Spatial and Seasonal Variations of
Hexachlorocyclohexanes (HCHs) and
Hexachlorobenzene (HCB) in the
Y U S H A N S U , *, †H A Y L E Y H U N G ,†
P I E R R E T T E B L A N C H A R D ,†
G R E G O R Y W . P A T T O N ,‡
R O L A N D K A L L E N B O R N ,§
A L E X E I K O N O P L E V ,|P H I L F E L L I N ,⊥
H E N R I K L I ,⊥C H A R L E S G E E N ,⊥
G A R Y S T E R N ,#B R U N O R O S E N B E R G ,#A N D
L E O N A R D A . B A R R I E@
Science and Technology Branch, Environment Canada,
4905 Dufferin Street, Toronto, Ontario M3H 5T4, Canada,
Battelle-Pacific Northwest Division, Richland, Washington
99352, Norwegian Institute for Air Research (NILU), P.O. Box
100, NO-2027, Kjeller, Norway, Center for Environmental
Chemistry SPA “Typhoon”, 82 Lenin Avenue, Obninsk, 249038,
Russia, AirZone One, Inc., 222 Matheson Boulevard E.,
Mississauga, Ontario L4Z 1X1, Canada, Freshwater Institute,
Department of Fisheries and Oceans, 501 University Crescent,
Winnipeg, MB R3T 2N6, Canada, and Atmospheric Research
and Environment Programme, World Meteorological
Organization, 7 bis, Avenue de la Paix,
BP2300, CH-1211 Geneva 2, Switzerland
Weekly high-volume air samples were collected between
2000 and 2003 at six Arctic sites, i.e., Alert, Kinngait,
and Little Fox Lake (LFL) in Canada, Point Barrow in
Alaska, Valkarkai in Russia, and Zeppelin in Norway.
Hexachlorocyclohexanes (HCHs) and hexachlorobenzene
(HCB) were quantified in all samples. Comparison showed
that R-HCH and HCB were homogeneously distributed in
the circumpolar atmosphere and uniform throughout
the seasons. However, significantly higher atmospheric
dependence of R-HCH and γ-HCH were found at LFL in
Yukon (YK), which is unique among the sites by virtue of its
high altitude and low latitude, resulting in higher
precipitation rates and summer temperatures. Strong
temperature dependence of R- and γ-HCH at this location
suggests that secondary emissions, i.e., re-evaporation
from surfaces, were more important at this site than others.
It is hypothesized that a higher precipitation rate at LFL
facilitated the transfer of R-HCH from the atmosphere to
On the other hand, higher temperature at LFL enhanced re-
evaporation to the atmosphere after the global ban of
technical HCH. In contrast to R-HCH and HCB, larger
spatial and seasonal differences were seen for γ-HCH
(a currently used pesticide), which likely reflect the
influence of different primary contaminant sources on
different Arctic locations. Fugacity ratios suggest a net
deposition potential of HCB from air to seawater, whereas
seawater/air exchange direction of R-HCH varies in the
Hexachlorocyclohexanes (HCHs) were applied globally as
technical HCH (major R-, ?-, and γ-isomer) and lindane
(purified γ-isomer) (1, 2). Technical HCH was banned from
use in North America in the 1970s, but it was used in China
until the 1980s and in India and the former Soviet Union
prairie region up to 2002 (3). Air concentrations of R-HCH
in the Arctic adjusted to changing global emissions quickly
of R-HCH between seawater and air reversed in the Arctic
from net deposition in the 1980s to net volatilization in the
1990s (5, 6). Modeling study further suggests that about half
of the global R-HCH inventory was in the Arctic oceans (7).
Hexachlorobenzene (HCB) was used for industrial and
agricultural purposes historically, and its production and
emissions peaked in the late 1970s and early 1980s. Current
HCB is from both secondary emissions (e.g., re-emission
from soils and sediments) and primary emissions (e.g.,
byproducts of chlorinated chemicals and incomplete com-
bustion processes) (8). Air concentrations of HCB showed
Compared to other organic contaminants, long-range
(11), and they dispersed faster globally (8). Improved
understanding of legacy R-HCH and HCB may facilitate
prediction of environmental pathways and fate of other
organic contaminants in the Arctic. In this study, a unique
large set of HCH and HCB measurements in Arctic air was
Barrow and Zeppelin (12-14). The overlapped sampling
periods at the six sites in 2000-2003 allow the comparison
Arctic atmosphere. These six sites cover a large area of the
Arctic and data comparison could provide insight into
potential contaminant sources (e.g., LRT or local secondary
emissions) and environmental behavior in the entire cir-
cumpolar atmosphere. Air measurements conducted in this
study, together with observations in seawater, may further
shed light on seawater/air exchange potentials.
Materials and Methods
Field Sampling. Samples were collected in the Canadian
(i.e., Little Fox Lake [LFL] and Kinngait [KNG]), American
(i.e., Point Barrow [PTB]), and Russian (i.e., Valkarkai [VKK])
Arctic between 2000 and 2003. During this period of time,
long-term air monitoring programs were also in operation
two sites were included to expand spatial coverage in this
study. The site map is shown in Figure 1. Detailed site
information and sampling periods can be found in Table S1
* Correspondingauthorphone: (416)739-4833;fax: (416)739-4281;
‡Battelle-Pacific Northwest Division.
§Norwegian Institute for Air Research (NILU).
|Center for Environmental Chemistry SPA “Typhoon”.
⊥AirZone One, Inc.
@World Meteorological Organization.
Environ. Sci. Technol. 2006, 40, 6601-6607
10.1021/es061065q CCC: $33.50
Published on Web 09/26/2006
2006 American Chemical SocietyVOL. 40, NO. 21, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY96601
of the Supporting Information. LFL is quite unique among
the six sites: (i) higher altitudeshigher precipitation rates;
(ii) lower latitudeshigher temperatures; (iii) the only inland
sitesstronger diurnal temperature variations.
over 7 days at all sites, except for ZPN, where a 48-hr sample
was collected weekly (∼1000 m3). Each sample set was
foam (PUF) plugs. Samples were prepared and extracted by
AirZone One for ALT, KNG, LFL, and PTB, whereas VKK
samples were extracted by Typhoon Laboratory in Russia.
Canada. Sampling and analytical methods can be found
elsewhere (12, 15). The samples at ZPN were collected,
extracted, and analyzed by the Norwegian Institute for Air
Quality Assurance/Quality Control (QA/QC). Strict QA/
QC procedures were followed as published previously (12,
15, 16). GFF and PUF blanks were taken once every four
weeks at all sites. Mean blank (B) and standard deviation
(SD) were calculated for PUF (i.e., BPUFand SDPUF) and GFF
(i.e., BGFFand SDGFF) individually at each site over the entire
as the mean B plus 3SD. Since total air concentration (i.e.,
AC composite) was composed of one GFF and two PUFs,
MDL of AC was calculated from BGFF, BPUF, SDGFF, and SDPUF
Mean blanks (BACor BGFF+ 2BPUF) and derived MDLs of
AC samples (MDLAC) are summarized in Table S2 of the
Supporting Information. Compounds below instrument
detection limits (IDLs) were substituted with2/3IDLs. Data
in Excel format upon request. Total sample number (n) and
in Table S2.
Results and Discussion
for individual HCHs and HCB in the current data analysis,
(<5%) of the total concentrations of HCHs and HCB in the
Arctic, e.g., at Alert (17).
Spatial and Seasonal Variations of Air Measurements.
To illustrate differences in seasonality of HCH and HCB air
concentrations, monthly averages were calculated by aver-
from the same year at each site. The monthly average
concentrations were further normalized by the total yearly
concentrations (i.e., sum of 12 monthly concentrations) to
enhance the seasonal profiles. Spatial variations were il-
lustrated by comparing overall and monthly mean concen-
trations of all HCHs and HCB at the six sites, whereas
among these sites. Note that sampling at VKK only occurred
during the warm period of July to September; therefore,
seasonal variability analysis does not include this site.
R-HCH. Monthly concentrations of R-HCH are shown in
Figure S1A for the six sites. Box-and-whisker plots in Figure
2A summarize all R-HCH air measurements at the six sites.
Figure 2A indicates that mean or median air concentrations
(i.e., ALT, KNG, PTB, and ZPN) (Table S3). Slightly higher
due to summer sampling only (i.e., July-September), since
summertime peaks were seen at the other stations as well
(Figures S1A and 2B). However, a Student’s t-test shows
significantly higher air concentrations of R-HCH measured
at LFL compared to the other four sites (p < 0.0001). To
illustrate seasonal variations, monthly concentrations were
was found at the low Arctic site of LFL. The monthly
normalized concentrations varied less than a factor of 3 and
i.e., higher concentrations in late summer and lower con-
centrations in winter. Relatively uniform distribution of
R-HCH with less seasonal variation in the high Arctic
HCH was phased out worldwide, which is also supported by
the nearly normal distribution of R-HCH air concentration
mean of R-HCH among the four high Arctic site was 23 ( 10
pg‚m-3(n ) 387). In other studies, air concentrations of
in July 2000 in the Atlantic Ocean between 75° N and 80° N
Using the Clausius-Clapeyron equation, the relative
can be assessed at a given sampling site (15, 20-22).
(P, Pa) against reciprocal temperature (T, K) for R-HCH are
summarized in Table S4 for all five sites except VKK, where
only five samples were taken. All regressions of R-HCH were
found statistically significant at a 95% confidence level (i.e.,
p < 0.05, Table S4). A higher correlation coefficient R2(0.50)
and steeper slope m (-2200 ( 430) were found at LFL
compared to the other four high Arctic sites. This suggests
that 50% of the variation in atmospheric R-HCH concentra-
tions can be explained by seasonal temperature changes.
secondary emissions of R-HCH from surrounding surfaces.
LFL is very close to Tagish (∼160 km southeast of LFL) of
Yukon (YK) where HiVol air sampling took place between
1992 and 1995 (15, 22). The slope m of R-HCH from this
study was comparable to that found at Tagish previously
(mTagish, R-HCH) -2395 ( 525) (15), although air concentra-
tions reduced approximately by a factor of 1.5, suggesting
that secondary emissions of R-HCH remained important in
FIGURE 1. Sampling site map.
MDLAC) (BGFF+ 2BPUF) + (SDGFF
66029ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 40, NO. 21, 2006
in the Arctic (1, 4). Since no concurrent soil measurements
from soils cannot be evaluated directly. However, water/air
exchange potential will be discussed later.
γ-HCH. Monthly average air concentrations of γ-HCH
are shown in Figure S1B. Larger spatial and seasonal
variations were observed for γ-HCH compared to R-HCH
(Figure S1A). Figure 2D lists all measurements of γ-HCH at
the six sites. Relative to R-HCH, differences between mean
and median values appeared greater for γ-HCH at each site
(Table S3), indicating that its air concentrations were not
normally distributed (see below). Mean concentration of
γ-HCH ranged from 2.7 pg‚m-3at PTB to 7.4 pg‚m-3at VKK.
The large variability in γ-HCH air concentrations was not
surprising since lindane was still registered for use between
2000 and 2003 in some countries (2, 3, 23). Seasonal profiles
were similar at the four sites in the high Arctic, showing
bimodal seasonal behavior (Figure 2E). This was previously
reported for both legacy and current-use pesticides at ALT
and has been termed “Spring Maximum Event” (13). One
were caused by application during the springtime followed
by tilling of soils in the fall. However, the red line in Figure
2E indicates different seasonality of γ-HCH at LFL.
and steeper slope m (-2900 ( 530) were found for γ-HCH
at LFL than the other sites. Steeper slope m indicates
secondary emissions of γ-HCH were more important at LFL
than the other Arctic sites. The slope m for γ-HCH was also
similar to what was observed at Tagish in the 1990s (mTagish,
γ-HCH ) -2700 ( 425) (15), suggesting the importance of
secondary sources in YK region. At LFL, temperatures were
above 0 °C between May and September and peaked in July
(14 °C, Figure S2A). However, elevated concentrations of
γ-HCH were found in spring and July-October (Figure 2E),
a 1-month lag compared to the air temperature profile. The
higher concentrations of γ-HCH during the summer were
consistent with temperature-driven secondary emissions at
LFL. Slightly higher concentrations of γ-HCH during the
of soils, respectively, and its consequent LRT to this site,
which was also observed at the other locations (Figure 2E).
FIGURE 2. Box-and-whisker plots for r-HCH (A), γ-HCH (D), r-/γ-HCH ratio (G), and ?-HCH (I); normalized monthly concentrations (i.e.,
of r-HCH (C, n ) 387) and natural log concentrations of γ-HCH (F, n ) 386) in circumpolar air (i.e., ALT, KNG, PTB, and ZPN). In the
box-and-whisker plots, the center box is bounded by the 25th and 75th percentiles, and whiskers indicate the 10th and 90th percentiles.
Dots are outliers of the 10th and 90th percentiles. The black and red horizontal lines represent the median and arithmetical mean,
VOL. 40, NO. 21, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY96603
of γ-HCH concentrations among the four high Arctic sites.
Unlike R-HCH, γ-HCH is not normally distributed. Instead,
a log-normal distribution describes the data better. This
reflects seasonal and spatial variations of γ-HCH in global
R-/γ-HCH. The ratio of R-/γ-HCH in air is used to follow
emission sources and transport of technical HCH versus
lindane (24). Ratios of R-/γ-HCH were calculated for every
sample at all sites and summarized in Figure 2G. The blue
mixture (i.e., 4-7) (5, 25). The mean ratios at KNG and PTB
were close to the value of the technical mixture, indicating
that HCHs were mostly affected by technical HCH at these
sites. On the other hand, lower mean ratios of R-/γ-HCH at
ALT and ZPN suggested mixed influence of technical HCH
and lindane usage. Higher ratios were observed at LFL and
R-HCH in the atmosphere (26). Furthermore, γ-HCH has a
lower Henry’s Law Constant (H) than R-HCH. Thus γ-HCH
preferentially partitions into seawater (27) and is more
lead to a lower residence time of γ-HCH in the atmosphere
compared to that of R-HCH. Emitted technical HCH in mid-
latitude source regions undergoes fractionation as it is
transported globally and ultimately to the Arctic (29, 30).
This may lead to high R-/γ-HCH ratios at LFL and VKK. The
sites, except for LFL (Figure 2H). The R-/γ-HCH ratio was
slightly enhanced during summer with a small decline in
spring and fall, resulting from weak seasonality of R-HCH
and elevated concentrations of γ-HCH in spring and fall
(Figure 2B and 2E). The different seasonal profile of R-/γ-
HCH at LFL is mainly because of higher concentrations of
γ-HCH observed during the fall.
?-HCH. In addition to R- and γ-HCH, measurements of
and toxic (25). Concentrations of ?-HCH were low in Arctic
air (17), and below MDL for greater than half the samples at
ALT, KNG, and LFL (Table S2). However, ?-HCH was above
MDL in 36 of 38 samples at PTB, and 3 of 5 samples at VKK.
and median concentrations of ?-HCH were found at PTB
and VKK. At 0 °C, the water solubility of ?-HCH is 6.2 and
11 times higher than R- and γ-HCH, and H of ?-HCH is 30
Oceanic flow through the Bering Strait is an important
environment (33). Both PTB and VKK are geographically
closer to the Bering Strait than the other sites (Figure 1),
where elevated seawater concentrations of ?-HCH were
observed (33). The high air concentrations suggest that
outgassing of ?-HCH from seawater was likely an important
source at PTB and VKK, as discussed later.
HCB. To avoid bias as a result of breakthrough, data
ambient temperature was below -5 °C (see Supporting
Information). This includes measurements in November-
March at LFL and in November-May at the other 4 sites
Monthly concentrations of HCB are shown in Figure 3A
for November-March at LFL and November-May at the
other four sites. Error bars here represent variations of HCB
among different sampling events in a month. Monthly
variations of HCB were less than a factor of 2 during the
selected periods at all sites, although temperature varied up
to 20 °C (Figure S2A), suggesting that variations of ambient
temperature did not greatly affect HCB concentrations in
the Arctic air. Differences of monthly average HCB concen-
trations were not large from site to site except LFL (Figure
3A). Individual site measurements are summarized in the
box-and-whisker plots of Figure 3B. Comparable mean and
median concentrations of HCB were observed at ALT, KNG,
PTB, and ZPN (Table S4). Relatively uniform distribution of
HCB concentration in the circumpolar air is supported by
LFL or VKK), as indicated by a red line in Figure 3C. The
homogeneity of HCB in the circumpolar air could be the
result of fairly slow removal processes (e.g., degradations
and dry/wet depositions) from the atmosphere and less
influence of primary emissions on the atmosphere (8, 10).
Mean concentration at these four high Arctic sites was 56 (
23 pg‚m-3(n ) 241) between November and May in 2000-
of 2002 at Cheeka Peak Observatory, Washington State (35-
57 pg‚m-3) (34). Comparable concentrations of HCB were
previously also reported in the northern hemisphere (55
Although HCB was homogeneous during the winter
months at the high Arctic sites, significantly higher concen-
trations of HCB (88 ( 14 pg‚m-3, n ) 11, p < 0.0001) were
found at LFL between November and March, which were
n ) 5) although breakthrough of HCB likely occurred at this
Effects of Emissions and Environmental Properties on
R- and γ-HCH Air Concentrations at Different Sites. Data
comparison shows that R- and γ-HCH behaved differently
at different Arctic sites. Since all sampling sites were located
in the remote Arctic far away from emission sources, HCHs
observed in Arctic air are likely the result of LRT. Global
usage of technical HCH peaked in the 1970s and declined in
the 1980s and 1990s (1); therefore, primary sources of
FIGURE 3. Monthly average air concentrations of HCB between November and May at five Arctic sites (A); box-and-whisker plots of HCB
concentrations (B); histogram of HCB concentration (n ) 241) among the four high Arctic sites (C), i.e., ALT, KNT, PTB, and ZPN (red line
represents normal distribution).
66049ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 40, NO. 21, 2006
used, these compounds could be transported via LRT and
deposited in the Arctic surfaces. Technical HCH was used
approximately 74% (6214 kt out of 8363 kt) of total technical
transport signals for some organic contaminants were
identified previously (22, 34, 35). In particular, air concentra-
tions of R- and γ-HCH observed at Tagish of YK positively
correlated with residence time over eastern Asia before
1995). When HCHs are atmospherically transported from
the source regions, they can undergo rain and snow
scavenging and deposition to surfaces. Thirty-year normal
climate data indicate that the yearly precipitation rate at
another western Arctic site, PTB (268 vs 112 mm, see details
in Figure S2B). Higher precipitation rate at the elevated site
of LFL may have led to enhanced deposition of HCHs
compared to PTB when technical HCH was still in use,
although the two sites could be subjected to different
influence of emission sources (Figure 1). After primary
emissions of HCHs ceased globally, it is believed that HCH
transfer between the atmosphere and soil reversed from net
above soils was presumably less contaminated with HCHs
than soils because current air concentration of HCHs was
efficient than that by rain (28). Therefore, snow cover could
act as an effective barrier and further reduce secondary
emissions of HCHs from soils in snow season (36), which is
the temperature rises above freezing, evaporation of HCHs
from soils becomes significant. In general, the temperature
at LFL is approximately 10 °C higher than that at other high
Arctic sites (Figure S2A). Warmer climate would enhance
secondary re-emissions of HCHs from soils to the atmo-
air concentrations of R-HCH observed at LFL. Furthermore,
stronger wind speed at this elevated site can accelerate
chemical exchange process between air and surface envi-
ronmental media because of increased mass transfer coef-
ficient. In order to quantitatively investigate effects of
way at LFL, an evaluative multi-media fate model, for
example, fugacity-based CoZMo-POP (37), is required to
simulate their transport pathways and environmental fate.
at locations such as LFL. Better understanding of chemical
exchange processes between air and surface environmental
media is particularly important at these Arctic locations, if
snow/ice-covered periods and areas were reduced in the
future as a result of climate change.
and air is one of the important inter-media transport
pathways in the circumpolar environment since water
accounts for a large part of earth’s surface. Uniform
concentrations of R-HCH and HCB in the circumpolar
atmosphere allow assessing their seawater/air exchange
fugacity ratio, which is defined as
where fWand fAare fugacity in seawater and air; CWand CA
are concentrations in seawater and air; H is Henry’s Law
Constant; R is the ideal gas constant; and TA is the air
temperature (5). Values of fW/fA> 1, fW/fA) 1, and fW/fA<
respectively. Fugacity ratio calculated below refers to air
temperature at 0 °C.
Seawater concentration of R-HCH varies spatially in the
concentration of R-HCH was observed in the atmosphere.
Higher concentrations of R-HCH were found in the central/
western Canadian Archipelago (∼2700-4700 pg‚L-1) and
lower concentrations were found in the northern Barents
Sea and Greenland Sea (∼400 pg‚L-1) (38, 39). The Tundra
Northwest 1999 expedition showed an increase in R-HCH
concentrations in seawater from the eastern to western
Canadian Archipelago (averages 1800-4500 pg‚L-1) (18).
of magnitude in the Arctic (i.e., ∼400-4700 pg‚L-1). Due to
the high residence time of seawater in the Arctic and slow
a few years. The extremes of the water concentrations are
selected (400 and 4700 pg‚L-1) for deriving fugacity ratio. CA
of R-HCH is the average of the circumpolar air (23 pg‚m-3)
in this study and H is 0.061 Pa‚m3‚mol-1at 0 °C (32). Based
and 5.5 for low and high water concentrations, respectively.
The H of R-HCH can be enhanced 21% by the salting-out
effect at 25 °C (32), and it becomes 0.074 Pa‚m3‚mol-1at 0
the salting-out effect, fugacity ratios fW/fA for R-HCH are
adjusted to 0.57 and 6.7 for low and high water concentra-
tions, respectively. This suggests that R-HCH was close to
equilibrium in the eastern Arctic, whereas it was over-
saturated at most of other locations, such as the central and
western Canadian Archipelago. Although large fugacity
of R-HCH during most of the year because most regions
have little open water even in summetime, especially in the
higher Arctic. It is notable that R-HCH volatilization from
the Arctic Ocean could be accelerated as the Arctic becomes
warmer and less ice-covered with climate change (18, 41).
Similar to air observations (i.e., average of 56 pg‚m-3),
relatively uniform distribution of HCB was also reported in
Arctic surface seawater, averaging 5.5 pg‚L-1(5-6 pg‚L-1)
(38). H of HCB is 3.7 Pa‚m3‚mol-1at 0 °C (42). Salting-out
effect increases H of HCB by 30% at 25 °C (43). Hence, H of
HCB is adjusted to 4.8 Pa‚m3‚mol-1at 0 °C if salinity effect
fW/fAof HCB is 0.21, suggesting that HCB was undergoing
net deposition from air to seawater in the Arctic.
Seawater concentration of ?-HCH was ∼250 pg‚L-1in
Chukchi Sea (32, 33). Median air concentrations of ?-HCH
at 0 °C (32). Calculated fugacity ratios (fW/fA) of ?-HCH are
1.4 and 0.50 at PTB and VKK, respectively, assuming 21%
enhancement as a result of salting-out. Therefore, elevated
inputs from external sources other than outgassing from
seawater likely also contributed to high ?-HCH in VKK air.
We would like to acknowledge numerous site operators.
Research Office of the National Oceanic and Atmospheric
Administration (NOAA), United States, and the Norwegian
fW/fA) CW× H/(CA× R × TA) (2)
VOL. 40, NO. 21, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY96605
Pollution Control Authorities, Norway. Y.S. is grateful to F.
Wania, T. F. Bidleman, and L. M. Jantunen for beneficial
Supporting Information Available
site information; discussion on potential breakthrough of
HCB; MDLs; mean, median, and range of concentrations at
each sites; regression results of temperature dependence;
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Received for review May 4, 2006. Revised manuscript re-
ceived July 12, 2006. Accepted July 21, 2006.
VOL. 40, NO. 21, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY96607