Perfluoroalkyl Acids Including Isomers in Tree Barks from a Chinese

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Perfluoroalkyl Acids including Isomers in Tree Barks from a Chinese Fluorochemical Manufacturing Park: Implication for Airborne Transportation Hangbiao Jin, GUO QIANG SHAN, Lingyan Zhu, Hongwen Sun, and Yi Luo Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b06241 • Publication Date (Web): 27 Jan 2018 Downloaded from http://pubs.acs.org on January 29, 2018

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Environmental Science & Technology

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Perfluoroalkyl Acids including Isomers in Tree Barks from a Chinese

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Fluorochemical Manufacturing Park: Implication for Airborne Transportation

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Hangbiao Jin1, 2, Guoqiang Shan1, Lingyan Zhu1, 2∗, Hongwen Sun1, Yi Luo1

5 6

1

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Education, Tianjin Key Laboratory of Environmental Remediation and Pollution

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Control, College of Environmental Science and Engineering, Nankai University,

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Tianjin 300071, P. R. China

Key Laboratory of Pollution Processes and Environmental Criteria, Ministry of

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2

11

Yangling, Shanxi 712100, P.R. China

College of Natural Resources and Environment, Northwest A&F University,

12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 ∗

To whom correspondence should be addressed. E-mail:[email protected]. Phone: +86-22-23500791. Fax: +86-22-23503722. 1

ACS Paragon Plus Environment


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ABSTRACT: Measurement of airborne perfluoroalkyl acids (PFAAs) is challenging,

31

but important for understanding their atmospheric transport. Tree bark is a good

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media for monitoring semi-volatile compounds in the atmosphere. Whether it could

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work as an indicator of airborne PFAAs was firstly examined in this study. Bark and

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leaf samples collected around a Chinese fluorochemical manufacturing park (FMP)

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were analyzed for PFAAs and their branched isomers. Total PFAA concentrations

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(∑PFAAs) in the bark (mean, 279 ng/g dw) and leaf (250 ng/g dw) samples were

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comparable. ∑PFAAs in the barks collected within the boundaries of the FMP were

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significantly (p < 0.05) higher than those outside the FMP, and displayed a decreasing

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spatial trend as the distance from the FMP increased. However, such spatial difference

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and trend were not observed for the leaves. PFAA compositional profiles in most of

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the tree barks were consistent to each other, but different from those in tree leaves.

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These results indicated that tree barks mainly accumulated airborne PFAAs, while

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uptake from soil and translocation could make partial contribution to those in leaves.

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PFOA and perfluorooctane sulfonate in barks had strictly consistent isomeric

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compositions with their ECF products. Overall, these results indicated that the bark

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could be a good indicator of airborne PFAAs with respect to their occurrence,

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isomeric signature, and atmospheric transport.

48 49 50 51 52 53 54 55 56 57 58 59 2


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INTRODUCTION. Perfluoroalkyl acids (PFAAs) are man-made chemicals with

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amphiphilic structures, and have been used for more than five decades in a variety of

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industrial and consumer products such as surfactants, nonstick coatings, aqueous

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fire-fighting foams, and lubricants.1, 2 PFAAs contain extremely strong and stable

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carbon-fluorine bonds, and therefore are environmentally persistent and resistant to

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heating, chemical reactions, and biodegradation in biota.3 Perfluoroalkyl carboxylates

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(PFCAs) and perfluoroalkyl sulfonates (PFSAs) make up two major PFAAs of

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worldwide concerns, especially for their homologues with eight carbons;

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perfluorooctanoate (PFOA) and perfluorooctane sulfonate (PFOS).4 Although PFOS

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and its salts were listed in Annex B of the international Stockholm Convention in

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2009,5 China continued their production since 2002.6,

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widespread use and persistence, PFAAs (mainly PFOA and PFOS) are ubiquitous in

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the global environment and have been detected in water,8 sediment,9 plants,10

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humans,11 and even in Arctic mammals.12

7

As a consequence of

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Historically, large-scale synthesis of PFAAs was primarily via electrochemical

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fluorination (ECF) and telomerization.2 The ECF process yields a mixture of linear

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and branched perfluoroalkyl isomers. For instance, ECF-derived PFOS and PFOA

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from the 3M Company, the major historic global producer, have a composition of ~30%

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and ~20% branched isomers, respectively.13-15 Telomerization yields an either

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straight-chain or isopropyl branched isomer in final products.16 It is reported that the

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industrial production of PFOS in large scale was only by the ECF process.15 PFAAs

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present in various environmental matrices are usually consisted of linear and multiple

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branched isomers.15 Isomer signature profiling of PFAAs has been developed to be a

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strong tool for distinguishing manufacturing origins (telomerization- versus

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ECF-derived), tracking emission sources, and investigating transport processes in the

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environment.15,

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compositions in seawater were utilized to elucidate their transport pathways in the

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world’s oceans.19 The PFOA isomeric patterns in house dust samples provided clues

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of historical and contemporary manufacturing sources of human exposure.20

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17, 18

For example, the features of PFOA and PFOS isomer

PFAAs are usually ionic and present as their conjugate anions, PFA-, at 3



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environmentally relevant water pH, which are considered to have negligible vapor

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pressures.21 For simplicity, they are still expressed as PFAAs throughout the

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manuscript. Once released in the environment, they are expected to have weak

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transport potentials via atmosphere. However, trace amount of PFAAs were identified

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in the environmental samples in Arctic regions, which has prompted investigations on

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their atmospheric transport capacities and mechanisms.22, 23 Giving the low volatility

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of PFAAs, earlier studies proposed that volatile precursor compounds (e.g.,

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perfluorosulfonamides and fluorotelomer alcohols) are transported to remote regions

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by atmosphere and subsequently degrade to PFAAs.24, 25 In consequence, many efforts

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have been paid to elucidate atmospheric transport behaviors of various PFAA

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precursors, but less were conducted for PFAAs.26-28 This is partially attributable to

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their low levels in the global atmosphere and lack of effective sampling techniques for

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airborne PFAAs. For example, monitoring of fluorinated compounds in the Canadian

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Arctic atmosphere using traditional active air samplers found that targeted PFAAs

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were all below their detection limits (generally < 0.2 pg/m3) in the gas phase.29

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Tree bark has been used as an excellent integrating passive air sampler for

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polycyclic aromatic compounds, polybrominated diphenyl ethers (PBDEs), and

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polychlorinated biphenyls (PCBs).30-32 Tree bark (specifically, rhytidome) is

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considered to be a dead plant tissue, but it has a high lipid content and comparatively

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larger surface area than other forms of vegetation (such as the leaf and root).33, 34 It

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accumulates both semi-volatile and particle-bound pollutants from the surrounding air

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and is inert to the chemicals dissolved in bark lipids.35, 36 In addition, comparing to the

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conventional high-volume active air sampler and polyurethane foam sampler, tree

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bark is easier and less expensive for sampling. Although PFAAs are nonvolatile, but

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previous field studies demonstrated that they could be transported to the surrounding

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environment via binding to atmospheric particles and/or aerosols.37 Based on this, we

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hypothesized that tree bark could be a suitable environmental matrix for evaluating

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airborne PFAAs.

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In this study tree leaf and bark samples were collected within and out of a

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fluorochemical manufacturing park (FMP), and analyzed with a developed isomer 4


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signature profiling method for PFAAs. Occurrence and spatial distribution of PFAAs

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in the collected samples were examined to investigate their emission sources and

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atmospheric

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perfluorohexane sulfonate (PFHxS), and PFOS were assessed based on their isomeric

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patterns. Their isomer-specific features in the barks were used to help understand their

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transport pathways in the atmosphere. Finally, the possibility of using tree bark as an

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indicator of airborne PFAAs was evaluated.

transport

behaviors.

The

manufacturing

origins

of

PFOA,

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EXPERIMENTAL SECTION

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Nomenclature. The acronyms of all individual PFAAs are listed in Table S1 of the

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Supporting Information (SI). We designate PFAAs as the total of PFAAs and their

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conjugate anions (PFA-s). The nomenclature of PFOA and PFOS isomers has been

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defined previously.18 Taking PFOA as an example, total branched PFOA isomers was

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termed as Br-PFOA, linear-chain PFOA as n-PFOA, perfluoroisopropyl as iso-PFOA,

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and 5-perfluoromethyl as 5m-PFOA. The chromatographically separated two

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branched PFHxS isomers were labeled as B1- and B2-PFHxS, respectively (SI Figure

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S1).

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Reagents, Standards, and Isomer Quantification. Milli-Q water, methanol,

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ammonium acetate (analytical-grade), formic acid (>98%), and ammonium hydroxide

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(NH4OH, 25% in water) were acquired from Fisher Scientific (Ottawa, ON, Canada).

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Authentic ECF manufactured PFOA (total branched isomers, ~22%) and PFOS

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(~30%) commercial standards were provided by the 3M Company (St. Paul, MN,

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America). All native and isotopically labeled standards, including perfluorobutanoate

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(PFBA),

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perfluoroheptanoate

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perfluorodecanoate (PFDA), perfluoroundecanoate (PFUnA), perfluorododecanoate

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(PFDoA),

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perfluorobutane sulfonate (PFBS), PFHxS, PFOS, T-PFOA, br-PFHxSK, and

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br-PFOSK, were purchased from Wellington Laboratories (Guelph, ON, Canada).

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The isomer signatures of T-PFOA and br-PFOSK were accurately characterized via

perfluoropentanoate (PFHpA),

perfluorotrdecanoate

(PFPeA),

perfluorohexanoate

(PFHxA),

PFOA,

perfluorononanoate

(PFNA),

(PFTrA),

perfluorotetradecanoate

5


(PFTeA),


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19

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quantify PFOA and PFOS isomer concentrations in samples, respectively.38 Albeit

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br-PFHxSK contains multiple branched PFHxS isomers, the exact percentages of

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isomer components and the authentic standards of individual branched PFHxS

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isomers were not commercially available. Therefore, linear PFHxS standard was used

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for semi-quantification of B1- and B2-PFHxS in samples.

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Sampling Sites and Sample Collection. A total of 24 bark and 24 leaf samples were

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collected in May 2012 (air temperature: 18-27 oC). As shown in the SI Figure S2,

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sampling sites were distributed within the FMP (site 01-08), along the S338

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Provincial Road (site 10-19), and next to Wangyu River (site 21-24) and Fushan River

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(site 25-27). This FMP has been in operation since 1999, and many fluorochemical

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companies (e.g., Dupont, Solvay, Arkema, and Daikin) have factories in the FMP.39

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Fluorochemical corporations in the FMP and the main commercial products,

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polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), with annual

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capacity are listed in the SI (Table S2). To our knowledge, this FMP is the largest

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manufacturing site for fluoropolymer- and fluorotelomer-related commercial products

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in China.37, 39

F nuclear magnetic resonance by the Wellington Laboratories and were used to

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Bark and leaf samples were predominantly taken from camphor (Cinnamomum

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camphora), cypresses (Platycladus orientalis), and magnolia (Magnolia grandiflora

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linn). Trees selected for sampling were mature and had average circumferences of

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~40 cm. Detailed description of the sampling locations and tree names can be found

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in Table S3. Only dry barks and fresh leaves (green in color) on trees were collected,

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and leaves with rips or rotten spots were avoided. Outer barks (n = 3-5) around the

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trunk (1.6-2.0 m above the ground) were scraped with stainless steel knives. The

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surface area and thickness of the bark were approximately 10 cm2 and 2 mm,

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respectively. Stainless steel scissors were used to collect whole fresh leaves (n =

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10-15) from tree branches at ~2 m above the ground. Stainless steel knives and

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scissors were sequentially rinsed with methanol and deionized water before each

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sampling. Bark and leaf collected at the same sampling site were pooled as individual

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sample. All collected samples were wrapped in aluminum foil, sealed in 6


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polypropylene (PP) bags, and kept at -80 °C until extraction. Control leaves and barks

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were collected from the trees (Cinnamomum camphora) at the Nankai University

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campus in Tianjin, China. Field blanks of the leaves from young trees (Cinnamomum

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camphora) were also transported with the real samples during the sampling campaign.

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Sample Pretreatment and Extraction. Extraction of PFAAs in leaves and barks

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followed the method described by Salamova et al.,32 with a few modifications (see SI

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for details). Briefly, all samples were freeze dried at -50 °C for 48 h, grinded with a

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porcelain mortar and pestle (FisherbrandTM, Thermo Scientific, ON, Canada), and

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sieved through a 1 mm mesh. One gram (in dry weight) of homogenized leaf or bark

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previously spiked with 5 ng of isotopically labeled standards (SI Table S1) was added

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into a 15 mL PP centrifuge tube (Corning, NY, America) and soaked with 10 mL of

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methanol. The mixture was shaken for 30 min at 200 rpm in a horizontal shaker,

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sonicated for 10 min, and centrifuged at 4000 rpm for 5 min. The supernatant was

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transferred to a new 50 mL PP tube. The above extraction process was repeated two

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more times and the extracts were combined, which was reduced to 4 mL under a

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gentle stream of high purity nitrogen. At this point, the remaining extracts were often

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dark colored (green or brown) and viscous in nature. Supelclean ENVI-Carb

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cartridges (500 mg/6 mL, Sigma-Aldrich, LA, America) were applied for further

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cleanup. The cartridge was conditioned with 10 mL of methanol, and then the extract

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was loaded and passed through it by gravity. The purified extract was evaporated to

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dryness and the residue was reconstituted in 50 µL of 50:50 (v/v) water/methanol for

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instrumental analysis of target analytes. Control and field blank samples were treated

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with the same extraction protocols.

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Instrumental Analysis. PFAAs and their isomers were separated and quantified

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using a Waters ACQUITY ultra-high performance liquid chromatography (UHPLC)

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coupled to a XEVO_TQS triple quadrupole mass spectrometer (MS/MS, Waters Co.,

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Milford, MA, America). Ten µL of extract was injected onto an Ascentis Express F5

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column (2.7 µm, 90 Å, 10 cm × 2.1 mm, Sigma-Aldrich, ON, Canada) equipped with

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a Zorbax C8 guard column (1.0 mm × 2.1 mm, Agilent Technologies, CA, America).

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The columns were maintained at 40 °C. The flow rate was maintained constant at 0.3 7



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mL/min. The initial conditions were 85% A (water contains 0.1% formic acid and 2

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mM ammonium acetate) and 15% B (methanol), and were held for 1 min, then

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ramped to 40% B by 1 min, increased to 65% B by 20 min, 100% B by 15 min, finally

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15% B and equilibrated for 5 min before the next injection. The mass spectrometer

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was operated in negative electrospray ionization and multiple reaction monitoring

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mode. Ions used for quantification and qualification and detailed UHPLC-MS/MS

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conditions are described in the SI.

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QA/QC. A solvent blank (50%/50% water/methanol) was injected with each batch of

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10 samples to monitor potential background contamination. The limits of detection

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(LODs) were defined as the concentration with a signal-to-noise ratio of three if the

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specific PFAA was undetectable in procedure blanks (n = 3). For the analytes

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appearing in the blanks, LODs were reported as the mean concentration plus three

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times the standard deviation of blanks (SI Table S4). Efficiency of extraction

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procedure was evaluated by spiking 1.0 ng of PFAAs into 1.0 g of field blank leaf (n

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= 4) or bark (n = 4) samples. The recoveries of the spiked leaf and bark samples were

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in the range of 71.3-115% and 79.5-111%, respectively (SI Table S4). The reported

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PFAA concentrations in collected samples were not corrected for recoveries. Internal

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standard method was used for quantification of PFAAs in the samples based on

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calibration curves. Additional matrix spiked recovery experiments were performed

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using T-PFOA, br-PFHxSK, and br-PFOSK standards, and the results confirmed that

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the isomeric profiles were conserved during extraction, indicating the matrix had

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minimal influence on isomer profiles, as reported previously.40

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RESULTS AND DISCUSSION

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Occurrence and Sources of PFAAs. All target analytes showed high detection

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frequencies in leaf (> 79%) and bark (> 83%) samples, and the concentrations of total

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PFCAs (∑PFCAs) were much greater than that of total PFSAs (∑PFSAs). This is

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reasonable since PFCAs as necessary additives are demanded in large amounts in

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manufacturing PTFE and PVDF in the FMP (SI Table S2). The concentration of total

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PFAAs (∑PFAAs, sum of ∑PFCAs and ∑PFSAs) in leaf (mean 250 ng/g dw, range 8


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46-1115 ng/g dw) and bark (279 ng/g dw, 37-774 ng/g dw) samples were comparable,

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and C4-C6 PFCAs, PFOA (C8-PFCA), and PFTeA (C14-PFCA) were always the

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dominant PFAAs (SI Table S5 and S6).

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Table 1 summarizes the concentrations of PFCAs and PFSAs in the bark and leaf

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samples. PFAAs in the bark samples were predominated by PFHxA (mean 168 ng/g

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dw, range 17-559 ng/g dw), accounting for 59% of ∑PFAAs (SI Figure S2), and

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followed by PFOA (37 ng/g dw, 4.0-269 ng/g dw), PFTeA (17 ng/g dw,

Perfluoroalkyl Acids Including Isomers in Tree Barks from a Chinese

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