A study of PCB concentrations and fluxes in lake
sediments was conducted to test the “global fractionation” hypothesis that deposition of semivolatile
organics will decline while more volatile congeners
will be enriched in polar regions. Sediment cores
were collected from 11 remote lakes in Canada ranging
from 49° N to 82° N and were dated using excess
210Pb and 137Cs. Sediment extracts
were analyzed for
up to 90 PCB congeners by capillary GC-ECD with
confirmation by GC/high-resolution MS. Total PCB
(∑PCB) concentrations in surface slices ranged
from 2.4 to 39 ng g-1 (dry wt) and showed no
latitudinal
trend. Fluxes (ng m-2
yr-1) and inventories of ∑PCB
as well as total tetra- to octachlorobiphenyls
declined with increasing north latitude while those
for di/trichlorobiphenyls showed no latitudinal trend.
The
proportion of di/trichloro congeners of ∑PCB also
increased significantly with latitude, while total octachlorobiphenyls declined. Maximum ∑PCB concentrations were observed in subsurface slices dating
to the 1960−1970s in most lakes except those in the
high Arctic, where maxima were generally in
surface slices. The onset of elevated ∑PCB
deposition
was delayed in the high Arctic (1950−1960s) relative
to the midlatitude and sub-Arctic lakes (1930−1940s).
The high proportions of lower chlorinated congeners
and the delayed appearance of PCBs are
consistent
with predictions of the global fractionation
model.
Sediment cores from six lakes in Canada ranging from
49°N to 81°N were analyzed for C10−C13 polychlorinated
n-alkanes (PCAs) with the intent of (i) examining the
depositional trends with increasing latitude, (ii) studying
the historical profiles and fluxes of PCAs in dated sediment
slices, and (iii) investigating possible in situ degradation.
Sediment slices were dated using 210Pb and 137Cs, and extracts
were analyzed for PCA concentrations by high resolution
gas chromatography electron capture negative ion high
resolution mass spectrometry (HRGC-ECNI/HRMS) in the
selected ion monitoring (SIM) mode. Concentrations of total
PCAs in surface sediments declined significantly from
135 ng/g (dry weight (dw)) in sediments from the southern
basin of Lake Winnipeg (50°N/96°W, Manitoba) to 4.52
ng/g in Hazen Lake (81°N/71°W, high Arctic); corresponding
surficial fluxes were 147 and 0.9 μg/m2 yr, respectively.
The high flux of PCAs to the south Lake Winnipeg basin
suggests local contamination. This was confirmed by analyzing
water collected from the Red River, a river that discharges
into the southern basin of Lake Winnipeg, in which
elevated levels of PCAs were detected (0.02−0.05 μg/L).
The surficial flux of PCAs to Fox Lake (61°N/135°W), a subarctic
lake in the Yukon, was also high, 34 μg/m2 yr. Much
lower fluxes were found in Lake Nipigon (49°N/89°W, N.
Ontario), 3 μg/m2 yr, the northern basin of Lake Winnipeg (52°N/98°W, Manitoba), 4 μg/m2 yr, and to Ya Ya Lake (69°N/134°W, Arctic) 0.45 μg/m2 yr. The remote locations of Hazen
and Ya Ya Lakes and the low levels of PCAs observed in
their corresponding sediment slices are consistent with long-range atmospheric transport. The profiles of PCAs in the
midcontinental lakes showed maxima in slices dated from
the early 1980s to the 1990s while that of ΣDDT showed
a maxima in the 1960s. The presence of PCAs in surface
sediments over a wide geographic area, including the
Canadian Arctic, suggests that these compounds, which
are components of commercial short chain chlorinated
paraffins, are regionally and globally distributed by long-range atmospheric transport.
Concentrations of toxaphene and other organochlorine compounds are high in fishes from subarctic Lake Laberge, Yukon Territory, Canada. Nitrogen isotope analyses of food chains and contaminant analyses of biota, water, and dated lake sediments show that the high concentrations of toxaphene in fishes from Laberge resulted entirely from the biomagnification of atmospheric inputs. A combination of low inputs of toxaphene from the atmosphere and transfer through an exceptionally long food chain has resulted in concentrations of toxaphene in fishes that are considered hazardous to human health.
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