Article pubs.acs.org/est
20 Years of Air−Water Gas Exchange Observations for Pesticides in the Western Arctic Ocean Liisa M. Jantunen,*,† Fiona Wong,‡ Anya Gawor,† Henrik Kylin,§,∥ Paul A. Helm,⊥ Gary A. Stern,# William M. J. Strachan,∇ Deborah A. Burniston,○ and Terry F. Bidleman†,◆ †
Air Quality Processes Research Section, Environment Canada, 6842 Eighth Line, Egbert Ontario, L0L 1N0 Canada Analytical Chemistry and Environmental Sciences (ACES), Stockholm University, SE-106 91 Stockholm, Sweden § Department of Thematic Studies − Environmental Change, Linköping University, SE-581 83 Linköping, Sweden ∥ Research Unit: Environmental Sciences and Development, North-West University, Private Bag X6001, Potchefstroom, 2520 South Africa ⊥ Environmental Monitoring and Reporting Branch, Ontario Ministry of the Environment, 125 Resources Road, West Wing, Toronto, Ontario, M9P 3V6 Canada # Centre for Earth Observation Science, University of Manitoba, 474 Wallace Building, 125 Dysard Road, Winnipeg, R3T 2N2 Canada ∇ Aquatic Ecosystem Protection Research Division and ○Water Quality Monitoring and Surveillance, Science and Technology Branch, Environment Canada, 867 Lakeshore Road, Burlington, Ontario, L7S 1A1 Canada ◆ Department of Chemistry, Umeå University, SE-901 87 Umeå, Sweden ‡
S Supporting Information *
ABSTRACT: The Arctic has been contaminated by legacy organochlorine pesticides (OCPs) and currently used pesticides (CUPs) through atmospheric transport and oceanic currents. Here we report the time trends and air−water exchange of OCPs and CUPs from research expeditions conducted between 1993 and 2013. Compounds determined in both air and water were trans- and cischlordanes (TC, CC), trans- and cis-nonachlors (TN, CN), heptachlor exo-epoxide (HEPX), dieldrin (DIEL), chlorobornanes (ΣCHBs and toxaphene), dacthal (DAC), endosulfans and metabolite endosulfan sulfate (ENDO-I, ENDO-II, and ENDO SUL), chlorothalonil (CHT), chlorpyrifos (CPF), and trifluralin (TFN). Pentachloronitrobenzene (PCNB and quintozene) and its soil metabolite pentachlorothianisole (PCTA) were also found in air. Concentrations of most OCPs declined in surface water, whereas some CUPs increased (ENDO-I, CHT, and TFN) or showed no significant change (CPF and DAC), and most compounds declined in air. Chlordane compound fractions TC/(TC + CC) and TC/(TC + CC + TN) decreased in water and air, while CC/(TC + CC + TN) increased. TN/(TC + CC + TN) also increased in air and slightly, but not significantly, in water. These changes suggest selective removal of more labile TC and/or a shift in chlordane sources. Water−air fugacity ratios indicated net volatilization (FR > 1.0) or near equilibrium (FR not significantly different from 1.0) for most OCPs but net deposition (FR < 1.0) for ΣCHBs. Net deposition was shown for ENDO-I on all expeditions, while the net exchange direction of other CUPs varied. Understanding the processes and current state of air−surface exchange helps to interpret environmental exposure and evaluate the effectiveness of international protocols and provides insights for the environmental fate of new and emerging chemicals.
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INTRODUCTION Atmospheric deposition has been recognized as a large, and in some cases the dominant, loading process for persistent organic pollutants (POPs) to the oceans.1−3 This is also true for the Arctic Ocean, although awareness is growing that ocean currents can transport persistent and relatively soluble chemicals, including some current-use pesticides (CUPs).3−8 Air−water gas exchange of chemicals is a “two-way street” and can alternate between net deposition and net volatilization in response to seasonally changing temperatures, atmospheric levels,9,10 cycles of biological productivity, particle sinking dynamics, and hydroxyl radical (OH) reactions.11−13 Over © XXXX American Chemical Society
longer time periods, declining atmospheric concentrations have led to the re-emission of hexachlorocyclohexanes (HCHs) from the Arctic Ocean.14−20 Exchanges of HCHs and other OCPs in subarctic, temperate, and tropical oceans have varied from net deposition to equilibrium to net volatilization.12,21−26 Modeling Special Issue: Ron Hites Tribute Received: March 13, 2015 Revised: June 25, 2015 Accepted: July 21, 2015
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DOI: 10.1021/acs.est.5b01303 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Environmental Science & Technology
Figure 1. Cruise map of samples taken between 1999 and 2013 in the Canadian Archipelago.
reported in water from the 1993−94 expeditions30,51 but not in air, and air−water exchange was not assessed. This paper reports the spatial distributions of OCPs other than HCHs and of several CUPs in surface water measured on arctic−subarctic expeditions between 1993 and 2013. Water and air concentrations from concurrent shipboard measurements were paired to estimate the gas exchange departure from the air−water equilibrium.
suggests that the global ocean has been losing DDT since 1977, with volatilization as the main loss process.27 Few assessments of gas exchange have been made for OCPs other than HCHs, and even fewer for CUPs, in the Arctic. Exchanges (net, unless stated otherwise) in the central Canadian Archipelago in 1993 were characterized as volatilization for hexachlorobenzene (HCB) and dieldrin (DIEL) and deposition for endosulfan-I (ENDO-I), and the exchange direction varied with the season for chlordanes and chlorobornanes (CHBs, e.g., toxaphene).28 The deposition of cis-chlordane (CC) and HCB and the variable exchange of trans-chlordane (TC) were found during 2004 in the eastern Arctic Ocean between Greenland and Svalbard,24 and HCB was depositing in the southern Beaufort Sea in 2008.20 ENDO-I is the most-studied CUP in the Arctic, whereas the data for other CUPs are fewer. ENDO compounds are widespread in Arctic Ocean water, snow, ice caps, and air.29−36 Based on measurements from 1993 to 2000, the deposition of ENDO-I was estimated across the Arctic Ocean.32 Gas exchange estimates for the Bering and Chukchi Seas and the North Pacific in 2010 indicated a net deposition of the CUPs trifluralin (TFN), dicofol, ENDO, dacthal (DAC), and chlorpyrifos (CPF).35 CUPs have been reported in arctic and subarctic lakes, ice caps, snow, and air.29,31,37−42 The CUPs DAC, CPF, and ENDOs have been reported in fish from Alaskan lakes,43 as well as ENDOs in arctic cod, ringed seal, and beluga33 and ENDO-I in zooplankton and fish in two lakes in the Norwegian Arctic.44 A similar suite of CUPs was found in wolves, caribou, marine invertebrates, and fish from the Canadian Arctic, where ENDO-I and the metabolite endosulfan sulfate (ENDO SUL) were the dominant compounds.45 Over the past 20 years, OCPs in arctic air46,47 and biota3,48 have generally declined due to restrictions or bans on usage. The long-term trends of OCPs at global air-monitoring stations, including those in the arctic, indicate that of 257 time series data sets, 93% and 71% give half-lives less than 20 and 10 y, respectively.49 We previously reported spatial distributions and gas exchange of HCHs in arctic−subarctic surface water15−17,20,50 Concentrations of other OCPs were
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EXPERIMENTAL SECTION Sampling Locations. The sampling of air and surface water was carried out on several expeditions in: (1) the Bering and Chukchi seas (Bering−Pacific, BERPAC-1993), (2) the northern Canada Basin (Arctic Ocean Section, AOS-1994), and (3) the Canadian Archipelago (Tundra Northwest, TNW-1999; International Polar Year, IPY-2007-2008, and ArcticNet-2010/ 2011/2013). Additional air samples were collected from the central Archipelago at Resolute Bay in 1999, as were air and water samples from near-Archipelago regions of the Labrador Sea and Gulf of St. Lawrence in 2007 (see Table S1 in the Supporting Information for details). A map of the cruise tracks is shown in Figure 1. Sampling, Analysis, and Quality Control. Air samples of 500−1500 m3 were collected from shipboard in all years and at Resolute Bay (Cornwallis Island, Nunavut, 74.70° N, 94.83° W) in 1999 with a glass fiber filter (GFF) to retain “particulate” compounds, followed by polyurethane foam (PUF) to trap the “gaseous” fraction. This method was used up until and including 1999, when the sample train was changed to a GFF−PUF/XAD-2 resin sandwich to capture the more volatile compounds with greater efficiency. Shipboard air sampling was done on the deck above the bridge in 1993−1994 cruises, but to avoid potential interference from the smoke stack, the sampling was later moved to the tip of the bow. Surface water (≤7 m) was collected into stainless steel cans with an overboard submersible pump or through a stainless steel line running 7 m below the ship. Canisters of water were kept sealed as much as possible during extraction to avoid contamination from the ship. Water was processed through a GFF; 40−200 L was passed through a column of XAD-2 resin B
DOI: 10.1021/acs.est.5b01303 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Environmental Science & Technology to retain “dissolved” species30 except on BERPAC-1993, where unfiltered water was extracted with dichloromethane in a Goulden apparatus.51 Analysis was performed by capillary gas chromatography−low-resolution electron capture negative ion mass spectrometry. Quality control consisted of analyzing blanks (field, sampling media, and procedural), determining the instrumental detection limits (IDLs), and monitoring the recoveries of spiked compounds. The details of analysis and quality control are provided in Tables S2 and S3 and the text in the Supporting Information.
melt, whereas lower concentrations were associated with the highest salinities (32−34 psu) and extensive ice cover. CHT is often reported at high concentrations in precipitation. CHT concentrations in the thousands of picograms per liter were found in snow from Resolute Bay (Pućko, University of Manitoba, from personal communication) and were predicted for the ice melt ponds from the Henry’s law partitioning.52 CHT concentrations in the range of 510−2400 pg L−1 were reported in snow and rain at high-elevation national parks in the United State,53 and a concentration of 2800 pg L−1 was found in a melt pond on Ward Hunt Island in the Canadian high arctic.41 The Pearson correlations between pesticides in water are shown in Table S6 in the Supporting Information for pairs where both species were quantifiable (NDs omitted). DAC showed the highest number of significant correlations (p < 0.05) with TC, ENDO-I, ENDO-II, ENDO SUL, and TFN. Correlations were found among the three chlordanes (TC, CC, and TN) and among the three endosulfan species (ENDO-I, ENDO-II, and ENDO SUL). ENDO-I and ENDO-II were not related to any other pesticides except DIEL (for ENDO-I), and HEPX, a soil metabolite,54 was correlated with ENDO SUL, another soil metabolite,33 and with DIEL and ΣCHBs but not with other chlordanes. DIEL correlated with HEPX, ENDO-I, ENDO SUL, and ΣCHBs. Apparent first-order changes in water concentrations were examined by regression of log CW versus year. IDLs were substituted for NDs. The results are summarized in Table 1 and Table S7 in the Supporting Information, where the numbers of the detectable and total samples are also given. The Bering and Chukchi seas and northern Canada Basin were sampled only in 1993 and 1994, whereas several expeditions traversed the Archipelago between 1999 and 2013. The time trends in water were derived by considering all of the measurements from 1993 to 2013 and only those from the Archipelago. The times for 50% change (t0.5, p < 0.05) from 1993 to 2013 ranged from 5.9 to 9.3 years for the depletion of HEPX, TC, CC, TN, and ENDO-II, and the changes for DIEL were not significant. ENDO-I increased, with a time for 50% increase of 21 years. CHBs were measureable in water on BERPAC-1993 and AOS1994, sought in six TNW-1999 samples, and not detected on IPY-2007. Thereafter, CHBs were not sought, and no time trends were estimated. The t0.5 values were smaller within the Archipelago (4.0−5.6 years for the depletion of TC, CC, TN, and ENDO-II); DIEL also decreased, with a t0.5 value of 2.5 years. ENDO-I showed an increasing t0.5 value of 11 years. The smaller t0.5 values for the Archipelago were a consequence of low or ND concentrations on the later expeditions (Table S4 in the Supporting Information). The apparent depletion of t0.5 was very small, although significant, for HEPX and ENDO SUL (0.72 and 0.79 years). CHT (1999−2013) and TFN (2007−2013) increased in the Archipelago (t0.5 of 3.5 and 2.4 years), and changes in DAC (1999−2013) and CPF (2007−2013) were insignificant. Our measurements are compared to those in previous reports in arctic and subarctic seawater for OCPs and ENDO-I (Table S8 in the Supporting Information). The overall means ± SD (pg L−1) for arctic waters derived from the means reported by all research groups are TC = 1.5 ± 2.0, CC = 1.6 ± 1.2, TN = 1.1 ± 1.1, HEPX = 7.1 ± 8.5, DIEL = 13 ± 9, ENDO-I = 3.1 ± 2.0, and ΣCHBs = 95 ± 74. Relative standard deviations (RSD) for these compounds in arctic and subarctic seawater
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RESULTS AND DISCUSSION Compounds sought in air and water since the early campaigns were DIEL, components of technical chlordane (TC, CC, transnonachlor (TN)), and metabolite heptachlor exo-epoxide (HEPX). The ΣCHBs (as technical toxaphene) and cisnonachlor (CN) were quantified in 1993, 1994, and 1999 but were below detection in 2007−2008 and not sought in later campaigns. The number of target CUPs increased over time. ENDO-I was the only CUPs measured on BERPAC-1993, and ENDO-II was added on AOS-1994. Chlorothalonil (CHT) and DAC were added on TNW-1999. Between 2007 and 2013, CUPs sought in air and water (A/W) or just air (A) were CPF (A/W), CHT (A/W), DAC (A/W), TFN (A/W), ENDOs and ENDO SUL (A/W), pentachlorothioanisole (PCTA) (A), and pentachloronitrobenzene (PCNB, quintozene) (A). Other compounds were sought but not detected, and the instrumental detection limits (IDLs) for all compounds in air and water are given in Table S2 in the Supporting Information. The concentrations of operationally defined “dissolved” OCPs and CUPs in water and “gaseous” compounds in air from all expeditions are summarized in Tables S4 and S5 in the Supporting Information as mean ± standard deviation (where NDs were replaced by IDLs), and positive and total samples. Pesticides in Arctic and Subarctic Water. Early expeditions traversed the Bering and Chukchi seas (BERPAC-1993) and the central Canada basin to the North Pole (AOS-1994). Later campaigns (TNW-1999, IPY-2007, IPY2008, ArcticNet-2010, ArcticNet-2011, and ArcticNet-2013) sampled the Canadian Archipelago repeatedly, but not all sites were visited each year, nor were all target compounds sought on every expedition. Table S4 in the Supporting Information lists the years when a specific compound was sought. For example, IPY-2007 covered the eastern Archipelago, whereas IPY-2008 focused on the southern Beaufort Sea off Banks Island. HEPX was sought on most Archipelago expeditions but not on TNW-1999. The concentrations of several OCPs in water (CW) have decreased over time and are currently approaching or below the IDLs of 0.1 pg L−1 for chlordane compounds, 0.2 pg L−1 for HEPX and DIEL, and 5 pg L−1 for ΣCHBs, assuming a 100 L sample (Table S2 in the Supporting Information). The mean detectabilities in water over all years were: HEPX, 67%; TC, CC and TN, 74−75%; DIEL, 75%; ΣCHBs, 51%; DAC, 98%; CHT, 78%; CPF, 95%; ENDO-I, 97%; ENDO-II, 76%; ENDO SUL, 68%; and TFN, 60%. the values of the mean CW (pg L−1) ± SD were: TC = 0.68 ± 0.60, CC = 0.82 ± 0.53, TN = 0.53 ± 0.38, HEPX = 12 ± 17, DIEL = 20 ± 20, ENDO-I = 3.1 ± 1.9, ENDO-II 1.4 ± 1.6, ENDO SUL 11 ± 13, ΣCHBs = 53 ± 41, DAC = 19 ± 12, CPF = 13 ± 12, CHT = 244 ± 619, and TFN = 1.9 ± 2.9. In 2011, CHT concentrations varied greatly, and the highest concentrations were associated with samples taken in regions with no ice cover and low salinity (26−30 psu) indicating recent snow and ice C
DOI: 10.1021/acs.est.5b01303 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
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Several CUPs have been reported in arctic and subarctic lakes in Canada at levels above those in ocean water. The CW values for ENDO-I and ENDO SUL ranged from 1 to 45 and from 19 to 43 pg L−1 in 1993−2005.33,41,58 CHT ranged from
