Shape-Dependent Transformation and Translocation of Ceria

Aug 29, 2017 - The association of physicochemical properties of CeO2-NPs (CeO2 nanoparticles) per se with their transformation is not well understood...
0 downloads 9 Views 1MB Size
Subscriber access provided by MT SINAI SCH OF MED

Letter

Shape-dependent Transformation and Translocation of Ceria Nanoparticles in Cucumber Plants Peng Zhang, Changjian Xie, Yuhui Ma, Xiao He, Zhiyong Zhang, Yayun Ding, Lirong Zheng, and Jing Zhang Environ. Sci. Technol. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.estlett.7b00359 • Publication Date (Web): 29 Aug 2017 Downloaded from http://pubs.acs.org on August 30, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Environmental Science & Technology Letters is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 16

Environmental Science & Technology Letters

1

Shape-dependent Transformation and Translocation of Ceria Nanoparticles in

2

Cucumber Plants

3

Peng Zhang,†,* Changjian Xie,† Yuhui Ma,† Xiao He,† Zhiyong Zhang,†,* Yayun Ding,† Lirong Zheng,#

4

Jing Zhang#†

5



6

Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China;

7

#

8

Chinese Academy of Sciences, Beijing 100049, China;

Key Laboratory for Biological Effects of Nanomaterials and Nanosafety,

Beijing Synchrotron Radiation Facility, Institute of High Energy Physics,

9 10

* Corresponding author.

11

E-mail addresses: [email protected]; [email protected]

12

Tel: +86-10-88233215; Fax: +86-10-88235294

13 14 15 16 17 18 19 20 21 22

1

ACS Paragon Plus Environment

Environmental Science & Technology Letters

Page 2 of 16

23

Abstract

24

The association of physicochemical properties of CeO2-NPs per se with their transformation is not well

25

understood. This study for the first time compared the translocation and transformation of octahedral,

26

cubic, rod, and irregular shaped CeO2-NPs in hydroponic cucumber plants. Cerium contents in roots

27

were close between different treatments, while shoots accumulated the highest (153 mg/kg) amount of

28

Ce in Rod like CeO2-NPs treatments. TEM and X-ray absorption near edge spectroscopy (XANES)

29

results all show that rod CeO2-NPs transformed faster and more than other CeO2-NPs, with nearly 40%

30

of Ce was in the form of Ce(III) species in roots (CePO4) and shoots (Ce carboxylates). Rod like CeO2-

31

NPs transformed to a higher degree than the other CeO2-NPs in solutions simulating the plant exudates,

32

indicating that rod like CeO2-NPs have the highest chemical reactivity. These results suggest that the

33

intrinsically different chemical reactivity of differently shaped CeO2-NPs resulted in their different

34

transformation and translocation capacity in plants. This study provides new insight into the

35

understanding of plant-NPs interaction, highlighting the significance of nanoparticle shape in assessing

36

their environmental behavior and impacts. We suggest that the shape influence should be also considered

37

for other nanomaterials and systems to accurately understanding the nano-bio interactions.

38 39 40 41 42 43 44 45

2

ACS Paragon Plus Environment

Page 3 of 16

Environmental Science & Technology Letters

46

Introduction

47

CeO2-NPs are of great interest for industrial, agricultural, and biomedical application due to their unique

48

redox-cycle property between oxidation states Ce(III) and Ce(IV).1,2,3 It was estimated that the global

49

production of CeO2-NPs will be 1000 tons per year.4 The release of CeO2-NPs to the environment is

50

inevitable which may affect the biota and environment.5,6 Exposure modeling has suggested that

51

terrestrial systems are important sinks for nanomaterials (NMs).7 As a result, NMs will interact with

52

plants, and may accumulate in plants and pose adverse effects to plant growth.6 Furthermore, transfer of

53

NMs from plants to high-trophic level organisms through food chain is also possible.8,9

54

CeO2-NPs were previously considered to be stable in the environment; however, recent studies have

55

shown that CeO2-NPs are prone to transform in plants, releasing Ce3+ ions and further transforming into

56

CePO4 or Ce carboxylates.10 Consequently, Ce will accumulate in plants in various forms rather than

57

only CeO2, and the transformation products may or at least partially contribute to the toxic effects of

58

CeO2.11

59

Transformation of CeO2-NPs is highly affected by their surroundings. CeO2-NPs can release

60

significant amount of Ce3+ ions in plant-free growth media depending on the media composition.12

61

Presence of organic matters such as arabic gum prevent agglomeration of CeO2-NPs thus maintain a

62

large reaction surface, which could promote the dissolution.12 Organic ligands such as EDTA and citrate

63

promote the dissolution by complexation with the surface Ce(III).10,12 Reducing substances such as

64

Fe(II) and ascorbic acids (Vc) can reduce the Ce(IV) to Ce(III) and release Ce3+.10,12 Plant root exudates

65

containing organic acids, reducing sugars and phenols promote the dissolution and reduction of CeO2-

66

NPs.10

67

Physicochemical properties of NMs also have significant impacts on their transformation. It was

68

reported that CeO2-NPs with smaller size released more Ce3+ ions in Lactuca plant roots.11 Citrate-

3

ACS Paragon Plus Environment

Environmental Science & Technology Letters

Page 4 of 16

69

functionalized CeO2-NPs transformed less than pristine CeO2-NPs in activated sludge reactor due to that

70

citrate functionalization may act as a barrier against the interaction of CeO2-NPs with bacteria.13

71

CeO2-NPs are usually manipulated into different shapes to achieve high catalytic capacity.14 However,

72

how shape of CeO2-NPs influence their transformation has not been studied. In fact, studies on other

73

NMs have shown that shape discrepancy may result in different biological effects and behavior. Fan et

74

al. found that octahedral Cu2O-NPs induced more severe oxidative stress to Daphnia magna than cubic

75

Cu2O-NPs.15 Oh et al. found that the viability of human lung fibroblast (IMR90) and mouse alveolar

76

macrophage (J774A.1) cells treated with poly(3,4-ethylenedioxythiophene) (PEDT) nanomaterials with

77

aspect ratio of 1.3 was nearly 20% less than that treated with PEDT with aspect ratio of 4.5.16 Syu at al.

78

found that decahedral silver NPs promoted Arabidopsis root growth, while spherical silver NPs showed

79

no effects.17 All these studies suggest that shape is a critical factor that should be considered when

80

assessing the environmental risk and safety of NMs.

81

Here, we exposed hydroponic cucumber plants to octahedral, cubic, rod-like, and commercial

82

irregularly-shaped CeO2-NPs, and compared their transformation and uptake in plants. The goal of this

83

study was to provide a deep insight into the behavior and fate of CeO2-NPs in plants and the link with

84

their physicochemical properties, and provide basis for safer design of CeO2-NPs.

85 86

Experimental

87

Synthesis and characterization of CeO2-NPs

88

All the chemicals used were of analytical purity. Octahedral CeO2-NPs (O-CeO2-NPs) was synthesized

89

by a precipitation method. Cubic and rod like CeO2-NPs (C-CeO2-NPs and R-CeO2-NPs) were

90

synthesized by hydrothermal methods. See details of CeO2-NPs syntheses in SI, Section 1, 1.1.

91

Commercial CeO2-NPs (S-CeO2-NPs) were purchased from Sigma-Aldrich. Purity of the nanoparticles

4

ACS Paragon Plus Environment

Page 5 of 16

Environmental Science & Technology Letters

92

was determined by ICP-MS. Primary particle sizes and morphology were determined by TEM (JEM

93

200CX, Japan). Zeta potential and hydrodynamic sizes of CeO2 NPs were analyzed by Zetasizer Nano

94

ZS90 (Malvern, UK).

95

Seedling culture and CeO2-NPs application

96

Cucumber seeds were purchased from Chinese Academy of Agricultural Sciences. Seeds were sterilized,

97

germinated and transferred into 250 mL beakers, and allowed to grow in 1/4 Hoagland solutions for 10

98

days in an artificial climate chamber. Each seedling was then exposed to 100 ml 2000 mg/L CeO2-NPs

99

suspensions in nutrient solutions. After 14 days, the seedlings were harvested for further analyses (see

100

details in SI, 1.2). 2000 mg/L was the maximum exposure concentration established by US EPA

101

guideline.18 According to our previous experiences, Ce uptake in shoots of cucumber at exposure

102

concentration less than 2000 mg/L is too low to acquire XANES spectra with good signal.

103

Quantification, localization and chemical species analysis of Ce in plant tissues

104

For TEM observation, fresh root apices were collected, fixed, dehydrated, embedded, and sectioned

105

following the standard procedures. Sections were then observed on a JEM-1230 (JEOL, Japan)

106

transmission electron microscope operating at 80 kV. Freeze-dried roots and shoots were digested with

107

nitric acid and hydrogen peroxide mixture, and the total Ce contents in roots and shoots were analyzed

108

by ICP-MS (Thermo, USA). For XANES analyses, dry roots and shoots were ground to fine powders,

109

pressed into thin slices (~2 mm). Ce LIII-edge (5723 eV) spectra were collected at ambient temperature

110

in the fluorescence mode at beamline 1W1B of Beijing Synchrotron Radiation Facility. XANES spectra

111

of reference compounds including CeO2-NPs, CePO4, Ce2(C2O4)3 as well as Ce(CH3COO)3 were also

112

collected. See details in SI, 1.3.

113

Transformation of CeO2-NPs in simulated solutions

5

ACS Paragon Plus Environment

Environmental Science & Technology Letters

Page 6 of 16

114

To compare the reactivity of differently shaped CeO2-NPs, CeO2-NPs were added into four solutions to

115

a concentration of 2000 mg/L: KH2PO4+citric acid (CA) + Vc, KH2PO4 + EDTA + Vc, KH2PO4 + CA +

116

catechol and KH2PO4 + EDTA + CAT. CA and EDTA represent organic acids, while Vc and CAT

117

represent reducing agents, both of which simulate the key components of plant root exudates. After 21

118

days, CePO4 and Ce3+ in the solutions were determined by FTIR and ICP-MS. See details in SI, 1.4.

119

Results and discussion

120

As shown in Figure S1 and Table S1, S-CeO2-NPs show irregular shape and the average particle size

121

was 26 ± 18 nm. Primary size of O-CeO2-NPs and C-CeO2-NPs were 25.2 ± 2.3 nm and 30.9 ± 12.4 nm.

122

R-CeO2-NPs show uniform sizes with diameter of 8.9 ± 0.9 nm and length of 106 ± 9 nm. All the CeO2-

123

NPs agglomerated fast in 1/4 Hoagland solution (Figure S2). Sizes of agglomerates for R-CeO2-NPs

124

were much larger than that for other CeO2-NPs.

125

Figure S3 reveals that all the CeO2-NPs showed no adverse effects on shoot and root biomass. Ce

126

contents in roots are not significantly different between different treatments (Figure 1). However, the Ce

127

contents in shoots in the R-CeO2-NPs treatment (153 mg/kg) were much higher than those (54 ~ 69

128

mg/kg) in the other treatments. This suggests that translocation of Ce in R-CeO2-NPs treated plant was

129

more efficient than that in other treatments (Figure S3).

130

Agglomeration is a critical factor that may affect the uptake and translocation of NPs in plants.

131

Formation of agglomerates would reduce the uptake by plants.19 However, DLS results suggest that R-

132

CeO2-NPs formed larger agglomerates than other CeO2-NPs (Table S1), which did not correlate with the

133

Ce uptake in shoots, indicating that there are other factors leading to the high Ce uptake in shoots in R-

134

CeO2-NPs treatment.

135

(Figure 1 here)

6

ACS Paragon Plus Environment

Page 7 of 16

Environmental Science & Technology Letters

136

Previous studies showed that PO43- can reduce the dissolved Ce concentrations by forming CePO4

137

precipitates,12 which consequently limits the translocation of Ce to shoots.20 This indicates that

138

translocation of Ce is highly associated with the transformation of CeO2. Figure 2 shows the temporal

139

transformation of CeO2-NPs on root surfaces. Transformation of S-CeO2-NPs, O-CeO2-NPs and C-

140

CeO2-NPs are overall synchronous. At the 7th day, a few needle- or rod-like clusters were visible among

141

the CeO2-NPs aggregates on the root surfaces (Figure 2A1-2A3). These clusters are CePO4 that have

142

been reported in previous studies.10 A few needle-like clusters were also observed in the intercellular

143

spaces in S-CeO2-NPs and O-CeO2-NPs treatments (Figure 2B1 and 2B2), whereas no particles were

144

found in C-CeO2-NPs treatments. In comparison, R-CeO2-NPs transformed faster than the other CeO2-

145

NPs. At the 7th day, most of the R-CeO2-NPs degraded into small particles on the root surfaces (Figure

146

2A4), and many CePO4 clusters were visible in the intercellular spaces (Figure 2B4). The amount of

147

CePO4 clusters on the root surface increased over time for all the treatments (Figure 2C1-2C4 and 2E1-

148

2E4). However, the amount of CePO4 in intercellular regions did not change significantly over time

149

(Figure 2D1-D3 and 2F1-F3) except for R-CNPs treatment, where large amount of need-like clusters

150

were visible in the intracellular spaces at 21th day (Figure 2F4).

151

The XANES spectra of roots in S-CeO2-NPs, O-CeO2-NPs and C-CeO2-NPs treatments show double

152

white lines (Figure 3A), indicating that the Ce predominantly remained as CeO2. In contrast, spectra of

153

roots in R-CeO2-NPs treatment presented a mixed feature of Ce(III) and Ce(IV), suggesting that R-

154

CeO2-NPs partially transformed to Ce(III) species. In shoots (Figure 3B), CeO2-NPs transformed in all

155

the treatments, as indicated by the presence of feature a.

156

(Figure 2 here)

157

(Figure 3 here)

7

ACS Paragon Plus Environment

Environmental Science & Technology Letters

Page 8 of 16

158

Linear combination fitting using standard references (Figure S4) revealed that more than 79% of the

159

Ce remained as CeO2 in roots in S-CeO2-NPs, O-CeO2-NPs and C-CeO2-NPs treatments; while in R-

160

CeO2-NPs treatments, more than 40% of the Ce presented as Ce(III) species, most of which were CePO4

161

and a small part were carboxylates (Figure 3C). More than 80% of Ce remained as CeO2 in shoots in S-

162

CeO2-NPs, O-CeO2-NPs and C-CeO2-NPs treatments, while only 62% remained as CeO2 in R-CeO2-

163

NPs treatment (Figure 3D). These results agree with the TEM results, suggesting that R-CeO2-NPs

164

transformed more than other CeO2-NPs.

165

We further calculated the absolute Ce(IV) and Ce(III) contents by multiplying their proportion by the

166

total Ce contents. Roots accumulated the lowest amount of Ce(IV) in R-CeO2-NPs treatment, which is

167

likely due to that R-CeO2-NPs formed large agglomerates thus reduced the adsorption/absorption in

168

roots. Ce(III) contents in roots were the highest in R-CeO2-NPs treatment, which agrees with the TEM

169

and LCF results. Interestingly, Ce(IV) and Ce(III) contents in shoots were both higher in R-CeO2-NPs

170

treatment than in other treatments. Degradation of R-CeO2-NPs into small particles on root surfaces

171

(Figure 2A4) may facilitate the movement of CeO2 and result in the high Ce(IV) uptake in shoots. Since

172

the transformation of CeO2-NPs occurs on the root surface rather than inside the plants,21 the high

173

Ce(III) contents in shoots could be attributed to high dissolving capacity of R-CeO2-NPs outside the

174

roots.

175

In a follow-up study, we incubated CeO2-NPs in simulated solutions which are composed of KH2PO4,

176

reducing agents, and low molecule organic acids. These components have been proved to have

177

significant impacts on the transformation of CeO2-NPs.9,12,19 We found that the reactivity of CeO2-NPs

178

follows the order: R-CeO2-NPs > S-CeO2-NPs > O-CeO2-NPs > C-CeO2-NPs (see detailed results and

179

discussion in SI, section 2, 2.5). The amount of CePO4 ((Figure S5) or Ce3+ (Figure S6) transformed

180

from R-CeO2-NPs were higher than those for other CeO2-NPs.

8

ACS Paragon Plus Environment

Page 9 of 16

Environmental Science & Technology Letters

181

CeO2-NPs with predominant facets of {100}/{110} planes are considered to be more catalytically

182

active than those with {111} planes.22 In this study, O-CeO2-NPs enclosed by eight {111} planes are

183

stable (Figure S7). S-CeO2-NPs exposed {111}, {200}, and {220} (Figure S8); however, S-CeO2-NPs

184

containing large amount of small particles have high surface area, thus also presenting high reactivity.

185

C-CeO2-NPs exposed {100} or {111} planes (Figure S9); besides, the sizes of C-CeO2-NPs are larger

186

than the other CeO2-NPs. This may account for the low reactivity and transformation of C-CeO2-NPs.

187

R-CeO2-NPs were enclosed by six active planes, i.e. four {110} and two {100} (Figure S10), thus

188

presenting the highest reactivity.

189

Taken together, our results suggest that the shape of CeO2-NPs determine their intrinsic chemical

190

reactivity, thus affecting their transformation and translocation in plants. Studies regarding the particle

191

shapes should be also introduced to other NMs and systems. This is not only important for

192

comprehensively understanding of the nano-bio interaction, but also for safer-design of NMs.

193

Acknowledgement

194

This work was financially supported by the National Natural Science Foundation of China (Grant No.

195

11405183, 11375009, 11575208, 11675190, 21507153), Ministry of Science and Technology of China

196

(Grant No. 2016YFA0201600).

197

Supporting Information

198

Supporting Information Available: Additional materials and methods information (CeO2-NPs syntheses,

199

seedling culture and CeO2-NPs application, sample preparation for TEM, ICP-MS, and XANES

200

analyses, transformation of CeO2-NPs in simulated solutions); complete results of characterization of

201

CeO2-NPs (Figure S1 and Table S1); photos of agglomeration of CeO2-NPs in nutrient solutions (Figure

202

S2); effects of CeO2-NPs on biomass production (Figure S3); translocation factors of CeO2-NPs in

203

plants (Figure S4); XANES spectra of reference compounds (Figure S5); complete results of simulation 9

ACS Paragon Plus Environment

Environmental Science & Technology Letters

Page 10 of 16

204

studies (Figure S6 and S7); HRTEM of CeO2-NPs (Figure S8-S11). This material is available free of

205

charge via the Internet at http://pubs.acs.org.

206

Notes

207

The authors declare no competing financial interest.

208

References

209

1.

210

Exposure, health and ecological effects review of engineered nanoscale cerium and cerium oxide

211

associated with its use as a fuel additive. Crit. Rev. Toxicol. 2011, 41, 213-229.

212

2.

213

chemi-sensor and photo-catalyst for environmental applications. Sci. Total Environ. 2011, 409, 2987-

214

2992.

215

3.

216

J.; Seal, S., Nanoceria as antioxidant: synthesis and biomedical applications. JOM-US 2008, 60, 33-37.

217

4.

218

ten engineered nanomaterials in Europe and the world. J. Nanopart. Res. 2012, 14, 1109.

219

5.

220

nanoparticles in the environment. Anal. Chem. 2013, 85, 3036-3049.

221

6.

222

of engineered nanomaterials in terrestrial environments. Environ. Sci. Technol. 2014, 48, 2526-2540.

223

7.

224

terrestrial environments. Acc. Chem. Res. 2012, 46, 854-862.

225

8.

226

transfer of Au nanoparticles from soil along a simulated terrestrial food chain. Environ. Sci. Technol.

227

2012, 46, 9753-9760.

228

9.

229

Torresdey, J.; White, J. C., Particle-size dependent accumulation and trophic transfer of cerium oxide

230

through a terrestrial food chain. Environ. Sci. Technol. 2014, 48, 13102-13109.

231

10.

Cassee, F. R.; van Balen, E. C.; Singh, C.; Green, D.; Muijser, H.; Weinstein, J.; Dreher, K.,

Khan, S. B.; Faisal, M.; Rahman, M. M.; Jamal, A., Exploration of CeO2 nanoparticles as a

Karakoti, A.; Monteiro-Riviere, N.; Aggarwal, R.; Davis, J.; Narayan, R. J.; Self, W.; McGinnis,

Piccinno, F.; Gottschalk, F.; Seeger, S.; Nowack, B., Industrial production quantities and uses of

Maurer-Jones, M. A.; Gunsolus, I. L.; Murphy, C. J.; Haynes, C. L., Toxicity of engineered

Gardea-Torresdey, J. L.; Rico, C. M.; White, J. C., Trophic transfer, transformation, and impact

Batley, G. E.; Kirby, J. K.; McLaughlin, M. J., Fate and risks of nanomaterials in aquatic and

Unrine, J. M.; Shoults-Wilson, W. A.; Zhurbich, O.; Bertsch, P. M.; Tsyusko, O. V., Trophic

Hawthorne, J.; De la Torre Roche, R.; Xing, B.; Newman, L. A.; Ma, X.; Majumdar, S.; Gardea-

Zhang, P.; Ma, Y.; Zhang, Z.; He, X.; Zhang, J.; Guo, Z.; Tai, R.; Zhao, Y.; Chai, Z.,

10

ACS Paragon Plus Environment

Page 11 of 16

Environmental Science & Technology Letters

232

Biotransformation of ceria nanoparticles in cucumber plants. ACS Nano 2012, 6, 9943-9950.

233

11.

234

toxicity of ceria nanoparticles to Lactuca plants. Nanotoxicology 2015, 9, 1-8.

235

12.

236

transformation of cerium oxide nanoparticles in plant growth media. J. Nanopart. Res. 2014, 16, 2668.

237

13.

238

Olivi, L.; Roche, N.; Wiesner, M. R., Transformation of pristine and citrate-functionalized CeO2

239

nanoparticles in a laboratory-scale activated sludge reactor. Environ. Sci. Technol. 2014, 48, 7289-7296.

240

14.

241

of CeO2 nanostructures: nanowires, nanorods and nanoparticles. Catal. Today 2009, 148, 179-183.

242

15.

243

of octahedral and cubic Cu2O micro/nanocrystals to Daphnia magna. Environ. Sci. Technol. 2012, 46,

244

10255-10262.

245

16.

246

response of poly (3, 4 ethylenedioxythiophene) nanomaterials. Small 2010, 6, 872-879.

247

17.

248

nanoparticles on Arabidopsis plant growth and gene expression. Plant Physiol. Biochem. 2014, 83, 57-

249

64.

250

18.

251

Toxicity, Tier I (vegetative Vigor); EPA 712- C-96-163; Public Draft. Office of Prevention, Pesticides

252

and Toxic Substances: Washington, DC, 1996.

253

19.

254

Dissolved cerium contributes to uptake of Ce in the presence of differently sized CeO2-nanoparticles by

255

three crop plants. Metallomics 2015, 7, 466-477.

256

20.

257

Transformation of ceria nanoparticles in cucumber plants is influenced by phosphate. Environ. Pollut.

258

2015, 198, 8-14.

259

21.

260

L., Where does the transformation of precipitated ceria nanoparticles in hydroponic plants take place?

261

Environ. Sci. Technol. 2015, 49, 10667-10674.

262

22.

Zhang, P.; Ma, Y.; Zhang, Z.; He, X.; Li, Y.; Zhang, J.; Zheng, L.; Zhao, Y., Species-specific

Schwabe, F.; Schulin, R.; Rupper, P.; Rotzetter, A.; Stark, W.; Nowack, B., Dissolution and

Barton, L. E.; Auffan, M.; Bertrand, M.; Barakat, M.; Santaella, C.; Masion, A.; Borschneck, D.;

Zhang, M.; Li, J.; Li, H.; Li, Y.; Shen, W., Morphology-dependent redox and catalytic properties

Fan, W.; Wang, X.; Cui, M.; Zhang, D.; Zhang, Y.; Yu, T.; Guo, L., Differential oxidative stress

Oh, W. K.; Kim, S.; Yoon, H.; Jang, J., Shape dependent cytotoxicity andproinflammatory

Syu, Y. Y.; Hung, J. H.; Chen, J. C.; Chuang, H. W., Impacts of size and shape of silver

US EPA, U.S. EPA. Ecological effects test guidelines. OPPTS 850.4150 Terrestrial Plant

Schwabe, F.; Tanner, S.; Schulin, R.; Rotzetter, A.; Stark, W.; von Quadt, A.; Nowack, B.,

Rui, Y.; Zhang, P.; Zhang, Y.; Ma, Y.; He, X.; Gui, X.; Li, Y.; Zhang, J.; Zheng, L.; Chu, S.,

Ma, Y.; Zhang, P.; Zhang, Z.; He, X.; Zhang, J.; Ding, Y.; Zhang, J.; Zheng, L.; Guo, Z.; Zhang,

Zhou, K.; Wang, X.; Sun, X.; Peng, Q.; Li, Y., Enhanced catalytic activity of ceria nanorods from

11

ACS Paragon Plus Environment

Environmental Science & Technology Letters

263

Page 12 of 16

well-defined reactive crystal planes. J. Catal. 2005, 229, 206-212.

264 265 266 267 268 269 270

Figure Captions

271

Figure 1. Ce contents in root and shoot of cucumber treated with CeO2-NPs.

272 273

Figure 2. TEM images of root sections of cucumber treated with S-CeO2-NPs (A1-F1), O-CeO2-NPs

274

(A2-F2), C-CeO2-NPs (A3-F3) and R-CeO2-NPs (A4-F4) for 7d (A and B), 14d (C and D), and 21d (E

275

and F). Surface and inside indicate that the images were collected at surface and inside of the root

276

sections, respectively. Red arrows indicate the CePO4 on the root surface or intracellular spaces.

277 278

Figure 3. Ce LIII edge XANES spectra of root (A) and shoot (B). Vertical dotted line marked the feature

279

of Ce(III) (a) and Ce(IV) (b and c), respectively. Percentage of Ce(IV) and Ce(III) species in root (C)

280

and shoot (D) Ce contents. Calculated contents of Ce(III) and Ce(IV) in root (E) and shoot (F).

281

12

ACS Paragon Plus Environment

Page 13 of 16

Environmental Science & Technology Letters

TOC 40x39mm (600 x 600 DPI)

ACS Paragon Plus Environment

Environmental Science & Technology Letters

Figure 1. Ce contents in root and shoot of cucumber treated with CeO2-NPs. 51x33mm (600 x 600 DPI)

ACS Paragon Plus Environment

Page 14 of 16

Page 15 of 16

Environmental Science & Technology Letters

Figure 2. TEM images of root sections of cucumber treated with S-CeO2-NPs (A1-F1), O-CeO2-NPs (A2-F2), C-CeO2-NPs (A3-F3) and R-CeO2-NPs (A4-F4) for 7d (A and B), 14d (C and D), and 21d (E and F). Surface and inside indicate that the images were collected at surface and inside of the root sections, respectively. Red arrows indicate the CePO4 on the root surface or intracellular spaces. 199x351mm (300 x 300 DPI)

ACS Paragon Plus Environment

Environmental Science & Technology Letters

Figure 3. Ce LIII edge XANES spectra of root (A) and shoot (B). Vertical dotted line marked the feature of Ce(III) (a) and Ce(IV) (b and c), respectively. Percentage of Ce(IV) and Ce(III) species in root (C) and shoot (D) Ce contents. Calculated contents of Ce(III) and Ce(IV) in root (E) and shoot (F). 182x245mm (600 x 600 DPI)

ACS Paragon Plus Environment

Page 16 of 16