Sorption of Perfluoroalkyl Phosphonates and Perfluoroalkyl

Subscriber access provided by UB + Fachbibliothek Chemie | (FU-Bibliothekssystem)

Article

Sorption of Perfluoroalkyl Phosphonates and Perfluoroalkyl Phosphinates in Soils Holly Lee, and Scott Andrew Mabury Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b04395 • Publication Date (Web): 22 Feb 2017 Downloaded from http://pubs.acs.org on February 26, 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 28

Environmental Science & Technology

Release F Point F

F O x P

F F

F

O

-O

F

F F

8 P

HO

y

OH

F F F

F F O F

10 P

HO

OH

ACS Paragon Plus Environment

O 6 P OH HO


1 2 3

Draft Manuscript

Sorption of Perfluoroalkyl Phosphonates and Perfluoroalkyl Phosphinates in Soils

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

Holly Lee* and Scott A. Mabury¥ * Sciex, 71 Four Valley Drive, Concord, Ontario, Canada, L4K 4V8 (Corresponding author) Phone: (289) 982-2285 Email: [email protected] ¥

Department of Chemistry, University of Toronto, 80 St. George St., Toronto, Ontario, Canada, M5S 3H6 Phone: (416) 978-1780 Email: [email protected]

ACS Paragon Plus Environment

Page 2 of 28

Page 3 of 28


46 47 48

Abstract

49

recently discovered perfluoroalkyl acids (PFAAs) that have been widely detected in house dust,

50

aquatic biota, surface water, and wastewater environments. The sorption of C6, C8, and C10

51

monoalkylated PFPAs and C6/C6, C6/C8, and C8/C8 dialkylated PFPiAs was investigated in

52

seven soils of varying geochemical parameters. Mean distribution coefficients, logKd*, ranged

53

from 0.2 to 2.1 for the PFPAs and PFPiAs and were generally observed to increase with

54

perfluoroalkyl chain length. The logKd* of PFPiAs calculated here (1.6–2.1) were similar to

55

those previously measured for the longer-chain perfluorodecane sulfonate (1.9, PFDS) and

56

perfluoroundecanoate (1.7, PFUnA) in sediments, but overall when compared as a class, were

57

greater than those for the perfluoroalkane sulfonates (-0.8–1.9, PFSAs), perfluoroalkyl

58

carboxylates (-0.4–1.7, PFCAs), and PFPAs (0.2–1.5). No single soil-specific parameter, such as

59

pH and organic carbon content, was observed to control the sorption of PFPAs and PFPiAs, the

60

lack of which may be attributed to competing interferences in the naturally heterogeneous soils.

61

The PFPAs were observed to desorb to a greater extent and likely circulate as aqueous

62

contaminants in the environment, while the more sorptive PFPiAs would be preferentially

63

retained by environmental solid phases.

Perfluoroalkyl phosphonates (PFPAs) and perfluoroalkyl phosphinates (PFPiAs) are

64 65 66 67

Introduction

68

documented in wastewater, surface water, and sediment samples collected downstream from

69

wastewater treatment plants (WWTPs).1–7 Analysis of WWTP sludge has consistently reported

70

ng/g concentrations of perfluoroalkyl carboxylates (PFCAs) and perfluoroalkane sulfonates

Urban discharge of perfluoroalkyl and polyfluoroalkyl substances (PFASs) has been well

2 ACS Paragon Plus Environment


71

(PFSAs), with perfluorooctanoate (PFOA, C8 PFCA) and perfluorooctane sulfonate (PFOS, C8

72

PFSA) typically observed as the dominant perfluoroalkyl acids (PFAAs), followed by longer

73

chain PFCAs and PFSAs (>8 perfluorinated carbons, CF’s).7–15 This profile reflects legacy

74

distribution in historical commercial production of PFASs, but is also consistent with the

75

demonstrated preference of longer-chain PFAAs to sorb to sediments,16–19 soils, 20 and sludge,21

76

all of which may act as potential sinks and reservoirs for the retention and remobilization of

77

these chemicals to the aqueous environment, respectively.

Page 4 of 28

78

Laboratory experiments using freshwater sediments16 and topsoils 20 indicated the

79

sorption of PFAAs exhibits a chain-length dependency in which their organic carbon-normalized

80

distribution coefficients (KOC) increase with the number of CF’s present in the perfluorocarbon

81

tail of the PFAAs studied. In the same studies, PFSAs were also observed to be more sorptive

82

than PFCAs of equal perfluorocarbon chain length. In contrast, no information has been reported

83

on the sorption capacity of the perfluoroalkyl phosphonates (PFPAs) and phosphinates (PFPiAs).

84

PFPAs and PFPiAs are PFAAs with their perfluorocarbon tails attached through a

85

carbon-phosphorus (C–P) bond to either a phosphonate (Rx-P(O)O2-; Cx PFPA) or phosphinate

86

(Rx-P(Ry)(O)O-; Cx/Cy PFPiA) headgroup (Table 1). These chemicals are currently marketed as

87

leveling and wetting agents in household cleaners22 and were historically used in United States

88

(US) pesticide formulations23 until 2008.24 Despite widespread observations of the C6, C8, and

89

C10 PFPAs in Canadian surface waters at pg/L concentrations,25 these chemicals were not

90

detected in any lake trout fillet homogenate sampled from the Great Lakes, whereas the C6/C6

91

and C6/C8 PFPiAs were observed at concentrations of up to 32 pg/g ww in the same samples.26

92

A similar absence of PFPAs was also observed in benthic worms in which PFPiAs were present

93

at 30–1900 pg/g ww.27 More recently, De Silva et al. reported ubiquitous detection of PFPiAs at


Page 5 of 28


94

112–15300 pg/g ww in the plasma of fish, dolphins, and birds sampled across North America.28

95

This difference is consistent with faster depuration kinetics previously observed for the PFPAs in

96

rainbow trout (4–5 days)29 and rats (1–3 days)30 than for the PFPiAs (6–53 days in rainbow trout;

97

2–4 days in rats).29,30 The C6/C6 and C6/C8 PFPiAs have been observed at 2–3 ng/g in WWTP

98

sludge,30 whereas analysis of various Dutch sludge and sediment samples did not reveal any

99

detection of the monitored C6, C8, and C10 PFPAs.31

100

The present study investigated the sorption of three PFPA (C6, C8, and C10) and three

101

PFPiA (C6/C6, C6/C8, and C8/C8) congeners in seven soils of varying geochemical properties.

102

The influence of structural features, such as the perfluorocarbon chain length and headgroup, on

103

sorption was investigated by comparing distribution coefficients for the six congeners to those

104

previously reported for the PFSAs and PFCAs. A number of laboratory and field studies have

105

shown evidence of PFAAs leaching from soils, that have been spiked with PFAAs32 or exposed

106

to contaminated street runoffs33 and WWTP sludge,32,34–36 to groundwater and surface water. As

107

such, desorption experiments were also performed to determine which of the subject PFPAs and

108

PFPiAs may be prone to remobilization into the aqueous phase and which to preferential

109

residence in the soil phase.

110 111 112

Materials and Methods Chemicals. Individual standards of C6, C8, and C10 PFPAs, and C6/C6, C6/C8, and

113

C8/C8 PFPiAs were obtained from Wellington Laboratories (Guelph, ON). However, the

114

amount of chemicals required and their costs to perform all sorption experiments precluded the

115

use of these analytical standards. Instead, the technical product, Masurf®-780 (Mason Chemical

116

Company, Arlington, IL), was used for the majority of these experiments. Using the individual



117

analytical standards from Wellington Laboratories, the percent composition of this technical

118

mixture was determined by standard addition to be 6.9±0.4% C6 PFPA, 5.8±0.4% C8 PFPA,

119

3.2±0.5% C10 PFPA, 4.3±1.0% C6/C6 PFPiA, 4.7±0.9% C6/C8 PFPiA, and 0.6±0.1% C8/C8

120

PFPiA. This percent composition was used to adjust the PFPA and PFPiA concentrations

121

reported here. Details on how this composition compared to that previously reported by D’eon

122

and Mabury30 and Lee and Mabury37 are provided in the Supporting Information (SI), as well as

123

a list of all other chemicals used in this study.

124

Page 6 of 28

Soils. Four loam soils (A–D) were collected around Southern Ontario, Canada, while

125

another loam soil (E) was collected in Athens, Georgia, US. The Elliott silt loam (F) and Florida

126

Pahokee peat (G) were obtained, air-dried and pre-sieved, from the International Humic

127

Substances Society (Golden, Colorado), and used as received. All other soils were sieved with a

128

2 mm stainless steel mesh prior to oven drying at 105oC and homogenized finely using a mortar

129

and pestle. Soil characterization data are provided in Table S1.

130

Batch Sorption Experiments. All sorption experiments were performed in compliance

131

with the Organization for Economic Cooperation and Development (OECD) guidelines for

132

studying sorption.38 Prior to all experiments, the soils were pre-equilibrated with 0.10 mM

133

mercuric chloride (HgCl2) and 0.01 M calcium chloride (CaCl2) in water by shaking overnight at

134

200 rpm.

135

A preliminary study was performed to determine the soil to solution ratio at which >50%

136

by mass of the chemical has sorbed to the soil and the time to reach sorption equilibrium, the

137

details of which are described in the SI. Except for C6 PFPA, 25) are likely necessary to retain these compounds in a larger aqueous

142

compartment for measurements. However, using different soil to solution ratios optimized for

143

each analyte’s sorptive capacity may not represent realistic field soil moisture conditions and

144

precludes a robust comparison of sorption parameters. As a result, a ratio of 1:10 (5 g: 50 mL)

145

and an equilibration time of 24 hours were chosen for the following experiments, as these

146

parameters were consistent with those used previously for investigating sorption of PFAAs in

147

sediments.16–19

148

Sorption kinetics were determined by equilibrating 5 g of each soil type with 50 mL of

149

0.01 M CaCl2, spiked with 10 μg/mL of Masurf, followed by sampling at 2, 4, 6, 8, and 24 hours.

150

The percentage of analytes remaining in the aqueous phase and their corresponding distribution

151

coefficients were determined based on separate analysis of the aqueous and soil phase upon

152

reaching equilibrium. This experiment was repeated at four other concentrations (0.5, 1, 5, and

153

50 μg/mL of Masurf), with the exception that the aqueous and soil phases were sampled only

154

once at 24 hours, and together with the sorption data determined at 10 μg/mL, five-point sorption

155

isotherms spanning two orders of magnitude were established. At the end of the experiment, the

156

unused portions of the aqueous phases collected at 24 hours from the controls, soil blanks, and

157

soils spiked with the target analytes were analyzed for dissolved organic carbon (DOC).

158

Desorption kinetics were determined by agitating 10 μg/mL of Masurf with 5 g of Soil A

159

and 50 mL 0.01 M CaCl2 until sorption equilibrium (i.e. 24 hours), after which the aqueous

160

phase was entirely removed and replaced with an equal volume of 0.01 M CaCl2 without the test

161

chemicals. The new mixtures were further agitated with periodic removal for analysis at 2, 4, 6,

162

24, 30, and 52 hours.



163

Page 8 of 28

In all the experiments, blanks consisting of soil and 50 mL 0.01 M CaCl2 without the test

164

chemicals were included to monitor for background contamination. A set of triplicate control

165

samples (n = 3), consisting of only Masurf in 0.01 M CaCl2 in the absence of soil, were also

166

included to test for the potential of abiotic degradation and adsorption to the container walls.

167

Analysis of these controls revealed 75%) of the C8 and C10 PFPAs and all three

255

PFPiAs to the container walls (Figure S2A), but similar declines in aqueous concentrations were 10 ACS Paragon Plus Environment


Page 12 of 28

256

also observed in Masurf-spiked water only. The fact that C6 PFPA remained mostly in the

257

aqueous phase of both sets of controls and also in the aqueous phases equilibrated with the

258

majority of the soils suggests complexation with Ca2+ and Hg2+ from the biocide may only

259

minimally impact PFPA and PFPiA sorption and this behavior is expected to persist for the

260

longer chain lengths as this interaction should be predominantly driven by the anionic headgroup

261

of the PFPAs and PFPiAs. As expected, the presence of soil greatly reduced this surface

262

adsorption to

Sorption of Perfluoroalkyl Phosphonates and Perfluoroalkyl

Recommend Documents