Extracting Metallic Nanoparticles from Soils for Quantitative Analysis

Subscriber access provided by Fudan University

Article

Extracting metallic nanoparticles from soils for quantitative analysis: Method development using engineered silver nanoparticles and SP-ICP-MS Dina M. Schwertfeger, Jessica R. Velicogna, Alexander H. Jesmer, Selin Saatcioglu, Heather A. O. McShane, Richard P. Scroggins, and Juliska I. Princz Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.analchem.6b04668 • Publication Date (Web): 12 Jan 2017 Downloaded from http://pubs.acs.org on January 16, 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.

Analytical Chemistry 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 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Analytical Chemistry

1

Title: Extracting metallic nanoparticles from soils for quantitative analysis:

2

Method development using engineered silver nanoparticles and SP-ICP-MS

3

Authors: D. M. Schwertfeger,† Jessica R. Velicogna,† Alexander H. Jesmer,† Selin Saatcioglu,‡

4

Heather McShane,§ Richard P. Scroggins,† Juliska I. Princz†,*

5 6

†

Biological Assessment and Standardization, Environment Canada, Ottawa, Canada

7

‡

Department of Civil and Environmental Engineering, Carleton University, Ottawa, Canada

8

§

Department of Natural Resource Sciences, McGill University, Montreal, Quebec, Canada

9

*

To whom correspondence may be addressed ([email protected])

10

ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 29

2 11

Abstract

12

Hindering progress in assessing the fate and toxicity of metallic engineered nanomaterials in the

13

soil environment is the lack of an efficient and standardized method to disperse soil particles and

14

quantitatively subsample the nanoparticulate fraction for characterization analyses. This study

15

investigated various soil extraction and extract preparation techniques for their ability to remove

16

nano-particulate Ag from a field soil amended with biosolids contaminated with engineered

17

silver nanoparticles (AgNP), while presenting a suitable suspension for quantitative SP-ICP-MS

18

analysis. Extraction parameters investigated included reagent type (water, NaNO3, KNO3, TSPP,

19

TMAH), soil-to-reagent ratio, homogenization techniques as well as procedures commonly used

20

to separate nanoparticles from larger colloids prior to analysis (filtration, centrifugation and

21

sedimentation). We assessed the efficacy of the extraction procedure by testing for the

22

occurrence of potential procedural artifacts (dissolution, agglomeration) using a dissolved /

23

particulate Ag mass ratio and by monitoring the amount of Ag mass in discrete particles. The

24

optimal method employed 2.5 mM TSPP used in a 1:100 (m/v) soil-to-reagent ratio, with

25

ultrasonication to enhance particle dispersion and sedimentation to settle out the micron-sized

26

particles. A spiked-sample recovery analysis showed that 96 ± 2% of the total Ag mass added as

27

engineered AgNP was recovered, which included recovery of 84.1% of the particles added, while

28

particle recovery in a spiked method blank was ~100%, indicating that both the extraction and

29

settling procedure have a minimal effect on driving transformation processes. A soil dilution

30

experiment showed that the method extracted a consistent proportion of nano-particulate Ag (9.2

31

± 1.4% of the total Ag) in samples containing 100, 50, 25 and 10% portions of the AgNP-

32

contaminated test soil. The nano-particulate Ag extracted by this method represents the upper

33

limit of the potentially dispersible nanoparticulate fraction, thus providing a benchmark with


Page 3 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


3 34

which to make quantitative comparisons, while presenting a suspension suitable for a myriad of

35

other characterization analyses.

36 37

Key words: soil extraction, biosolids, nanomaterials, complex matrix

38



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 29

4 39

INTRODUCTION

40

With the increasing use of metal-based engineered nanoparticles (ENP) in consumer and

41

industrial products and their likely release into the environment1, the potential risks of

42

nanomaterials on environmental systems are currently under investigation by government

43

regulatory agencies that require quantitative data to assess and compare these substances’ risks2-

44

3

45

concentrations of a toxicant are compared against predicted toxicity thresholds4. However, risk

46

assessments for engineered nanoparticles are particularly challenging because they do not always

47

conform to the conventional tools of risk assessment. For example, toxicological behaviour of

48

trace metals are often related to exposure to the quantity of the total bioavailable mass;5 however,

49

for nanomaterials it is also relevant to consider exposure to particle number, particle size and

50

active surface area3. While identifying, counting and characterizing engineered nanomaterials in

51

aqueous environmental media is riddled with complexities6, the multi-phase and dynamic nature

52

of soils poses further challenges in carrying out these assessments for the terrestrial environment.

53

There has yet to be a standard method for quantitatively sampling the potentially dispersible

54

nano-particulate fraction, which could then be used for further quantitative and qualitative

55

characterization analyses.

. During the environmental risk assessment process, predicted environmental exposure

56

Manufactured Ag nanoparticles (AgNP) are one of the most widely used, and thus studied

57

nanomaterials6, with the soil environment being an important exposure route due to land

58

application of processed sewage sludge (i.e., biosolids), which are considered a major sink for

59

AgNP1 released from consumer products. Manufactured AgNP are primarily used for their anti-

60

microbial properties, presumably arising from the slow release of Ag+ as particles oxidize;7

61

however, a growing number of studies have documented AgNP toxicity to non-target


Page 5 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


5 62

organisms8. Toxicity may occur via nano-specific mechanisms, such those causing oxidative

63

stress9-11 or those induced from the direct uptake of the particle into living cells, or toxicity may

64

occur via mechanisms involving the dissolved free ion (Ag+) released from AgNP12. It is

65

unknown how significant these nano-specific mechanisms are compared to those involving Ag+

66

when exposure occurs in the soil environment. While a number of toxicity studies have been

67

conducted using natural soil exposures,13-16 the utility of these studies for environmental risk

68

assessment is limited by their lack of quantitative exposure characterization.

69

One of the most reliable and efficient quantification tools already established in most

70

environmental laboratories is the ICP-MS. Recent advances in ICP-MS technology and

71

computation has allowed for the sizing and counting of metallic nanoparticles.17-18 The use of

72

ICP-MS requires samples be in an aqueous form and free of large particles (generally considered

73

> 1 μm), thus necessitating soil extraction and phase separation techniques (e.g., centrifugation

74

and filtering). By definition, all soil analyses based on extraction techniques are operationally

75

defined. This means that measured values are inextricably linked to the overall method used to

76

acquire the data, that is, the series of procedures including soil preparation, extracting reagent

77

and procedure and phase separation technique. The challenge with using such data, from a risk

78

assessment perspective, is the lack of comparability for data obtained from different methods. It

79

would therefore be beneficial to use a standardized method for soil extraction / phase separation

80

that is suitable for subsequent nanoparticulate characterization analyses.

81

While development of a comprehensive method for extracting metallic nanoparticles from

82

contaminated soils and/or biosolids has yet to be presented in the scientific literature, a number

83

of studies have employed various soil extraction and phase separation techniques, often without

84

much justification or validation. De-ionized water has been used to extract metallic NPs in



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 29

6 85

transformation, mobility and toxicity studies.19-20 In these studies, where a surrogate of the

86

natural “pore water” is meant to be extracted, just enough water is added to saturate soils, or

87

form a saturated paste, which is a method traditionally used to extract and assess soluble salts,

88

that is, constituents in the soil that readily re-solubilize upon wetting.21 When soils are dried

89

prior to storage and/or extraction, soil particles flocculate or agglomerate as they come into

90

closer proximity to each other with the collapse of their hydration shells.22 This drives

91

aggregation and precipitation reactions that would not necessarily occur to soils in situ and are

92

thus considered artifacts of the soil drying procedure.23 While using freshly sampled soil would

93

be suitable for this kind of saturated pore water extraction, it is simply not practical or feasible

94

for most experimental designs. Unlike de-ionized water, that offers very little (chemically) to

95

help disperse flocculated soil particles, it would seem advantageous to rehydrate and extract

96

nanoparticles from dried soils using a reagent that could facilitate re-dispersion of both natural

97

soil, and engineered, nanoparticles.

98

Dilute salt reagents (e.g., 0.01 M NaCl2, 0.01 M KNO3, 0.01 M CaCl2) are generally used to

99

mimic the electrolytic properties of in situ soil pore water and have been commonly used to

100

extract fractions of bioavailable trace metals.24-25 KNO3 has traditionally been used to extract

101

electrostatically bound trace metals (i.e., ionic metal forms) and a recent study demonstrated how

102

0.01 M KNO3 could be used to extract and analyze both Ag+ and AgNP forms within the same

103

extract.26 While this scenario was advantageous from a mass balance perspective, the extracts

104

showed only moderate soil dispersion and resulted in large dissolved-to-particulate Ag ratios,

105

which is not ideal for SP-ICP-MS analysis. Sodium in an extracting reagent has the advantage of

106

promoting the dispersion of soil particles. The relatively small ratio of charge-to-hydrated radius

107

of the Na+ ion forms a large electrostatic double layer around particles driving electrostatic


Page 7 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


7 108

repulsion between particles.22 It is this electrostatic repulsion that is the major factor controlling

109

the dispersion of engineered NP’s from soil particles.27 This would be particularly useful in cases

110

where aluminosilicate clay is a major component of nanoparticle heteroaggregates.28 The

111

literature shows that NaCl has been used to extract naturally occurring Fe- and Al-(hydr)oxide

112

nanoparticles29 as well as engineered Ag nanoparticles.30

113

The usefulness of the more alkaline extracting reagents, such as NaOH, tetrasodium

114

pyrophosphate (TSPP) and tetramethylammonium hydroxide (TMAH), lies in their ability to

115

disperse/dissolve soil organic matter (SOM), which has been found to be a major binding agent

116

in the formation of heteroaggregates involving metallic nanoparticles in soils.28 TSPP is

117

commonly used to disperse soil particles prior to particle size analysis.31 Regelink et al.29 found

118

that 2 mM TSPP (adjusted to pH 7.7 to 8.8) extracted significantly more nano-sized Fe-

119

(hydr)oxide than both 1 mM NaOH (pH 9.0) and 0.01 mM NaCl, moreover, the larger Fe-

120

(hydr)oxide concentrations in the TSPP extract corresponded to larger concentrations of

121

dissolved organic carbon. The strongly alkaline TMAH has been used to dissolve biological

122

tissues in order to release and disperse Au and Ag nanoparticles for sizing and quantification via

123

SP-ICP-MS.32 The use of TMAH to extract nanoparticles from soils has not yet been tested.

124

A variety of techniques have been employed to separate out the nano-sized particles from

125

larger particles contained in soil suspensions, a necessary step in preparing samples for ICP-MS

126

analyses. In the Cornelis et al. study28 researchers used 0.45 µm cellulose-acetate centrifugal

127

filters to extract nano-sized particulates from their saturated soil samples, while Unrine et al.20

128

sequentially centrifuged (1000 x g for 5 min) and filtered samples using a glass microfiber filter

129

and the commonly used 0.2 µm nylon syringe filter. In a study comparing the effect of pH on the

130

speciation of naturally occurring Fe nanoparticles, Neubauer et al.33 centrifuged their soil



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 29

8 131

suspensions at 3900 x g for 10 min followed by filtration through 0.45 um cellulose acetate filter.

132

Studies investigating Ag recovery after passing AgNP suspensions through various filtering

133

apparatus show recoveries as low as 12% for some brands of 0.45 µm centrifugal filters34 and

134

73% for sequential 30 mm and 1 µm borosilicate glass syringe filtration.19 There has yet to be

135

any consensus on how to prepare soil suspensions for analyses that require removal of micron-

136

sized particles, such as SP-ICP-MS and field-flow fractionation (FFF) techniques.

137

In this study, we investigated different extraction methods for their efficacy in removing

138

nano-particulate Ag from soils amended with biosolids which had been spiked with engineered

139

AgNP. The subsequent SP-ICP-MS analysis allowed us to count Ag-containing nanoparticles

140

and obtain the mass of Ag within each particle, while at the same time measuring the

141

concentration of dissolved Ag. Our approach to designing an optimal soil extraction procedure

142

was to liberate the most Ag nanoparticles from the soil matrix, while minimizing nanoparticle

143

dissolution and agglomeration processes, which would incur procedural artifacts.

144

MATERIALS AND METHODS

145

Nanomaterials. Silver nanoparticles with nominal diameters of 25 nm and 40 nm were

146

purchased from nanoComposix (San Diego, CA) as PVP-coated (88%), dispersible, silver nano-

147

spheres (i.e., powder form) and are hereto referred to by their nominal diameters. The bulk of the

148

work (i.e., soil extraction experiments, centrifugation and sedimentation studies) was carried out

149

with the 40 nm particles, while the sample filtration study included the 25 nm particles.

150

Nanomaterial characterization (independent of the supplier’s) was carried out using transmission

151

electron microscopy (TEM) (Tecnai G2 F20 TEM) with energy-dispersive X-ray spectroscopy

152

(EDS), dynamic light scattering (DLS) (MalvernTM Nano ZS Zetasizer) and SP-ICP-MS (Perkin

153

Elmer NexION 300D). Details of the characterization methods are presented elsewhere.35 Upon


Page 9 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


9 154

receipt of the nanomaterials, stock suspensions of the 25 and 40 nm AgNP were prepared to the

155

nominal Ag concentrations of 20 mg L-1 and 15 g L-1, respectively, using NanopureTM water

156

(Barnstead 2-cartridge water filtration system, > 18.3 MΩ·cm, TOC < 10 ppb). TEM images of

157

these stock suspensions showed that both nanomaterials were well dispersed in water (Fig. S1)

158

with most particles falling within the suppliers’ size specifications of 23.1 ± 6.9 nm for the 25

159

nm particles and 38.6 ± 9.8 nm for the 40 nm particles. Further characterization results are

160

presented and discussed in the Supporting Information.

161

Soil and biosolids. Test soils (Batch A and B) were prepared by mixing AgNP-spiked

162

biosolids with uncontaminated field soil. The soil used was an agricultural sandy loam (5.8

163

pHCaCl2, 12.5 g kg-1 total organic carbon and 9% clay, 0.11 μg g-1 total Ag) which was air-dried

164

and sieved (< 2 mm). Fresh biosolids (~ 20% solids w/w, 8.0 pH, 7.3 μg g-1) were obtained from

165

a municipal wastewater treatment plant located in Southern Quebec. Biosolids were stored

166

frozen and thawed when needed by mixing with NanopureTM water to form a slurry, then aged in

167

sealed containers for 48 h at room temperature. The average redox potential of the aged slurry

168

was -180 mV based on triplicate measurements using a Thermo-Scientific Redox/ORP electrode.

169

An aliquot of the 15 g L-1 AgNP (40 nm) dispersion was added to the slurry, homogenized using

170

a vortex mixer, aged a further 48 h at room temperature and subsequently added to the soil at a

171

rate of 10 g biosolids (dry weight) per kg of soil, in order to achieve a nominal Ag concentration

172

of 833 µg g-1 soil and a soil moisture content of 24%. Soil Batches A and B were prepared at

173

different times and Batch A was aged two weeks prior to sub-sampling and air-drying, while

174

Batch B was sub-sampled immediately and air-dried. Air-dried samples were stored in sealed

175

plastic bags at ~ 6°C. A test soil contaminated with AgNO3 (Batch C, nominal Ag concentration



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 29

10 176

= 833 μg g-1) was prepared in the same manner as Batch A, but AgNO3 was added to biosolids

177

instead of AgNP.

178

Soil extraction experiments. Three soil extraction experiments were carried out to test

179

various extraction parameters. Details of the various treatments are provided in Table 1. In

180

Extraction Experiment #1, test soil from Batch A was used to compare four extracting reagents:

181

sodium nitrate (0.01 M NaNO3); tetrasodium pyrophosphate (TSPP) (0.25 mM Na4P2O7),

182

potassium nitrate (0.01 M KNO3), and NanopureTM water. In addition to type of reagent,

183

ultrasonication homogenization techniques were tested which included use of an ultrasonic wand

184

(60 watts, OMNI International Sonic Ruptor 250 ultrasonic homogenizer, micro-titanium tip, 20

185

kHz) and an ultrasonic bath (Branson 3510, 40 kHz, 130 watts). The extraction technique was

186

carried out as follows: 8 g (air dry) test soil was weighed into a 50-mL polypropylene centrifuge

187

tube and mixed with 40 mL of extracting solution which gave a soil-to-reagent ratio of 1:5

188

(g:mL). Samples were mixed on a rotary mixer (30 rpm) for 30 min followed by one of three

189

homogenization treatments: ultrasonic wand (2 min), ultrasonic bath (20 min) or no

190

ultrasonication but samples were further mixed on the rotary mixer for an additional 20 min.

191

Separation of nano- from micron-sized particles was conducted by centrifuging samples at 6000

192

x g for 20 min followed by passing supernatants through a tandem 0.45 µm/ 0.22 μm nylon

193

syringe filter (Millex® Millipore). Filtrates were then stored at 6°C in the dark overnight, prior to

194

SP-ICP-MS analysis the next day. All samples were extracted in triplicate.

195

Extraction Experiment #2 investigated the effects of increasing the concentration of TSPP

196

(0.25 mM, 2.5 mM and 25 mM), as well as decreasing the soil-to-reagent ratio from 1:10 to 1:50.

197

Also included was a soil sample to which no manufactured AgNPs were added, but instead the


Page 11 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


11 198

soil was spiked with AgNO3 (i.e., Soil Batch C). This sample was extracted with 2.5 mM TSPP

199

using a 1:10 soil:reagent ratio. Also under investigation was the use of the strongly alkaline

200

reagent, tetramethylammonium hydroxide (25% TMAH). The extraction procedure for samples

201

involving the TSPP reagent was the same as that in Experiment 1, except for the sample

202

treatment with soil-to-reagent ratio of 1:50, for which 50-mL of reagent was mixed with 1 g soil.

203

After mixing on the rotary mixer for 30 min, all samples were homogenized using the ultrasonic

204

wand for 2 min. Instead of removing micron-sized particles with centrifugation and filtration

205

procedures, sample suspensions were left to settle overnight (~ 18 h) at room T, in the dark,

206

allowing large particles to sediment out. To avoid sampling particles > 1 µm, sub-samples were

207

taken between 0.5 and 1.0 cm depth from the sample surface, as calculated using Stoke’s law,36

208

assuming ideal spherical particles. The extraction procedure for samples with the TMAH

209

extraction was as follows: 0.5 g of soil was weighed into a 30-mL polypropylene tube, 10 mL of

210

25% TMAH was added and the mixture was homogenized in the ultrasonic bath, at room T, for 1

211

h. Sedimentation was carried out same as the TSPP samples. All samples were extracted in

212

duplicate.

213

A fresh batch of AgNP-contaminated test soils (i.e., Batch B) was used for Extraction

214

Experiment #3 and all samples were extracted with 2.5 mM TSPP reagent using soil:reagent

215

ratios of 1:10 or 1:100, and were mixed for 30 min, except for one sample for which the mixing

216

time of 24 h was investigated. In addition, a soil dilution series was prepared which contained

217

mixtures of 50/50, 25/75, and 10/90 (w/w) of Batch B soil / uncontaminated soil, resulting in

218

nominal total soil Ag concentrations of 424, 212 and 85 μg g-1. All samples were extracted in

219

duplicate, homogenized with the ultrasonication wand for 1.5 min and sedimentation was used to

220

facilitate nano/micron particle separation. Note: the time used for homogenization with the wand



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 29

12 221

was reduced from 2 min to 1.5 min in order to minimize heating of the wand. Following

222

Extraction Experiment #3, the optimal extraction procedure was identified and used to

223

investigate AgNP recovery from spiked samples, which has been described in detail in the

224

Supporting Information.

225

Filtration and centrifuge experiments. To investigate potential AgNP and Ag+ loss from

226

filtration procedures often used to separate micron-sized from nano-sized particles, four sets of

227

samples were prepared: two sets were prepared with the 25 nm AgNP material and two sets with

228

AgNO3. Sample solutions were prepared in either water (Nanopure™) or a filtered soil extract.

229

The filtered soil extract was prepared by extracting the uncontaminated test soil with 0.01 M

230

KNO3 using a soil-to-solution ratio of 1:5, mixing on a rotary mixer for 30 min followed by

231

centrifugation at 6000 x g for 20 min, then filtering through a tandem 0.45/0.22 μm syringe filter.

232

Each sample set consisted of 100-mL solutions prepared with low, medium and high Ag

233

concentrations, ranging from 2 to 150 μg L-1. Three 10-mL sub-samples were passed through a

234

tandem 0.45 μm/0.22 μm nylon syringe filter and total Ag was analyzed by ICP-MS (standard

235

mode) before and after filtration. To investigate potential AgNP loss from centrifuge procedures,

236

two sets of AgNP (40 nm) suspensions were prepared: one set prepared in a water (NanopureTM)

237

matrix, the other in a filtered soil extract matrix that was prepared in the same manner as

238

described above, except 0.25 mM TSPP was used to extract the uncontaminated soil instead of

239

KNO3. For each matrix, samples were prepared with low and high Ag concentrations which

240

ranged from 2 to 200 μg L-1. Triplicate 50-mL sub-samples were centrifuged in a ThermoFisher

241

Scientific Legend X1R Centrifuge using three different procedures: 1000 x g for 15 min, 3000 x

242

g for 15 min and 6000 x g for 20 min. Initial sample suspensions and resulting supernatants were

243

analyzed for total Ag by ICP-MS (standard mode).


Page 13 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


13 244

ICP-MS and SP-ICP-MS Analysis. All ICP-MS analyses were conducted using a

245

PerkinElmerTM NexION 300D ICP-MS. Total Ag in solutions/suspensions were determined on

246

samples acidified to 1% HNO3 (TraceMetalTM Grade, Fisher Chemical) at least 24 h prior to

247

analysis, using the ICP-MS in standard mode. Calibration solutions were prepared fresh daily

248

from a silver standard (1000 mg L-1 in 2% HNO3, High-Purity Standards) and indium (1 µg L-1)

249

was used as the internal standard. Samples were analyzed in duplicate, with relative standard

250

deviations (RSD) ≤ 10% between the duplicate readings or samples were re-analyzed. A 1 µg L-1

251

solution of Ag in 1% HNO3 was used for quality control (QC) purposes and analyzed after every

252

ten samples. Ag recovery in the QC sample was between 90 to 110%, or the preceding set of

253

samples was re-analyzed after re-calibration.

254

SP-ICP-MS analysis was performed using the same ICP-MS, but operating in single particle

255

mode using the SyngistixTM Nano-Application module (PerkinElmer Inc., Waltham, MA).

256

Instrumental and data acquisition parameters of the analysis are provided in Table 2. Transport

257

efficiency was determined by the particle size method37 using a 60 nm Au suspension (NIST

258

Reference Material 8013) for reference. Dissolved Ag calibration was performed using solutions

259

ranging from 0.1 to 10 µg L-1 prepared using the purchased Ag stock solution previously

260

mentioned, while Ag particle calibration was performed using suspensions prepared with 30 and

261

60 nm silver nano-sphere suspensions purchased from Ted Pella (Redding, CA). Particle sizes of

262

the Ted Pella AgNP were verified by TEM and were found to fall within the supplier’s

263

specifications. For SP-ICP-MS analysis, all particles detected were assumed to be spherical and

264

pure Ag0 with a density of 10.49 g cm-3. While this assumption likely holds true for the AgNP in

265

the calibration and original stock suspensions, particles detected in the soil extracts likely include

266

a variety of transformation products formed by the interactions of the manufactured AgNP with



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 29

14 267

constituents in the biosolids / soil and thus particle geometry and mass fraction of the Ag analyte

268

are actually unknown. Thus for the analysis of particulate Ag in the soil extracts, the data was

269

processed using a default spherical shape and mass fraction of 1 in order to calculate an

270

equivalent mono-metal particle size, denoted with the subscript “eqv” (e.g., sizeeqv), indicative,

271

not of an actual particle size, but a reference size to aid in the understanding of the Ag mass

272

detected. Particle size distributions (PSD and PSDeqv) were fit to a log normal smoothing

273

function from which mean and mode particle sizes (or sizeseqv) were derived. Further details of

274

the SP-ICP-MS analysis are provided in Supporting Information.

275 276

RESULTS AND DISCUSSION

277

Soil extraction experiments. In Extraction Experiment #1, the 0.25 mM TSPP reagent

278

extracted significantly (p < 0.01) more Ag particles than the other reagents, given the same

279

homogenization procedure (Fig. 1). Likewise, the use of the ultrasonic wand always extracted

280

significantly (p < 0.01) more particles compared to the other homogenization treatments. For a

281

given reagent, use of the ultrasonic wand extracted 2- to 5-fold more particles than the ultrasonic

282

bath and on average 12-fold more particles than using no ultrasonication. Furthermore, the use of

283

either ultrasonic technique did not appear to enhance the extractability of dissolved Ag to the

284

same extent, as indicated by the lower dissolved-to-particulate Ag mass ratios (Table 1). The

285

lower the ratio, the less likely the extraction procedure is causing particle dissolution, or

286

targeting the dissolved Ag fraction, and is thus considered an indication of greater particle

287

extraction efficiency. The combination of using the ultrasonication wand with the 0.25 mM

288

TSPP reagent resulted in extracting the greatest concentration of particles while showing the

289

lowest dissolved-to-particulate mass ratio (Table 1). This procedure extracted 1250 ± 180 x 106


Page 15 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


15 290

Ag-containing nanoparticles per g soil which represents 0.05% of the total Ag in the soil. The

291

particles extracted by all reagents contained similar amounts of Ag mass, as indicated by

292

equivalent mono-metal particle sizes: mode sizeeqv ranged from 34.5 to 39.9 nm (Table 1), while

293

mean sizeeqv ranged from 34.7 to 44.6 nm. While this equivalent size was consistent with the 40

294

nm AgNP initially added to the soil, it is doubtful that the particles, or particle surfaces,

295

remained untransformed during the biosolids-aging and soil-aging procedures. It should be noted

296

that the SP-ICP-MS is not a speciation technique, thus secondary precipitates (e.g., Ag2S, AgCl)

297

may be included in this analysis, as well as Ag deposited onto organic or clay surfaces, if there is

298

enough Ag mass to be included in the particulate fraction.

299

In Extraction Experiment #2, we investigated if increasing the concentration of TSPP would

300

further enhance the efficacy of the extraction. Unlike the first experiment where all homogenized

301

extracts were centrifuged and filtered, in this experiment sedimentation was used to settle out

302

large particles (see subsequent section on filtration and centrifuge experiments). Increasing the

303

TSPP concentration 10-fold (to 2.5 mM) extracted 3.2-fold more particles (Fig. 2) and reduced

304

the dissolved-to-particulate mass ratio from 5.5 to 2.5 (Table 1). However, increasing the TSPP

305

concentration to 25 mM resulted in unstable SP-ICP-MS readings and repeated failure of the SP-

306

ICP-MS quality control, likely due to Na interference. Thus, in order to supply more active TSPP

307

per g of soil, the soil-to-reagent ratio was lowered from 1:5 to 1:50. This 10-fold decrease in the

308

extraction ratio liberated twice as many particles (Fig. 2). Interestingly, using the lower ratio did

309

not extract any more dissolved Ag, thus the dissolved-to-particle ratio was reduced by about half,

310

to 1.3. The use of the extracting reagent 25% TMAH extracted a similar particle concentration as

311

the 2.5 mM TSPP extraction; however, the TMAH extracted much more dissolved Ag resulting

312

in the larger dissolved-to-particulate mass ratio of 10.7 (Table 1). This was probably due to



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 16 of 29

16 313

more complete digestion of the SOM which would have released more organically-complexed

314

Ag, but did not seem to improve the dispersion/extraction of AgNPs. We found that the TMAH

315

extracts were darker and more viscous than the TSPP extracts, and as such, the 18 h

316

sedimentation time was not sufficient to settle out larger particles. Despite dilution, these extracts

317

proved a challenge to analyze by SP-ICP-MS, for which even replicate readings from the same

318

extract showed RSD > 50%.

319

The TSPP extraction of the AgNO3-contaminated soil resulted in the detection of particulate

320

Ag for which the modal sizeeqv was 31.2 nm (Table 1). These data suggest the formation of

321

detectable Ag precipitates in the biosolids/soil mixture which is consistent with observations by

322

other researchers. For example, Whitely et al.19 detected nanoparticles (< 80 nm, mean diameters

323

≤ 40 nm) containing Ag in the soil pore waters from soils amended with AgNO3 and sewage

324

sludge using an AF4/ICP-MS analysis. Based on the redox potential and pH of our incubated

325

biosolids, and the relatively large availability of S, the formation of Ag2S is highly likely38,

326

particularly in the AgNO3 where Ag+ is added directly to the biosolids; however, these are not

327

conditions that would thermodynamically favor complete AgNP dissolution and precipitation of

328

Ag2S within the AgNP treatments, and thus particulate Ag2S is likely mixed with intact AgNP,

329

although varying degrees of surface transformations of the AgNP are likely.39 Once extracted,

330

further particle analysis can be made with regards to elemental composition by analyzing

331

samples for other elements/isotopes by SP-ICP-MS or by the use of imaging techniques (i.e.,

332

TEM/EDS). In addition, samples may be analyzed for the presence of known solid-phase species

333

(e.g., using EXASF or dark-field hyperspectral imaging).

334

In Soil Extraction Experiment #3, the effect of lowering the soil-to-reagent ratio was

335

investigated again, but this time the ratios compared were 1:10 and 1:100. The 10-fold lowering


Page 17 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


17 336

of the extraction ratio resulted in a 20-fold increase in the number of particles extracted, while

337

the dissolved-to-particulate mass ratio decreased from 2.1 to 1.2 (Table 1). Results of the soil

338

dilution test showed that the TSPP extraction procedure extracted Ag particles in a fairly

339

consistent and predictable manner (Table 3). The number of particles extracted from samples

340

containing 50, 25 and 10% portions of the AgNP-contaminated soil were 70, 27 and 16% of the

341

number of particles detected in the AgNP-contaminated soil, while no significant changes to

342

particle sizeeqv were observed (Table 1). The proportion of particulate Ag mass relative to the

343

total Ag remained fairly constant, ranging from 7.5 to 11%. These data suggest that the

344

extraction procedure does not elicit a dose-dependent AgNP transformations.

345

Using the finalized extraction method, the number of particles recovered in the spike-recovery

346

sample was 84.1% of those measured in the reference suspension. Similarly 84.8% of the

347

particulate Ag mass was recovered (Table S1, supporting Information). A portion of the

348

unrecovered particulate Ag mass was recovered in the dissolved fraction resulting in 96.8%

349

recovery of the total Ag added. While these results suggest some degree of particle dissolution

350

may have occurred, no significant changes in sizeeqv were detected in the recovered particles

351

(Fig. S4). Neither particle dissolution, nor agglomeration, were evident in the spiked method-

352

blank, which showed ~ 100% recovery for all three Ag parameters. Thus the apparent AgNP

353

dissolution in the spiked soil samples likely occurred from interactions of the freshly added

354

AgNP and soil constituents, and not from the AgNP interaction with the TSPP reagent.

355

Other researchers have found TSPP to be a highly effective reagent for extracting metallic

356

nanoparticles from soil. Regelink et al.29 found that 2 mM TSPP extracted more Fe and Al

357

(hydr)oxide nanoparticles than either 5 mM NaCl or 1 mM NaOH, and related the efficacy of the

358

TSPP extraction to the greater extractability of SOM they also observed in TSPP extracts, thus



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 29

18 359

reasoning greater disaggregation of organo-mineral aggregates. Pyrophosphate is a tetravalent

360

anion and is thus highly effective at replacing SOM adsorbed onto mineral nanoparticulate

361

surfaces leading to greater extraction of SOM and mineral particles associated with organo-

362

mineral heteroaggregates. Scavenging and binding di- and tri-valent elements (i.e., Ca2+, Al3+,

363

Fe2+) that are normally complexed to, and flocculate, soil humic and fulvic components, would

364

also act to further disperse agglomerated SOM.39 While the TSPP used in the Regelink et al.

365

study was adjusted to pH 9.0, to avoid dissolution of the Fe- and Al-(hydr)oxide nanoparticles

366

under study, we did not lower the pH in our study given that these nano-(hydr)oxides likely

367

interact with engineered AgNP to form heteroaggregates28 thus their dissolution should further

368

enhance AgNP extractability. However, it should be noted that if one was trying to extract

369

engineered metallic oxide nanoparticles (e.g., CuO, CeO2), it would be best to understand oxide

370

particle solubility in the extremely alkaline conditions (> pH 10) of the TSPP solution, and lower

371

the reagent pH as necessary.

372

Filtration and Centrifuge Experiments. Results of the filtration experiment showed that

373

despite the stated particle size cut-off being almost an order of magnitude larger than the AgNP

374

used the experiment (i.e., 25 nm), the filtration procedure resulted in significant retention of

375

particles. Filtration retained 11 to 39% of Ag in the AgNP dispersions prepared in the water

376

matrix, and 67 to 72% of Ag in the dispersions prepared in the soil matrix (Table 4). In contrast,

377

retention of dissolved Ag (i.e., Ag+) by the filters was negligible, regardless of matrix. Initial Ag

378

concentration of the solutions did not appear to influence the degree of Ag retention by the filter.

379

Soil particles likely contributed to the clogging of filter pores which exacerbated filter retention

380

of particulate Ag, but had little effect on the dissolved species.


Page 19 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


19 381

Results from the centrifugation experiment also revealed significant loss of AgNP in the

382

supernatant, even at the lowest speed of 1000 x g, which consistently showed recovery rates of

383

80 to 87%, with the initial AgNP concentration and sample matrix having little effect (Fig. 3).

384

Ag recovery in samples worsened with increased centrifuge speed and significantly lower

385

recoveries were observed in samples with higher initial AgNP concentrations. It is highly likely

386

that extracts from Extraction Experiment #1 were impacted by the combination of centrifuge and

387

filtration procedures used. Based on the losses observed in the filtration/centrifuge experiments,

388

predicted that sample 1-1A would contain 70 to 86% fewer Ag particles than sample 2-1, which

389

was essentially a replicate of 1-1A, but for which sedimentation was used to separate micron-

390

sized from nano-sized Ag particles. This estimate was not far off from the actual value: sample

391

1-1A showed approximately 68% fewer particles than sample 2-1 and a larger dissolved-to-

392

particulate mass ratio (Table 1), as expected.

393

While filtering has often been used to separate out larger particles, our results clearly show

394

that filtering with tandem 0.45 / 0.22 μm nylon filters removed a significant portion of the 25 nm

395

particles. This is consistent with the findings of other researchers using similar and different

396

types of filters.19, 34, 41 The accumulation of evidence suggests that filtering is not an appropriate

397

procedure to remove large particles from environmental samples prior to SP-ICP-MS analysis.

398

And while we found that the centrifugation procedures we used also removed a significant

399

portion of nanoparticles, further experimentation could be performed to potentially optimize

400

centrifuge speeds and times. However, the study by Gimbert et al.41 showed that removal of

401

nanoparticles by centrifugation was variable depending on soil type, suggesting that it may be

402

difficult to develop a centrifuge procedure suitable for a wide variety of soil types. Similar to the

403

conclusions of the Gimbert et al. study, we found that sedimentation was the most useful



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 29

20 404

technique to settle out large particles. However, unlike the Gimbert et al. study, where they

405

observed re-aggregation of nanomaterials in their water extracts with prolonged sedimentation

406

times (> 6 h), the TSPP seemed to keep particles dispersed during the full sedimentation time of

407

16 to 18 h, as supported by the spiked sample and spiked blank AgNP recoveries.

408

CONCLUSIONS

409

Results from this study showed that the 2.5 mM TSPP reagent, used in a soil-to-reagent ratio of

410

1:100 (g mL-1), with the added agitation of a sonication wand, extracted the greatest number of

411

AgNP per g of soil and was associated with the smallest relative dissolved Ag fraction. While

412

increasing the mixing time from 30 min to 24 h may potentially extract even more particles, the

413

added time to this procedure should be weighed against the increase in extraction efficiency for a

414

particular test soil. The procedure was shown to extract AgNP in a consistent manner,

415

proportional to the total Ag concentration, and did not appear drive particle dissolution nor

416

agglomeration, but rather, it allowed for a “snap-shot” of the quantity (i.e., number) of the

417

potentially dispersible Ag-containing nanoparticles in a soil, as well as the quantity of Ag mass

418

contained within them, as indicated by the particle sizeeqv. This is particularly useful when

419

investigating the relative changes to, or effects of, nanoparticles within a set of soil samples as is

420

often the case with transformation and ecotoxicity studies. Sedimentation was the best procedure

421

to separate large particles from the nano-particulates in extracts prior to sub-sampling for SP-

422

ICP-MS analysis. Because filtration and centrifugation removed significant portions of AgNP,

423

these procedures should not be used for quantitative analyses. These results provide a rational

424

basis for a standardized soil extraction method that is relatively free of procedural artifacts and

425

results in a quantitative sub-sample of the mineral/metallic soil nanoparticulate fraction that is

426

compatible with SP-ICP-MS analysis and likely suitable for other characterization techniques.


Page 21 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


21 427

ACKNOWLEDGMENTS

428

Funding was provided through the Chemicals Management Plan through Environment and

429

Climate Change Canada. We thank Dr. J. Wang for his contribution for TEM-EDS imaging and

430

analysis, Helene Lalande at McGill University for her expertise in the total Ag analysis in soils

431

and Dr. B. Örmeci in the Department of Civil and Environmental Engineering, Carleton

432

University for her cooperation in the project. Also, thanks to Equilibrium Environmental Inc.

433

(Greg Huber) for the collection of the test soil and the Saint-Hyacinthe wastewater treatment

434

facility for supplying the biosolids.

435

SUPPORTING INFORMATION

436 437

The Supporting Information includes: (1) Characterization of nanomaterials; (2) SP-ICP-MS analytical details; and (3) Spike-recovery analysis (experimental details and results).

438

REFERENCES

439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460

(1) Gottschalk, F.; Nowack, B., The release of engineered nanomaterials to the environment. J. Environ. Monitor. 2011, 13 (5), 1145-1155. (2) Regulatory Cooperation Council (RCC), Nanotechnology Initiative, Final Report on Priority Setting: Development of a joint nanomaterial classification scheme; Available at: Government of Canada NanoPortal (http://nanoportal.gc.ca), accessed May 28, 2012. (3) Bleeker, E. A. J.; Evertz, S.; Geertsma, R. E.; Westra, J.;Wijnhoven, S. W. P. Assessing health and environmental risks of nanoparticles; Dutch National Institute for Public Health and the Environment (RIVM) Report 2014-0157 (2015). The Netherlands. (4) Leeuwen, C. J. v.;Vermeire, T. G. Risk Assessment of Chemicals: An introduction. 2nd ed.; Springer: Dordrecht, The Netherlands, 2007. (5) W. Peijnenburg, T. Jager, Monitoring approaches to assess bioaccessibility and bioavailability of metals: Matrix issues. Ecotox. Environ. Safe. 2003, 56, 63. (6) Wijnhoven, S. W. P.; Peijnenburg, W. J. G. M.; Herberts, C. A.; Hagens, W. I.; Oomen, A. G.; Heugens, E. H. W.; Roszek, B.; Bisschops, J.; Gosens, I.; Van De Meent, D.; Dekkers, S.; De Jong, W. H.; van Zijverden, M.; Sips, A. J. A. M.;Geertsma, R. E. Nano-silver - a review of available data and knowledge gaps in human and environmental risk assessment. Nanotoxicol. 2009, 3 (2), 109-138. (7) Liu, J.; Hurt, R. H. Ion Release Kinetics and Particle Persistence in Aqueous Nano-Silver Colloids. Environ. Sci. Technol. 2010, 44 (6), 2169-2175. (8) Bondarenko, O.; Juganson, K.; Ivask, A.; Kasemets, K.; Mortimer, M.;Kahru, A. Toxicity of Ag, CuO and ZnO nanoparticles to selected environmentally relevant test organisms and mammalian cells in vitro: a critical review. Arch. toxicol. 2013, 87 (7), 1181-1200.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 29

22 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506

(9) Fabrega, J.; Fawcett, S. R.; Renshaw, J. C.;Lead, J. R. Silver nanoparticle impact on bacterial growth: effect of pH, concentration, and organic matter. Environ. Sci. Technol. 2009, 43 (19), 7285-7290. (10) Aruguete, D. M.; Hochella, M. F. Bacteria-nanoparticle interactions and their environmental implications. Environ. Chem. 2010, 7 (1), 3-9. (11) von Moos, N.; Slaveykova, V. I. Oxidative stress induced by inorganic nanoparticles in bacteria and aquatic microalgae - state of the art and knowledge gaps. Nanotoxicol. 2014, 8 (6), 605-630. (12) Jose Ruben, M.; Jose Luis, E.; Alejandra, C.; Katherine, H.; Juan, B. K.; Jose Tapia, R.;Miguel Jose, Y. The bactericidal effect of silver nanoparticles. Nanotechnol. 2005, 16 (10), 2346-2353. (13) Velicogna, J.; Ritchie, E.; Scroggins, R. P.; Princz, J. I. A comparison of the effects of silver nanoparticles and silver nitrate on a suite of soil dwelling organisms in two field soils. Nanotoxicol. 2016, 10 (8), 1144-1151. (14) Diez-Ortiz, M.; Lahive, E.; Svendsen, C.; Spurgeon, D. J.; Kille, P.; Powell, K.; Morgan, A. J.; Jurkschat, K.; Van Gestel, C. A. M.; Mosselmans, J. F. W. Uptake routes and toxicokinetics of silver nanoparticles and silver ions in the earthworm Lumbricus rubellus. Environ. Toxicol. Chem. 2015, 34 (10), 2263-2270. (15) Schlich, K.; Klawonn, T.; Terytze, K.; Hund-Rinke, K. Hazard assessment of a silver nanoparticle in soil applied via sewage sludge. Environ. Sci. Eur. 2013, 25 (17), 23. (16) Coleman, J. G.; Kennedy, A. J.; Bednar, A. J.; Ranville, J. F.; Laird, J. G.; Harmon, A. R.; Hayes, C. A.; Gray, E. P.; Higgins, C. P.; Lotufo, G.; Steevens, J. A. Comparing the effects of nanosilver size and coating variations on bioavailability, internalization, and elimination, using Lumbriculus variegatus. Environ. Toxicol. Chem. 2013, 32 (9), 2069-2077. (17) Degueldre, C.; Favarger, P. Y. Colloid analysis by single particle inductively coupled plasma-mass spectroscopy: a feasibility study. Colloid. Surface. A 2003, 217 (1-3), 137-142. (18) Degueldre, C.; Favarger, P. Y.; Wold, S. Gold colloid analysis by inductively coupled plasma-mass spectrometry in a single particle mode. Anal. Chim. Acta 2006, 555 (2), 263-268. (19) Whitley, A. R.; Levard, C.; Oostveen, E.; Bertsch, P. M.; Matocha, C. J.; Kammer, F. v. d.; Unrine, J. M. Behavior of Ag nanoparticles in soil: Effects of particle surface coating, aging and sewage sludge amendment. Environ. Pollut. 2013, 182 (0), 141-149. (20) Unrine, J. M.; Hunyadi, S. E.; Tsyusko, O. V.; Rao, W.; Shoults-Wilson, W. A.; Bertsch, P. M. Evidence for bioavailability of Au nanoparticles from soil and biodistribution within earthworms (Eisenia fetida). Environ. Sci. Technol. 2010, 44 (21), 8308-8313. (21) Miller, J.; Curtin, D. Electrical Conductivity and Soluble Ions. In Soil Sampling and Methods of Analysis, 2nd ed., Carter, M. R.; Gregorich, E. G., Eds. CRC: 2007. (22) McBride, M. B. Environmental Chemistry of Soils; Oxford Press: New York, N.Y., 1994. (23) Anderson, J. A. H.; Hooper, M. J.; Zak, J. C.;Cox, S. B. Characterization of structural and functional diversity of indigenous soil microbial communities in smelter-impacted and nonimpacted soils. Environ. Toxicol. Chem. 2009, 28 (3), 534-541. (24) McBride, M. B.; Pitiranggon, M.; Kim, B. A Comparison of Tests for Extractable Copper and Zinc in Metal-Spiked and Field-Contaminated Soil. Soil Sci. 2009, 174 (8), 439-444. (25) Menzies, N. W.; Donn, M. J.; Kopittke, P. M., Evaluation of extractants for estimation of the phytoavailable trace metals in soils. Environ. Pollut. 2007, 145 (1), 121-130. (26) Schwertfeger, D. M.; Velicogna, J.; Alexander, J.; McShane, H.; Scroggins, R. P.; Princz, J. I. Ion exchange technique (IET) to characterize Ag+ exposure in soil extracts contaminated


Page 23 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


23 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552

with engineered silver nanoparticles. 2016. Environ. Chem. Accepted for publication Nov. 21.Need DOI. (27) Baalousha, M.; Stolpe, B.; Lead, J. R., Flow field-flow fractionation for the analysis and characterization of natural colloids and manufactured nanoparticles in environmental systems: A critical review. J. Chrom. A 2011, 1218 (27), 4078-4103. (28) Cornelis, G.; Pang, L.; Doolette, C.; Kirby, J. K.; McLaughlin, M. J. Transport of silver nanoparticles in saturated columns of natural soils. Sci. Total Environ. 2013, 463–464 (0), 120130. (29) Regelink, I. C.; Weng, L.; Koopmans, G. F.; van Riemsdijk, W. H. Asymmetric flow field-flow fractionation as a new approach to analyse iron-(hydr)oxide nanoparticles in soil extracts. Geoderma 2013, 202–203 (0), 134-141. (30) Peyrot, C.; Wilkinson, K. J.; Desrosiers, M.; Sauvé, S. Effects of silver nanoparticles on soil enzyme activities with and without added organic matter. Environ. Toxicol. Chem. 2014, 33 (1), 115-125. (31) Kroetsch, D.; Wang, C. Particle Size Distribution. In Soil Sampling and Methods of Analysis, 2nd ed.; Carter, M. R.; Gregorich, E. G., Eds. CRC Press: 2007. (32) Gray, E. P.; Coleman, J. G.; Bednar, A. J.; Kennedy, A. J.; Ranville, J. F.; Higgins, C. P. Extraction and Analysis of Silver and Gold Nanoparticles from Biological Tissues Using Single Particle Inductively Coupled Plasma Mass Spectrometry. Environ. Sci. Technol. 2013, 47 (9), 14315-14323. (33) Neubauer, E.; Schenkeveld, W. D. C.; Plathe, K. L.; Rentenberger, C.; von der Kammer, F.; Kraemer, S. M.; Hofmann, T. The influence of pH on iron speciation in podzol extracts: Iron complexes with natural organic matter, and iron mineral nanoparticles. Sci. Total Environ. 2013, 461–462 (0), 108-116. (34) Cornelis, G.; Kirby, J. K.; Beak, D.; Chittleborough, D.; McLaughlin, M. J. A method for determination of retention of silver and cerium oxide manufactured nanoparticles in soils. Environ. Chem. 2010, 7 (3), 298-308. (35) Schwertfeger, D. M.; Velicogna, J.; Jesmer, A.; Scroggins, R. P.; Princz, J. I. SP-ICP-MS Analysis of Metallic Nanoparticles in Environmental Samples with Large Dissolved Analyte Fractions. Anal. Chem. 2016. DOI:10.1021/acs.analchem.6b02716 (36) Hillel, D. Texture, Particle Size Distribution and Specific Surface. In Introduction to Soil Physics, Academic Press Inc.: San Diego, California, 1982; pp 33-37. (37) Pace, H. E.; Rogers, N. J.; Jarolimek, C.; Coleman, V. A.; Higgins, C. P.; Ranville, J. F. Determining transport efficiency for the purpose of counting and sizing nanoparticles via single particle inductively coupled plasma mass spectrometry. Anal. Chem. 2011, 83 (24), 9361-9369. (38) Lindsay, W. L. Silver. In Chemical Equilibria in Soils; Blackburn Press: Caldwell, New Jersey, 1979; pp 300-304. (39) Kaegi, R.; Voegelin, A.; Ort, C.; Sinnet, B.; Thalmann, B.; Krismer, J.; Hagendorfer, H.; Elumelu, M.; Mueller, E. Fate and transformation of silver nanoparticles in urban wastewater systems. Water Res. 2013, 47 (12), 3866-3877. (40) Hall, G. E. M.; Vaive, J. E.; MacLaurin, A. I. Analytical aspects of the application of sodium pyrophosphate reagent in the specific extraction of the labile organic component of humus and soils. J. Geochem. Explor. 1996, 56, 23-36. (41) Gimbert, L. J.; Haygarth, P. M.; Beckett, R.; Worsfold, P. J. The Influence of Sample Preparation on Observed Particle Size Distributions for Contrasting Soil Suspensions using Flow Field-Flow Fractionation. Environ. Chem. 2006, 3 (3), 184-191.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 29

24 553 554 555 556 557

Tables and Figures Table 1. Treatment details and selected results for the soil extraction experimentsa sample ID

soil batch

ratio soil: extracting reagent reagent

Extraction Experiment #1 1-1A A 0.25 mM TSPP 1-1B A 0.25 mM TSPP 0.25 mM TSPP 1-1C A 1-2A A 0.01 mM NaNO3 1-2B A 0.01 mM NaNO3 0.01 mM NaNO3 1-2C A 1-3A A 0.01 mM KNO3 0.01 mM KNO3 1-3B A 1-3C A 0.01 mM KNO3 1-4A A water 1-4B A water 1-4C A water Extraction Experiment #2 2-1 A 0.25 mM TSPP 2-2 A 2.5 mM TSPP 2-3 A 25 mM TSPP 2-4 A 2.5 mM TSPP 2-5 A 25% TMAH 2-6 C-AgNO3 2.5 mM TSPP Extraction Experiment #3 3-1 3-2 3-3 3-4 3-5 3-6

558 559 560 561

B B B B (50%) B (25%) B (10%)

2.5 mM TSPP 2.5 mM TSPP 2.5 mM TSPP 2.5 mM TSPP 2.5 mM TSPP 2.5 mM TSPP

mix time (min)

nano/ ultrasonica micron size -tion separation

mean sizeeqv (nm)

log [part.] (g-1 soil)

ratio diss./ part.

1:5 1:5 1:5 1:5 1:5 1:5 1:5 1:5 1:5 1:5 1:5 1:5

30 30 50 30 30 50 30 30 50 30 30 50

wand bath none wand bath none wand bath none wand bath none

C/F C/F C/F C/F C/F C/F C/F C/F C/F C/F C/F C/F

37.3 37.0 35.3 38.6 39.1 NA 36.3 35.3 34.5 39.6 39.9 NA

9.1 8.6 8.0 8.4 7.8 NA 8.2 7.9 7.8 8.8 8.1 NA

6.4 8.1 44 17 34 NA 20 39 45 13 23 NA

1:5 1:5 1:5 1:50 1:50 1:10

30 30 30 30 30 30

wand wand wand wand bath wand

SED SED SED SED SED SED

37.3 39.8 NA 35.5 38.4 31.2

9.6 10.1 NA 10.4 10.0 9.1

5.5 2.5 NA 1.3 10.7 4.4

1:10 1:10 1:100 1:100 1:100 1:100

30 1440 30 30 30 30

wand wand wand wand wand wand

SED SED SED SED SED SED

33.4 37.7 35.5 35.8 37.4 36.0

9.6 9.9 10.9 10.8 10.4 10.1

2.1 1.3 1.2 1.3 1.4 1.3

a

C/F = centrifuge and filtration (0.45/0.2 µm); SED = sedimentation; part = particles containing Ag; ratio diss./part. is the mass of Ag detected in the dissolved fraction divided by the mass of particulate Ag based on SP-ICP-MS; mean sizeeqv is based on the diameter of a mono-metal (Ag0) spherical particle; NA = not analyzed.


Page 25 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


25 562 563

Table 2. SP-ICP-MS instrumental and analytical details parameter group ICP-MS component

parameter

parameter value

ICP-MS model

Spray chamber

Perkin Elmer NexION 300D Low pressure PFA nebulizer Cyclonic, glass

Neb gas flow

1.04 L min-1

Plasma RF power

1600 W

Sample flow rate

0.270 mL min-1

Analyte monitored

107

Sample introduction

Manual with 60 s rinse, 20 s read delay

Transport efficiency Instrument dwell time Sample analysis time Readings per sample

9.1 to 9.4%

Nebulizer

ICP-MS settings

Single Particle Parameter

564 565 566 567 568 569 570 571

572 573 574 575 576 577 578 579

Ag

50 µs 60 s (or more) ~ 1.2 x 106 (or more)

Table 3. SP-ICP-MS Results for Soil Dilution Series (Extraction Experiment #3)a sample ID

total Ag (µg g-1)

particle concentration (109 part. g-1)

part. Ag/ total Ag (%)

3-3 3-4 3-5 3-6

848 424 212 85

88 (1) 62 (7) 24 (1) 13.7 (0.4)

7.5 (0.9) 10 (2) 8.4 (0.5) 11 (2)

a

The results are the mean of duplicate extractions; standard error is provided in brackets; total Ag for sample 3-3 was measured by ICP-MS (standard mode) on HNO3-digest samples, whereas total Ag values for all other samples were calculated as 50%, 25% or 10% of the measured value.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 29

26 580 581 582 583

Table 4. Total Ag in samples measured before and after filtration through a tandem 0.45 μm/0.22 μm nylon syringe filtera total Ag (µg L-1) Ag form

584 585 586

matrix

conc. level

before

after

% mean loss (SE)

AgNP

water

low med high

2.2 15.0 93.0

2.0 5.0 56.7

11 (1 ) 67 (3) 39 (2)

AgNP

soil extract

AgNO3

water

AgNO3

soil extract

low med high low med high low med high

2.2 14.4 126.6 2.1 52.3 170 2.7 54.4 158

0.6 4.0 42.0 2.1 51.8 162 2.5 54.6 154

72 (3) 72 (2) 67 (3) 0 (0.05) 1 (0.1) 5 (0.1) 6 (0.2) 0 (0.1) 3 (0.1)

a

SE = standard error of three replicates.


Page 27 of 29

27 587 1500

wand bath none

106 part. g-1 soil

1200 900 600 300 0

588 589 590 591 592 593 594 595 596 597 598 599 600 601

TSPP

KNO3

NaNO3

water

Figure 1. Results from Extraction Experiment #1. Particle concentrations in test soils (106 particles g-1 soil) resulting from the use of various extracting reagents (0.25 mM TSPP, 0.01 M KNO3, 0.01 M NaNO3, water), and the use of various homogenization techniques (ultrasonication wand, ultrasonication bath and no ultrasonication). Bars represent 95% confidence limits (α = 0.05) derived for the mean of three replicates.

30 25

109 parts g-1 soil

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


20 15 10 5 0

602 603 604 605 606 607 608

0.25 mM 2.5 mM 2.5 mM 25% TMAH TSPP (1:5) TSPP (1:5) TSPP (1:50) (1:50)

Figure 2. Particle concentrations (109 particles g-1 soil) in extracts from Extraction Experiment #2. Bars represent 95% confidence limits (α = 0.05) derived for the mean of two replicates.



28 609 water - low water - high soil extract - low soil extract - high

100

75

% Recovery

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 29

50

25

610 611 612 613 614 615 616 617 618 619

1000 x g

3000 x g

6000 x g

Figure 3. Silver % recovery in supernatants after centrifuging AgNP (40 nm) suspensions at three different speeds. Suspensions contained either low (2 or 15 µg L-1) or high (200 µg L-1) concentrations of total Ag and were prepared in either a simple water matrix or in a filtered soil extract matrix (0.25 mM TSPP). Bars represent standard error calculated for triplicate samples.


Page 29 of 29

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


29 620

TOC Artwork:

621 622

623 624


Extracting Metallic Nanoparticles from Soils for Quantitative Analysis

Recommend Documents