Perfluoroalkyl Acids in Great Lakes Precipitation and Surface Water

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Characterization of Natural and Affected Environments

Perfluoroalkyl Acids in Great Lakes Precipitation and Surface Water (2006 – 2018) Indicate Response to Phase-outs, Regulatory Action, and Variability in Fate and Transport Processes Sarah B Gewurtz, Lisa E. Bradley, Sean Backus, Alice Dove, Daryl McGoldrick, Hayley Hung, and Helena Dryfhout-Clark Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.9b01337 • Publication Date (Web): 24 Jun 2019 Downloaded from pubs.acs.org on July 18, 2019

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Environmental Science & Technology

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Perfluoroalkyl Acids in Great Lakes Precipitation

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and Surface Water (2006 – 2018) Indicate Response

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to Phase-outs, Regulatory Action, and Variability in

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Fate and Transport Processes

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Sarah B. Gewurtz,† Lisa E. Bradley,*,† Sean Backus,† Alice Dove,† Daryl McGoldrick,† Hayley

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Hung,‡ Helena Dryfhout-Clark,‡

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†

Water Quality Monitoring and Surveillance, Environment and Climate Change Canada, 867

9 10 11

Lakeshore Road, Burlington, Ontario L7S 1A1, Canada ‡

Air Quality Processes Research Section, Environment and Climate Change Canada, 4905 Dufferin Street, Toronto, Ontario M3H 5T4, Canada

ACS Paragon Plus Environment

1


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ABSTRACT: Perfluoroalkyl acids (PFAAs) were determined in precipitation from three

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locations across the Great Lakes between 2006 and 2018 and compared to surface water.

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Perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) concentrations generally

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decreased in precipitation, likely in response to phase-outs/regulatory actions. In comparison,

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shorter-chained PFAAs, which are not regulated in Canada, did not decrease and

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perfluorohexanoate and perfluorobutanoate (PFBA) recently increased, which could be due to their

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use as replacements as the longer-chained PFAAs are phased-out by industry. PFOS and PFOA

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concentrations were greater in Lake Ontario precipitation than in the more remote locations. In

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comparison, PFBA concentrations were comparable across locations, suggesting greater

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atmospheric transport either through its more volatile precursors and/or directly in association with

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particles/aerosols. In Lake Ontario, comparison of PFAAs in precipitation to surface water

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provides evidence of sources (e.g., street dust and wastewater effluent) in addition to wet

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deposition to surface water, whereas wet deposition appears to be dominant in Lakes Huron and

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Superior. Our results suggest that source control of shorter-chained PFAAs may be slow to be

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reflected in environmental concentrations due to emissions far from the location of detection and

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continued volatilization from existing in-use products and waste streams.


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TABLE OF CONTENTS (TOC)/ABSTRACT ART

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INTRODUCTION

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Concern over perfluoroalkyl acids (PFAAs) has increased in recent years despite phase-outs and

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regulatory actions ongoing since the early 2000s.1,2,3 Much of this concern is due to the derivation

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of regulatory criteria and advisory guidance for PFAAs that are lower than previous values1,4,5 as

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well as the finding that the drinking water supply of approximately six million U.S. residents may

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have concentrations of perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) above

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the United States Environmental Protection Agency (USEPA) advisory level of 70 ng/L.2

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The fate and transport of PFAAs are complex and difficult to predict because, unlike many other

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persistent organic contaminants, they are confounded by their surfactant-properties and more

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volatile precursors.6 As such, detailed long-term assessments are critical for determining if

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environmental concentrations are responding to phase-outs, regulatory actions, and control

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measures on a vast array of sources. Precipitation and surface water are ideal media for evaluating

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PFAAs. Despite the fact that PFAAs are not considered volatile under environmental conditions,

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they are commonly detected in the atmosphere as a result of their association with particles and

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aerosols and following transformation of their more volatile precursors.7,8,9 Precipitation reflects

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atmospheric concentrations10 and is an important removal mechanism of PFAAs from the

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atmosphere through sequestration of particles11 and/or sorption of PFAAs from the atmosphere to

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water droplets.10,12 Precipitation has been shown to impact PFAA concentrations in surface

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water,13 groundwater,14 and soil.15 In comparison, surface water can reflect a variety of sources,

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including point source releases in addition to atmospheric deposition.13,16,17,18,19 Surface water is

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also relevant in terms of human exposure given its importance with respect to drinking water,

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which is a major source of PFAAs to humans.20 Therefore, simultaneous assessment of PFAA

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concentrations in precipitation and surface water can generate hypotheses related to fate and


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transport and the relative importance of atmospheric deposition versus local anthropogenic sources

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in influencing surface water concentrations. This information has implications for source control.

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Chemicals whose fate and transport are largely influenced by atmospheric transport and wet

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deposition would be more difficult to control as they may have been emitted to the environment

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far from the location of detection.

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The first objective of this study was to use a high-resolution dataset to assess the time trends of

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PFAAs in precipitation at three locations across the Laurentian Great Lakes between 2006 and

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2018 to test the hypothesis that phase-outs and regulatory measures have resulted in reduced

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concentrations of PFAAs in the environment.

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differences in the role of atmospheric deposition as a source to surface water. Precipitation

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samples were integrated on a monthly basis and compared to open surface water measurements

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collected three or four times across the Great Lakes between 2008 and 2017. These datasets were

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generated in support of Environment and Climate Change Canada (ECCC)’s mandate to monitor

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the quality of the environment for Canadians and priorities under the Chemicals Management Plan.

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Given that the Great Lakes span 244,106 km2 and range from highly urbanized Lakes Erie and

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Ontario to the more remote Lake Superior, the datasets also provide a unique opportunity to assess

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spatial differences in fate and transport and the relative importance of the atmosphere as a potential

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source. To our knowledge, this is the first study to evaluate high-resolution temporal trends of

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PFAAs in precipitation over more than ten years.

The second objective was to assess spatial

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MATERIALS AND METHODS

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Sample Collection. Integrated monthly precipitation samples were collected between April

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2006 and August 2018 from three locations in the Great Lakes basin: Point Petre, Burnt


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Island/Evansville, and Sibley (Supporting Information (SI) Figure SI1).

Point Petre

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(43.8428, -77.1536) is located in eastern Lake Ontario and is considered a lightly populated rural

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region, 160 km east of Toronto, ON and approximately 85 km north of Rochester, NY.21 Burnt

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Island (45.8283, -82.94801)/Evansville (45.8181, -81.3386) is considered a remote site that is

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located on the southwestern end of Manitoulin Island in northern Lake Huron, about 140 km

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southeast of Sault Ste. Marie, ON.21 Burnt Island was the station of sample collection between

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April 2006 and March 2013, after which the site was shut down. In July 2013, the site was

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relocated to Evansville, 22 km to the east on Manitoulin Island. The Evansville site is not close to

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significant sources and, due to its close proximity to Burnt Island, the relocation is not expected to

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influence atmospheric concentrations of PFAAs. Sibley (48.4986, -88.6694) is located on the

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northwest corner of Lake Superior and is considered a remote location about 90 km east of Thunder

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Bay, ON and approximately 300 km northeast of Duluth, Minnesota.21 Monthly integrated

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precipitation samples were collected using a MIC-B wet-only precipitation automated sampler

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(Meteorological Instruments of Canada, Thornhill, ON). The samples were collected in a sample

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bucket lined with a polyethylene bag with an opening of 0.0314 m2. After each month, the samples

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were transferred to 2 L high-density polyethylene (HDPE) bottles for shipment. The excess

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portion of any sample greater than 2 L was measured in a graduated cylinder and then discarded.

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The samples were transported to ECCC’s Canada Centre for Inland Waters (CCIW, Burlington,

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ON, Canada) and stored at -10 ºC until analysis.

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Surface water samples were collected using a pole sampler from a 1 m depth at open water

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stations in Lakes Ontario (March/April 2008, 2012, 2013, and 2015), Erie (April/May 2012, 2013,

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2014, and 2015), Huron/Georgian Bay (May/June 2012, 2014, and 2017), and Superior (May 2008

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and 2016) (SI Figure SI1 and SI Table SI1). HDPE sample bottles were rinsed twice with sample


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water before filling. Samples were collected in the spring when there is a high degree of mixing

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in the water column.22 Following collection, the samples were transported to CCIW and stored at

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4 °C until analysis.

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Chemical and Instrumental Analysis. Extraction and instrumental analysis of PFAAs in

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surface water and precipitation samples collected up until November 2017 were conducted by SGS

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AXYS Analytical Services Ltd. (SGS AXYS, Victoria, BC, Canada) with SGS AXYS Method

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MLA-060. Precipitation samples collected from December 2017 onwards were analyzed using

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SGS AXYS Method MLA-110. In brief, MLA-060 and MLA-110 involve analysis of samples by

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liquid chromatography-tandem mass spectrometry (LC-MS/MS), following solid-phase extraction

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(SPE) and selective elution procedures as described in the Supporting Information and detailed

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previously.23 For both methods, the separation employed a gradient elution with a mobile phase

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comprised of acetonitrile and aqueous ammonium acetate and calibration curves were based on

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six to eight calibration levels. PFAA quantification was performed using an isotope dilution

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internal standard approach by comparing the area of the quantification ion to that of the labeled

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standard and correcting for response factor. The samples were spiked with surrogate standards

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prior to extraction and recovery standards prior to analysis with LC-MS/MS (SI Table SI2).

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The SGS AXYS Methods MLA-060 and MLA-110 are accredited to ISO 17025 standards by

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the Canadian Association for Laboratory Accreditation Inc. (CALA) and SGS AXYS routinely

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participates in inter-laboratory comparison studies. Both methods use similar SPE and LC-MS/MS

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approaches and data from the two methods are considered equivalent. Details on differences and

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method equivalence are shown in the Supporting Information. A procedural blank and spiked

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reference sample, consisting of a commercially available brand of bottled drinking water that was

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tested by lot for PFAA background, were analyzed with each sample batch. PFAAs were not


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detected in any of the 74 blank samples analyzed except for trace level detections listed in the

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Supporting Information. Mean recoveries in native PFAA spiked matrices ranged from 97% to

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100% (n = 59). 5% of samples within each sample set were analyzed in duplicate. Duplicate

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samples were required to have a relative percent deviation of less than 40%. Reporting limits were

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determined by prorating the concentration of the lowest calibration limit for the sample size and

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extract volume. Concentrations were quantified if the peak met the retention time requirement for

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a given chemical and the signal to noise ratio was greater than three. Detected concentrations in

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precipitation that were in the region above the 3:1 signal to noise ratio and below the reporting

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limit were J-flagged, which denotes estimated values.

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Data Analysis. Data analysis was performed on PFAAs that were detected (including J-flagged

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data) in greater than 30% of the samples, namely perfluorobutanoate (PFBA), perfluoropentanoate

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(PFPeA),

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perfluorononanoate (PFNA), perfluorodecanoate (PFDA), perfluoroundecanoate (PFUnA), and

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perfluorododecanoate (PFDoA). Given the relatively low detection frequency ranging from 5%

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to 65% (30% to 86% including J-flagged data) (SI Table SI3), methods for statistical analysis were

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selected for their ability to handle censored measurements. We treated J-flagged data as detected

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measurements in statistical analysis. However, they were distinguished from detected data above

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the reporting limit in tables and figures. Statistical analysis of precipitation time trends with the

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Seasonal Kendall trend test and spatial patterns were completed on u-scores, as recommended by

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Helsel24 for datasets with multiple reporting limits. The u-score was calculated as the sum of the

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algebraic sign of differences comparing the ith observation to all other observations within the

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same variable as follows:

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=∑

perfluorohexanoate

(

−

(PFHxA),

perfluoroheptanoate

(PFHpA),

PFOA,

) ACS Paragon Plus Environment

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where ui is the u-score of the ith observation and xi and xk are the concentration values of the ith

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and kth observations, respectively. The u-score forms the basis of the well-known Mann-Whitney

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test and is related to Kendall’s tau and the calculation of Kaplan-Meier percentiles.24 In the

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calculation of u-scores, when a detected concentration cannot be determined to be higher or lower

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than a non-detect value, the sign of the difference is considered zero.

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Previous studies have found that PFAA depositional flux is greatest at the beginning of a rainfall

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event (first few millimeters of deposition)25 and concentrations may become diluted when the

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amount of precipitation is high (> 2 mm).10 As such, we completed the statistical analysis for

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PFAAs in precipitation on both a concentration- and flux-basis, where flux (ng/m2) = PFAA

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concentration in the sample (ng/L) × volume of precipitation during the sampling period (L) /

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surface area of the bucket used for sampling (0.0314 m2). The relationships between PFAA

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concentration u-scores and volume of precipitation and between volume of precipitation and time

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were evaluated with the Mann-Kendall and Seasonal Kendall trend tests, respectively.26

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Time trends were analyzed using two methods: the Seasonal Kendall trend test26 on u-scores and

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the Digital Filtration (DF) technique on concentration values.27,28,29 Only detected and J-flagged

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data were included in the DF technique, as has been done previously.28 The F-test was used to

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assess the significance of the coefficient of determination (r2) between the trend derived by the DF

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model and the measured data. First-order half-lives or doubling times were approximated as

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ln(2)/k where k was defined as the linear regression slope of the DF-estimated concentrations

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versus time. It should be noted that PFAAs did not necessarily decline/increase linearly or

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consistently in the first order manner throughout the entire monitoring period. Therefore, half-

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lives and doubling times are only used to compare the relative rates of decline/increase in


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concentrations between chemicals. Additional technical details of the DF technique are presented

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in the Supporting Information.

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Principal component analysis (PCA) was conducted to explore overall spatial patterns. Factor

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loadings were rotated using the Varimax normalized rotation. Two factors were retained based on

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the results of the Scree test. PCA assumes a constant rate of change between points in space.24 In

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order to evaluate if this assumption influenced the results of the PCA, we also applied nonmetric

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multidimensional scaling (NMDS), which plots distances between points in the same rank order

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as distances in a resemblance matrix between sites, and makes no assumptions about linear

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relationships.24 We used Euclidean distance to calculate the resemblance matrix. The initial runs

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of the PCA and NMDS found that the results were highly influenced by non-detect values of

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PFPeA, PFUnA, and PFDoA, which were only detected in 51%, 47%, and 32% of the samples,

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respectively. As such, the PCA and NMDS were re-run and presented with the following PFAAs:

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PFBA, PFHxA, PFHpA, PFOA, PFNA, and PFDA.

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Finally, analysis of similarity (ANOSIM), using Euclidean distance to calculate the resemblance

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matrix, was used to test for significant differences in PFAA patterns between locations and

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between precipitation and surface water. ANOSIM is a nonparametric multivariate procedure that

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operates on ranks of resemblances and uses permutation tests to obtain p-values.24

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Statistical analyses were performed at the α = 0.05 significance level. R Version 3.4.4 was used

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for all statistical methods except for the DF model application. U-scores were calculated using the

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R script uscore.r.30 The Mann-Kendall and Seasonal Kendall tests for trends were conducted using

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the kendallTrendTest and kendallSeasonalTrendTest functions of the EnvStats package.31 The

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PCA was conducted using the principal function of the psych package.32 The NMDS and


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ANOSIM tests were applied using the metaMDS and anosim functions, respectively, of the vegan

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package.33

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RESULTS AND DISCUSSION

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PFAAs in Precipitation and Surface Water. PFAA concentrations in precipitation and surface

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water collected in the Great Lakes are presented in SI Tables SI4 and SI5, respectively, and

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summarized in SI Table SI3. Concentrations of PFAAs in Great Lakes precipitation were

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comparable to other locations observed in previous studies, particularly in remote and rural

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locations, although sometimes in heavily urbanized regions as well.9,13,34,35 This is not surprising

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given that the more volatile precursors of some PFAAs are transported far distances in the

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atmosphere, leading to their occurrence in remote locations,28 as discussed below. In addition,

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PFAAs can be emitted directly to air in the form of aerosols or particles, which can also be

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transported through the atmosphere.7,8,9

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comparable to previous open water measurements from the Great Lakes.23,36

Surface water concentrations observed here were

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Canadian Federal Environmental Quality Guidelines (FEQGs) exist for PFOS and the maximum

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concentrations of PFOS observed in surface water (7.4 ng/L in Lake Ontario on April 21, 2015)

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and precipitation (14 ng/L at Point Petre in February 2007) were more than two orders of

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magnitude below the FEQG for surface water of 6,800 ng/L that is intended to protect all forms of

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aquatic life for indefinite exposure periods.37 Furthermore, Health Canada has published drinking

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water screening values for the majority of PFAA compounds evaluated in this study that range

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from 20 ng/L for PFNA to 30,000 ng/L for PFBA38 and the PFAA concentrations observed here

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were at least 8-fold lower than these values. It should be noted, however, that the maximum PFAA


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concentrations observed in surface water in this study were just below the lowest screening and

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guidance values published by regulatory agencies throughout the world.1

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Time Trends. Time trends of PFAA concentrations in Great Lakes precipitation between April

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2006 and August 2018 are presented in SI Figures SI2a, b, and c. Time trends for four selected

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PFAAs are presented in Figure 1 (PFBA and PFHxA) and Figure 2 (PFOA and PFOS). Although

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time trends of PFAAs in Great Lakes precipitation vary among chemicals and locations, some

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overall patterns are evident. For example, PFOA, PFNA, PFDA, and PFOS, for the most part,

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significantly decreased over time (Seasonal Kendall trend test, p < 0.05, SI Table SI6) with

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approximate half-lives of less than 15 years as determined through application of the DF technique.

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PFNA and PFDA at Sibley and PFDA at Burnt Island/Evansville were the only exceptions with

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longer half-lives of 22, 67, and 20 years, respectively. These overall decreasing trends were likely

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in response to North-American phase-outs and regulatory actions for PFOS, PFOA, and other long-

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chained perfluoroalkyl carboxylates (PFCAs) and their precursors ongoing since the early

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2000s.1,39 Although PFUnA and PFDoA are also long-chained PFCAs, their concentrations did

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not monotonically decrease between April 2006 and August 2018. PFUnA and PFDoA are less

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water soluble than PFOA, PFNA, PFDA, and PFOA40 and percent detection was relatively low

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(46% and 31%, respectively) for these chemicals in Great Lakes precipitation (SI Table SI3),

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which may be influencing their observed trends. PFBA, PFPeA, PFHxA, and PFHpA did not

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decrease monotonically at the three Great Lakes sites between April 2006 and August 2018

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(Seasonal Kendall trend test, p > 0.05), with the exception of PFBA at Burnt Island/Evansville (p

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= 0.02) and PFHpA at Point Petre (p = 0.023). Furthermore, the DF trend line indicates that

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concentrations of PFBA and PFHxA appear to be increasing in most recent years (~2010/2014 to

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2018 at Point Petre and Burnt Island and ~2016 to 2018 at Sibley) (Figure 1). These results may


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not be surprising considering that these short-chained PFCAs and their precursors have not been

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regulated in Canada37 and are being used as replacement chemicals for PFOS, PFOA, and the

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longer-chain PFCAs.41 For example, PFBA is an impurity in perfluorobutane sulfonyl fluoride-

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based derivatives currently used as a replacement for perfluorooctane sulfonyl fluoride in surface

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treatment products.41 In addition, in response to the 2010/2015 USEPA voluntary stewardship

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program, most aqueous film forming foam (AFFF) manufacturers have switched to short-chain

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(C6) fluorotelomer-based per- and polyfluoroalkyl substances (PFAS).42

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Time trends of PFAA concentrations in Great Lakes surface water were not statistically

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evaluated due to the fact that only two (Superior), three (Huron), and four (Erie and Ontario)

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years/sampling events were evaluated between 2008 and 2017. More than four years of data are

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typically required to detect the changes in PFAA concentrations observed in the environment.43

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For PFAAs detected in Lake Ontario (i.e., the shorter chained-PFCAs containing eight or fewer

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carbon atoms and PFOS), surface water concentrations were within the upper range of those

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observed in precipitation. A similar pattern was observed in Huron surface water except for PFBA.

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The concentrations of PFBA in Huron surface water was comparable to precipitation. The

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frequency of detection of PFAAs was low in Superior surface water (SI Table SI3). Only two

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chemicals, PFBA and PFOA, with detection frequencies of 36% and 55%, were detected in

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Superior surface water, at concentrations comparable and slightly elevated compared to

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precipitation, respectively. These results are discussed below.

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PFAA concentration u-scores in precipitation decreased significantly with precipitation volume

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in about 50% of the chemicals/locations (Mann-Kendall, p < 0.05, SI Table SI7). There was no

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monotonic relationship (Mann-Kendall, p > 0.05) between PFAA concentration u-scores and

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precipitation volume for the remaining chemicals/locations. These results correspond to previous


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studies10,25 and indicate that PFAA concentrations in precipitation are, in some cases, dependent

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on the volume of precipitation within each sampling month. Precipitation volume did not change

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significantly with time at Point Petre (Seasonal Kendall trend test, p = 0.60, tau = -0.03, Z = -0.53)

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or Burnt Island/Evansville (Seasonal Kendall trend test, p = 0.77, tau = 0.019, Z = 0.29) but

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increased at Sibley (Seasonal Kendall trend test, p = 0.0010, tau = 0.25, Z = 3.3). However, the

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overall time trends of PFAAs in Great Lakes precipitation were consistent whether evaluated on a

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concentration- or flux-basis (SI Figure SI2 and SI Table SI6).

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The DF-derived seasonal trend lines indicated considerable intra-annual variability of PFAAs in

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precipitation on both a concentration- and flux-basis (Figure 1, Figure 2, and SI Figure SI2).

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However, no consistent seasonal patterns were evident, which corresponds to previous findings

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for PFAAs in precipitation collected from two locations in Japan between June 2006 and June

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200810 and PFOA and PFNA at three northeastern U.S. sites in 1998 and 1999.35

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Spatial Patterns. The PCA conducted on PFAA concentration (Figure 2) and flux (SI Figure

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SI3) u-scores indicated that precipitation collected at Point Petre in Lake Ontario grouped

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separately from Burnt Island/Evansville (Huron) and Sibley (Superior) with relatively high scores

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for factor 2, which was generally associated with PFOS. PFOA also loaded relatively high on

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factor 2, with values slightly below PFOS. Application of ANOSIM showed that the pattern of

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concentrations and fluxes at Point Petre were significantly different than Burnt Island (R = 0.17

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and 0.15 for concentration and flux, respectively, p = 0.001) and Sibley (R = 0.19 and 0.24 for

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concentration and flux, respectively, p = 0.001) but there were no significant differences between

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Burnt Island and Sibley (R = 0.012 and -5.7×10-5, p = 0.078 and 0.48 for concentration and flux,

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respectively). Point Petre is considered a lightly populated rural region. However, it is relatively

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close (160 km and 85 km, respectively) to major urban centers of Metropolitan Toronto, ON


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(population = 6.4 million) and Rochester, NY (population = 208,046). As such, it is likely that

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relatively elevated PFOS and PFOA concentrations in precipitation at this location results from

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the influence of human activity, as found in other studies for PFOS and in some cases

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PFOA.9,44,45,46 PFOS and PFOA are not considered volatile; however, they can be released into

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the gas phase from point sources indirectly in the form of their more volatile precursors,

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transported in the atmosphere in the gas phase, and then degraded to PFOS and PFOA.9,47,48,49

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PFOS and PFOA can also be emitted from point sources to the atmosphere directly in the form of

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particles and/or aerosols and travel through the air associated with particles/aerosols.8,49,50,51

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Recent studies show that PFAAs can enrich significantly in sea spray aerosols and be emitted to

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the atmosphere;11,52,53 although only about 3% of the aerosolized PFOA and PFOS were estimated

291

to be transported and deposited to land areas.52 In comparison, all three locations had similar factor

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1 scores, which were generally associated with PFBA and other short-chained PFCAs. PFBA,

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other short-chain PFCAs, and their precursors such as the fluorotelomer alcohols (FTOHs) are

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more volatile compared to the longer-chained PFAAs, are found at higher concentrations in gas

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compared to particle phase in air, and are subject to transport in the atmosphere (either through

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their precursors and/or associated with particles/aerosols).28,40,54 Furthermore, as discussed by

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Wong et al.,28 atmospheric transformation of certain volatile hydrofluorocarbons and

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hydrofluoroethers to PFBAs could have occurred, which has been demonstrated in laboratory

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studies under zero or low NOx conditions.55,56 This provides evidence that the major source of

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PFBA and other short-chain PFCAs to Great Lakes precipitation is through long-range

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atmospheric transport, which leads to similar concentrations throughout Great Lakes precipitation.

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Our results correspond with those of Wong et al.28 who found that air concentrations of PFBA at

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Alert, located in the Canadian high Arctic (median = 1.7 pg/m3, range:

Perfluoroalkyl Acids in Great Lakes Precipitation and Surface Water

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