Polystyrene Nanoplastics-enhanced Contaminant Transport: Role of

Subscriber access provided by UNIVERSITY OF TOLEDO LIBRARIES

Article

Polystyrene Nanoplastics-enhanced Contaminant Transport: Role of Irreversible Adsorption in Glassy Polymeric Domain Jin Liu, Yini Ma, Dongqiang Zhu, Tianjiao Xia, Yu Qi, Yao Yao, Xiaoran Guo, Rong Ji, and Wei Chen Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b05211 • Publication Date (Web): 08 Feb 2018 Downloaded from http://pubs.acs.org on February 8, 2018

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 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 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 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 34

Environmental Science & Technology

1

Polystyrene Nanoplastics-enhanced Contaminant Transport:

2

Role of Irreversible Adsorption in Glassy Polymeric

3

Domain

4 5

Jin Liu,1,2 Yini Ma,2 Dongqiang Zhu,3 Tianjiao Xia,1 Yu Qi,1 Yao Yao,2 Xiaoran Guo,2

6

Rong Ji,2* Wei Chen1*

7 1

8

College of Environmental Science and Engineering, Ministry of Education Key

9

Laboratory of Pollution Processes and Environmental Criteria, Tianjin Key Laboratory of

10

Environmental Remediation and Pollution Control, Nankai University, Tianjin 300350,

11

China 2

12 13 14 15

State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing 210023, China

3

School of Urban and Environmental Sciences, Peking University, Beijing 100871, China

16 17

Manuscript prepared for Environmental Science & Technology

18 19

*To whom correspondence may be addressed: (Phone/fax) 86-25-8968-0581,

20

86-22-6622-9516; (e-mail) [email protected], [email protected].

21 1

ACS Paragon Plus Environment


22

TOC Art

23 24

2


Page 2 of 34

Page 3 of 34


25

ABSTRACT

26

Nanoplastics (NPs) are becoming an emerging pollutant of global concern. A

27

potential risk is that NPs may serve as carriers to increase the spreading of co-existing

28

contaminants. In this study, we examined the effects of polystyrene nanoplastics (PSNPs,

29

100 nm), used as a model NP, on the transport of five organic contaminants of different

30

polarity in saturated soil. The presence of low concentrations of PSNPs significantly

31

enhanced the transport of nonpolar (pyrene) and weakly polar

32

(2,2',4,4'-tetrabromodiphenyl ether) compounds, but had essentially no effects on the

33

transport of three polar compounds (bisphenol A, bisphenol F and 4-nonylphenol). The

34

strikingly different effects of NPs on the transport of nonpolar/weakly polar versus polar

35

contaminants could not be explained with different adsorption affinities, but was

36

consistent with the polarity-dependent extents of desorption hysteresis. Notably,

37

desorption hysteresis was only observed for nonpolar/weakly polar contaminants, likely

38

because nonpolar compounds tended to adsorb in the inner matrices of glassy polymeric

39

structure of polystyrene (resulting in physical entrapment of adsorbates), whereas polar

40

compounds favored surface adsorption. This hypothesis was verified with supplemental

41

adsorption and desorption experiments of pyrene and 4-nonylphenol using a dense,

42

glassy polystyrene polymer and a flexible, rubbery polyethylene polymer. Overall, the

43

findings of this study underscore the potentially significant environmental implication of

44

NPs as contaminant carriers.

3



45

INTRODUCTION

46

The occurrence of microplastics (MPs) and nanoplastics (NPs) in the environment is

47

becoming an increasing concern, as large quantities of these materials have been detected

48

in environmental media ranging from surface waters and sediments to beach sands and

49

deep-sea waters all over the world.1-4 MPs are operationally defined as plastic particles

50

smaller than 5 mm.5, 6 In the environment MPs can further break down to form NPs (with

51

sizes less than 1 µm or 100 nm,7, 8 depending on different classifications) through

52

prolonged mechanical abrasion, UV radiation, and microbial activity.8, 9 Moreover, NPs

53

may also be introduced to the natural environment from use of consumer products.10 It has

54

been shown that MPs and NPs can affect the metabolism, growth, mortality, and

55

reproduction of aquatic organisms,11, 12 in similar ways as many engineered

56

nanomaterials.13-15 Additionally, accumulation and persistence of MPs and NPs may

57

eventually cause these materials to reach the levels that can affect the functioning and

58

biodiversity of soil.16, 17

59

Owing to their high surface-to-volume ratio and high surface hydrophobicity, MPs

60

and NPs have strong adsorption affinities for a range of environmental contaminants, in

61

particular, highly hydrophobic organic chemicals such as polychlorinated biphenyls,

62

polycyclic aromatic hydrocarbons, polybrominated diphenyl ethers, and perfluorinated

63

surfactants.18-23 Thus, there is a growing concern on an “indirect” effect of MPs and NPs,

64

that is, these materials may serve as carriers to enhance the bioaccumulation of

65

contaminants in living organisms,11, 24-27 and may also result in the so-called “Trojan

66

Horse” effects.28-30 Similarly, MPs and NPs may serve as carriers for environmental

67

contaminants in soil, facilitating the spreading of contaminants.31, 32 Between MPs and 4


Page 4 of 34

Page 5 of 34


68

NPs, the latter will likely have stronger effects on contaminant transport. Specifically,

69

NPs are much smaller in size, which gives them not only greater adsorption affinities for

70

contaminants (e.g., due to the larger surface areas),18, 27 but also high colloidal stability

71

and mobility.33

72

Previous studies on nanoparticles-facilitated contaminant transport indicate that the

73

extent of facilitated transport of contaminants relies largely on the nature of

74

nanoparticles–contaminant interaction.30, 34, 35 In particular, at low nanoparticle (i.e.,

75

“carrier”) concentrations significant facilitated transport of organic contaminants requires

76

not only strong adsorption of contaminants to the carriers, but also significant desorption

77

hysteresis (a collective term referring to both slow desorption kinetics and

78

thermodynamically irreversible adsorption36-38) of contaminants from the carriers.30, 39-41

79

Desorption hysteresis can either be due to the physical entrapment of contaminants in the

80

complex matrices of the carriers, or strong specific adsorptive interactions that lead to

81

irreversible binding of contaminants to the carriers.35 To date, little is known about how

82

the capability of NPs as contaminant carriers varies as a function of contaminant and

83

plastics properties. Even though lessons can be learned from previous work on other

84

nanoparticles (e.g., engineered carbon nanomaterials),29, 30, 42, 43 it is not always possible

85

to extrapolate the specific effects of NPs on contaminant transport from findings using

86

other nanoparticles, considering their differences in size, shape, chemical compositions,

87

pore structures, and aggregation properties in aqueous solutions, to mention a few.

88

The objective of this study was to examine the capabilities of NPs to enhance the

89

transport of common organic contaminants in saturated porous media, and to reveal the

90

predominant mechanisms responsible for NPs-facilitated transport. Polystyrene 5



91

nanoplastics (PSNPs) were selected as representative model NPs, because polystyrene

92

accounts for approximately 90% of the total plastic demand and is widely found in the

93

environment.27, 44 Additionally, polystyrene particles have been used as a probe MPs and

94

NPs in many research to investigate the detrimental effects of MPs and NPs on

95

organisms.11, 27, 45, 46 Five model organic compounds, including pyrene,

96

2,2',4,4'-tetrabromodiphenyl ether (BDE47), bisphenol A (BPA), bisphenol F (BPF) and

97

4-nonylphenol (4-NP) were selected as the test contaminants to represent organic

98

contaminants of varied polarity and hydrophobicity. Additionally, pyrene and BDE47 are

99

persistent organic contaminants, and BPA, BPF and 4-NP are common endocrine

100

disruptor compounds.47-49 The effects of PSNPs on the transport of the five contaminants

101

were examined at different PSNPs concentrations, using column transport experiments.

102

Batch adsorption and desorption experiments of the contaminants were carried out to

103

understand the differential effects of PSNPs on the transport of nonpolar/weakly polar

104

compounds versus that of polar compounds. Environmental implications are discussed.

105 106 107

MATERIALS AND METHODS Materials. Fluorescent PSNPs, supplied as an aqueous suspension of polymeric

108

particles (1% solids by weight), were purchased from Thermo Fisher Scientific Inc.

109

(Fremont, CA). The average particle size, confirmed with scanning electron microscopy

110

(SEM) (S-3400 N II, Hitachi, Japan) by measuring more than 200 individual particles

111

(see Supporting Information (SI) Figure S1), was 80.4 ± 7.9 nm. The Fourier transform

112

infrared (FTIR) transmission spectra of the PSNPs (SI Figure S2), obtained using a

113

Thermo Nicolet NEXUS 870 spectrometer (Thermo Nicolet Corporation, Madison, WI), 6


Page 6 of 34

Page 7 of 34


114

confirmed that material was free of surface functional groups. Two micro-sized (50−100

115

µm) polymers, including a polystyrene and a low-density polyethylene, were obtained

116

from J&K Chemical (Beijing, China) and Sigma−Aldrich (St. Louis, MO), respectively.

117

14

C-labeled pyrene (2.18 GBq/mmol) was purchased from American Radiolabeled

118

Chemicals (St. Louis, MO). 14C-labeled BDE47 (2.44 GBq/mmol), BPA (0.74 GBq/mmol),

119

BPF (2.82 GBq/mmol) and 4-NP (2.78 GBq/mmol) were synthesized using 14C-labeled

120

phenol as a precursor. The physicochemical characteristics of the compounds are given in

121

SI Table S1. Non-labeled pyrene, BDE47, BPA, BPF and 4-NP (all with purity >99%) were

122

purchased from Sigma−Aldrich (St. Louis, MO).

123

Lula soil was collected from a ranch near Lula, OK, USA. The soil contained 45%

124

sand, 36% silt and 19% clay. The fractional organic carbon (fOC) value of the soil was

125

0.37%. The particle size distribution of the soil (SI Figure S3) was measured using a laser

126

diffraction particle size analyzer (Mastersizer 3000, Malvern, U.K.). The uniformity of the

127

soil was 0.65, and the coefficient of uniformity was 8.50.

128

Column Transport Experiments. Lula soil was dry-packed into Omnifit

129

borosilicate glass columns (10 cm × 0.66 cm, Bio-Chem Valve Inc., Boonton, NJ) with

130

10-µm stainless-steel screens (Valco Instruments Inc., Houston, TX) on both ends. Each

131

column contained approximately 3.5 g of soil (dry-weight) with an average length of

132

approximately 7.0 cm. The columns were operated in an upward direction using syringe

133

pumps (KD Scientific, Holliston, MA). Once packed, the column was flushed at a flow rate

134

of 3 mL/h with at least 100 mL deionized water followed by 180 mL background

135

electrolyte solution (0.5 mM NaCl). The porosity and dead volume were determined by

136

inverse-fitting the breakthrough curves (BTCs) of KBr (used as a conservative tracer). 7



137

The experimental protocols of the column experiments are summarized in Table 1 and

138

SI Table S2. To prepare the influents, the as-purchased PSNPs suspension was first

139

ultrasonicated at 100 W (Vibra-Cell VCX800, Sonics & Material, Newtown, CT) for 5 min

140

and then diluted with a background electrolyte of 0.5 mM NaCl in amber glass vials to give

141

the working PSNPs concentrations of 5.0−20.3 mg/L. Immediately after adding the PSNPs

142

suspension, a stock solution of an organic contaminant in methanol was added to each vial

143

to give a contaminant concentration of approximately 10 µg/L. The volume percentage of

144

methanol was kept below 0.1% (v/v) to minimize cosolvent effects. The vials were sealed

145

with Teflon-lined screw caps and equilibrated by tumbling end-over-end at 3 rpm. The

146

concentrations of dissolved and PSNPs-adsorbed contaminants in the influents were

147

determined using a negligible depletion solid-phase micro-extraction approach (see SI for

148

detailed procedures). The transmission electron microscopy (TEM) images (JEM-2100,

149

JEOL, Tokyo, Japan) of the working suspensions showed that PSNPs were well dispersed

150

(SI Figure S4) and were stable during the course of column experiments, as indicated by

151

the essentially overlapping dynamic light scattering (DLS) (ZetaSizer Nano ZS, Malvern

152

Instruments, Worcestershire, U.K.) profiles over 14 d (SI Figure S5). The average

153

hydrodynamic diameters of PSNPs in different influents were characterized with DLS,

154

and the ζ potential values was measured using a ZetaSizer Nano ZS system (Malvern

155

Instruments, Worcestershire, U.K.); these data are summarized in Table S2.

156

In a typical column experiment, the influent was pumped into the column from a

157

100-mL glass syringe (SGE Analytical Science, Victoria, Australia). After 60 pore

158

volumes (PV), a background electrolyte of 0.5 mM NaCl was used to flush the columns,

159

until contaminant concentration in the effluent was below the detection limit. Effluent 8


Page 8 of 34

Page 9 of 34


160

samples were collected every 2–3 PV. Each collected sample was split into two aliquots to

161

measure the concentrations of PSNPs and contaminants. The concentrations of PSNPs

162

were determined using a fluorescence spectrometer (FluoroMax-4, Horiba Scientific,

163

Edison, NJ) (SI Figure S6), based on a pre-established calibration curve of PSNPs (SI

164

Figure S7). (Adsorption of the five contaminants had no effects on the fluorescence

165

intensity of PSNPs; SI Figure S8). The contaminants were quantified by determining

166

radioactivity using a liquid scintillation counter (LS6500, Beckman Coulter, Fullerton, CA)

167

(the detailed procedures are given in SI). In the experiments of pyrene and BDE47,

168

selected effluent samples were taken to verify that the contaminants in the effluents were

169

mainly associated with the PSNPs, using a previously developed method.41 In the

170

experiments of BPA and BPF, the contaminants in the influent and effluent of randomly

171

selected samples were analyzed using reversed-phase high-performance liquid

172

chromatography (Agilent HPLC Series 1100, Agilent Technologies, Germany) with a

173

radio flow detector to confirm that no degradation of BPA and BPF occurred in the soil

174

column (representative chromatograms are shown in SI Figure S9).

175

Batch Adsorption and Desorption Experiments. Adsorption experiments to

176

PSNPs were carried out using a batch adsorption approach.50 Aliquots of 5, 10, or 20 mg/L

177

PSNPs suspension in 0.5 mM NaCl were added to a series of 20-mL amber glass vials.

178

Then, a certain amount of a contaminant stock solution was added to each of the vials. The

179

vials were sealed with Teflon-lined screw caps and tumbled end-over-end at 3 rpm for 2 d

180

(for BPA and BPF) or 14 d (for pyrene, BDE47, and 4-NP) to reach adsorption

181

equilibrium.27, 51, 52 Afterward, the above-mentioned negligible depletion solid-phase

182

microextraction approach was used to determine the concentrations of dissolved and 9



183

PSNPs-adsorbed contaminants. Each adsorption isotherm data point was run in duplicate.

184

In desorption experiments the suspensions in selected vials in the adsorption isotherm

185

experiments were each split into two aliquots of equal volumes (approximately 10 mL) in

186

two 20-mL amber glass vials. Then, adsorbate-free background electrolyte was added to

187

each vial. The diluted suspensions were equilibrated by tumbling the vials end-over-end at

188

3 rpm, to initiate desorption of the adsorbate from PSNPs. The aqueous-phase

189

concentrations of the contaminants were measured using the negligible depletion

190

solid-phase microextraction approach mentioned above. The total mass of the adsorbate in

191

each vial was also measured. The concentrations in the adsorbed phase were obtained

192

based on mass balance. Two data points of each adsorption isotherm were selected to do

193

the desorption experiments. Each desorption experiment was run in duplicate.

194 195 196

For the convenience of quantification and comparison of desorption hysteresis, the hysteresis index (HI) was calculated:53 HI =

qed − qes qes

(1)

T ,Ce

197

where qed is adsorbed-phase concentration observed in the desorption experiment that is

198

in equilibrium with an aqueous-phase concentration Ce, and qes is the adsorbed-phase

199

concentration calculated from Ce assuming that desorption is reversible. If desorption is

200

completely reversible, HI is equal to 0; the higher the HI value, the greater degree of

201

desorption hysteresis. The subscripts T and Ce specify constant conditions of temperature

202

and equilibrium concentration of solute.

203 204

The sorption isotherms of the contaminants to Lula soil, as well as adsorption and desorption experiments of pyrene and 4-NP to and from micro-sized polystyrene and 10


Page 10 of 34

Page 11 of 34


205

polyethylene, were obtained using a batch approach developed in our previous study (see

206

SI for detailed procedures).54

207 208 209

RESULTS AND DISCUSSION Nanoplastics Significantly Enhance Transport of Nonpolar and Weakly Polar

210

Organic Contaminants. The presence of small amount of PSNPs (5.0 to 20.0 mg/L)

211

significantly enhanced the transport of the model nonpolar organic contaminant, pyrene,

212

and the weakly polar organic contaminant, BDE47 (Figure 1). In the absence of PSNPs in

213

the influent, negligible breakthrough of pyrene or BDE47 was observed after 80 PV.

214

However, the presence of 5.0−20.0 mg/L PSNPs in the influent resulted in significantly

215

increased transport of both pyrene and BDE47. For pyrene, the maximum breakthrough

216

(as indicated by C/C0) increased to 33.9 ± 0.2% in the presence of 5.1 mg/L PSNPs, and

217

to 61.8 ± 0.2% when the concentration of PSNPs was 19.4 mg/L. Similarly, the

218

maximum breakthrough of BDE47 reached 29.7–49.8% in the presence of 5.0−20.0 mg/L

219

PSNPs.

220

Nanoplastics Had Negligible Effects on Transport of Polar Organic

221

Contaminants. In contrast to the significant transport enhancement effects of PSNPs on

222

pyrene and BDE47, the presence of PSNPs (5.0–20.3 mg/L) in the influent had

223

essentially no effects on the transport of the three polar compounds, i.e., BPA, BPF, and

224

4-NP (Figure 2). In the absence of PSNPs, the three compounds exhibited different

225

degrees of mobility: BPA was relatively mobile, with maximum breakthrough of 86.7%;

226

the less mobile BPF reached a maximum breakthrough of 57.0%; 4-NP exhibited the

227

lowest mobility, with maximum breakthrough reaching only 4.6%. Interestingly, for all 11



228

three compounds the BTCs in the presence of PSNPs overlapped with the one without

229

PSNPs, indicating that PSNPs played minimal roles in the transport of these three

230

compounds. It is particularly intriguing and counterintuitive that PSNPs had essentially

231

no effects on the transport of 4-NP, in that, 4-NP exhibited similar low mobility to pyrene

232

and BDE47 and PSNPs significantly facilitated the transport of pyrene and BDE47. Thus,

233

the remarkable difference in the transport-enhancement effects between 4-NP and

234

pyrene/BDE47 indicates that different transport-enhancement mechanisms were in play

235

for polar vs. nonpolar/weakly polar organic contaminants.

236

Differential Effects on Transport of Nonpolar/Weakly Polar vs. Polar

237

Contaminants Cannot Be Explained with Different Adsorption Affinities. While

238

strong binding of contaminants to colloidal particles is a prerequisite for

239

colloid-enhanced transport of contaminants, the remarkable differences in the effects of

240

PSNPs on the transport of nonpolar/weakly polar vs. polar contaminants cannot be

241

explained with the differences in adsorption affinities of PSNPs for these compounds.

242

Among the five compounds tested, both of the nonpolar/weakly polar compounds

243

(pyrene and BDE47), as well as one of the polar compounds (4-NP) exhibited very low

244

mobility in the absence of PSNPs (Figures 1 and 2). Thus, for these three compounds,

245

any significant transport enhancement in the presence of PSNPs should be largely

246

attributable to the co-transport of the contaminant with PSNPs (this was verified

247

experimentally with selected effluent samples of pyrene and BDE47, as the mass of these

248

contaminants in the dissolved phase was largely below the detection limits, i.e., most of

249

the contaminants detected in the effluent should have been those originally adsorbed to

250

PSNPs in the influent). Since 92–98% of pyrene in the influent was bound to PSNPs 12


Page 12 of 34

Page 13 of 34


251

(Table 1) and the breakthrough of PSNPs reached ~69.0% (Figure 1a), the high

252

breakthrough of pyrene (33.9–61.8%) (Table 1) is justified. Similarly, the 29.7–49.8%

253

breakthrough of BDE47 was consistent with its strong adsorption to PSNPs (Table 1).

254

Intriguingly, 4-NP also adsorbed to PSNPs strongly, in that 44–70% of 4-NP in the

255

influent was adsorbed to PSNPs (Table 1), and in the column experiments of 4-NP the

256

breakthrough of the carriers (i.e., PSNPs) also reached ~64.7%. Thus, it would be

257

reasonable to expect that PSNPs should also markedly enhance the transport of 4-NP,

258

which was not the case (Figure 2c).

259

Differential Effects on Transport of Nonpolar/Weakly Polar vs. Polar

260

Contaminants Are Attributable to Different Extents of Desorption Hysteresis. In our

261

previous studies we demonstrated that at low nanoparticle concentrations the significance

262

of transport-enhancement effects largely depends on how irreversibly a contaminant is

263

adsorbed to the nanoparticles.35 Thus, one explanation for the different effects of PSNPs

264

on the transport of pyrene/BDE47 versus 4-NP is that pyrene and BDE47 exhibited

265

stronger irreversible adsorption to PSNPs than did 4-NP. This can be understood with the

266

following analysis on the effects of PSNPs on contaminant transport, considering two

267

extreme cases: 1) desorption of contaminants from PSNPs is instantaneous and

268

completely reversible; and 2) desorption is completely irreversible. If assuming

269

desorption is instantaneous and completely reversible, then the maximum contaminant

270

breakthrough can be estimated using the following equation:35

271 272

C / C0 =

V + CPSNPs ⋅ V ⋅ K d_PSNPs V + msoil ⋅ K d_soil + CPSNPs ⋅ V ⋅ K d_PSNPs

(2)

where CPSNPs (kg/L) is the concentration of PSNPs in the effluent; V (mL) is the volume 13



273

of the suspension flowed through the column; msoil (g) is the mass of soil in the column;

274

and Kd_PSNPs (L/kg) and Kd_soil (L/kg) are the distribution coefficients of 4-NP, pyrene, or

275

BDE47 to PSNPs and soil, respectively (Kd_PSNPs and Kd_soil can be obtained from the

276

sorption isotherms in Figure 3). The simulation results (Figure 4) indicate that for all

277

three contaminants if desorption from PSNPs is completely reversible, then PSNPs (even

278

at 20 mg/L, the highest tested concentration) would have little effect on the transport of

279

these contaminants. This is because the mass of PSNPs was too low compared with that

280

of soil organic matter, which competed with PSNPs for contaminants (even though

281

adsorption affinities of pyrene, BDE47, and 4-NP to PSNPs were approximately 3–4

282

orders of magnitude higher than those to the soil). If assuming desorption of

283

contaminants from PSNPs is completely irreversible, then the BTCs of contaminants can

284

be estimated based on the BTCs of PSNPs and the mass fractions of contaminants

285

adsorbed to PSNPs in the influents (Table 1). For instance, the BTCs of pyrene and

286

BDE47 would overlap with the BTCs of the PSNPs, since essentially all the pyrene and

287

BDE47 in the influents were bound to PSNPs. Accordingly, by comparing the BTCs of a

288

contaminant with the estimated ones assuming the two extreme cases, one can

289

qualitatively understand how irreversibly a contaminant was bound to PSNPs during the

290

transport in the column.

291

Figure 4 shows that the BTC of pyrene nearly overlaps with (sits only slightly below)

292

the estimated one assuming completely irreversible adsorption. In comparison, the BTC

293

of BED47 falls considerably below the estimated one assuming completely irreversible

294

adsorption, but is substantially above that assuming desorption is completely reversible.

295

Interestingly, the BTC of 4-NP is only slightly upshifted compared with that assuming 14


Page 14 of 34

Page 15 of 34


296

instantaneous and reversible desorption. Evidently, the differential effects of PSNPs on

297

the transport of nonpolar/weakly polar compounds versus polar contaminants were

298

attributable to the different extents of desorption hysteresis of these compounds from

299

PSNPs.

300

We confirmed the dependency of irreversible adsorption to PSNPs on contaminant

301

polarity using batch desorption experiments. Figure 5 compares the desorption of the five

302

contaminants from PSNPs (10 mg/L). Remarkable desorption hysteresis of pyrene and

303

BDE47 were observed, whereas the desorption of all three polar contaminants was

304

essentially reversible. Strikingly, among pyrene, BDE47 and 4-NP the hysteresis index

305

values follow the order of pyrene (0.52–0.63) > BDE47 (0.31–0.43) >> 4-NP (0.04–0.16),

306

corroborating the different extents of desorption hysteresis estimated based on Figure 4.

307

Thus, the fact that transport enhancement by PSNPs was only observed for

308

nonpolar/weakly polar contaminants is attributable to the strong desorption hysteresis of

309

such compounds to PSNPs. Note that even though only pyrene and BDE47 were selected

310

for the nonpolar and weakly polar group, the difference between these two compounds

311

appears to indicate that the degree of desorption hysteresis depended on the polarity of

312

the compounds (i.e., pyrene is less polar than BDE47, see SI Table S1).

313

Polarity-dependent Desorption Hysteresis Is Linked to Glassy Polymeric

314

Structure of Polystyrene Nanoplastics. Our previous studies showed that desorption

315

hysteresis of organic contaminants from nanoparticles is attributable to two processes, i.e.,

316

entrapment of contaminants in porous nanoparticle aggregates, and irreversible

317

adsorption due specific polar interactions between contaminant and nanoparticles (e.g.,

318

hydrogen bonding).35, 41 Thus, nanoparticles in the form of nano-aggregates (e.g., C60 15



319

aggregates, or graphene oxide under solution chemistry conditions favoring aggregation,

320

e.g., at high ionic strength) can enhance the transport of nonpolar compounds without

321

incurring any specific polar interactions. In contrast, well dispersed nanoparticles (e.g.,

322

graphene oxide at low ionic strength) can only enhance the transport of highly polar

323

compounds (e.g., 1-naphthol, which exhibits irreversible adsorption to graphene oxide

324

through H-bonding).35 The fact that PSNPs were free of surface functional groups (FTIR

325

spectrum, SI Figure S2), as well as the observation that desorption hysteresis was only

326

observed for nonpolar and weakly polar compounds, indicate that the cause of the strong

327

desorption hysteresis observed for pyrene and BDE47 had to be the physical entrapment

328

of these contaminants in PSNPs.

329

Interestingly, the PSNPs dispersed well in the influents of column experiments (SI

330

Figure S4), as the hydrodynamic diameters of PSNPs were around 100 nm (only slightly

331

higher than the true sizes of the particles (SI Figure S1)), with very low polydispersity

332

index (SI Table S2). Furthermore, neither prolonged sitting time nor increased particle

333

and contaminant concentrations resulted in noticeably increased tendency of particle

334

aggregation (SI Figure S5; SI Table S3 and Figure S10). Based on the above analysis, we

335

offer the following hypothesis to explain the vastly different degrees of desorption

336

hysteresis between nonpolar and polar compounds from PSNPs. That is, adsorption of

337

nonpolar versus polar compounds occurred in different domains of PSNPS, leading to

338

polarity-dependent desorption hysteresis. Polystyrene is known to have dense, glassy

339

structure, due to the cross-linking of chains.55, 56 For nonpolar, highly hydrophobic

340

organic compounds the inner spaces of such glassy structure are favorable adsorption

341

sites due to micropore-filling,57 and desorption from these inner spaces into the bulk 16


Page 16 of 34

Page 17 of 34


342

aqueous solution is energetically unfavorable, and can be highly hysteretic.51, 58, 59 Note

343

that physical entrapment in the glassy domains of soil organic matter has been considered

344

a major mechanism controlling desorption hysteresis of hydrophobic organic compounds

345

from soil.37, 59 In comparison, polar and less hydrophobic organic contaminants have a

346

much lower tendency in entering the glassy polymeric domain and likely favor surface

347

adsorption. Accordingly, desorption of polar contaminants from polystyrene would be

348

much more reversible.

349

To verify this hypothesis, we conducted additional adsorption and desorption

350

experiments of pyrene and 4-NP using two micro-sized polystyrene and polyethylene

351

polymers. The two polymers were similar in size and shape, but varied in polymeric

352

structure. In particular, the polyethylene material had relatively rubbery and flexible

353

structure, whereas the polystyrene material had dense, glassy polymeric structure. As

354

expected, desorption hysteresis of pyrene was only observed on the glassy polystyrene

355

but not on the rubbery polyethylene (Figure 6), consistent with the hypothesis that the

356

significant desorption hysteresis of nonpolar compounds was linked to the rigid glassy

357

polymeric inner structure of PSNPs. In contrast, desorption of 4-NP from both

358

polystyrene and polyethylene was essentially reversible, in line with the hypothesis that

359

polar compounds favor surface adsorption. Moreover, the desorption kinetics data show

360

that desorption of pyrene from the rubbery polyethylene was very fast, in that apparent

361

desorption equilibrium was reached within 2 h, whereas desorption from the glassy

362

polystyrene was much slower (Figure 7a). This striking difference further corroborates

363

the physical entrapment of pyrene within glassy polymeric structures, as compared with

364

partitioning driven desorption from rubbery polymers. Notably, rapid desorption kinetics 17



365

of 4-NP was observed not only on the rubbery polyethylene, but also on the glassy

366

polystyrene, as apparent desorption equilibrium was reach within 2 h (Figure 7b),

367

consistent with the proposed surface adsorption mechanism for 4-NP.

368

Environmental Implications. The wide spreading of MPs and NPs in the

369

environment has drawn concerns about their potential detrimental environmental effects.

370

The findings of this study underscore a potentially significant environmental implication

371

of NPs, that is, NPs may significantly enhance the spreading of organic contaminants in

372

the environment. Given the potentially high concentrations of NPs in the environment,42

373

these materials may become one of the most important contaminant carriers. Even though

374

only one specific type of nanoplastics was tested in this study, the interesting observation

375

that the polymeric structures of nanoplastics fundamentally determine the significance of

376

NP-enhanced contaminant transport (and consequently, resulting in highly

377

compound-specific effects) warrants further studies using nanoplastics covering a wide

378

range of variables of polymeric properties.

379 380

Acknowledgments. This project was supported by the National Natural Science Foundation

381

of China (Grants 21425729 and 21237002), the National Key Research and Development

382

Program of China (2016YFC1402203), and the Ministry of Science and Technology of

383

China (Grant 2014CB932001).

384 385

Supporting Information Available: Procedures used to determine of the concentrations of

386

dissolved and PSNPs-adsorbed organic contaminants, detailed procedures of liquid

387

scintillation counting, procedures of sorption experiments to Lula soil, and adsorption and 18


Page 18 of 34

Page 19 of 34


388

desorption experiments to and from micro-sized polymers; tables summarizing the

389

physicochemical characteristics of contaminants, average hydrodynamic diameter and ζ

390

potential of PSNPs in the influents, and particle size distribution of PSNPs as affected by

391

particle and contaminant concentrations; figures showing the SEM images, FTIR spectra,

392

TEM images, fluorescence spectra, and calibration curves of PSNPs, particle size

393

distribution of Lula soil, particle size distribution of PSNPs as affected by sitting time and

394

concentrations of contaminants and particles, effects of contaminant adsorption on the

395

measurement of fluorescence intensity of PSNPs, as well as representative

396

radio-chromatograms of BPA and BPF. This information is available free of charge via the

397

Internet at http://pubs.acs.org.

398 399

Notes—The authors declare no competing financial interest.

400 401

REFERENCES

402

1.

403

J. Nanoplastic in the North Atlantic subtropical gyre. Environ. Sci. Technol. 2017, 51 (23),

404

13689-13697.

405

2.

406

Microplastics in sediments: A review of techniques, occurrence and effects. Mar. Environ.

407

Res. 2015, 111, 5-17.

408

3.

409

evaluation of surface micro- and mesoplastic pollution in pelagic ecosystems of the

410

Western Mediterranean Sea. Environ. Sci. Pollut. Res. 2015, 22 (16), 12190-12197.

Ter Halle, A.; Jeanneau, L.; Martignac, M.; Jardé, E.; Pedrono, B.; Brach, L.; Gigault,

Van Cauwenberghe, L.; Devriese, L.; Galgani, F.; Robbens, J.; Janssen, C. R.

Faure, F.; Saini, C.; Potter, G.; Galgani, F.; Alencastro, L. F. D.; Hagmann, P. An

19



411

4.

Phuong, N. N.; Zalouk-Vergnoux, A.; Poirier, L.; Kamari, A.; Châtel, A.; Mouneyrac,

412

C.; Lagarde, F. Is there any consistency between the microplastics found in the field and

413

those used in laboratory experiments? Environ. Pollut. 2016, 211, 111-123.

414

5.

415

Workshop on the Occurance, Effects, and Fate of Microplastic Marine Debris 2009;

416

Technical Memorandum NOSOR& R-30; Department of Commerce, National Oceanic

417

and Atmospheric Administration: Washington, DC, 2009.

418

6.

419

Microplastics in four estuarine rivers in the Chesapeake Bay, U.S.A. Environ. Sci. Technol.

420

2014, 48 (24), 14195-14202.

421

7.

422

environment-sources, fates and effects. Sci. Total Environ. 2016, 566-567, 15-26.

423

8.

424

environment. Critical Review. In: Bergmann M, Gutow L, Klages M (eds) Marine

425

Anthropogenic Litter. Springer, Berlin, ISBN 978-3-319-16510-3, p 325-340.

426

9.

427

Environ. Sci.: Processes Impacts. 2015, 17 (10), 1712-1721.

428

10. Hernandez, L. M.; Yousefi, N.; Tufenkji, N. Are there nanoplastics in your personal

429

care products? Environ. Sci. Technol. Lett. 2017, 4 (7), 280-285.

430

11. Chae, Y.; An, Y. J. Effects of micro- and nanoplastics on aquatic ecosystems: Current

431

research trends and perspectives. Mar. Pollut. Bull. 2017, 124 (2), 624-632.

432

12. Besseling, E.; Wang, B.; Lürling, M.; Koelmans, A. A. Nanoplastic affects growth of S.

433

obliquus and reproduction of D. magna. Environ. Sci. Technol. 2014, 48 (20),

Arthur, C.; Baker, J.; Bamford, H. Proceedings of the International Research

Yonkos, L. T.; Friedel, E. A.; Perezreyes, A. C.; Ghosal, S.; Arthur, C. D.

da Costa, J. P.; Santos, P. S. M.; Duarte, A. C.; Rocha-Santos, T. (Nano)plastics in the

Koelmans, A. A.; Besseling, E.; Shim, W. J. 2015. Nanoplastics in the aquatic

Mattsson, K.; Hansson, L. A.; Cedervall, T. Nano-plastics in the aquatic environment.

20


Page 20 of 34

Page 21 of 34


434

12336-12343.

435

13. Reddy, P. V. L.; Hernandez-Viezcas, J. A.; Peralta-Videa, J. R.; Gardea-Torresdey, J. L.

436

Lessons learned: Are engineered nanomaterials toxic to terrestrial plants? Sci. Total

437

Environ. 2016, 568, 470-479.

438

14. Lv, J.; Zhang, S.; Luo, L.; Zhang, J.; Yang, K.; Christie, P. Accumulation, speciation

439

and uptake pathway of ZnO nanoparticles in maize. Environ. Sci.: Nano. 2015, 2 (1),

440

68-77.

441

15. Zhang, M.; Gao, B.; Chen, J.; Li, Y. Effects of graphene on seed germination and

442

seedling growth. J. Nanopart. Res. 2015, 17 (2), 78.

443

16. Rillig, M. C. Microplastic in terrestrial ecosystems and the soil? Environ. Sci. Technol.

444

2012, 46 (12), 6453-6454.

445

17. Petersen, E. J.; Zhang, L.; Mattison, N. T.; O’Carroll, D. M.; Whelton, A. J.; Uddin, N.;

446

Nguyen, T.; Huang, Q. G.; Henry, T. B.; Holbrook, R. D.; Chen, K. L. Potential release

447

pathways, environmental fate, and ecological risks of carbon nanotubes. Environ. Sci.

448

Technol. 2011, 45 (23), 9837-9856.

449

18. Velzeboer, I.; Kwadijk, C. J. A. F.; Koelmans, A. A. Strong sorption of PCBs to

450

nanoplastics, microplastics, carbon nanotubes, and fullerenes. Environ. Sci. Technol. 2014,

451

48 (9), 4869-4876.

452

19. Liu, L.; Fokkink, R.; Koelmans, A. A. Sorption of polycyclic aromatic hydrocarbons

453

to polystyrene nanoplastic. Environ. Toxicol. Chem. 2015, 35 (7), 1650-1655.

454

20. Chua, E. M.; Shimeta, J.; Nugegoda, D.; Morrison, P. D.; Clarke, B. O. Assimilation of

455

polybrominated diphenyl ethers from microplastics by the marine amphipod, Allorchestes

456

compressa. Environ. Sci. Technol. 2014, 48 (14), 8127-8134. 21



457

21. Llorca, M.; Farré, M.; Karapanagioti, H. K.; Barceló, D. Levels and fate of

458

perfluoroalkyl substances in beached plastic pellets and sediments collected from Greece.

459

Mar. Pollut. Bull. 2014, 87 (1–2), 286-291.

460

22. Bao, L. J.; Jing, Y.; Zeng, E. Y. Sorption of PBDE in low-density polyethylene film:

461

Implications for bioavailability of BDE-209. Environ. Toxicol. Chem. 2011, 30 (8),

462

1731-1738.

463

23. Hüffer, T.; Hofmann, T. Sorption of non-polar organic compounds by micro-sized

464

plastic particles in aqueous solution. Environ. Pollut. 2016, 214, 194-201.

465

24. Rochman, C. M.; Hoh, E.; Kurobe, T.; Teh, S. J. Ingested plastic transfers hazardous

466

chemicals to fish and induces hepatic stress. Sci. Rep. 2013, 3 (7476), 3263.

467

25. Browne, M. A.; Niven, S. J.; Galloway, T. S.; Rowland, S. J.; Thompson, R. C.

468

Microplastic moves pollutants and additives to worms, reducing functions linked to health

469

and biodiversity. Curr. Biol. 2013, 23 (23), 2388-2392.

470

26. Koelmans, A. A.; Besseling, E.; Wegner, A.; Foekema, E. M. Plastic as a carrier of

471

POPs to aquatic organisms: A model analysis. Environ. Sci. Technol. 2013, 47 (14),

472

7812-7820.

473

27. Ma, Y.; Huang, A.; Cao, S.; Sun, F.; Wang, L.; Guo, H.; Ji, R. Effects of nanoplastics

474

and microplastics on toxicity, bioaccumulation, and environmental fate of phenanthrene in

475

fresh water. Environ. Pollut. 2016, 219, 166-173.

476

28. Deng, R.; Lin, D.; Zhu, L.; Majumdar, S.; White, J. C.; Gardea-Torresdey, J. L.; Xing,

477

B. Nanoparticle interactions with co-existing contaminants: Joint toxicity,

478

bioaccumulation and risk. Nanotoxicology. 2017, 11 (5), 591-612.

479

29. Koelmans, A. A.; Bakir, A.; Burton, G. A.; Janssen, C. R. Microplastic as a vector for 22


Page 22 of 34

Page 23 of 34


480

chemicals in the aquatic environment: Critical review and model-supported

481

reinterpretation of empirical studies. Environ. Sci. Technol. 2016, 50 (7), 3315-3326.

482

30. Hofmann, T.; von der Kammer, F. Estimating the relevance of engineered

483

carbonaceous nanoparticle facilitated transport of hydrophobic organic contaminants in

484

porous media. Environ. Pollut. 2009, 157 (4), 1117-1126.

485

31. Sojitra, I.; Valsaraj, K. T.; Reible, D. D.; Thibodeaux, L. J. Transport of hydrophobic

486

organics by colloids through porous media 1. Experimental results. Colloids Surf., A 1995,

487

94 (2-3), 197-211.

488

32. Johari, W. L.; Diamessis, P. J.; Lion, L. W. Mass transfer model of

489

nanoparticle-facilitated contaminant transport in saturated porous media. Water Res. 2010,

490

44 (4), 1028-1037.

491

33. Li, Y.; Wang, Y.; Pennell, K. D.; Abriola, L. M. Investigation of the transport and

492

deposition of fullerene (C60) nanoparticles in quartz sands under varying flow conditions.

493

Environ. Sci. Technol. 2008, 42 (19), 7174-7180.

494

34. Wang, L.; Huang, Y.; Kan, A. T.; Tomson, M. B.; Chen, W. Enhanced transport of

495

2,2′,5,5′-polychlorinated biphenyl by natural organic matter (NOM) and

496

surfactant-modified fullerene nanoparticles (nC60). Environ. Sci. Technol. 2012, 46 (10),

497

5422-5429.

498

35. Qi, Z.; Hou, L.; Zhu, D.; Ji, R.; Chen, W. Enhanced transport of phenanthrene and

499

1-naphthol by colloidal graphene oxide nanoparticles in saturated soil. Environ. Sci.

500

Technol. 2014, 48 (17), 10136-10144.

501

36. Brusseau, M. L.; Rao, P. S. C.; Gillham, R. W. Sorption nonideality during organic

502

contaminant transport in porous media. Crit. Rev. Environ. Control 1989, 19 (1), 33-99. 23



503

37. Luthy, R. G.; Aiken, G. R.; Brusseau, M. L.; Cunningham, S. D.; Gschwend, P. M.;

504

Pignatello, J. J.; Reinhard, M.; Traina, S. J.; Weber, W. J., Jr.; Westall, J. C. Sequestration

505

of hydrophobic organic contaminants by geosorbents. Environ. Sci. Technol. 1997, 31 (12),

506

3341-3347.

507

38. Kan, A. T.; Fu, G.; Hunter, M.; Chen, W.; Ward, C. H.; Tomson, M. B. Irreversible

508

sorption of neutral hydrocarbons to sediments: Experimental observations and model

509

predictions. Environ. Sci. Technol. 1998, 32 (7), 892-902.

510

39. Sen, T. K.; Khilar, K. C. Review on subsurface colloids and colloid-associated

511

contaminant transport in saturated porous media. Adv. Colloid Interface Sci. 2006, 119

512

(2–3), 71-96.

513

40. Bold, S.; Kraft, S.; Grathwohl, P.; Liedl, R. Sorption/desorption kinetics of

514

contaminants on mobile particles: Modeling and experimental evidence. Water Resour. Res.

515

2003, 39 (12), 1329.

516

41. Zhang, L.; Wang, L.; Zhang, P.; Kan, A. T.; Chen, W.; Tomson, M. B. Facilitated

517

transport of 2,2',5,5'-polychlorinated biphenyl and phenanthrene by fullerene nanoparticles

518

through sandy soil columns. Environ. Sci. Technol. 2011, 45 (4), 1341-1348.

519

42. Burton, G. A., Jr. Stressor exposures determine risk: So, why do fellow scientists

520

continue to focus on superficial microplastics risk? Environ. Sci. Technol. 2017, 51 (23),

521

13515-13516.

522

43. Hüffer, T.; Praetorius, A.; Wagner, S.; von der Kammer. F.; Hofmann, T. Microplastic

523

exposure assessment in aquatic environments: Learning from similarities and differences

524

to engineered nanoparticles. Environ. Sci. Technol. 2017, 51 (5), 2499-2507.

525

44. Andrady, A. L.; Neal, M. A. Applications and societal benefits of plastics. Philos. 24


Page 24 of 34

Page 25 of 34


526

Trans. R. Soc., B. 2009, 364 (1526), 1977-1984.

527

45. Cole, M.; Lindeque, P.; Fileman, E.; Halsband, C.; Galloway, T. S. The impact of

528

polystyrene microplastics on feeding, function and fecundity in the marine copepod

529

Calanus helgolandicus. Environ. Sci. Technol. 2015, 49 (2), 1130-1137.

530

46. Setälä, O.; Fleming-Lehtinen, V.; Lehtiniemi, M. Ingestion and transfer of

531

microplastics in the planktonic food web. Environ. Pollut. 2014, 185 (4), 77-83.

532

47. Stockholm Convention on Persistent Organic Pollutants. In Adoption of Amendments

533

to Annexes A, B, and C. Decisions SC-4/13, 2009.

534

48. Chen, D.; Kannan, K.; Tan, H.; Zheng, Z.; Feng, Y. L.; Wu, Y.; Widelka, M. Bisphenol

535

analogues other than BPA: Environmental occurrence, human exposure, and toxicity—a

536

review. Environ. Sci. Technol. 2016, 50 (11), 5438-5453.

537

49. Sharma, V. K.; Anquandah, G. A. K.; Yngard, R. A.; Kim, H.; Fekete, J.; Bouzek, K.;

538

Ray, A. K.; Golovko, D. Nonylphenol, octylphenol, and bisphenol-A in the aquatic

539

environment: A review on occurrence, fate, and treatment. J. Environ. Sci. Health A. 2009,

540

44 (5), 423-442.

541

50. Wang, F.; Haftka, J. J. H.; Sinnige, T. L.; Hermens, J. L. M.; Chen, W. Adsorption of

542

polar, nonpolar, and substituted aromatics to colloidal graphene oxide nanoparticles.

543

Environ. Pollut. 2014, 186, 226-233.

544

51. Teuten, E. L.; Rowland, S. J.; Galloway, T. S.; Thompson, R. C. Potential for plastics

545

to transport hydrophobic contaminants. Environ. Sci. Technol. 2007, 41 (22), 7759-7764.

546

52. Bakir, A.; Rowland, S. J.; Thompson, R. C. Enhanced desorption of persistent organic

547

pollutants from microplastics under simulated physiological conditions. Environ. Pollut.

548

2014, 185 (4), 16. 25



549

53. Huang, W.; Weber, W. J., Jr. A distributed reactivity model for sorption by soils and

550

sediments. 10. Relationships between desorption, hysteresis, and the chemical

551

characteristics of organic domains. Environ. Sci. Technol. 1997, 31 (9), 2562-2569.

552

54. Yang, W.; Duan, L.; Zhang, N.; Zhang, C.; Shipley, H. J.; Kan, A. T.; Tomson, M. B.;

553

Chen, W. Resistant desorption of hydrophobic organic contaminants in typical chinese

554

soils: Implications for long-term fate and soil quality standards. Environ. Toxicol. Chem.

555

2008, 27 (1), 235-242.

556

55. Bakir, A.; Rowland, S. J.; Thompson, R. C. Competitive sorption of persistent organic

557

pollutants onto microplastics in the marine environment. Mar. Pollut. Bull. 2012, 64 (12),

558

2782-2789.

559

56. Pascall, M. A.; Zabik, M. E.; Zabik, M. J.; Hernandez, R. J. Uptake of polychlorinated

560

biphenyls (PCBs) from an aqueous medium by polyethylene, polyvinyl chloride, and

561

polystyrene films. J. Agric. Food Chem. 2005, 53 (1), 164-169.

562

57. Schwarzenbach, R. P.; Gschwend, P. M.; Imboden, D. M., Environmental Organic

563

Chemistry, 2nd Edition; Wiley Interscience: New York, USA, 2003.

564

58. Pignatello, J. J. Soil organic matter as a nanoporous sorbent of organic pollutants. Adv.

565

Colloid Interface Sci. 1998, 76–77 (2), 445-467.

566

59. Carroll, K. M.; Harkness, M. R.; Bracco, A. A.; Balcarcel, R. R. Application of a

567

permeant/polymer diffusional model to the desorption of polychlorinated biphenyls from

568

Hudson River sediments. Environ. Sci. Technol. 1994, 28 (2), 253-258.

569

26


Page 26 of 34

Page 27 of 34


Table 1. Experimental Setups and Breakthrough Results of Column Experiments Column properties No.

1

a

Length

Bulk density

(cm)

(g/cm3)

7.08

1.49

Effluent properties a

Influent properties

Porosity

0.44

Contaminant pyrene

Contaminant

PSNPs

concentration

concentration

(µg/L)

(mg/L)

10.39

0

Mass fraction of pH

contaminant on PSNPs (%)

C/C0_PSNPs

C/C0_cont.

(%)

(%)

6.7

-b

-

1.7 ± 0.1

2

6.81

1.39

0.47

pyrene

8.93

5.1

6.8

92

65.4 ± 0.2

33.9 ± 0.2

3

6.90

1.39

0.48

pyrene

10.16

10.9

6.5

96

69.0 ± 0.3

56.1 ± 0.4

4

6.92

1.40

0.47

pyrene

9.93

19.4

6.9

98

65.2 ± 1.9

61.8 ± 0.2

5

7.21

1.48

0.44

BDE47

10.98

0

6.5

-

-

3.6 ± 0.1

6

6.85

1.39

0.48

BDE47

10.12

5.0

6.7

96

61.6 ± 0.2

29.7 ± 2.5

7

6.98

1.38

0.48

BDE47

8.16

11.4

6.8

98

67.1 ± 0.4

37.9 ± 0.6

8

6.90

1.41

0.47

BDE47

10.60

20.0

6.7

99

67.6 ± 0.6

49.8 ± 0.8

9

7.08

1.51

0.43

BPA

9.86

0

6.8

-

-

86.7 ± 0.5

10

6.85

1.41

0.47

BPA

10.78

5.0

6.7 6.8 6.8 6.9 6.7 6.6 6.7

9.8

65.2 ± 0.1

84.6 ± 0.1

14

62.5 ± 0.2

85.5 ± 0.2

22

64.3 ± 0.1

85.8 ± 0.4

-

-

57.0 ± 0.7

21

64.1 ± 0.8

55.5 ± 0.6

30

64.3 ± 0.1

56.7 ± 0.5

41

63.7 ± 0.7

56.3 ± 0.3

11

7.20

1.47

0.44

BPA

11.15

11.1

12

7.22

1.45

0.45

BPA

11.14

20.3

13

7.15

1.50

0.44

BPF

9.13

0

14

7.02

1.42

0.46

BPF

11.39

5.0

15

7.20

1.44

0.46

BPF

10.39

10.4

16

7.16

1.41

0.47

BPF

9.58

20.2

17

6.82

1.36

0.49

4-NP

9.76

0

6.5

-

-

4.6 ± 0.1

18

6.82

1.35

0.49

4-NP

10.64

5.0

6.7

44

61.9 ± 0.3

6.3 ± 0.4

19

6.90

1.40

0.47

4-NP

9.73

10.0

6.6

61

62.5 ± 0.2

6.9 ± 0.3

20

6.90

1.42

0.46

4-NP

10.32

17.8

6.6

70

64.7 ± 0.5

6.4 ± 0.2

Average value of last three data points of respective BTCs before flushed with background solutions. C/C0_PSNPs and C/C0_cont. represent the ratio of effluent PSNPs and

contaminant conentrations to their initial total concentrations in the influent. b not applicable. 27



Page 28 of 34

1.4

1.4

1.2

1.2

1.0

1.0

0.8

0.8

0.6

0.6

0.4

0.4

0.2

0.2

0.0

C/C0_Pyrene

C/C0_PSNPs

(a) Pyrene

0.0 0

20

40

60

80

0

20

40

PV

60

80

PV 1.4

1.2

1.2

1.0

1.0

0.8

0.8

0.6

0.6

0.4

0.4

0.2

0.2

0.0

0.0 0

20

40

60

80

0

20

40

PV

60

80

PV

0 mg/L PSNPs

5 mg/L PSNPs 20 mg/L PSNPs

10 mg/L PSNPs

Figure 1. Effects of PSNPs on transport of pyrene (Columns 1–4) and BDE47 (Columns 5–8) in saturated soil. The left panel shows the BTCs of PSNPs, and the right panel shows the BTCs of the contaminants.

28


C/C0_BDE47

C/C0_PSNPs

(b) BDE47 1.4

Page 29 of 34


1.4

1.2

1.2

1.0

1.0

0.8

0.8

0.6

0.6

0.4

0.4

0.2

0.2

0.0

C/C0_BPA

C/C0_PSNPs

(a) BPA 1.4

0.0 0

20

40

60

80

0

20

PV

40

60

80

PV

1.2

1.2

1.0

1.0

0.8

0.8

0.6

0.6

0.4

0.4

0.2

0.2

0.0

0.0 0

20

40

60

80

0

20

PV

C/C0_PSNPs

1.4

C/C0_BPF

1.4

40

60

80

PV

(c) 4-NP

1.4

1.2

1.2

1.0

1.0

0.8

0.8

0.6

0.6

0.4

0.4

0.2

0.2

0.0

C/C 0_4-NP

C/C0_PSNPs

(b) BPF 1.4

0.0 0

20

40

60

80

0

20

PV

40

60

80

PV

0 mg/L PSNPs

5 mg/L PSNPs 20 mg/L PSNPs

10 mg/L PSNPs

Figure 2. Effects of PSNPs on transport of BPA (Columns 9–12), BPF (Columns 13–16) and 4-NP (Columns 17–20) in saturated soil. The left panel shows the BTCs of PSNPs, and the right panel shows the BTCs of the contaminants.

29



(b) BDE47

104

104

103

103

102

102

10

q (mg/kg)

q (mg/kg)

(a) Pyrene

1

100 10-1 10-2

101 100 10-1 10-2

10-3 10-5

10

-4

10

-3

10

-2

10-3 10-6

10-5

C e (mg/L)

10-3

(d) BPF 104

103

103

102

102

q (mg/kg)

q (mg/kg)

(c) BPA

1

100 10-1 10-2

101 100 10-1 10-2

10-3 10-4

10

-3

10

-2

10

-1

10-3 10-4

10-3

C e (mg/L)

104

10-4

Ce (mg/L)

104

10

Page 30 of 34

10-2

10-1

Ce (mg/L)

(e) 4-NP

q (mg/kg)

103 102 101 100 10-1

soil PSNPs

10-2 10-3 10-5

10-4

10-3

10-2

C e (mg/L)

Figure 3. Adsorption isotherms of pyrene (a), BDE47 (b), BPA (c), BPF (d) and 4-NP (e) to Lula soil and PSNPs. The error bars represent the mean deviations of duplicates.

30


Page 31 of 34


(b) BDE47

1.2

1.2

1.0

1.0 C/C 0_BDE47

C/C 0_Pyrene

(a) Pyrene

0.8 0.6 0.4 0.2

0.8 0.6 0.4 0.2

0.0

0.0 0

20

40

60

80

0

20

PV

40

60

80

PV

(c) 4-NP 1.2

C/C0_4-NP

1.0 0.8 0.6 0.4

Experimental Estimated, Scenario 1 Estimated, Scenario 2

0.2 0.0 0

20

40

60

80

PV

Figure 4. Comparison between experimentally observed BTCs (Columns 4, 8, and 20) and the estimated ones assuming one of the two idealized scenarios: 1) desorption of contaminant from PSNPs is instantaneous and completely reversible (eq. 2); and 2) desorption from PSNPs is completely irreversible.

31



(b) BDE47 104

103

103

q (mg/kg)

q (mg/kg)

(a) Pyrene 104

102

102

HI = 0.52 ~ 0.63 101 10-5

10-4

10-3

HI = 0.31 ~ 0.43 101 10-6

10-2

10-5

C e (mg/L)

10-4

10-3

C e (mg/L)

(c) BPA

(d) BPF 103

q (mg/kg)

103

q (mg/kg)

Page 32 of 34

102

102

HI = 0.12 ~ 0.15

HI = 0.02 ~ 0.12 101 10-4

10-3

10-2

101 10-4

10-1

C e (mg/L)

10-3

10-2

10-1

C e (mg/L)

(e) 4-NP

q (mg/kg)

103

102

HI = 0.04 ~ 0.16 101 10-5

10-4

10-3

10-2

C e (mg/L)

Figure 5. Desorption data of pyrene (a), BDE47 (b), BPA (c), BPF (d) and 4-NP (e) from PSNPs (10 mg/L), using one-step desorption experiments. For each contaminant two desorption data points were obtained, one at a relatively high contaminant concentration (hollow squares) and one at a low concentration (hollow triangles). The filled circles are adsorption data. Hysteresis index (HI) values were calculated using eq. 1. 32


Page 33 of 34


(a) Pyrene 60

PE 80

40

q (mg/kg)

q (mg/kg)

50

100 PS

30 20

60 40 20

10 0 0.000

0.004

0.008

0 0.000

0.012

0.001

0.002

Ce (mg/L)

C e (mg/L)

(b) 4-NP 60

50

40

q (mg/kg)

q (mg/kg)

50

60 PS

30 20 10 0 0.000

PE

40 30 20 10

0.010

0.020

0 0.000

0.030

0.005

C e (mg/L)

0.010

0.015

0.020

Ce (mg/L)

Figure 6. Adsorption and desorption isotherms of pyrene and 4-NP to and from micro-sized polystyrene and polyethylene. The filled circles are adsorption data and hollow symbols are desorption data. The error bars represent the mean deviations of duplicates.

33



(b) 4-NP

40

30

35

25 qt (mg/kg)

qt (mg/kg)

(a) Pyrene

Page 34 of 34

30 25

20 15

20

10 0

2

4

6

8

10 12 14

0

2

Time (h)

4

6

8

10 12 14

Time (h)

Figure 7. Desorption kinetics of pyrene and 4-NP from micro-sized polystyrene (filled symbols) and polyethylene (hollow symbols). The error bars represent the mean deviations of duplicates.

34


Polystyrene Nanoplastics-enhanced Contaminant Transport: Role of

Recommend Documents