Polychlorinated biphenyls (PCBs) in air and seawater of the Atlantic Ocean: sources, trends and processes.
ABSTRACT Air and seawater samples were collected on board the RV Polarstern during a cruise from Bremerhaven, Germany to Cape Town, South Africa from October-November 2005. Broad latitudinal trends were observed with the lowest sigma27PCB air concentration (approximately 10 pg m(-3)) in the South Atlantic and the highest (approximately 1000 pg m(-3)) off the west coast of Africa. Sigma(ICES)PCBs ranged from 3.7 to 220 pg m(-3) in air samples and from 0.071 to 1.7 pg L(-1) in the dissolved phase seawater samples. Comparison with other data from cruises in the Atlantic Ocean since 1990 indicate little change in air concentrations over the remote open ocean. The relationship of gas-phase partial pressure with temperature was examined using the Clausius-Clapeyron equation; significant temperature dependencies were found for all PCBs over the South Atlantic, indicative of close air-water coupling. There was no temperature dependence for atmospheric PCBs overthe North Atlantic, where concentrations were controlled by advection of contaminated air masses. Due to large uncertainties in the Henry's Law Constant (HLC), fugacity fractions and air-water exchange fluxes were estimated using different HLCs reported in the literature. These suggest that conditions are close to air-water equilibrium for most of the ocean, but net deposition is dominating over volatilization in parts of the transect. Generally, the tri- and tetrachlorinated homologues dominated the total flux (> 70%). Total PCB fluxes (28, 52, 118, 138, and 153) ranged from -7 to 0.02 ng m(-2) day(-1).
- SourceAvailable from: John H Offenberg[show abstract] [hide abstract]
ABSTRACT: To determine if elevated levels of atmospheric contaminants in urban areas enhance atmospheric deposition to adjacent surface waters, precipitation was sampled at three stations along a transect from Chicago, IL, across southern Lake Michigan. Rainwater was collected during several storms in July 1994 and January 1995 in southern Chicago aboard the R/V Lake Guardian positioned 15 km east of downtown Chicago and at a rural site along the southeastern shore of the lake as part of the study Atmospheric Exchange Over Lakes and Oceans (AEOLOS). Total PCB concentrations in Chicago precipitation ranged from 4.1 ng/L (January 19, 1995) to 189 ng/L (July 21, 1994) and were 2−3 orders of magnitude higher than the measured regional background concentrations. Concentra tions of PCBs in urban precipitation were dominated by particle-bound congeners, implying PCB enrichment in rainwater due to efficient scavenging of highly contaminated particulate matter from the urban atmosphere. PCB levels in precipitation falling over southern Lake Michigan were from two to as much as 400 times greater than the measured regional background concentration, indicating that the “urban plume” of Chicago increases atmospheric deposition of contaminants to Lake Michigan over spatial scales of tens of kilometers. Enriched urban precipitation extending out over Lake Michigan provides 50−400% greater PCB wet deposition loadings than background precipitation.Environmental Science & Technology - ENVIRON SCI TECHNOL. 04/1997; 31(5).
- [show abstract] [hide abstract]
ABSTRACT: Air and precipitation samples were collected along an urban to over-water to rural transect across the northern Chesapeake Bay as a preliminary investigation into the spatial extent of elevated atmospheric concentrations of urban-derived persistent organic pollutants. Air samples were collected daily from June 3–9, 1996, along the transect as part of the Atmospheric Exchange over Lakes and Oceans project. Total (gas + particle bound) atmospheric polycy-clic aromatic hydrocarbon concentrations [∑-PAH] ranged from 0.4 to 114 ng/m, and gas phase polychlorinated bi-phenyl concentrations [∑-PCB] ranged from 0.02 to 3.4 ng/m. Strong concentration gradients were found for both PAHs and PCBs, with the highest concentrations in the city and the lowest at the downwind rural site. Gas and particle bound PAHs varied independently in the city, possibly due to strong but geographically separated emission sources. A precipitation event collected during westerly winds contained fourfold higher ∑-PAH and twelvefold higher ∑-PCB concentrations at the over-water site than at the rural background location, further indicating that the urban plume extends from Baltimore, MD, over the northern Chesapeake Bay over a spatial scale of approximately 30 km.Journal of The Air & Waste Management Association - J AIR WASTE MANAGE ASSOC. 01/1999; 49(8):959-965.
- [show abstract] [hide abstract]
ABSTRACT: Air concentrations of PCBs and PAHs were measured in the urban/industrial complex of Chicago, IL, over southern Lake Michigan, and in a non-urban area as part of the AEOLOS (Atmospheric Exchange Over Lakes and Oceans) Project. Air samples were collected simultaneously in intensive experiments during May and July 1994 and January 1995 in order to determine the influence of contaminated air masses from the Chicago urban/industrial complex on the southern Lake Michigan atmosphere. Gas phase ∑PAH concentrations over the lake 10−20 km offshore ranged from 0.8 to 70 ng/m3 while urban air concentrations were 27−430 ng/m3. Photooxidation of gas phase PAHs during the day resulted in daytime over-lake concentrations that were 75% less than corresponding nighttime concentrations. Gas phase ∑PCB concentrations ranged from 0.14 to 1.1 ng/m3 over the lake and from 0.27 to 14 ng/m3 in the urban area. ∑PCB concentrations varied seasonally as a result of higher volatilization during the summer. The highest concentrations occurred when the air flow was from the urban/industrial area encompassing Evanston, IL, to Gary, IN, toward the lake, and concentrations were near regional background when the wind was from any other direction. The urban air emissions increased the average coastal atmospheric concentrations above the continental background signal by factors of 12 and 4 for ∑PAHs and ∑PCBs, respectively. Because of photooxidation of gas phase PAHs during the day, the average daytime concentration was increased by only a factor of 5 while the average nighttime concentration was increased by a factor of 18.Environmental Science & Technology - ENVIRON SCI TECHNOL. 06/1997; 31(7).
Polychlorinated Biphenyls (PCBs) in
Air and Seawater of the Atlantic
Ocean: Sources, Trends and
R O S A L I N D A G I O I A , *, †L U C A N I Z Z E T T O ,‡
R A I N E R L O H M A N N ,§J O R D I D A C H S ,|
C H R I S T I A N T E M M E ,⊥A N D
K E V I N C . J O N E S†
Centre for Chemicals Management and Department of
Environmental Science, Lancaster Environment Centre,
Lancaster University, Lancaster, LA1 4YQ, U.K., Department
of Chemical and Environmental Science, University of
Insubria, Via Valleggio, 11, Como, Italy, Graduate School of
Oceanography, University of Rhode Island, Narragansett, U.S.,
Department of Environmental Chemistry, IIQAB-CSIC, Jordi
Girona 18-24, Barcelona 08034, Catalunya, Spain, and
Department for Environmental Chemistry, Institute for
Coastal Research, Forschungszentrum Geesthacht GmbH,
GKSS, Max-Planck-Str. 1 D-21052 Geesthacht, Germany
Received June 14, 2007. Revised manuscript received
October 17, 2007. Accepted November 1, 2007.
Air and seawater samples were collected on board the RV
Town, South Africa from October–November 2005. Broad
latitudinal trends were observed with the lowest Σ27PCB air
(∼1000 pg m-3) off the west coast of Africa. ΣICESPCBs
ranged from 3.7 to 220 pg m-3in air samples and from 0.071
with other data from cruises in the Atlantic Ocean since
1990 indicate little change in air concentrations over the remote
open ocean. The relationship of gas-phase partial pressure
with temperature was examined using the Clausius-Clapeyron
equation; significant temperature dependencies were found
coupling. There was no temperature dependence for
were controlled by advection of contaminated air masses.
Due to large uncertainties in the Henry’s Law Constant (HLC),
fugacity fractions and air–water exchange fluxes were
estimated using different HLCs reported in the literature. These
suggest that conditions are close to air–water equilibrium for
most of the ocean, but net deposition is dominating over
volatilization in parts of the transect. Generally, the tri- and
tetrachlorinated homologues dominated the total flux (>70%).
Total PCB fluxes (28, 52, 118, 138, and 153) ranged from -7
to 0.02 ng m-2day–1.
bans on their production came into force. Urban/industrial
delivery of these pollutants to water and terrestrial surfaces.
As a result of their semivolatility and persistence, PCBs have
been found in the Arctic and in other remote areas of
the globe, where they were not used (4–6). Many studies
have shown that PCBs are declining in the atmosphere of
source regions (7–11). However, 30 years after they were
banned, PCBs remain ubiquitous in the environment and
ambient levels in the environment (8, 10, 11).
Deep oceans are believed to be a final sink of these
pool (12, 13). Knowledge of the equilibrium status and/or
net direction of the flux between air and water are essential
been extensively studied previously for PCBs in the Great
Lakes region of North America, Chesapeake Bay, and other
coastal areas of the mid-Atlantic region, and European seas
exchange in understanding the environmental fate of POPs
at local, regional and global scales. Despite the importance
of partitioning between air and water for these pollutants,
oceans such as the Atlantic are reported in the literature.
This may be because of the difficulties in collecting reliable
air and water samples on board ships and the large volumes
of seawater needed to detect POPs.
The present study follows on a previous investigation
conducted in 2001 (17) along a North–south transect in the
Atlantic Ocean, which aimed to only delineate atmospheric
spatial trends for a range of POPs. This paper will present
PCB data in air and seawater collected on the RV Polarstern
in October–November 2005 during transit from Germany to
South Africa. Simultaneous air and water measurements of
PCBs were performed across the same cruise track for the
first time, while adopting measures to check for the occur-
rence of “ship-made” interferences (18, 19). The main aims
if possible, time-trends for atmospheric PCBs over the open
(iii) explore the relationship between gas-phase concentra-
tions and temperature and (iv) discuss their state of equi-
librium between the air and the seawater.
Materials and Methods
on board the RV Polarstern during a cruise from Germany
to South Africa. Air samples were taken on the observation
deck, about 20 m above the sea level. Two high-volume air
samplers placed windward and operating at 0.25–0.27 m3
hours integrated air samples were collected with an average
volume of 150 m3. The 12 h samples collected from the two
high-vols operating in parallel were then bulked in the
Both particulate and gas-phase were captured on a glass
* Corresponding author phone: +441524593974; fax: +441524593985;
‡University of Insubria.
§University of Rhode Island.
|Department of Environmental Chemistry, IIQAB-CSIC.
⊥Forschungszentrum Geesthacht GmbH.
Environ. Sci. Technol. 2008, 42, 1416–1422
14169ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 42, NO. 5, 200810.1021/es071432d CCC: $40.75
2008 American Chemical Society
Published on Web 01/19/2008
relative wind direction was between 0–90° and 270–0° and
from any potential ship contamination. After sampling, the
PUFs and GFFs were transferred into solvent rinsed alumi-
num tins and stored in freezers at -20 °C until analysis.
in and on board of the RV Polarstern, to monitor the
background air concentrations of the ship and to determine
if the ship has the potential to be a source of contamination
for the samples. PCB data resulting from the passive air
samplers and active air sampling on board (in this and
ship for these compounds (19).
Seawater samples were collected from a stainless steel
pipe at 8 m depth, using the ship’s intake system located in
the keel. The average flow rate was ∼1.2 L min-1. A typical
sample volume water was 600–700 L. Both particle and
dissolved seawater phases were collected using a GFF (GFF
52 with 0.7 µm of nominal pore size) and a 95 mL XAD-2
resin column respectively. Only data for the dissolved phase
are reported here because of contamination problems with
particle phase field blanks.
Sample Processing. Air Samples for PCBs Analysis. All
samples were handled and extracted in a dedicated clean
laboratory at Lancaster University, which has filtered,
charcoal-stripped air and positive pressure conditions. PUF
plugs were pre-extracted with dichloromethane (DCM) for
16 h using a Soxhlet apparatus. GFFs were precombusted at
450 °C. Each air sample (gas + particle) was spiked with a
28, 52, 101, 138, 153, 180) and individually extracted in a
concentrated using rota-evaporation and nitrogen-evapora-
tion. A multilayer 20 mm id acid silica column containing a
60), 2 g of basic silica (Merck Silica 60), 1 g of activated silica
(Merck Silica 60), 4 g of acid silica (Merck Silica 60), 1 g
were eluted through gel permeation columns containing 6 g
of Biobeads SX 3 and concentrated to 100 uL. Each sample
30 [13C12] PCB 141 and [13C12] PCB 208 as internal standards.
Seawater Samples. XAD-2 columns were pre-extracted
with acetone, hexane, and DCM and exchanged to pre-
extracted Milli-Ro water and analyzed separately. XAD-2
columns were eluted with 50 mL of methanol and then with
concentrated to ∼500 µL and fractionated in a glass column
(10 mm ID) packed with 3 g of silica activated overnight at
PCBs. Fraction 1 was processed by using the same meth-
odology described for the air samples.
The samples were analyzed by gas-chromatography–
mass-spectrometry (GC-MS) with an EI+ source operating
in selected ion mode (SIM). Details of the instruments,
(20, 21). The following compounds were monitored in air
and seawater samples: tri-PCBs 18, 22, 28, and 31; tetra-
PCBs 44, 49, 52, 53, 70, and 74; penta-PCBs 87, 90/101, 95,
99, 105, 110, 118, and 123; hexa-PCBs 138, 141, 149, 151,
153/132; hepta- PCBs 180, 183, and 187.
Quality Assurance/Quality Control. All analytical proce-
dures were monitored using strict quality assurance and
control measures. Laboratory blanks, travel blanks (PUFs
and GFFs that just traveled) and field blanks constituted 10,
10, and 30%, respectively, of the total number of samples
showing there was no contamination during sample pro-
cessing in the laboratory. Travel blanks and field blanks
showed similar compound concentrations, indicating mini-
mal contamination during storage, sampling and transport.
Samples were blank corrected using the mean of the field
blanks and the method detection limits (MDL) were derived
from the field blanks and quantified as 3 times the stan-
dard deviation of the mean blank concentrations. MDLs
were collected on board the RV Polarstern during transit in
results from the replicates show that the uncertainty on the
air sampling ranges from 10–20%. Breakthrough tests for
air and water sampling were performed. These tests were
done by deploying two GFF filters and two PUFs plugs for
air, and two XAD columns and two GF/Fs one on the top of
the other for water. The breakthrough tests were performed
under different temperature conditions between 20 and 30
°C. Breakthrough tests showed that concentrations on the
back up XAD column and PUFs of the lighter compounds
were around 10–20% of the first column for both cruises
suggesting that breakthrough was not a major concern for
13C12-PCBs as surrogate standards for PCBs and they ranged
from 85–107% for air and dissolved phase samples. Results
cleanup method efficiencies were monitored by spiking
cleaned GFFs and PUFs plugs with validation standards for
PCBs and extracting and analyzing those PUFs and GFFs in
from 90 to 110% for all compounds.
data were from PODAS (Polarstern Data System) on board
the vessel, an online management system that collects
nautical and scientific parameters from a multitude of
measuring devices installed on the vessel. Air and water
temperature, wind speed and wind direction were obtained
from the system every 5 min. NOAA’s HYSPLIT model and
the NCEP/NCAR Global Reanalysis data set were used to
calculate back trajectories (BTs) and atmospheric mixing
height. BTs were traced for 7 days with 1 h steps at 00:00
coordinated universal time (UTC) at 500 m above sea level.
Results and Discussion
Air and Seawater Concentrations: Introductory Remarks.
A total of 42 air samples were collected along the cruise
transect. Supporting Information (SI) Tables 1 and 3 sum-
marize the results for PCB air concentrations. The sum of
the twenty-seven measured PCBs (Σ27PCBs) ranged from 10
to 1000 pg m-3with 35–75% accounted for Cl3Bs and Cl4Bs
in the North Atlantic and 50–85% in the South Atlantic. The
from 3.7 to 220 pg m-3and constituted ∼33% of the Σ27PCBs
detected. Figure 1 shows the spatial distribution of the
ΣICESPCBs along the transect. Highest PCB concentrations
of Africa from 22 °N to 7 °N (40–220 pg m-3, sites 14–21),
whereas the lowest concentrations were measured in the
South Atlantic Ocean. ΣICESPCBs were <10 pg m-3in this
VOL. 42, NO. 5, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 1417
they were not detected in ca. 30% of the samples. Air mass
back trajectories showed that samples collected in the most
and had not been in contact with land for at least 7 days
before reaching the samplers.
Measurements of PCBs in seawater are challenging
because of the low levels and the potential of shipboard and
analytical laboratory contamination. Detecting trace POPs
which introduces a number of practical difficulties. Short-
term changes in the dissolved phase concentrations are
(n ) 15) of seawater samples were obtained. However, they
represent one of the first comprehensive and reliable data
sets of PCB concentrations in Atlantic seawater.
Cl4Bs constituting 50–85% of what could be detected in the
North Atlantic and 67–95% in the South Atlantic. The
ΣICESPCBs ranged from 0.071 to 1.7 pg L-1and contributed
30% to the total Σ27PCBs detected. SI Tables 2 and 3sum-
marize the water concentrations results. Figure 1 shows
the spatial distribution of the ΣICESPCBs during the cruise
transect. The highest PCB concentrations (ΣICESPCBs ) 1.7
pg L-1) were observed at the equator in the upwelling
region, whereas the lowest PCB concentration was mea-
sured in the Southern Ocean where the ΣICESPCB concen-
tration was e0.50 pg L-1. The heavier PCB congeners (90/
101, 138, 153, and 180) were only detected in three out of
nine samples in the South Atlantic Ocean. Congener
profiles for the ICES PCBsin air and water were compared
for the North and the South Atlantic (SI Figure 2). Air and
water show the same congener profile, with PCB 28 and
52 being the most abundant congeners in the North
and South Atlantic.
It can be difficult to reliably compare data obtained by
different research groups at different times; such analysis
should be done cautiously. PCB seawater concentrations in
this study are lower than those measured by Iwata et al. (22)
who reported a PCB concentration of 26 pg L-1in the North
Atlantic and 8.3 pg L-1in the Southern Indian Ocean. The
whereas the South Atlantic concentrations were in good
Elevated Concentrations off the West Coast of Africa
and North America as the most significant source regions of
PCBs (23, 24). Despite this, the highest concentrations
detected on the transect were in samples taken ∼400 km off
the west coast of Africa, between 22–7 °N. High PCB
FIGURE 1. Black arrows represent broad origin of the air masses during the cruise on board the RV Polarstern. The blue arrows
represent cool sea surface currents, while the red arrows represent warm sea surface currents. Number 1–43 are the site locations.
Black bars indicate concentrations of ΣICES PCBs in air along the cruise (n ) 43). Note: the bars centre on the average sample
location. Key: largest bar ) 220 pg m-3(site 18); smallest bar ) 3.7 pg m-3(site 43). B) Detailed figure of the West African coast,
showing the PCB congener profiles for the high samples and 72 h back trajectories for each sample.
1418 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 42, NO. 5, 2008
trade wind region, where Jaward et al. (17) measured a
maximum of 120 pg m-3ΣICESPCBs around 5 °N, as in this
study. Relatively high values (up to 90 pg ΣICESPCBs m-3)
were also observed in this region (5–8 °N) by Schreitmuller
et al. (25) during a RV Polarstern cruise in 1990 and 1991.
Given these high concentrations, it is appropriate to discuss
the potential sources of these elevated levels and factors
Factors Potentially Affecting the Levels off West Africa.
Introductory Remarks. UNEP has recently compiled infor-
the lack of information for Africa (26). Limited information
for Ghana and the north or northeast African continent
indicated much lower concentrations than measured here,
off the west African coast (27, 28).
by large quantities of Saharan dust and biomass burning
the ITCZ air masses came partly from Africa (16–19), and
the West Sahara and Mauritania. A simple calculation can
be carried out to estimate the required source strength, if a
source(s) were located on the western African land mass, by
assuming: the ship was ∼400 km from the coast when
receiving the high levels, giving a travel time in the range of
to 3 × 10-2kg hr-1. This is comparable to the estimated
strength which would be regionally important. Given the
high levels found in this region previously, there are
apparently an ongoing source(s), which may be associated
on the transect.
parts of the world, which have not been properly stored or
disposed of (26). Any equipment currently in use in west
Africa is likely to be old and may have become damaged/
leaky. Elevated temperatures in Africa would presumably
has now been targeted through the International POPs
Elimination Program (IPEP) (29).
Biomass burning is widespread, especially in the tropics
such as west-central Africa (30). SI Figure 4 shows monthly
fire hotspots in Africa for October and November 2005,
the map that during November 2005 (when these high
samples were observed) the number of fires increased. Fires
serve to clear land for shifting cultivation, to convert forests
to agricultural and pastoral lands, and to remove dry
vegetation, to promote agricultural productivity and the
growth of higher yield grasses. Trace gases and aerosol
climate (30). Eckhardt et al. (31) recorded high PCB con-
in North America in summer 2004 and when agricultural
waste burned in Russia in spring 2006. They hypothesized
that biomass burning can cause high volatilization of
previously deposited PCBs from soil. This region of central
and western Africa is particularly prone to fires and this
possible source should be considered in future studies.
Maritime Sources: Shipping. An additional explanation
for these high PCB levels may be the ship traffic along the
west coast of the African continents, which appears to be
dominated by the oil industry. This and the use of old ships
for maritime traffic might have contributed to these high
Possible Environmental Factors. The Sahara is the major
source on Earth of mineral dust (60–200 × 106tonnes per
areas, and can thus reach high altitudes; from there it can
be transported worldwide by winds, covering distances of
thousands of kilometers. It has been shown that wind
abrasion of wax particles from leaf surfaces over the central
and eastern Africa, enhanced by a “sandblasting effect”, is
most probably the dominant process of terrigenous lipid
contribution to aerosols (32). It is possible that PCBs
accumulated in vegetation can adsorb to aerosol with the
same mechanism and be transported over great distances.
Further research and additional measurements on the
Data Sets for the Atlantic. PCBs air concentrations have
TABLE 1. Mean (±Std Dev) Atmospheric Concentrations (pg m-3) of PCBs in the North and South Atlantic Ocean As
Reported by Different Authors in Different Studies
et al.1990 (25)
Jaward et al.
5.7 ( 3
22 ( 12
15 ( 7
2.2 ( 1
4 ( 2.4
3.4 ( 1.7
0.7 ( 0.5
53 ( 24
12 ( 10
6 ( 5
1.4 ( 4
1.5 ( 1.5
2.9 ( 2.3
6.1 ( 5
1.2 ( 0.87
31 ( 28
21 ( 3.8
8.2 ( 1.8
10 ( 15
4 ( 0.39
7.5 ( 7.9
13 ( 3
22 ( 3
87 ( 34
14 ( 8
11 ( 15
13 ( 15
2.5 ( 2.3
6.5 ( 6.9
5.2 ( 6
1.5 ( 1.7
53 ( 55
3.5 ( 2
14 ( 12
13 ( 10
2.4 ( 2.8
6 ( 7
5 ( 6
1.35 ( 1.9
44 ( 33
6.9 ( 5
6 ( 5
3 ( 1.9
0.77 ( 0.44
1.4 ( 1.1
4 ( 3.2
0.70 ( 0.40
22 ( 17
3 ( 2
1.9 ( 0.9
1.0 ( 0.7
0.4 ( 0.1
0.5 ( 0.4
0.4 ( 0.3
0.2 ( 0.3
7 ( 4.4
6 ( 5.9
2.6 ( 2.5
2.8 ( 1.4
0.36 ( 0.39
1.7 ( 1.5
1.6 ( 1.6
0.61 ( 0.27
16 ( 14
VOL. 42, NO. 5, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY 9 1419
since 1990. Thus, a comparison of these studies may give
insights into changing levels and distributions of PCBs over
the Atlantic Ocean. This must be done cautiously, because
they only reflect limited seasons (spring/summer in the
southern hemisphere and autumn/winter in the northern
earlier (i.e., different ships, different methods and different
Table 1 presents PCBs data for four different cruises.
Measurements by Schreitmuller et al. (25) and Durham et al.
of this study is in good agreement with those measured by
Schreitmuller et al. (25), Durham et al. (33) and Jaward et al.
(17) in the North and South Atlantic. The ΣICESPCBs measured
by Schreitmuller et al. (25) in the South Atlantic are 2 times
higher than those measured in this study, but this may be due
took the ship close to Brazil. Land-based measurements in
2002–2003 at Saint Helena (16S, 5.45W) in the South Atlantic
gave ΣICES PCBs concentrations in the same range of those
measured on the ship in the South Atlantic (typically 2–10 pg
m-3, Lancaster group, unpublished data). In summary, these
data sets appear to have similar concentrations over the 15
contrast, several studies have shown that PCBs are declining
in the atmosphere of Europe, North America and the Arctic,
a factor of 8–10, presumably sufficiently different to be
detectable. The lack of a measured difference perhaps implies
that air concentrations in these remote oceanic environments
at the land-based locations close to sources. Interestingly,
Panshin and Hites (34) compared PCB in oceanic air over
Bermuda in 1992/1993 with those in the 1970s at the same
et al. (7) also concluded that the atmospheric concentrations
remained unchanged over a period of 6 years. Axelman et al.
(35) argued that these observations indicated PCBs may be
removed slowly from the environment, when viewed from a
the remote areas of the earth rather than being permanently
removed from global cycling. This implies that source-remote
uniformly distributed (35).
Dependence of Gas-Phase PCBs on Temperature. The
Clausius-Clapeyron equation was used to describe the
relationship between the ambient temperature and the gas-
phase partial pressure of PCBs. Details of the equation are
given in the Supporting Information. Figure 2 shows an
interesting and important contrast between the northern
and the southern hemispheres. Gas-phase PCB concentra-
tions in the South Atlantic displayed stronger temperature
dependencies than those in the North Atlantic. PCBs in the
North Atlantic displayed no significant correlation between
regions (e.g., as discussed above for those samples close to
Africa), whereas PCB levels in the South Atlantic are driven
by temperature changes via air–water exchange with the
controlled by revolatilization from surfaces, while a flatter
concentration levels (36, 37).
Air-seawater Equilibrium of Selected PCB Congeners.
For PCBs, air–water exchange between the atmosphere and
surface waters is a dominant transport process, influencing
and regional atmosphere (13). Because of the lack of
to the development of models combining sea surface
measurements of concentrations with parametrizations for
the gas exchange rate (38–40). There are large uncertainties
in making such estimations (41–43) because of large un-
cal properties of the compounds such as the Henry’s Law
constant (HLC). The fugacity in the water was therefore
estimated by using values from different sources, namely Li
et al. (41), Bamford et al. (42), and ten Hulscher (43).
Fugacity Ratios. Fugacity ratios were used to assess the
equilibrium status of PCBs between the air and the water
are given in the Supporting Information. The fugacity
quotients are plotted in SI Figure 5. A positive fugacity
quotient indicates a net downward flux (deposition, fAIR>
fW), whereas a net upward flux (volatilization, fW > fAIR) is
indicated by a negative quotient. An estimate of the errors
analytical error of air and water (perhaps ( 10%) and the
(i.e., a propagated error in FFwis of ca. 40% is shown on SI
Calculations suggested air–water equilibrium conditions
dominate at most of the sites in South Atlantic, whereas net
deposition dominates in the North (off the west coast of
Africa and Europe), using the three different HLC values.
However, if the Bamford et al. (42) HLC values are used, a
decrease in the fugacity ratios by a factor of 2 is observed.
This is more enhanced for the heavier PCBs which are
Air–Water Exchange Fluxes. Gas exchange rates were
calculated using a modified version of the Withman two-
film resistance model as described elsewhere (13). The
in the Supporting Information. The net flux was calculated
FIGURE 2. lnP versus 1/T plot for selected PCB congeners in
the north and south hemisphere.
1420 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 42, NO. 5, 2008
for each location where simultaneous measurements of air
and seawater were performed. The mass transfer coefficient
(vaw) was calculated for every 5 min wind speed during
calculation of the flux.
The absorptive fluxes were typically more than 90% of
is dominating. Generally, the tri and tetrachlorinated ho-
mologues dominated the flux profiles, accounting for more
than 70% of the total flux. Σ5PCB flux (28, 52, 118, 138, and
153) ranged from -7 to 0.02 ng m-2day-1by using Li et al.
(41) HLC values, from -6 to 0.7 ng m-2day-1by using HLC
values from Bamford et al. (42) and from -6.6 to 0.6 ng m-2
day-1by using the ten Hulscher et al. (43) values. There are
flux of ca. -60 ng m-2day–1in the North Atlantic and ca.
-20 ng m-2day–1in the Southern Indian Ocean, 2–3 times
higher than those of this study.
We thank the crew on the RV Polarstern as well as the
scientists for their excellent support and cooperation. We
their assistance during sampling on the ship and Dr Soenke
Lakaschus for support and helpful discussions. We thank
Dr. Gareth O. Thomas and Dr. Robert G. M. Lee for their
work. We gratefully acknowledge financial support from the
Department of the Environment, Food and Rural Affairs
(DEFRA) on POPs at Lancaster University.
Supporting Information Available
This material is available free of charge via the Internet at
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