Organophosphate Esters in Sediment of the Great Lakes

Subscriber access provided by UNIV TORONTO

Article

Organophosphate Esters in Sediment of the Great Lakes Dandan Cao, Jiehong Guo, Yawei Wang, Zhuona Li, Kang Liang, Margaret B. Corcoran, Soheil Hosseini, Solidea M.C. Bonina, Karl J. Rockne, Neil C. Sturchio, John P. Giesy, Jing-fu Liu, An Li, and Guibin Jiang Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b05484 • Publication Date (Web): 13 Jan 2017 Downloaded from http://pubs.acs.org on January 15, 2017

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

Environmental Science & Technology 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

Environmental Science & Technology

Organophosphate Esters in Sediment of the Great Lakes

Dandan Cao,† Jiehong Guo,‡ Yawei Wang,*,†,# Zhuona Li,‡ Kang Liang,† Margaret B. Corcoran,∥ Soheil Hosseini,§ Solidea M. C. Bonina,§ Karl J. Rockne,§ Neil C. Sturchio,∥ John P. Giesy,⊥ Jingfu Liu,† An Li,*,‡ Guibin Jiang†

†

State Key Laboratory of Environmental Chemistry and Ecotoxicology, Research Center for

Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China ‡

School of Public Health, University of Illinois at Chicago, Chicago, Illinois 60612, USA

§

Department of Civil and Materials Engineering, University of Illinois at Chicago, Chicago,

Illinois 60612, USA ∥

Department of Earth and Environmental Sciences, University of Illinois at Chicago, Chicago,

Illinois 60612, USA ⊥

Department of Veterinary Biomedical Sciences and Toxicology Centre, University of

Saskatchewan, Saskatoon SK S7N 0W0, Canada #

University of Chinese Academy of Sciences, Beijing 100049, China

*

Corresponding authors

Yawei Wang: Tel: +86 010 62849124; e-mail: [email protected]. An Li: Tel: 1-312-996-9597; e-mail: [email protected].

1 ACS Paragon Plus Environment


Page 2 of 29

1

ABSTRACT

2

This is the first study on organophosphate esters (OPEs) flame retardants and plasticizers in the

3

sediment of the Great Lakes. Concentrations of 14 OPEs were measured in three sediment cores

4

and 88 Ponar surface grabs collected from Lakes Ontario, Michigan, and Superior of North

5

America. The sum of these OPEs (Σ14OPEs) in Ponar grabs averaged 2.2, 4.7, and 16.6 ng g-1 dw

6

in Lakes Superior, Michigan, and Ontario, respectively. Multiple linear regression analyses

7

demonstrated statistically significant associations between logarithm concentrations of Σ14OPEs

8

as well as selected congeners in surface grab samples and sediment organic carbon content as

9

well as a newly developed urban distance factor. Temporal trends observed in dated sediment

10

cores from Lake Michigan demonstrated that the recent increase in depositional flux to sediment

11

is dominated by chlorinated OPEs, particularly tris(2-chloroisopropyl) phosphate (TCPP), which

12

has a doubling time of about 20 years. Downward diffusion within sediment may have caused

13

vertical fractionation of OPEs over time. Two relatively hydrophilic OPEs including TCPP had

14

much higher concentrations in sediment than estimated based on equilibria between water and

15

sediment organic carbon. Approximately a quarter (17 tonnes) of the estimated total OPE burden

16

(63 tonnes) in Lake Michigan resides in sediment, which may act as a secondary source releasing

17

OPEs to the water column for years to come.

18


Page 3 of 29


19

■ INTRODUCTION

20

Phosphorus is one of the most effective elements for retarding fire.1 Organophosphate esters

21

(OPEs) are widely used as flame retardants in plastics, textiles, electronic equipment, furniture,

22

and building materials.2, 3 Non-chlorinated alkyl phosphates have also been used as plasticizers,

23

hydraulic fluids, lacquer, anti-foam agents, glues and extractants for some metals.3 Use of OPEs

24

began in the early 20th century, then increased rapidly during the 1940s and continued for later

25

decades.1 With the phasing out of polybrominated diphenyl ethers (PBDEs) during the 2000s,

26

production and use of OPEs as alternative flame retardants have increased significantly in recent

27

years.4, 5

28

Similar to other additive flame retardants, OPEs inevitably enter the environment during

29

their production, use or disposal. It was estimated that approximately 80% of the annual

30

consumption of OPE hydraulic fluids escaped to the environment through leakage from

31

hydraulic systems in the 1960s.1 OPEs have been detected in various environmental

32

compartments, including indoor air and dust, the atmosphere, wastewater and sludge, surface and

33

drinking water, sediment, and biological samples including human blood, milk, and placenta.3, 6-8

34

In the United States, there are at least four manufacturers of OPE flame retardants,9 although

35

locations of their production facilities are not clear.

36

In the Great Lakes region, concentration of OPEs in air was found to be ~100- to

37

~1200-fold greater than those of brominated flame retardants.10, 11 Similarly, concentrations of

38

OPEs in water collected from Lakes Erie, Michigan, and Huron were greater than concentrations

39

of brominated flame retardants.12 OPEs were also found in fish, herring gulls and their eggs in

40

the Great Lakes region.13-16 Sediments, which can serve as a sink or potential source of organic 3 ACS Paragon Plus Environment


Page 4 of 29

41

pollutants, have been found to be contaminated with OPEs in locations around the world.17-20

42

However, to our knowledge, there were no published reports on OPEs in the sediments of the

43

Great Lakes prior to this study. This represents a major gap in our knowledge of the

44

environmental fate of OPEs in the largest freshwater system in the world.

45

To date, relatively hydrophobic chemical pollutant groups have been investigated

46

extensively in environmental monitoring efforts, especially those using sediment of natural

47

waters. In comparison, the behavior of persistent organic pollutants with polar functional groups

48

is less understood. Molecules of OPEs possess both polar and nonpolar moieties, thus are

49

considered amphiphilic. The octanol-water partition coefficient (Kow) spans 10 orders of

50

magnitude among the 14 OPE flame retardants and plasticizers listed in the Supporting

51

Information, Table S1. Once in sediment, all of these OPEs are considered persistent with

52

estimated half lives ranging from months to >4 years.21

53

In this paper, we report measured concentrations of the 14 OPE flame retardants and

54

plasticizers in sediment samples collected from Lakes Ontario, Michigan, and Superior. The

55

acquired data set enabled an examination of the spatial distribution pattern and temporal trend as

56

well as the influencing factors. The distribution between sediment particulate matter and pore

57

water in the sediment was assessed, based on equilibrium partitioning theory; and the

58

dependence of such phase distributions on the physicochemical property of the analytes was

59

examined.

60

■MATERIALS AND METHODS

61

Collection and Characterization of Sediments. Sediments were collected from Lakes

62

Michigan, Superior, and Ontario during 2010 to 2013 onboard the USEPA Research Vessel R/V 4 ACS Paragon Plus Environment

Page 5 of 29


63

Lake Guardian. Sampling locations are shown in Figure 1, and site information is provided in

64

Table S2. A total of 88 Ponar grab samples were collected. Sediment cores were collected at

65

three sites in southern (M009), central (M024), and northern (M047) Lake Michigan. Detailed

66

sampling methods are provided in the Supporting Information.

67

Water and solid contents, porosity, wet and dry bulk density, particle density, and

68

sediment organic carbon (OC) were measured by use of standard methods described elsewhere.22

69

Segments of cores were dated by use of profiles of 210Pb, 241Am, 226Ra, and 137Cs.23 Activities of

70

these isotopes were quantified by use of gamma spectroscopy using well-type HPGe detectors.

71

Mass sedimentation rate and focusing factor were derived from activities of

72

previously.24

73

Identification and Quantification of OPEs. Concentrations were measured for 14 OPEs,

74

including trimethyl phosphate (TMP), triethyl phosphate (TEP), tri-n-propyl phosphate (TPrP),

75

tri-iso-butyl phosphate (TiBP), tri-n-butyl phosphate (TnBP), tris(2-butoxyethyl) phosphate

76

(TBEP), tris(2-ethylhexyl) phosphate (TEHP), triphenyl phosphate (TPhP), cresyl diphenyl

77

phosphate (CDPP), tri-m-cresyl phosphate (TCrP), 2-ethylhexyl diphenyl phosphate (EHDPP),

78

tris(2-chloroethyl)

79

tris(1,3-dichloro-2-propyl) phosphate (TDCP). Chemical Structures and basic information on

80

each of the 14 OPEs are summarized in Table S1.

phosphate

(TCEP),

tris(2-chloroisopropyl)

phosphate

210

Pb as detailed

(TCPP),

and

81

Laboratory procedures included extraction by ultrasonication, clean-up using solid phase

82

extraction cartridges, and analysis by liquid chromatography-tandem mass spectrometry

83

(LC-MS/MS). Details of these methods are described in SI, and instrument operational



Page 6 of 29

84

parameters are summarized in Table S3. Typical extracted ion chromatograms of a sediment

85

extract and an OPE standard mixture are given in Figure S1.

86

Quality Control. A matrix blank was a sediment sample from about 50 cm depth of a core

87

collected in 2011 from the Yellow Sea of China. Fourteen OPEs of 20 ng each were spiked into

88

1.0 g of the matrix blank with triplicates. The recoveries of 12 OPEs ranged from 78% to 108%

89

(Table S3). The recoveries of EHDPP and TEHP were 47% and 27%, respectively. The relative

90

standard deviations (RSD) of measured OPE concentrations in the matrix spike ranged from

91

3%-13% except for TEHP, which had an RSD of 38%. Results reported in this paper were not

92

adjusted by the spiking recoveries.

93

Three field blanks (Na2SO4, pre-purified by baking at 500 °C overnight) from Lakes Superior,

94

Michigan, and Ontario, respectively, were processed in the same manner as collected sediment

95

samples. TCPP, TiBP, TnBP, and TBEP were detected in the field blanks in the concentration

96

range of N.Q. – 0.44 ng g-1 dw. On average, Σ14OPEs in the field blank comprised 1%, 10%, and

97

23% of the concentration in Ponar grab sediment samples from Lakes Ontario, Michigan, and

98

Superior, respectively. One procedural blank (consisting of only extracting solvent) was

99

analyzed with every batch of samples, and TCPP, TiBP, TPhP and TnBP were commonly

100

detected at lower levels (3 but Lake Michigan > Lake Superior (Figure 1, Table S4 and

134

S5). This rank order is similar to those previously reported for PBDEs,25-27, 32 PCBs,25-27 and

135

other emerging flame retardants.33,34 In Lake Superior, concentrations of Σ14OPEs were greater at

136

southeastern sites (S001, S002, and S110) than at other sites (Table S4). Proximity of these sites

137

to the cities of Sault Ste Marie and Marquette, MI, suggests inputs from local sources. In herring

138

gull eggs collected in Agawa Rocks which is near sites S001 and S002, OPE concentrations

139

appear to have greatly increased from 2004 to 2010.16 In Lake Michigan, higher concentrations

140

(Σ14OPEs > 10 ng g-1 dw) and inventories (> 60 ng cm-2) were found in the southeast (M009,

141

M011, and M061) and near Sleeping Bear Dunes (M093a). Sampling sites near Chicago and

142

Milwaukee (M010, M020 and M030) are in non-depositional zone of Lake Michigan; sediments

143

collected from these sites were sandy with less organic carbon ( 0.35 and p < 6×10-4, excluding TCPP and TiBP for which r > 0.24 and p < 0.03).

198

The UDF2 values are included in Table S2 for all the sampling locations.

199

In addition to potential source locations, the concentrations of OPEs exhibited increases

200

with increasing sediment OC content. Studies on sorption mechanisms of OPEs on soil and

201

sediment particles are currently scarce.36, 37 While organic matter of the sediments accommodates

202

nonpolar organics predominantly by hydrophobic interaction, stronger specific interactions

203

involving electron donor/acceptor or hydrogen bond could occur between numerous polar

204

functional groups of the natural organic matter and the polar moieties of sorbates such as OPEs.

205

With UDF2 and sediment OC content as independent variables, multiple linear regression

206

models were developed and are presented in Figure 3 and Table S8. Sediment OC and impact of

207

human activities are the main controlling factors influencing the distribution of OPEs in the

208

sediment across the three lakes, together accounting for approximately 59% of the variance in

209

concentration for Σ14OPEs.

210

There is evidence that OPEs undergo long-range atmospheric transport.10, 38 The OPEs

211

targeted in this work vary widely in their volatility, with vapor pressure ranging from 10-5

212

to >100 Pa (Table S1). We found that the relative abundance of OPEs differs largely among the

213

three lakes (Figure S2). In Lake Superior, the congeners with the greatest concentrations were

214

relatively volatile TiBP and TnBP. In comparison, heavier congeners TBEP and TCrP had

215

greater detection rates and concentrations in Lakes Michigan and Ontario. The mean ratio (TiBP

216

+ TnBP) / (TBEP + TCrP) in Lake Superior was 10.7, which is much greater than those in Lakes

217

Michigan (1.9) and Ontario (0.46). With higher vapor pressures, TiBP and TnBP are more likely



Page 12 of 29

218

to enter air and reach remote locations via atmospheric transport. In contrast, the heavier TBEP

219

and TCrP have greater Koc thus are more likely to bind to sediments after local inputs.

220

Temporal Trends and Downward Mobility. OPEs have already been used for >150 years;3

221

however, information for production volume during the earlier years is not available. As shown

222

in Figure 2, in deeper sediments dated before year 1900, concentrations of Σ14OPEs were low

223

and relatively constant but still greater than the MDL. After 1900, concentrations and fluxes of

224

Σ14OPEs began to increase and peaked in the 1970s to 1980s. A decrease was observed in

225

sediments deposited in the 1990s; however, a rebound after 2000 was observed at all three sites

226

although the number of data points is limited. At sites M047 and M024, the highest

227

concentrations and fluxes of Σ14OPEs were in the uppermost segments of cores. At site M009,

228

Σ14OPEs in surficial segment dated 2009 was 28 ng g-1 dw, which is almost double 16 ng g-1 dw

229

observed in sediments deposited during the late 1990s, although still below the historical peak of

230

41 ng g-1 dw in core segment deposited during the 1960s (Figure 2). Net depositional fluxes of

231

OPEs at these sites were estimated using equation [S3]. The recent depositional fluxes were 0.83,

232

0.19, and 0.25 ng m-2 yr-1 for Σ14OPEs at sites M009, M024, and M047, respectively. The

233

observations are clear evidence of the re-emergence of OPEs as environment pollutants. The

234

recent increasing trend is consistent with observations of OPEs in other environmental matrices,7,

235

39

236

consumer goods.4, 40, 41 The observed increases in the environment may also reflect the tripled

237

worldwide production volume of OPEs - from approximately 100,000 tonnes per year in 1992 to

238

341,000 tonnes per year in 2007.42

and can be attributed to large scale replacement of PBDEs with OPE flame retardants in


Page 13 of 29


239

Different time trends were observed among targeted OPEs. The above-mentioned

240

increases in recent years appear to be dominated by the rapid increase of chlorinated congeners

241

(Figure 2, lower panels), especially TCPP. Exponential increases were observed for TCPP at all

242

three coring sites since the 1950s, with apparent doubling time t2 around 20 years (Figure 4). It

243

has been reported that the consumption of TCPP has continued to increase since the mid-1960s.43

244

After the phase-out of the more toxic TCEP and with increasing use of polyurethane foam,

245

production of TCPP (a replacement of TCEP) has increased markedly from the 1980s.43 In 2000,

246

worldwide production of TCPP was 36,000 metric tons; in recent years, TCPP represents ~80%

247

of the chlorinated OPEs produced in Europe.44 TCPP was found to be the dominant (at 180 ng/g)

248

among eight OPEs in the sediment of Liverpool Bay and the Rivers Mersey and Tees in UK.45 It

249

was detected in air, water and bird eggs from the Great Lakes region.10-14, 16 These observations

250

highlight the need to establish benchmarks for TCPP in various environmental media to prevent

251

adverse biological effects. In contrast to TCPP, all alkyl and aryl OPEs with the exception of

252

TBEP decreased expoentially at site M009 after 1960, with apparent half-lives (t0.5) ranging from

253

15 to 40 years (Figure 4). The production of TCrP was predicted to decline ~5% each year

254

during the period of 1978-1982.46 TBEP displayed no trend over the core depth. Both increases

255

and decreases in the depositional fluxes were observed at M024 and M047 depending on

256

individual OPEs, but most trends were statistically insignificant (p > 0.05).

257

For compounds that are relatively water soluble, therefore mobile in aqueous phase, the

258

chronological profile recorded in dated sediment cores may not be in good agreement with the

259

actual deposition history. For example, extensive downward transport of herbicide atrazine (log

260

Koc = 2.35) as well as some perfluorinated compounds in sediment cores of Lake Michigan was

261

reported.23, 24 Assuming equilibrium conditions, the distribution between particle and pore water 13 ACS Paragon Plus Environment


Page 14 of 29

262

of sediment depends on hydrophobicity of the chemical (log Koc), the solid-to-water mass ratio

263

(rsw), and the organic content of the particles (foc), but is independent of chemical concentration.

264

Thus, the fraction of the compound in pore water of the sediment can be estimated using the

265

equation below.47 Figure 5A illustrates the results of applying this equation to the sediment of

266

this work.

267

f iw =

1 1 + rsw ⋅ K oc ⋅ f oc

[eq. 1]

268

The targeted OPEs vary widely in their affinity to organic matter, with log Koc ranging

269

from 1.10 to 6.87 (Table S1). It is clear from Figure 5A, while OPEs with log Koc > ~5 are

270

almost completely associated with sediment particles, a significant portion of OPEs with log Koc

271

< ~3 can be present in pore water. This may have facilitated post-depositional transport to deeper

272

sediment due to downward diffusion over time. We observed that, in all three cores, the summed

273

fraction of less hydrophobic congeners (log Koc < 3.5) exhibits a rapid rise to near unity in deeper

274

sediment (Figure 5B). Higher downward mobility of the more polar congeners relative to those

275

more hydrophobic is likely to cause fractionation of a chemical mixture over the depth of

276

sediments in a sufficiently long time period. The occurrence of natural fractionation of the OPEs

277

in lake sediments over time is yet to be confirmed by future studies. Congener-specific

278

information of the production and use history, especially that before 1900, is highly desired.

279

Transformation after burial is another process that may affect the apparent time trend

280

observed in sediment cores. Non-chlorinated alkyl and aryl OPEs, such as TiBP, TnBP, TCrP,

281

TPhP and TBEP, tend to be more readily biodegradable than chlorinated OPEs such as TCPP,


Page 15 of 29


282

TCEP and TDCP.7, 42 However, the occurrence of degradation of OPEs cannot be confirmed

283

based on the chronological profiles recorded in the three sediment cores of this work.

284

Load Estimation and Phase Distribution between Water and Sediment.

285

Concentration data are available for 11 OPEs dissolved in bulk water samples collected in spring

286

2012 from Lake Michigan, at a central location (latitude 44.2, longitude -87.3) and a southern

287

location (latitude 41.9, longitude –87.6).12 By multiplying the volume of water in Lake Michigan

288

(4,920 km3) with the reported ΣOPEs concentration (9.3 ng/L)12, the total load of OPEs

289

dissolved in the lake water is roughly 46 tonnes. Compared with the total load of 17 tonnes in the

290

sediment (Table 1), it appears that about 27% of the OPEs in Lake Michigan resides in the

291

sediment. This percentage is about 20% if the calculation is based on the same set of seven

292

congeners (TCEP, TCPP, TDCP, TPhP, TnBP, TBEP, and TEHP) reported in water12 and

293

sediment. The sum of 63 tonnes does not include the amounts in suspended or settling

294

particulates and living biota, for which data are not available.

295

TCPP, TnBP, and TBEP had >50% detection frequency in this work in the Ponar grab

296

sediment samples collected in lower (latitude

Organophosphate Esters in Sediment of the Great Lakes

Recommend Documents