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Atmospheric Exchange of Persistent Chemicals in Bothnian Bay, Northern Baltic Sea

Final Report Summary - BAYEX (Atmospheric Exchange of Persistent Chemicals in Bothnian Bay, Northern Baltic Sea)

Executive summary

Pollution of the Baltic Sea has been extensively investigated for polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polychlorinated biphenyls (PCBs), but there have been fewer measurements of organochlorine pesticides (OCPs). This two-year project was designed to provide the first measurements of OCPs, current-use pesticides (CUPs) and some naturally occurring organobromine compounds in air and water of the northern Baltic Sea (Bothnian Bay and Bothnian Sea, BB-BS) and investigation of the air-water gas exchange process that links them.

Passive air samplers using polyurethane foam discs were deployed at two sites in southern BB and one site in northern BB to integrate air concentrations over three-month periods from July 2011 to August 2012. Pumped high volume (hi-vol) samples were taken with a glass fibre filter - polyurethane foam trap over 3-48 hours at a southern BB site during May-August 2012. Surface water from BB-BS was passed through a glass fibre filter followed by a column of XAD-2 resin. After extraction of the collection media and cleanup, samples were analysed for target compounds by capillary gas chromatography - electron capture negative ion mass spectrometry. Isotope-labelled compounds were added as surrogates to monitor recoveries during these steps. Target compounds were the OCPs hexachlorocyclohexanes, hexachlorobenzene, dieldrin, chlordanes and endosulfans; CUPs chlorpyrifos, dacthal (chlorthal dimethyl), trifluralin and chlorothalonil; and naturally occurring 2,4-dibromoanisole and 2,4,6-tribromoanisole.

All target compounds were found in air and water except trifluralin and chlorothanonil, which not quantifiable due to chromatographic interferences. Levels of OCPs and CUPs chlorpyrifos and dachthal found in this study ranged between those reported in the Arctic Ocean and the North American Great Lakes. Results for air agreed well with measurements at the Environmental Monitoring and Evaluation Program (EMEP) monitoring stations on the west coast of Sweden and arctic Finland.

Gas exchange direction was determined in relation to equilibrium partitioning expressed by the Henry's law constant, and fluxes were estimated using the Whitman two-film model. Most compounds were near air-water equilibrium, with excursions toward net volatilisation or deposition depending on the water temperature and extent of binding to dissolved organic carbon (DOC) in the water column. Consistent net volatilisation was found for bromoanisoles and chlordanes and net deposition for endosulfans. Gas exchange fluxes to BB were compared to 'bulk' deposition loadings to BB and its catchment by precipitation and dry particle deposition, derived from reported a site near southern BB and EMEP stations. Total loadings to BB were about equal to bulk deposition loadings to BB catchment for HCHs and chlordanes, whereas catchment deposition was about four times higher for endosulfans. Results suggest that bulk deposition to the catchment followed by river runoff could be an important pathway of toxic chemicals to BB.

Proportions of isomers and enantiomers were examined for selected compounds as indicators of sources and pathways. The proportion of metabolite endosulfan sulphate to parent endosulfans was much higher in seawater than in air or bulk deposition, suggesting deposition of parent compounds to the catchment followed by oxidative conversion to the sulphate and river runoff into BB. Proportions of chlordane and alpha-hexachlorocyclohexane enantiomers were examined in air samples collected in the Canadian Arctic during 1994-2000. Differences were found in winter-spring vs. summer-fall which suggested seasonal shifts in sources and delivery processes which may be partly under climatic control.

Knowledge gaps and recommendations for future research and monitoring were:
a) Improve spatial and temporal coverage of air, water and bulk deposition measurements,
b) Quantify links between atmospheric deposition to the catchment, delivery of the chemicals to small streams, and subsequent transport to BB by rivers,
c) Quantify hydrophobic compound association with DOC and its impact on gas exchange and runoff from the catchment,
d) Conduct forensic investigations using chemical profiles to elucidate sources, fate pathways and climate change influences,
e) Determine the significance of bromoanisoles to the natural bromine cycle and in pathways that convert precursor bromophenols to higher molecular weight bioaccumulating compounds,
f) Integrate of project findings and subsequent investigations into mass budgets and models of persistent chemicals in BB.

SUMMARY DESCRIPTION OF PROJECT CONTEXT AND OBJECTIVES

Objectives

1. Measure the seasonal trends of target chemicals in the air and water of Bothnian Bay.
2. Determine air-water fugacity gradients and atmospheric fluxes to and from Bothnian Bay.
3. Estimate direct precipitation loadings to the Bay.
4. Employ chemical tracers to follow gas exchange and indicate changes in transport and fate.
5. Recommend a monitoring and research strategy for long-term assessment of loadings to the Bay.

Methods

Field and laboratory measurements consisted of collecting air and surface water samples and analysing them for target chemicals: legacy organochlorine pesticides (OCPs) hexachlorocyclohexanes (alpha- and gamma-HCH), hexachlorobenzene (HCBz), trans-chlordane (TC), cis-chlordane (CC), trans-nonachlor (TN), cis-nonachlor (CN), metabolite heptachlor exo-epoxide (HEPX), dieldrin (DIEL), endosulfan-I (ENDO-I), endosulfan-II (ENDO-II), metabolite endosulfan sulphate (ENDO SUL); current-pesticides (CUPs) chlorpyrifos (CPF), dacthal (DAC, chlorthal dimethyl), trifluralin (TFN) and chlorothalonil (CHT), and two naturally occurring compounds that are metabolites of brominated phenols: 2,4-dibromoanisole (DBA) and 2,4,6-tribromoanisole (TBA).

Passive air samplers using polyurethane foam discs were deployed at two sites in southern BB and one site in northern BB to integrate air concentrations over three-month periods from July 2011 to August 2012. Pumped high volume (hi-vol) samples were taken with a glass fibre filter–polyurethane foam trap over 3-48 hours at a southern BB site during May-August 2012. Surface water from BB-BS was passed through a glass fibre filter followed by a column of XAD-2 resin. Air and water sampling media were extracted with organic solvents and cleaned up on a florisil column. Chemical analysis was carried out by capillary gas chromatography with detection by electron capture negative ion low-resolution mass spectrometry (GC-ECNI-LRMS). Carbon-13 or deuterium-labelled compounds were added as surrogates to monitor recoveries during extraction and cleanup operations.

Results and discussion

These are the first measurements in air and seawater of northern Sweden for many of the target compounds. All target compounds were quantified except TFN and CHT, which could not be determined due to chromatographic interferences. Variations in concentrations, temporally and spatially, were rather small. The overall relative standard deviations (RSDs) were 56 and 52% for water and air, compared to analytical precisions of 29 and 13%. Levels found in this study ranged between those reported in the Arctic Ocean and the North American Great Lakes. Results for air agreed well with measurements at the Environmental Monitoring and Evaluation Program (EMEP) stations at Råö (Sweden west coast) and Pallas (arctic Finland).

Net directions of air-sea exchange were volatilisation of chlordanes and bromoanisoles, deposition of endosulfans and variable deposition or volatilisation of the other compounds. Fluxes (ng/m2*month) and loadings (kg/y) to BB by gas exchange were compared to 'bulk' deposition (precipitation + dry particle deposition) to BB and to its catchment. Loadings to BB by gas deposition (positive), bulk deposition (positive) and gas volatilisation (negative) were 34, 6.2 and -37 kg/y for HCHs; 3.0 0.47 and -6.3 kg/y for chlordane compounds; and 5.2 5.5 and -0.80 kg/y for endosulfans. Total deposition loadings to BB (3.8E10 m2) by gas and bulk processes were about equal to bulk deposition to BB catchment (2.8E10 m2) for HCHs and chlordanes, whereas catchment deposition was about four times higher for endosulfans. Especially strong volatilisation was found for BAs, with estimated release to the atmosphere from BB of 1300 kg/y. The loadings budgets suggest that deposition to the catchment followed by riverine runoff could be a major source of the target compounds to BB. The links between catchment deposition, transfer to streams and riverine discharge to BB emerged as a major knowledge gap in this study.

The present situation of gas exchange loadings was compared to a simple future scenario in which conditions were changed by a 2-3 deg C temperature rise and disappearance of ice cover in BB. Air and water concentrations of the compounds and levels of DOC in the water were assumed to remain the same in the future scenario. Increases of 50-60% in deposition and volatilisation loadings were predicted for most compounds, largely due to loss of ice cover and consequent longer period of open water for gas exchange to occur.

The proportions of compounds within the same chemical class were examined to give insight to transport and fate processes. Among the three endosulfans, ENDO-I was most prevalent in air; ENDO-I, ENDO-II and ENDO SUL were about equal in bulk deposition; and ENDO SUL greatly dominated in seawater. The much higher proportion of ENDO SUL in seawater suggests bulk deposition of all three compounds to the catchment followed by oxidative conversion of the parent ENDOs to ENDO SUL and subsequent riverine transport of ENDO SUL to BB. Ratios of TC/CC and alpha-HCH/gamma-HCH in air varied seasonally in a manner which suggested that volatilization from BB or photochemical degradation (for TC) might be influencing air concentrations.

Recommendations for future research and monitoring

A list of knowledge gaps and recommendations for filling them is presented at the end of this report.

These include:
a) Improve spatial and temporal coverage of air, water and bulk deposition measurements,
b) Quantify links between atmospheric deposition to the catchment, delivery of the chemicals to small streams, and subsequent transport to BB by rivers,
c) Quantify hydrophobic compound association with DOC and its impact on gas exchange and runoff from the catchment,
d) Conduct forensic investigations using chemical profiles to elucidate sources, fate pathways and climate change influences,
e) Determine the significance of bromoanisoles to the natural bromine cycle and in pathways that convert precursor bromophenols to higher molecular weight bioaccumulating compounds such as bromodioxins and methoxylated PBDEs,
f) Integrate project findings and subsequent investigations into mass budgets and models of persistent chemicals in BB.

This should include consideration of food web bioaccumulation and magnification and forecasting of climate-induced changes.

DESCRIPTION OF THE MAIN SCIENCE AND TECHNOLOGY (S&T) RESULTS/FOREGROUNDS

Introduction

The BAYEX project determined current atmospheric loadings of persistent chemicals in Bothnian Bay, the northernmost basin of the Baltic Sea. The study measured loadings to the Bay as governed by seasonally changing concentrations in air and water, temperature, ice cover and primary productivity. Based on results of the study, recommendations are made for continued monitoring, process studies and modelling which lead to prediction and documentation of climate-induced effects on future loadings. The organohalogen compounds in this study have been shown to undergo long-range transport and deposition in the Arctic. Most are legacy organochlorine pesticides (OCPs) and a few are current-use pesticides (CUPs). Two brominated anisoles were included, which are natural products of marine algae and also have anthropogenic origins. A further introduction and rationale for the project can be found in the BAYEX proposal (1).

Materials and methods

Sampling locations

Water samples were collected from shipboard in Bothnian Bay (BB) and Bothnian Sea (BS) during July 2011 and May 2012. Afterwards, sampling was restricted to areas around Holmon (63.78N 20.88E) in southern BB, in July 2012, January 2013 and April 2013. All samples were from the surface (upper 5 m). Those taken in January and April were through holes drilled in the ice.

High volume air samples were collected from shipboard in May 2012 and thereafter from Holmon at Bergudden lighthouse during May-August 2012 and April 2013. Passive air samplers were initially deployed at Holmön (marine) and Svartberget, Krycklan Catchment (inland, 64.23N 19.55 E) in July 2011 and at Haparanda Sandskar (marine, 65.60N 23.90E) in September 2011. Thereafter they were changed every 3-4 months to provide seasonal coverage. Passive samplers were deployed in duplicate, ca. 2 m above ground in clearings surrounded by woodland.

Separately from this project, 'bulk' deposition (precipitation + dry particle) samples were collected in 2009-2010 at Krycklan and Abisko (arctic Sweden, 68.35N 18.83E) and analysed for persistent chemicals by Seth Newton, a M.Sc. student in Environmental Chemistry at Umea University (2,3). Data from that study and from two Environmental Monitoring and Evaluation Programme (EMEP) stations on the west coast of Sweden at Rao (57.39N 11.91E) and in arctic Finland at Pallas (68.16N 24.04E) (4,5) were used to compare bulk deposition to gas exchange loadings.

Collection methods

Water samples were collected with PVC Niskin bottles on a rosette and immediately transferring the water to a stainless steel can (shipboard) or by dipping the can directly (Holmon). Water volumes of 40 L were passed through glass fibre D (2.7 um) followed by glass fibre F (0.7 um) filters and collected into a second stainless steel can. Filtered water was spiked with recovery surrogate compounds, and passed through a column containing 70 mL settled volume of XAD-2 resin at 150 mL/min, using a peristaltic pump. Details of media preparation and sampling are given in (6).

High volume (hi-vol) air sampling was carried out using a Whatman 2000 glass fiber filter followed by a two polyurethane foam (PUF) plugs (polyether type, 7.8 cm diameter x 7.5 cm thick, density 0.021 g/cm3) according to (7). Collection times ranged from 2-72 hours at 0.5 m3/min, resulting in sampled volumes of 55-2200 m3. Flow rate was monitored with an orifice calibrator, traceable to a Sierra mass flowmeter at Environment Canada.

Passive samplers were the Shoeib-Harner type, which uses a PUF disc (polyether type, 14 cm diameter x 1.35 cm thick, density 0.021 g/cm3) as the collection medium, mounted in a stainless steel enclosure which keeps out direct sunlight and precipitation, but allows air circulation (8-10). A sampling rate of 4 m3/day was assumed, based on the mean of 4.5±1.7 m3/day from previous experience (10).

Analytical methods

Air and water sampling media were extracted with hexane and dichloromethane, respectively. Only the gaseous phase (PUF plugs) and dissolved phase (XAD-2 resin) have been analysed, since the main intent of the study was to determine air-water gas exchange. Filters are frozen for future use. Extracts were cleaned on a Florisil column (2) and concentrated in isooctane to 200 uL.

Analysis was carried out by capillary gas chromatography-low resolution mass spectrometry in the electron capture negative ion mode (GC-ECNI-LRMS) using an Agilent GC-Mass Selective Detector operated in the selected ion monitoring mode. The column was HP-5, 30 m x 0.25 mm i.d. 0.25 um film. Samples were quantified vs. three mixtures of standard compounds (AccuStandard or Supelco Corp.) which spanned an order of magnitude in concentrations; C-13 labelled PCB-105 was added as an internal standard for volume correction. Sample quantification procedures followed those in (9,10).

Target compounds were the OCPs insecticides hexachlorocyclohexanes (alpha- and gamma-HCH), hexachlorobenzene (HCBz), trans-chlordane (TC), cis-chlordane (CC), trans-nonachlor (TN), cis-nonachlor (CN), heptachlor exo-epoxide (HEPX), dieldrin (DIEL), endosulfan-I (ENDO-I), endosulfan-II (ENDO-II), endosulfan sulphate (ENDO SUL); CUPs chlorpyrifos (CPF, insecticide), dacthal (DAC, chlorthal dimethyl, herbicide) and trifluralin (TFN, herbicide), chlorothalonil (CHT, fungicide); and two naturally occurring brominated compounds, 2,4-dibromoanisole (DBA) and 2,4,6-tribromoanisole (TBA).

Quality control

Two ions were monitored for target compounds and one for surrogates. Ratios of quantifying/qualifying ions for target compounds were required to be within ±20% of those for standards for a satisfactory analysis.

Results and discussion

Organohalogens in surface water

Most abundant were the bromoanisoles, HCHs and metabolite ENDO SUL at 72-250 pg/L, followed by DIEL and HCBz at 10-14 pg/L. Compounds in the 1-4 pg/L range were TC, CC, TN, ENDO-I, DAC and CPF. ENDO-II and CN were 0.6 and 0.3 pg/L. HEPX was below the LOD of 6 pg/L in nearly all samples and is not listed. TFN and CHT could not be quantified due to interferences, noted as obvious distortion of the chromatographic peaks or failure of quantifying/qualifying ion ratios to meet the ±20% of standard values criterion. Duplicate samples were collected off Holmön in July 2012 and January 2013.

Levels of target compounds in surface water were fairly uniform throughout the BB and BS, with % relative standard deviations (RSD) ranging from 27-109% and an overall %RSD of 56%, which can be compared to the analytical precision (% difference between duplicates) of 29%. Mean concentrations in BS (including Holmon samples) vs. BB were significantly different only for DIEL (p less than 0.05).

BB-BS and the Arctic are similar for dieldrin, endosulfans and HCBz. Chlordane levels in the BB-BS are comparable to those in the Great Lakes and above arctic concentrations. HCH levels in the BB-BS are above those in the North Atlantic and Greenland Sea, and below Great Lakes and Canadian Arctic values.

Bromoanisoles in seawater of the Northern Hemisphere have only been reported previously in the Canadian Arctic, and at lower levels than in the BS-BB. Bromoanisoles and their precursor phenols are formed naturally from reactions between haloperoxidase with humic substances in oceans (16) and found in marine algae (17) and sponges from the Great Barrier Reef (16) and Antarctica (18). They are also formed by biomethylation of bromophenols, which are produced anthropogenically as fumigants, wood preservatives, industrial intermediates, and as byproduct in chlorination of water containing bromide ions (19,20). Bromophenols may be precursors of polybrominated dibenzo-p-dioxins (21-23) and methoxylated polybrominated diphenyl ethers (23), found in Baltic fish, shellfish and algae.

Organohalogens in air

Duplicate samplers were deployed at each location, and the overall absolute difference was 13±14%. The collection of passive samplers should be linear over time to reflect the integrated air concentrations over the deployment period. Although collection of the more volatile species DBA, TBA and HCBz may be linear in the colder seasons, PUF-air equilibrium was probably approached in warmer periods and the overall results for these compounds are not considered quantitative.

Mean differences between compound concentrations at two stations were compared using a paired t-test. Differences were not significant between Holmön and Krycklan for periods 1-3, when data were available for both stations (p greater than 0.05) but were significant (p less than 0.05) between either station and Sandskär for Period 1.

Seasonal trends in air (Objective 1)

Variations in air concentrations over four seasons were derived by combining Holmön and Krycklan passive air sampling data over the periods of deployment. The seasons were: fall-winter (F-W, October 2011-January 2012), winter-spring (W-S, January-May 2012), spring-summer (S-S, May-August 2012) and summer-fall (S-F, July-October 2011). Weaker seasonal changes were seen for gamma-HCH, ENDOs and chlordanes. A slight increase in gamma-HCH was seen in S-S, suggestive of the 'spring peak' noted in earlier studies when lindane was in use (28,29), then concentrations dropped in S-F and F-W. ENDOS showed a peak in S-F. Although the fluctuations in chlordane compounds were not large, they showed strikingly different seasonality. CC and TN were practically invariant throughout the year, whereas TC was about 2 times higher in the colder (W-S and F-W) than in the warmer (S-S and S-F) halves of the year. Cycles of TC/CC ratios with maxima in the cold seasons and minima in the warm seasons occur annually in arctic air (24,25,30). Further discussion is provided in the section on compound proportions.

Gas exchange between air and surface water (Objective 2)

The potential for gas exchange was judged from the fugacities of the compound in water and air (fw, fa, Pa):

fw = CwH (1)

fa = CaRTa (2)

FR = fw/fa = CwH/CaRTa (3)

where Cw and Ca are the dissolved and gaseous concentrations of the compound in water and air (mol/m3), H is the Henry's law constant (H, Pa*m3/mol) at the temperature of the surface water, R = 8.31 Pa*m3/mol*K, and Ta is the air temperature (K) (11,15,31). Fugacity ratios (FR) ‹1, =1 and ›1 indicate net deposition, equilibrium and net volatilisation, respectively.

Since neither water nor hi-vol air concentrations varied markedly over the study, mean concentrations were taken for gas exchange estimates. Henry's law constants and their temperature parameters were the thermodynamically consistent 'final adjusted values' (FAVs) (32-34) where available, or experimental values from other sources (35-37).

It is important to reiterate that gas exchange estimates are based on gaseous species in air and dissolved species in water. During hi-vol air sampling, the gaseous fraction is retained by the PUF trap after passage through a glass fibre filter which captures 99.9% of particles ‹0.3 um. The GF/F filters used for water sampling collect particles › 0.7 um and species that are colloidal or associated with dissolved organic carbon (DOC) are not retained. The dissolved/colloidal compounds that were found on the XAD-2 resin column were speciated by using the partition coefficient between DOC/water: Kdoc = (ng/kg)doc/(ng/L)water. Kdoc was determined for Nordic reference aquatic humic material by Matyas Ripszam, Department of Chemistry, Umeå University. The fraction of 'truly dissolved' compounds was estimated from:

Fdiss = 1/(KdocCdoc + 1) (4)

Propagated uncertainty in FR was estimated from uncertainties in Cw, Ca and H:

(RSD FR)^2 = (RSD Cw)^2 + (RSD Ca)^2 + (RSD H)^2 (5)

The RSD for H was assumed to be 0.20 (15). The resulting RSD for FR was 0.79 or FR = 1.00 ± 0.79 at equilibrium. Numbers of water and air samples were 11-14 and 8-17, respectively. FRs outside the 0.3-1.7 window indicated significant departure from water-air equilibrium at p ‹0.05 and were interpreted as net volatilisation or deposition.

Considering case (A), chlordane compounds and bromoanisoles were volatilising at all temperatures and HCBz, DIEL and alpha-HCH were volatilising at 15 deg C or higher. ENDO-I was depositing at 15 deg C or lower and was barely within the equilibrium window at 20 deg C. Adjusting for binding to DOC in case (B) lowered FRs in general and raised the temperature threshold for transition from deposition to equilibrium or volatilisation in some cases.

Gas exchange fluxes were estimated using the Whitman two-film model, which considers resistances to transfer in the air and water films. The model with fugacity definitions is summarized in the following equations (13,31,38).

Nd = Dawfa (6)

Nv = –Dawfw (7)

Nnet = Nd + Nv (8)

Daw = 86400Kaw/H (9)

1/Kaw = 1/kw + RT/Hka (10)

Nd, Nv and Nnet are deposition (positive), volatilisation (negative) and net fluxes (mol/m2*d), Daw (mol/m2*d*Pa) is the overall mass transfer coefficient and 86400 = s/d. 1/Kaw is the overall resistance to transfer expressed on a water-phase basis, but includes resistances in both the water (1/kw) and air (RT/Hka) films. Mass transfer coefficients for the individual water and air films (kw and ka, m/s) have been determined in field experiments and estimated using several models (31,38-40). Those used in this project were estimated from the models of Mackay and Yeun (38,40).

ka = 1.0E-3 + 4.62E-4*(6.1 + 0.63*U10)^0.5*U10*Sca^-0.67 (11)

kw = 1.0E-6 + 1.44E-2*Ustar^2.2*Scw^-0.5 (12)

Ustar = 1.0E-2*(6.1+0.63*U10)^0.5*U10 (13)

where U10 the wind speed at 10 m height (m/s), Ustar is the friction velocity (m/s), and Scw and Sca are the Schmidt numbers (dimensionless) for compounds in water and air. Scw and Sca for di- to octachlorobiphenyls, and Sca for HCH, are listed in (38), and were used to estimate Scw and Sca for the target compounds in this study by matching to compounds of similar molecular weight. For the compounds considered here at a wind speed of 5 m/s, kw and ka have values of about 5E-6 and 4E-3 m/s, respectively. The water (1/ka) and air (RT/Hka) films offer equal resistances to transfer at H = 3.0 Pa*m3/mol and 293K. Air- or water-film resistances dominate the total resistance at lower and higher values of H, respectively.

Assumptions in these estimates were: constant Cw and Ca, constant wind speed of 5 m/s and Tw = Ta. Temperature variation of Schmidt numbers was not considered. Adjustments were made for binding to DOC in water. Fluxes were also estimated using a different set of models for kw and ka which are based on relationships to U10 and molar volumes or sum of atomic diffusion volumes instead of Schmidt numbers (31). The mean difference in the two sets of flux estimates for chlordanes, endosulfans and alpha-HCH at 20 deg C was 21%.

Although it is generally true that the potential for volatilisation (FR) increases at warmer water temperatures, the effect on flux is not straightforward. Comparing exchanges at 0 deg C vs. 15 deg C, volatilisation fluxes of the low-H compounds increase by factors of 2.0-4.2 but there is no change in the deposition fluxes. The opposite occurs for the high-H compounda HCBz, DBA and TBA, going from 0 deg C and 15 deg C lowers the deposition flux by a factor of 2.4-2.8 but produces little change in the volatilisation flux. The chlordanes exhibit intermediate behaviour. The reason is that temperature also influences Kaw and Daw through the Henry's law constant, as seen from eq. 9-10. This effect, along with variable wind speed, has been recognised in modelling gas exchange in the global oceans (41).

Future trends in gas exchange (Objective 2)

Within this decade, profound changes are forecast for temperature and ice conditions in the Baltic Sea. Surface water temperatures in the BB–BS are predicted to increase by about 1.5-2.5 deg C in winter and 2.5-3.5 deg C in summer (42). Most of the Baltic will become ice-free, except in the furthest north of BB, where a 20-25% reduction in the ice season length is predicted (43). Future trends in air concentrations of the target compounds are difficult to anticipate. HCBz, chlordanes and HCHs in air at arctic monitoring stations have shown downward trends over the last 10-15 years, with times for 50% decrease of 5-26 y (24,25). However, some compounds are 'levelling out' or even increasing since 2000, possibly due to increased mobilisation from secondary sources (24,25,44).

Flux estimates at the present time were made on a monthly basis by assuming constant air and water concentrations, constant DOC and varying water temperatures (January-December = 0,0,0,0,3,8,15,17,13,8,5 deg C). Ice cover was assumed to be complete from January-April, and thus no gas exchange fluxes were calculated for those months. Fluxes for the other eight months were summed were summed to give annual fluxes in ng/m2*y and gas exchange loadings to BB (3.8E10 m2) in kg/y. Other conditions of compound concentrations and DOC were unchanged. Absolute magnitudes of deposition and volatilisation loadings of all compounds increase in the future scenario, by factors of about 50-60%. Similar factors of change are predicted for net loadings, except for DIEL. Deposition and volatilisation loadings were nearly equal for DIEL and there was little change between the present situation and future scenario.

Comparison of gas exchange to bulk deposition loadings (Objective 3)

Precipitation and dry deposition measurements were planned for this study, but were not made. Instead, data sets were obtained from 'bulk' deposition collections of HCHs and chlordanes at Krycklan and Abisko during 2009-2010 (2,3), and at Råö and Pallas in 2005-2006 (4). These compounds and endosulfans were measured at Råö and Pallas in 2011 (5). Geometric mean bulk deposition fluxes (ng/m2*month) for 2009-2011 were multiplied by the areas of BB (3.8E10 m2) or the BB catchment (2.8E11 m2) and 12 months to estimating loadings.

Proportions of compounds as indicators of sources and pathways (Objective 4)

Endosulfans

Proportions of endosulfans differed greatly among air, bulk deposition and seawater. ENDO-I dominated in passive air samples, with ENDO-I/ENDO-II ratios of 50-140, and this ratio ranged from 19-165 in hi-vol air samples. ENDO SUL was seldom detected in passive air samples, but the larger air volumes permitted its determination in the hi-vol measurements, with resulting ENDO-I/ENDO SUL ratios of 12-44. Bulk deposition contained more equal proportions of the three compounds, ratios of the geometric mean concentrations were ENDO-I/ENDO-II = 2.1 ENDO-I/ENDO SUL = 0.94. Ratios of ENDO-I/ENDO-II in seawater ranged from 0.8-16 whereas ENDO SUL was by far the dominant form with ENDO-I/ENDO-SUL = 0.002-0.083. Reasons for these differences may reside partly in the physicochemical properties, ENDO-II and ENDO SUL are more water soluble and have lower vapour pressures and Henry's law constant than ENDO-I (33,47)), and would therefore be expected to be more efficiently scavenged by precipitation scavenging of gases and aerosols. Nonetheless, ENDO SUL is so greatly enriched in seawater that other processes are suggested. Oxidation converts ENDO-I and ENDO-II to ENDO SUL, whereas abiotic hydrolysis favours formation of endosulfan diol and lactone. ENDO SUL is the main persistent terminal residue in soils, sediments and plant surfaces (47). Noting that bulk deposition contributes more sum-ENDO to the BB catchment than to BB itself (see above), it is plausible that oxidation of the parent ENDO compounds takes place in the catchment and rivers then deliver ENDO SUL to BB.

Chlordanes

Technical chlordane is a mixture of about 140 compounds with main components TC, CC, TN and heptachlor. The insecticide was used since the late 1940s in agriculture, home lawns and gardens, and as a termiticide. The major U.S. manufacturer stopped producing chlordane in 1997 and it was one of the original 12 compounds in the Stockholm Convention on POPs. China continued to produce chlordane until 2004.

TC/CC ratios at the passive sampling station show an annual cycle, higher in fall-spring and lower in summer-fall. This is in accord with long-term observations of similar TC/CC cycles at arctic air monitoring stations (including Pallas) (24,25,30). Reasons for this seasonality are not well understood, but the most-quoted hypothesis is that TC is more photolabile and is preferentially depleted in the seasons with more light (24,25,30). An alternate hypothesis is that ratios are driven by seasonal differences in volatilisation rates of the two isomers, which have different temperature dependencies (30). Surprisingly, TC/CC ratios derived from spring-summer hi-vol measurements at Holmön and shipboard are much higher than those from the passive samplers. A possible explanation may be that TC/CC in seawater is also high , and chlordanes were undergoing net volatilisation during this study. If so, it is curious why the TC/CC ratios in hi-vol samples taken at Bergudden light at Holmön should be so different from those at the Holmön passive sampling site only a few hundred meters away. Other processes may be involved, such as revolatilisation of deposited chlordanes from land surfaces on Holmön.

Further insight to air-surface exchange and sources can be obtained by considering the chirality of TC and CC. Each isomer consists of two mirror-image enantiomers, designated (+) and (-) according to the direction of polarised light rotation. The enantiomer ratio (+)/(-) in the technical chlordane product is 1.00 or the enantiomer fraction EF = (+)/[(+) + (-)] = 0.50 (racemic). Enantiomers have the same physicochemical properties, and so their proportion is not altered by simple physical and chemical processes such as volatilisation, deposition, hydrolysis or OH radical reactions. However, enzymes are also chiral molecules and can react preferentially with one enantiomer. Enantioselective degradation of chlordanes is common in agricultural and background soils. A compilation of soil data from around the world shows preferential depletion of (+)TC and (-)CC, resulting in residues with EFs ‹ 0.50 for TC and › 0.50 for CC (48,49). TC and CC tend to be racemic in soils near house foundations with high chlordane levels (50) and indoor air of homes treated for termite control (51).

A task in this project was to examine EFs of chlordanes in a series of archived air sample extracts from the Råö and Pallas stations, supplied by IVL. Although extracts from 2001-2006 have been received, they have not yet been analysed by GC-ECNI-LRMS on chiral-phase columns, nor have samples from BB been analysed by this technique. To replace this missing information, a new set of EF data was obtained by analysing archived extracts of air samples collected during 1994-2000 at the Canadian Arctic station Alert (82.50N 62.33W). Enantioselective analysis by GC-ECNI-LRMS was carried out by Liisa Jantunen, and data were examined by digital filtration analysis (24) by Hayley Hung, both of Environment Canada.

Previous work had shown nonracemic TC (EF ‹ 0.50) in air at Alert, Pallas and Rörvik (57.25N 11.56E close to Råö) during the late 1990s-2001, but racemic TC (EF = 0.50) in 1971 atmospheric deposition samples from Sweden and Iceland (52). EFs of TC in sediments of a Canadian Arctic lake were closer to the racemic value in the 1960s-70s and farther from racemic in the 1990s (52,53). Similar trends have been observed in sediments of U.S. streams and reservoirs (54). The change in enantiomer proportions of TC over time reflects worldwide use of racemic technical chlordane in the 1970s contrasted with declining usage and a greater contribution of nonracemic 'secondary' soil emission sources in recent times. Analysis of the new set of Alert air extracts also showed nonracemic TC during the mid- to late 1990s.

As noted in other studies (24,25,30), TC/CC ratios (or Ftc) were lower in summer-fall and higher in winter-spring. Interestingly, EFs followed the same seasonal cycles with means of winter annual maxima 0.483 ± 0.004 and summer annual minima 0.456 ± 0.007 (49). The EF cycles suggest seasonal differences in chlordane sources; e.g. greater contribution of racemic termiticide emissions from home air ventilation in winter-spring vs. nonracemic soil emissions in summer-fall. These residues, when subjected to preferential photochemical degradation of TC in summer-fall, might produce Ftc profiles which match those of the TC EFs.

HCHs

The ratio alpha-HCH/gamma-HCH indicates transition from use of technical HCH (60-70% alpha-HCH, 10-12% gamma-HCH) to lindane (pure gamma-HCH). Global usage of technical HCH was estimated at 10 Mt between 1948-1997 and emissions peaked in the late 1970s – early 1980s (55). Sharp decreases in emissions occurred after 1983 when China stopped technical HCH usage (55). Between 1970-1996, approximately 382 Kt of technical HCH and 81Kt of lindane were used in Europe; technical HCH dominated until the late 1970s and was overtaken by lindane in later years (56). All HCH isomers were added to the Stockholm Convention in 2009, and today secondary emissions from soil and water are estimated to control declines in the atmosphere (57).

Ratios of alpha-HCH/gamma-HCH averaged 0.85 ± 0.36 in BB-BS water, 2.1 ± 0.9 in passive air samples and 1.3 ± 0.7 in hi-vol air samples. Seasonal variations from the passive network were 0.58 in winter-spring, 1.3 in spring-summer, 3.0 in summer-fall and 2.3 in fall-winter. Volatilisation fluxes from BB during spring-fall averaged -84 and -54 ng/m2*month for alpha-HCH and gamma-HCH. The ratio of these fluxes (1.6) is the predicted alpha-HCH/gamma-HCH ratio in air if sea-to-air exchange alone were the controlling factor.

Enantiomer proportions of chiral alpha-HCH provide further information about exchange processes. The alpha-HCH in the Baltic Sea is depleted in the (+) enantiomer, and volatilisation has been traced by the appearance of nonracemic alpha-HCH in the air boundary layer (58). Transitions in the composition of alpha-HCH take place in the air boundary layer of the Arctic Ocean, from nearly racemic during ice cover to nonracemic and depleted in the (+) enantiomer following the spring-summer ice breakup (13,59).

As for chlordanes, samples from BB and those received from IVL have not yet been analysed for alpha-HCH enantiomers. Instead, EF results have been interpreted from the 1994-2000 Alert air samples. The means of winter maxima and summer minima EFs over the seven years were 0.506 ± 0.003 and 0.498 ± 0.005 significantly different at p less than 0.01 (49). Potential sources in winter-spring are long-range transport of racemic alpha-HCH (EF = 0.5) from technical HCH usage and poorly controlled waste, and secondary emissions from soils where alpha-HCH is preferentially depleted in the (-) enantiomer (EF › 0.5) (48,49). This signal becomes modified in spring-summer, when alpha-HCH depleted in the (+) enantiomer (EF ‹ 0.5) is volatilised from ice-free areas of the Arctic Ocean and advected to Alert. The intensity of the summer cycles seems to be increasing in the later years of the study and may be related to increasing loss of seasonal ice in the Arctic. Increasing air concentrations of alpha-HCH and other persistent organochlorines at Svalbard since 2000 has been correlated to higher surface air temperature and decreased ice cover (44).

Conclusions

-This two-year project has provided the first measurements of OCPs and natural brominated compounds in air and water of the northern Baltic and investigation of the exchange processes that link them. Levels of target compounds found in this study ranged between those reported in the Arctic Ocean and the North American Great Lakes. Results for air agreed well with measurements at the Environmental Monitoring and Evaluation Program (EMEP) stations at Råö (Sweden west coast) and Pallas (arctic Finland).

-Gas exchange fluxes were estimated in both positive (deposition) and negative (volatilisation) directions, and many compounds were close to air-water equilibrium or undergoing net volatilisation. Net deposition was consistently estimated for endosulfan compounds.

- Especially strong volatilisation was found for the naturally occurring BAs, with an estimated net release to the atmosphere of 1300 kg/y from BB. This is only the second investigation of air-sea exchange BAs, the first being in the Canadian Arctic (13). The magnitude of this release, from a relatively small part of the entire Baltic Sea, suggests its importance in the natural bromine cycle and transport of organobromine compounds inland.

- Annual loadings to BB by gas exchange were compared to 'bulk' deposition (precipitation + dry particle deposition) to BB and its catchment. Gas exchange dominated loadings to BB itself for HCHs and chlordane compounds, whereas gas exchange and bulk deposition were comparable for endosulfans. Loadings to the catchment and BB were comparable for HCHs and chlordanes, and four times greater to the catchment for endosulfans.

- The loadings budget suggests that deposition to the catchment followed by riverine discharge could be a major pathway to BB. A simple scenario of increasing temperatures and loss of ice cover predicted a 50-60 increase in deposition and volatilisation loadings to BB, largely due to a longer open-water season.

- The proportions of compounds within the same chemical class, and enantiomers of chiral compounds, were examined to give insight to transport and fate processes. Among the three endosulfans, ENDO-I was most prevalent in air; ENDO-I, ENDO-II and ENDO SUL were about equal in bulk deposition; and ENDO SUL greatly dominated in seawater. The much higher proportion of ENDO SUL in seawater suggests bulk deposition of all three compounds to the catchment followed by oxidative conversion of the parent ENDOs to ENDO SUL and subsequent riverine transport to BB, which lends support to the conclusion from the mass budget. Ratios of TC/CC and alpha-HCH/gamma-HCH in air varied seasonally in a manner which suggested that volatilisation from BB or photochemical degradation (for TC) might be influencing air concentrations.

- Individual enantiomers of TC and alpha-HCH were determined in air samples collected in the Canadian Arctic at Alert between 1994-2000. Regular cycles in the EFs of each compound suggested transport from different source types which vary seasonally in strength. Winter-spring emissions of chlordanes by ventilation of termiticide-homes treated may dominate over more degraded soil sources in winter-spring, and vice-versa in summer-fall. Transport alpha-HCH in winter-spring may come from the (small) ongoing use of technical HCH and from soil emissions in temperate regions, contrasted with summer release of alpha-HCH from unfrozen areas of the Arctic Ocean.

Recommendations for future research and monitoring (Objective 5)

- This project has provided a first view of air and water contamination of BB by toxic chemicals other than PCBs and PCDD/Fs. The one-year study was insufficient to fully evaluate seasonal/spatial trends. It is recommended that further monitoring of air and water be conducted, and the list of compounds be expanded to include more 'new and emerging' chemicals of concern.

- Passive air sampling should be continued to provide integrated coverage. However the present method of PUF collection is not adequate for volatile compounds like HCBz and BAs. Consideration should be given to using alternative sorbents such as XAD-impregnated PUFs (60,61). Passive sampling should be augmented with hi-vol collection, which gives a more accurate measure of air concentrations needed for gas exchange estimated.

• In addition to gas exchange estimates, bulk deposition measurements are critical to constructing loadings budgets for BB and its catchment. The database for these is inadequate at present, and estimates for this project were made from only one site near BB (Krycklan), with supporting data from more distant stations in arctic Finland, Sweden and on the Swedish west coast. It is recommended that bulk deposition collections continue at Krycklan and that consideration be given to establishing another bulk deposition site further to the north and near BB.

- There are presently no air nor bulk deposition collections on the Finland side of BB, and that is viewed as a desireable activity to improve spatial coverage.

- Further investigation of spatial/temporal distribution of contaminants in water is needed, especially near estuaries. Water sampling was a stumbling block in this project. A 40-L sample is adequate for some analytes but marginally low for others. Processing even a 40-L sample on board ship is difficult. Consequently fewer water measurements were made than anticipated. More effort should be put into water sampling and consideration given to alternative ways of preconcentrating analytes from different water volumes. Effects of DOC on collection efficiencies by sorbent resins (e.g. XAD-2) requires attention.

- The links between catchment deposition, transfer to streams and riverine discharge to BB emerged as a major knowledge gap in this study. Further bulk deposition measurements coupled with stream monitoring could provide much-needed information on the proportion of deposition that is transferred out of the catchment and how this varies with physicochemical properties of the different compounds.

- Association of hydrophobic compounds with DOC has a strong effect on water/air partitioning (FR) and consequently on gas exchange loadings. Similarly, binding to DOC may influence the mobilisation of deposited chemicals from the catchment to streams and transport into BB. These processes become all the more central to the loadings question considering that climate change is anticipated to increase DOC discharge into BB. Studies of hydrophobic compound binding by DOC from diverse sources should be continued and expanded, with the goal of unifying the information into a predictive model.

- Forensic investigations using chemical profiles should be expanded to elucidate sources, fate pathways and climate change influences. Including enantioselective analysis in long-running atmospheric and aquatic monitoring programs could reveal large-scale climatic impacts on microbial processing of chiral chemicals in soil and water, as well as continuing primary-secondary source transitions.

- Further investigation of naturally-occurring BAs is warranted to place their emissions in perspective with other natural light organobromine compounds (e.g. bromoform) and heavier bioaccumulating ones (e.g. bromodioxins, methoxylated PBDEs) and precursor bromophenols.

- Information from this project, and from activities recommended above, should be integrated into a comprehensive mass budget and model of transport, loading and cycling of persistent chemicals in BB. This should include consideration of food web bioaccumulation and magnification and forecasting of climate-induced changes.

Acknowledgements

This project could not have been carried out without the support and assistance of many individuals. First, I thank Mats Tysklind, Dept. of Chemistry, Umeå University (UmU), for hosting me during the Incoming International Fellowship (IIF) and providing unending moral and financial support for this research. Passive air samplers were located and set up with help of Olle Nygren (UmU), Hjalmar Laudon, Lena Jonsson and Tomas Holmgren (Swedish University for Agricultural Sciences, SLU) and Staffan Svanberg (Bosmina Co.). Olle also collected hi-vol air samples and water samples at Holmön. Collection of shipboard water samples was done with the help of Kathleen Agosta and several from the Dept. of Ecology and Environmental Geochemistry (EMG, UmU): Agneta Andersson, Owen Rowe, Daniela Figueroa, Joanne Paczkowska, Chatarina Karlsson. Seth Newton (Chemistry, UmU and Dept. of Applied Environmental Sciences, Stockholm University), Karin Wiberg (Dept. of Aquatic Sciences and Assessment, SLU), Eva Brorström-Lundén (IVL) and Katarina Hansson (IVL) shared unpublished bulk deposition data. Matyas Ripszam and Peter Haglund (Chemistry, UmU) shared unpublished KDOC measurements. Thanks also to the Umeå Marine Sciences Centre (UMF) and captain/crew of Kustbevakning for ship support to collect water samples. On the other side of the ocean, thanks to Environment Canada (EC) for granting me a leave of absence to carry out this work and to colleagues at EC who collaborated in this project, especially Liisa Jantunen, Hayley Hung, Tom Harner and Jianmin Ma.

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POTENTIAL IMPACT AND DISSEMINATION ACTIVITIES

Persistent chemicals have been previously investigated in air and deposition in Sweden, but most have been PCDD/Fs and PCBs, and few studies have been in the arctic-subarctic region of the country. BAYEX brings benefits to Sweden and the European community by producing the first loading estimates for the target chemicals for the northern Baltic and complimenting atmospheric measurements at EMEP stations. The project benefits the EU project ARCRISK through comparison of data from our subarctic air and water measurements with those at Svalbard, providing northern Baltic data for use in ARCRISK modelling activities, and interpreting enantiomer measurements in the Canadian Arctic to indicate seasonal transitions in sources and transport processes.

Activities and results of BAYEX will feed into the ongoing Swedish project ECOCHANGE (Ecosystem Dynamics in the Baltic Sea in a Changing Climate Perspective) by providing data for a preliminary assessment of current and projective future loadings of the target compounds to the northern Baltic, and in planning new research directions. For example, the gas exchange fluxes and loadings budgets are supportive of further investigations into the critical roles of DOC in mobilisation of toxic chemicals and in riverine delivery to the Baltic, and the rather large emissions of the naturally occurring bromoanisoles from BB suggests future research in this direction (see Recommendations, above). One goal for the coming 1-2 years will be to contribute to s special issue of the journal Ambio which will focus on ecosystem changes in the Baltic Sea.

dissemination of project results and implications has/will be achieved through publications in primary scientific journals and presentations at professional conferences, workshops and seminars. An interview on BAYEX was done with the Umeå Marine Science Centre on January 11, 2012 as part of ECOCHANGE outreach and another is planned.

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