Bioaccumulation and Effects of CdTe/CdS Quantum Dots on Chlamydomonas reinhardtii – Nanoparticles or the Free Ions?

Abstract

In order to properly assess the environmental risk of engineered nanoparticles (ENP), it is necessary to determine their fate (including dissolution, aggregation, and bioaccumulation) under representative environmental conditions. CdTe/CdS quantum dots (QD), such as those used in medical imaging, are known to release Cd(2+) due (mainly) to the dissolution of their outer shell. In this study, Chlamydomonas reinhardtii was exposed to either a soluble Cd salt or QD at similar concentrations of total Cd. Free Cd concentrations were measured using the Absence of Gradients and Nernstian Equilibrium Stripping technique. QD dissolution increased with decreasing pH and with increasing QD concentration. When exposed to QD, bioaccumulation was largely accounted for by dissolved Cd. Nonetheless, QD were shown to be taken up by the cells and to provoke unique biological effects. Whole transcriptome screening using RNA-Seq analysis showed that the free Cd and the QD had distinctly different biological effects.

Transcriptome Sequencing (RNA-seq) Analysis of the Effects of Metal Nanoparticle Exposure on the Transcriptome of Chlamydomonas reinhardtii

“…In order to ensure that the exposure conditions elicited a response while minimizing secondary effects and lethality, conditions were selected by considering prior reports of their toxicological effects for nAg (31), nTiO 2 (1), nZnO (32), and QDs (33). The physicochemical properties and effects of the NPs change following their aggregation (17,34), dissolution (12,20,70), or coating with biological substances (e.g., proteins [35]), since these parameters affect the interfacial properties, including the rates of surface-mediated reactions, dissolution, redox reactions, and generation of ROS (36). Therefore, the sizes of the NPs were quantified in the exposure medium (Table 1).…”

“…C. reinhardtii was added at a cell density of 1 cm 2 ml Ϫ1 to five flasks (300 ml) containing the exposure medium and one of the following: control (no NP), 1 mg liter Ϫ1 nTiO 2 , 1 mg liter Ϫ1 nZnO, 1 mg liter Ϫ1 nAg, or 0.125 mg liter Ϫ1 QDs. Preliminary experiments showed that the lower concentration of QDs still induced significant changes at the transcriptomic level (12). Cell densities, sizes, and surface distributions were determined using a Coulter Multisizer 3 particle counter (50-m orifice; Coulter Electronics).…”

“…This eukaryotic green alga is widely used as a model organism for metal homeostasis, metal-induced stress responses, and ecotoxicology, and it is increasingly being subjected to transcriptome profiling (12)(13)(14)(15) 2 has a worldwide production of up to 10,000 metric tons/year, and about 1,000 tons of nZnO and nAg are produced yearly, whereas QD production does not exceed 10 metric tons/year (16). RNA-seq was used to characterize the transcriptomic effects of four different metal-based NPs in order to determine (i) their physiological effects on C. reinhardtii, (ii) how cells respond to these effects, and (iii) the degrees of similarity of the effects of the different NPs.…”

Stability of core/shell quantum dots—role of pH and small organic ligands

“…CdSe, CdTe, and CdS coated with hydrophilic deprotonated thiol ligands were shown to be unstable at a relatively low pH range, between 2 and 7, because of the dissociation of the QD-ligand coordinating bonds from the QD surface (Aldana et al 2001(Aldana et al , 2005. Studies on QD-organism interactions also have indicated that QD toxicity may at least be partially attributed to the release of toxic ions (Kloepfer et al 2003;Mahendra et al 2008;Priester et al 2009;Aruguete et al 2010;Domingos et al 2011). Aruguete et al (2010) observed an increase of the released Cd from CdSe/CdS QD when incubated in the Pseudomonas aeruginosa growth medium in presence of nitrilotriacetic acid (NTA), which was explained by the NTA ability to chelate Cd ion.…”

The Effect of DNA and Sodium Cholate Dispersed Single-Walled Carbon Nanotubes on the Green Algae Chlamydomonas reinhardtii

“…Work using this model organism has shown toxicity and uptake of silver nanoparticles, quantum dots, and titanium dioxide nanoparticles [15][16][17]. Additionally, C. reinhardtii has been used in finding toxic effects of SWCNT poorly suspended in solution with no surfactant [18].…”