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Cd2+ Toxicity to a green alga Chlamydomonas reinhardtii as influenced by its adsorption on TiO2 engineered nanoparticles.

Yang WW, Miao AJ, Yang LY - PLoS ONE (2012)

Bottom Line: A pseudo-first order kinetics was found for the time-related changes in the amount of Cd(2+) complexed with TiO(2)-ENs.Algal growth was less suppressed in treatments with comparable total Cd(2+) concentration but more TiO(2)-ENs.No detectable amount of TiO(2)-ENs was found to be associated with the algal cells.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, Jiangsu Province, China.

ABSTRACT
In the present study, Cd(2+) adsorption on polyacrylate-coated TiO(2) engineered nanoparticles (TiO(2)-ENs) and its effect on the bioavailability as well as toxicity of Cd(2+) to a green alga Chlamydomonas reinhardtii were investigated. TiO(2)-ENs could be well dispersed in the experimental medium and their pH(pzc) is approximately 2. There was a quick adsorption of Cd(2+) on TiO(2)-ENs and a steady state was reached within 30 min. A pseudo-first order kinetics was found for the time-related changes in the amount of Cd(2+) complexed with TiO(2)-ENs. At equilibrium, Cd(2+) adsorption followed the Langmuir isotherm with the maximum binding capacity 31.9, 177.1, and 242.2 mg/g when the TiO(2)-EN concentration was 1, 10, and 100 mg/l, respectively. On the other hand, Cd(2+) toxicity was alleviated in the presence of TiO(2)-ENs. Algal growth was less suppressed in treatments with comparable total Cd(2+) concentration but more TiO(2)-ENs. However, such toxicity difference disappeared and all the data points could be fitted to a single Logistic dose-response curve when cell growth inhibition was plotted against the free Cd(2+) concentration. No detectable amount of TiO(2)-ENs was found to be associated with the algal cells. Therefore, TiO(2)-ENs could reduce the free Cd(2+) concentration in the toxicity media, which further lowered its bioavailability and toxicity to C. reinhardtii.

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A representative transmission electron microscope (TEM) image (a) and the elemental composition of the interesting spots on it (b), as investigated with an energy dispersive X-ray (EDX) spectrometer, for a cell slice of C. reinhardtii exposed to 100 mg/l TiO2-ENs but without any addition of Cd2+.
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pone-0032300-g005: A representative transmission electron microscope (TEM) image (a) and the elemental composition of the interesting spots on it (b), as investigated with an energy dispersive X-ray (EDX) spectrometer, for a cell slice of C. reinhardtii exposed to 100 mg/l TiO2-ENs but without any addition of Cd2+.

Mentions: Potential TiO2-EN accumulation (including both cell surface adsorbed and intracellular accumulated ones) by C. reinhardtii was then quantified with GFAAS. As shown in Fig. 4, the bioaccumulated concentration of TiO2-ENs ([TiO2-ENs]cell) was in the range of 3.85–7.06 pg/cell for the second toxicity experiment in the presence of 100 mg/l TiO2-ENs. Although [TiO2-ENs]cell decreased slightly with the enhancement of [Cd2+]T, it was statistically insignificant (p>0.05). Additionally, a substantial accumulation of TiO2-ENs was only detected in the two highest TiO2-EN concentration treatments (30 and 100 mg/l) for the third toxicity test. Given that TiO2-ENs had a diameter of 46.6 nm on average, there should be 4.8×104–8.9×104 particles associated with a single algal cell as equivalent to approximately 1000 particles within each cell slice (100 nm thick) mounted on the TEM copper grid when 100 mg/l TiO2-ENs were applied. However, no TiO2-ENs were found either inside the cells or adsorbed on the cell surface after several cell slices were investigated with suspicious spots scanned by the EDX spectrometer (Fig. 5). It implies that most of the Ti signal determined by GFAAS might come from the additional TiO2-EN aggregates intercepted by the 1.2 µm membrane in the presence of C. reinhardtii, which cannot be subtracted with the control treatments containing the same concentrations of Cd2+ and TiO2-ENs but no algal cells. TiO2-ENs can attach to various algal species. The green alga P. subcapitata could even carry TiO2-ENs with weight 2.3 times higher than their own on the cell surface [14], [36], [37]. The adsorption of TiO2-ENs was found to be dependent on the pH of the medium and maximum adsorption was observed at pH = 5.5 (comparable to the pHpzc of bare TiO2-ENs) [38]. It implies that electrostatic attraction played a critical role in the interactions between TiO2-ENs and algal cells. As the pHpzc of TiO2-ENs we used is around 2, their surface was negatively charged in WCm (pH = 7.5) the same as that of the algal cells themselves. Therefore, a negligible amount of TiO2-ENs would be expected to be associated with C. reinhardtii unless other forces such as hydrogen bonding overrides the electrostatic and steric repulsion between the cells and ENs as observed by Schwab et al. [39]. The lack of direct contact between polyacrylate-coated TiO2-ENs might be another reason why they were less toxic than bare TiO2-ENs.


Cd2+ Toxicity to a green alga Chlamydomonas reinhardtii as influenced by its adsorption on TiO2 engineered nanoparticles.

Yang WW, Miao AJ, Yang LY - PLoS ONE (2012)

A representative transmission electron microscope (TEM) image (a) and the elemental composition of the interesting spots on it (b), as investigated with an energy dispersive X-ray (EDX) spectrometer, for a cell slice of C. reinhardtii exposed to 100 mg/l TiO2-ENs but without any addition of Cd2+.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3293805&req=5

pone-0032300-g005: A representative transmission electron microscope (TEM) image (a) and the elemental composition of the interesting spots on it (b), as investigated with an energy dispersive X-ray (EDX) spectrometer, for a cell slice of C. reinhardtii exposed to 100 mg/l TiO2-ENs but without any addition of Cd2+.
Mentions: Potential TiO2-EN accumulation (including both cell surface adsorbed and intracellular accumulated ones) by C. reinhardtii was then quantified with GFAAS. As shown in Fig. 4, the bioaccumulated concentration of TiO2-ENs ([TiO2-ENs]cell) was in the range of 3.85–7.06 pg/cell for the second toxicity experiment in the presence of 100 mg/l TiO2-ENs. Although [TiO2-ENs]cell decreased slightly with the enhancement of [Cd2+]T, it was statistically insignificant (p>0.05). Additionally, a substantial accumulation of TiO2-ENs was only detected in the two highest TiO2-EN concentration treatments (30 and 100 mg/l) for the third toxicity test. Given that TiO2-ENs had a diameter of 46.6 nm on average, there should be 4.8×104–8.9×104 particles associated with a single algal cell as equivalent to approximately 1000 particles within each cell slice (100 nm thick) mounted on the TEM copper grid when 100 mg/l TiO2-ENs were applied. However, no TiO2-ENs were found either inside the cells or adsorbed on the cell surface after several cell slices were investigated with suspicious spots scanned by the EDX spectrometer (Fig. 5). It implies that most of the Ti signal determined by GFAAS might come from the additional TiO2-EN aggregates intercepted by the 1.2 µm membrane in the presence of C. reinhardtii, which cannot be subtracted with the control treatments containing the same concentrations of Cd2+ and TiO2-ENs but no algal cells. TiO2-ENs can attach to various algal species. The green alga P. subcapitata could even carry TiO2-ENs with weight 2.3 times higher than their own on the cell surface [14], [36], [37]. The adsorption of TiO2-ENs was found to be dependent on the pH of the medium and maximum adsorption was observed at pH = 5.5 (comparable to the pHpzc of bare TiO2-ENs) [38]. It implies that electrostatic attraction played a critical role in the interactions between TiO2-ENs and algal cells. As the pHpzc of TiO2-ENs we used is around 2, their surface was negatively charged in WCm (pH = 7.5) the same as that of the algal cells themselves. Therefore, a negligible amount of TiO2-ENs would be expected to be associated with C. reinhardtii unless other forces such as hydrogen bonding overrides the electrostatic and steric repulsion between the cells and ENs as observed by Schwab et al. [39]. The lack of direct contact between polyacrylate-coated TiO2-ENs might be another reason why they were less toxic than bare TiO2-ENs.

Bottom Line: A pseudo-first order kinetics was found for the time-related changes in the amount of Cd(2+) complexed with TiO(2)-ENs.Algal growth was less suppressed in treatments with comparable total Cd(2+) concentration but more TiO(2)-ENs.No detectable amount of TiO(2)-ENs was found to be associated with the algal cells.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, Jiangsu Province, China.

ABSTRACT
In the present study, Cd(2+) adsorption on polyacrylate-coated TiO(2) engineered nanoparticles (TiO(2)-ENs) and its effect on the bioavailability as well as toxicity of Cd(2+) to a green alga Chlamydomonas reinhardtii were investigated. TiO(2)-ENs could be well dispersed in the experimental medium and their pH(pzc) is approximately 2. There was a quick adsorption of Cd(2+) on TiO(2)-ENs and a steady state was reached within 30 min. A pseudo-first order kinetics was found for the time-related changes in the amount of Cd(2+) complexed with TiO(2)-ENs. At equilibrium, Cd(2+) adsorption followed the Langmuir isotherm with the maximum binding capacity 31.9, 177.1, and 242.2 mg/g when the TiO(2)-EN concentration was 1, 10, and 100 mg/l, respectively. On the other hand, Cd(2+) toxicity was alleviated in the presence of TiO(2)-ENs. Algal growth was less suppressed in treatments with comparable total Cd(2+) concentration but more TiO(2)-ENs. However, such toxicity difference disappeared and all the data points could be fitted to a single Logistic dose-response curve when cell growth inhibition was plotted against the free Cd(2+) concentration. No detectable amount of TiO(2)-ENs was found to be associated with the algal cells. Therefore, TiO(2)-ENs could reduce the free Cd(2+) concentration in the toxicity media, which further lowered its bioavailability and toxicity to C. reinhardtii.

Show MeSH
Related in: MedlinePlus