calculated to be low in both strains relative to Ag(+), suggesting that AgNP internalization across the cell membrane was limited.

Transformations of silver nanoparticles in wastewater effluents: links to Ag bioavailability

“…The possible causes for reduced bioavailability in a wastewater medium include i) the complexation of Ag + ions by organic/inorganic ligands that render them non-bioavailable and ii) the presence of numerous ions in a wastewater medium that compete for Ag biouptake (competition) [42][43][44]. In contrast with the majority of previous studies where bioaccumulation experiments were conducted in simple growth media [18][19][20], Ag + bioavailability in the wastewater was greatly reduced due to the complex nature of the medium. were not significantly different from 0 (one-tailed t-test; p<0.05) (Table S4).…”

“…Typically, ENMs released from household and industrial commodities find their way through waste disposal streams and into wastewater treatment plants (WWTPs) [8,19].…”

“…Upon their release into the wastewater systems, Ag NPs will be subject to different environmental forces and may be transformed into various chemical species, such as dissolved Ag species, Ag2O, Ag2S and AgCl [8,19,20]. One of the most important processes that govern Ag NP transformations is sulfidation.…”

“…Under anaerobic conditions, which are common in wastewater systems, the presence of high hydrogen sulfide concentrations are expected; the sulfides likely react with oxidized Ag to form more thermodynamically favourable Ag2S species [19]. Indeed, previous studies have shown that Ag NPs are converted to Ag2S NPs during their transport through WWTPs and that the sulfidation process may start even earlier-for example, in urban sewer systems prior to their arrival at WWTPs [19]. It has been suggested that the Ag NP sulfidation process may follow either a heterogeneous mechanism (above 0.8 µM of sulfide)…”

“…[16] and Miao et al [17] suggested that toxicity was directly attributed to the NPs, whereas Navarro et al [18] and Piccapietra et al [19] attributed the main toxicity of Ag NPs to the release of Ag + . There are also suggestions that Ag + and other dissolved Ag species could be generated locally at the biological interface following its interaction with Ag NPs [15,18].…”