Environ. Sci. Technol. 2010, 44, 3280–3285
Biogeochemical Controls on PCB Deposition in Hudson Bay Z O U Z O U A . K U Z Y K , * ,†,‡,| R O B I E W . M A C D O N A L D , †,§ SOPHIA C. JOHANNESSEN,§ AND G A R Y A . S T E R N †,‡ Centre for Earth Observation Science, Department of Environment and Geography, University of Manitoba, Winnipeg, Manitoba, Canada, R3T 2N2, Freshwater Institute, Fisheries & Oceans Canada, 501 University Crescent, Winnipeg, Manitoba, Canada, R3T 2N6, and Institute of Ocean Sciences, Fisheries & Oceans Canada, 9860 West Saanich Road, P.O. Box 6000, Sidney, British Columbia, Canada, V8L 4B2
Received December 31, 2009. Revised manuscript received March 20, 2010. Accepted April 1, 2010.
PCB concentrations, congener patterns, and fluxes were examined in 13 dated and organically characterized (C, N, δ13C, δ15N) marine sediment cores from Hudson Bay, Canada, to investigate the importance of organic matter (OM) supply and transport to PCB sequestration. Drawdown of PCBs, supported by marine primary production, is reflected in elevated ∑PCB concentrations and more highly chlorinated PCB signatures in surface sediments underlying eutrophic regions. Sediments in oligotrophic regions, which are dominated by “old” marine OM, have lower PCB concentrations and weathered signatures. For the surface of Hudson Bay, average atmospheric deposition appears to be very low (ca. 1.4 pg ∑PCBs cm-2 a-1) compared to fluxes reported for nearby lakes (ca. 44 pg ∑PCBs cm-2 a-1). 210Pb fails to provide a means to normalize the fluxes, highlighting important differences in the biocycling of 210 Pb and PCBs. Unlike 210Pb, atmospheric PCB exchange with the water’s surface is partially forced by the aquatic organic carbon cycle. The extremely low atmospheric deposition of PCBs to the surface of Hudson Bay is likely a reflection of the Bay’s exceptionally low productivity and vertical carbon fluxes. If future marine production and vertical flux of carbon increase due to loss of ice cover or change in river input as consequences of global warming, PCB deposition would also increase.
nection between PCBs and the aquatic organic cycle has received little attention, partly because PCBs are expensive and difficult to measure, and partly because a sufficient understanding of a system’s organic cycle rarely accompanies PCB data. In Hudson Bay, Canada (Figure 1), a region undergoing rapid climate change (3), a detailed understanding of the organic carbon cycle has been assembled, based on broad sampling of rivers, seawater, and sediments (6-10). As part of these studies, 13 sediment cores were dated, modeled for mixing, and their organic records were interpreted in the context of sources and processes leading to deposition at the various sites (9). These cores, therefore, provide an exceptional basis to interpret concurrent PCB records at the scale of Hudson Bay. Hudson Bay is a large (841 × 103 km2), estuarine, shelflike sea located at the southern margin of the Arctic. Like other coastal oceans (cf 11.), Hudson Bay has a complex organic carbon cycle, with three main sources of organic matter (marine primary production, river-derived terrestrial OM, and recycled OM associated with resuspended sediments) and high variability internally, reflecting gradients in productivity and external supply as well as dynamic transport. These gradients offer an advantage for investigating how PCBs are affected by the organic supply and transport processes. Here, PCB congener data for 210Pb-dated and organically characterized (C, N, δ13C, lignin) marine sediment cores from Hudson Bay, Canada are examined to determine connections between this contaminant and the organic carbon cycle.
Materials and Methods The collection and processing of the 13 sediment cores used in this study have been described previously (8, 9). The cores were collected from the Canadian Coast Guard Ship Amundsen in September-October 2005 using a box corer (maximum penetration 50 cm). The cores were immediately sectioned into 1 cm intervals for the top 10 cm, 2 cm intervals for the next 10 cm, and 5 cm intervals for the remainder of the core. Sediment from the outermost 5 cm of the box was discarded. Each section (sample) was homogenized in a thoroughly precleaned I-Chem glass jar, subsampled for elemental and
Introduction Contaminants such as polychlorinated biphenyls (PCBs) associate with organic carbon in aquatic systems (1, 2), and this association then dictates the contaminant’s transport and fate, including entry into food webs or burial in sediments. Therefore, change in the organic system (terrestrial or marine) due, for example, to altered climate (3), implies change in contaminant pathways (4, 5). The con* Corresponding author phone: (418) 654-3767; e-mail:
[email protected]. † University of Manitoba. ‡ Freshwater Institute. § Institute of Ocean Sciences. | Current address: INRS-ETE, Universite´ du Que´bec, 490 rue de la Couronne, Que´bec, Que´bec, Canada, G1K 9A9. 3280
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 44, NO. 9, 2010
FIGURE 1. Concentrations of ∑PCBs in surface sediments of Hudson Bay expressed per gram dry weight of sediment (black bars) and after adjustment (using regression residuals) for partial dependence on sediment particle size and organic carbon content (white bars). 10.1021/es903832t
2010 American Chemical Society
Published on Web 04/14/2010
TABLE 1. Sediment Core Properties and Sedimentation Parametersa no.
depth (m)
lat. (N)
long. (W)
SML (cm)
Kb1 (cm-2 a-1)
3 4 5 6 7 8 9 10 11 12 13 14 15
395 153 112 119 106 150 34 200 86 116 145 244 430
62° 45′ 60° 11′ 58° 25′ 55° 24′ 55° 26′ 56° 43′ 55° 32′ 59° 03′ 58° 44′ 59° 59′ 60° 26′ 61° 24′ 63° 03′
79° 00′ 79° 18′ 78° 22′ 77° 59′ 80° 32′ 80° 48′ 84° 57′ 87° 33′ 91° 30′ 91° 57′ 89° 22′ 86° 13′ 74° 19′
8 3 10 3 2 5 2 3 2 3 2 3 0
5 0.4 1.5 1 0.1 0.4 1 2 1 0.3 0.4 0.5 0
∑PCB inv. (pg cm-2)
sedimentation rate (g cm-2 a-1)
1460 513
0.17 (0.12-0.25) 0.058 (0.04-0.09) 0.10 (0.09-0.12) 0.12 (0.06-0.16) 0.054* (0.02-0.07) 0.13 (0.12-0.25) 0.23 (0.22-0.32) 0.04* (0.03-0.06) 0.22* (0.15-0.30) 0.16* (0.13-0.20) 0.06* (0.06-0.10) 0.032 (0.03-0.04) 0.07* (0.02-0.08)
1320 1280 208
245
a SML ) surface mixed layer depth; Kb1 ) upper layer mixing rate (Kb2 ) 0.01 cm2 a-1 for all cores except 15 (∼0 cm2 a-1)). * Indicates sedimentation rate should be interpreted as maximum value.
isotopic analyses, and then frozen. At the end of the cruise, one set of subsamples was freeze-dried and ground and distributed to the Environmental Radiochemistry Laboratory at the University of Manitoba for radioisotope analyses. Geochronologies were constructed for each core using profiles of excess 210Pb and a model that incorporates a surface mixed layer, and verified against 137Cs and, in some cases, contaminant Pb (9). A second set of subsamples was ovendried at 60 °C and then distributed to the University of British Columbia for elemental and isotopic analyses. The organic carbon content (%OC) of the sediments was determined by difference from measurements of total C using a Carlo Erba NA-1500 elemental analyzer (12) and total inorganic C determined by CO2 coulometry. Stable carbon isotopes (δ13C) were determined on acidified samples and stable nitrogen isotopes (δ15N) on separate, untreated subsamples, using the element analyzer coupled to an isotope ratio mass spectrometer (13). PCB congeners (Supporting Information (SI) Table S1) were quantified by AXYS Analytical Services Ltd., Sidney BC, using high-resolution gas chromatography/high-resolution mass spectrometry (HRGC/HRMS) in accordance with EPA method 1668A (14). Rigorous quality assurance/quality control (QA/QC) was maintained, and blank values (sum of all detected congeners (∑PCBs)) were generally
