Scavenging amphipods: sentinels for penetration of mercury and persistent organic chemicals into food webs of the deep Arctic Ocean

Archived specimens of the scavenging amphipod Eurythenes gryllus, collected from 2075 to 4250 m below the surface on five expeditions to the western and central Arctic Ocean between 1983 and 1998, were analyzed for total mercury (∑Hg), methyl mercury (MeHg), polychlorinated biphenyls (PCBs) and other industrial or byproduct organochlorines (chlorobenzenes, pentachloroanisole, octachlorostyrene), organochlorine pesticides (OCPs), and polybrominated diphenyl ethers (PBDEs). Median ∑Hg concentrations ranged from 70 to 366 ng g(-1) wet weight (ww). MeHg concentrations (3.55 to 23.5 ng g(-1) ww) accounted for 1.7 to 20.1% (median 3.7%) of ∑Hg. ∑Hg and MeHg were positively and significantly correlated with ww (∑Hg r(2) = 0.18, p = 0.0004, n = 63; MeHg r(2) = 0.42, p = 0.0004, n = 25), but not significantly with δ(13)C nor δ(15)N. Median concentrations of total persistent organic pollutants (POPs) ranged from 9750 to 156,000 ng g(-1) lipid weight, with order of abundance: ∑TOX (chlorobornanes quantified as technical toxaphene) > ∑PCBs > ∑DDTs > ∑chlordanes > ∑mirex compounds > ∑BDEs ∼ ∑chlorobenzenes ∼ octachlorostyrene > α-hexachlorocyclohexane ∼ hexachlorobenzene ∼ pentachloroanisole. Enantioselective accumulation was found for the chiral OCPs o,p'-DDT, cis- and trans-chlordane, nonachlor MC6 and oxychlordane. Lipid-normalized POPs concentrations were elevated in amphipods with lipid percentages ≤10%, suggesting that utilization of lipids resulted in concentration of POPs in the remaining lipid pool. Multidimensional Scaling (MDS) analysis using log-transformed physiological variables and lipid-normalized organochlorine concentrations distinguished amphipods from the central vs western arctic stations. This distinction was also seen for PCB homologues, whereas profiles of other compound classes were more related to specific stations rather than central-west differences.

Importance of Arctic zooplankton seasonal migrations for α-hexachlorocyclohexane bioaccumulation dynamics

Like most zooplankton, Calanus hyperboreus undergoes seasonal migration spending late spring and summer grazing at the surface and the rest of the year in diapause at depth. As a result, in the Arctic Ocean this copepod resides for part of the year in the hexachlorocyclohexane (HCH) enriched surface water and for part of the year at depth where HCH undergoes significant microbial degradation resulting in far lower concentrations (~3 times for α-HCH). We collected C. hyperboreus from summer and winter from the Amundsen Gulf and measured their α-HCH concentrations, enantiomeric compositions, and bioaccumulation factors (BAFs) to investigate how this copepod responds to the change in exposure to α-HCH. C. hyperboreus collected in winter were also cultured for 5 weeks under surface water conditions without feeding to investigate bioconcentration dynamics following spring ascent. Concentration of α-HCH was 2-3 times higher in individuals from the summer than those from the winter. Log BAF from the summer (feeding period) does not exceed log BCF (bioconcentration factor) from the culturing experiment (no feeding) suggesting that α-HCH concentration in C. hyperboreus is maintained through equilibration rather than feeding. After the spring ascent from deep waters, C. hyperboreus approach equilibrium partitioning with the higher surface water concentrations of α-HCH within 3-4 weeks with about 60% of bioconcentration taking place in the first week. The C. hyperboreus α-HCH chiral signature also reflects ambient seawater and can therefore be used as a determinant of residence depth. Even though a single cycle of seasonal migration does not result in a significant redistribution of α-HCH in the water column, this process could have a significant cumulative effect over longer time scales with particular local importance where the zooplankton biomass is high and the ocean depth is great enough to provide substantial vertical concentration gradients.

Mercury biomagnification in marine zooplankton food webs in Hudson Bay

While much research has been carried out on mercury in large marine mammals and associated food webs in northern regions, comparatively less has been conducted on lower trophic levels including zooplankton and the subsequent transfer to predators, which marks the entry of mercury into northern marine food webs. We present here the first database for mercury uptake and transfer exclusively within zooplankton food webs in northern marine waters. We have investigated both total (THg) and monomethylmercury (MMHg) concentrations, and isotopic signatures (δ(15)N and δ(13)C) in individual zooplankton taxa collected over a period of eight years (2003-2010) from across Hudson Bay (including Hudson Strait and Foxe Basin) as part of research icebreaker cruises. δ(15)N values ranged from 3.4 to 14.0‰, implying trophic levels ranging from 1 to 4, and THg concentrations ranged from 5 to 242 ng g(-1) dw. Food web linkages were identified within the data set, and mercury biomagnification was evident both with THg and MMHg concentrations increasing from prey to predator, and with trophic magnification factors (TMFs). Total mercury and MMHg transfer in a unique prey-predator linkage (Limacina helicina-Clione limacina) are investigated and discussed with regard to known physiological and biochemical characteristics. The results suggest that exposure to mercury at higher trophic levels including humans can be affected by processes at the bottom of Arctic marine food webs.

PBDE and PCB accumulation in benthos near marine wastewater outfalls: the role of sediment organic carbon

Polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) were measured in sediments and benthic invertebrates near submarine municipal outfalls in Victoria and Vancouver, B.C., Canada, two areas with contrasting receiving environments. PBDE concentrations in wastewater exceeded those of the legacy PCBs by eight times at Vancouver and 35 times at Victoria. Total PBDE concentrations in benthic invertebrates were higher near Vancouver than Victoria, despite lower concentrations in sediments, and correlated with organic carbon-normalized concentrations in sediment. Principal Components Analysis indicated uptake of individual PBDE congeners was determined by sediment properties (organic carbon, grain size), while PCB congener uptake was governed by physico-chemical properties (octanol-water partitioning coefficient). Results suggest the utility of sediment quality guidelines for PBDEs and likely PCBs benefit if based on organic carbon-normalized concentrations. Also, where enhanced wastewater treatment increases the PBDEs to particulate organic carbon ratio in effluent, nearfield benthic invertebrates may face increased PBDE accumulation.

Total and methylated mercury in the Beaufort Sea: the role of local and recent organic remineralization

Mercury is a major contaminant in the Arctic marine ecosystem. While extensive studies have been conducted on mercury in the Arctic's atmosphere and biota, far less is known about the distribution and dynamics of mercury species in the Arctic Ocean. Here, we present vertical profiles for total mercury (Hg(T)) and total methylated mercury (MeHg(T), sum of monomethylmercury and dimethylmercury) from the Beaufort Sea of the Arctic Ocean at locations with differing sea ice conditions. The concentration of Hg(T) ranged from 0.40 to 2.9 pM, with a surface enrichment that can be attributed to a combination of sea ice-modified atmospheric deposition and riverine input. The concentration of MeHg(T) ranged from <0.04 to 0.59 pM, with a subsurface peak occurring at the same depth as a nutrient maximum with lower dissolved oxygen, which is consistent with the recent findings in the Pacific Ocean, Southern Ocean, and Mediterranean Sea. However, unlike the interior ocean regions, the nutrient maximum in the Beaufort Sea is predominantly an advective feature produced over the Chukchi Shelf. On the basis of the short lifetime of monomethylmercury in seawater, we propose that the MeHg(T) profile in the Beaufort Sea reflects the local, short-term remineralization of labile organic matter, and not the larger signal of organic remineralization advected from the Chukchi Sea in the halocline. The finding that MeHg(T) is produced locally, reflecting recent strength of organic matter cycling, not only explains wide variance in MeHg(T) in seawater and biota over time and space, but also implies that MeHg(T) could be used as an indicator of the recent export flux of labile organic matter.

Mechanisms and implications of α-HCH enrichment in melt pond water on Arctic sea ice

During the summer of 2009, we sampled 14 partially refrozen melt ponds and the top 1 m of old ice in the pond vicinity for α-hexachlorocyclohexane (α-HCH) concentrations and enantiomer fractions (EFs) in the Beaufort Sea. α-HCH concentrations were 3 - 9 times higher in melt ponds than in the old ice. We identify two routes of α-HCH enrichment in the ice over the summer. First, atmospheric gas deposition results in an increase of α-HCH concentration from 0.07 ± 0.02 ng/L (old ice) to 0.34 ± 0.08 ng/L, or ~20% less than the atmosphere-water equilibrium partitioning concentration (0.43 ng/L). Second, late-season ice permeability and/or complete ice thawing at the bottom of ponds permit α-HCH rich seawater (~0.88 ng/L) to replenish pond water, bringing concentrations up to 0.75 ± 0.06 ng/L. α-HCH pond enrichment may lead to substantial concentration patchiness in old ice floes, and changed exposures to biota as the surface meltwater eventually reaches the ocean through various drainage mechanisms. Melt pond concentrations of α-HCH were relatively high prior to the late 1980-s, with a Melt pond Enrichment Factor >1 (MEF; a ratio of concentration in surface meltwater to surface seawater), providing for the potential of increased biological exposures.

Biomagnification of polychlorinated biphenyls in a harbor seal (Phoca vitulina) food web from the Strait of Georgia, British Columbia, Canada

Polychlorinated biphenyl (PCB) biomagnification was characterized in a harbor seal food web in the Strait of Georgia, British Columbia, Canada. Trophic magnification factors (TMFs) for PCBs averaged 3.6, with a range of 0.7 to 9.4. The TMFs for individual congeners correlated with log K(OW) (r(2) = 0.56, p < 0.001), reflecting the role that physicochemical properties play in driving the biomagnification of PCBs in marine food webs. However, TMFs differed among PCB structure activity groups, clearly indicating an additional role for metabolic transformation of certain PCBs. The known feeding preferences of harbor seals enabled the calculation of trophic level-adjusted biomagnification factors (BMF(TL)) for PCBs in this species, which averaged 13.4 and ranged from 0.2 to 150.6. Metabolic transformation in seals explained some of the variation in congener-specific biomagnification, with lower BMF(TL) values for PCB congeners with meta- and parachlorine unsubstituted positions. Principal components analysis revealed the distinct roles played by trophic level, log K(OW), and metabolic transformation in explaining the notable differences in PCB patterns among harbor seals, their pups, and their prey. In the present study, the authors estimate there to be approximately 76 kg of PCBs in the biota of the Strait of Georgia, of which 1.6 kg is retained by harbor seals.

There is no 1954 in that core! Interpreting sedimentation rates and contaminant trends in marine sediment cores

Marine sediment preserves a useful archive for contaminants and other properties that associate with particles. However, biomixing of sediments can smear the record on a scale of years to thousands of years, depending on sedimentation rate and on the depth and vigour of mixing within a particular sediment. Where such mixing occurs, dates can no longer be associated with discrete sediment depths. Nevertheless, much can still be learned from biomixed profiles, provided that mixing is accounted for. With no modelling at all, it is possible to calculate an inventory of a contaminant at a site and a maximum possible sedimentation rate, and to determine whether the contaminant has increased or decreased over time. Radiodating the core with (210)Pb permits the estimation of sedimentation and mixing rates, which can be combined with the surface contaminant concentration to estimate an approximate flux of the contaminant. Numerical models that incorporate sedimentation and mixing rates (determined using (210)Pb and other transient signals with known deposition histories) can provide the basis to propose plausible histories for contaminant fluxes.

Effect of receiving environment on the transport and fate of polybrominated diphenyl ethers near two submarine municipal outfalls

The fate of contaminants entering the marine environment through wastewater outfalls depends on the contaminant's persistence and affinity for particles. However, the physical characteristics of the receiving environment, for example, current velocity and sedimentary processes, may be even more important. Because of the complexity of natural settings and the lack of appropriate comparative settings, this is not frequently evaluated quantitatively. The authors investigated the near-field accumulation of particle-reactive polybrominated diphenyl ethers (PBDEs) entering coastal waters by way of two municipal outfalls: one discharging into a high-energy, low-sedimentation environment near Victoria, BC, Canada; the other into a low-energy, high-sedimentation environment, near Vancouver, BC. The authors used ²¹⁰Pb profiles in box cores together with an advection-diffusion model to determine surface mixing and sedimentation rates, and to model the depositional history of PBDEs at these sites. Surprisingly, 88 to 99% of PBDEs were dispersed beyond the near-field at both sites, but a greater proportion of PBDEs was captured in the sediment near the Vancouver outfall where rapid burial was facilitated by inorganic sediment supplied from the nearby Fraser River. Although the discharge of PBDEs was much lower from the Victoria outfall than from Vancouver, some sediment PBDE concentrations were higher near Victoria.

How does climate change influence Arctic mercury?

Recent studies have shown that climate change is already having significant impacts on many aspects of transport pathways, speciation and cycling of mercury within Arctic ecosystems. For example, the extensive loss of sea-ice in the Arctic Ocean and the concurrent shift from greater proportions of perennial to annual types have been shown to promote changes in primary productivity, shift foodweb structures, alter mercury methylation and demethylation rates, and influence mercury distribution and transport across the ocean-sea-ice-atmosphere interface (bottom-up processes). In addition, changes in animal social behavior associated with changing sea-ice regimes can affect dietary exposure to mercury (top-down processes). In this review, we address these and other possible ramifications of climate variability on mercury cycling, processes and exposure by applying recent literature to the following nine questions; 1) What impact has climate change had on Arctic physical characteristics and processes? 2) How do rising temperatures affect atmospheric mercury chemistry? 3) Will a decrease in sea-ice coverage have an impact on the amount of atmospheric mercury deposited to or emitted from the Arctic Ocean, and if so, how? 4) Does climate affect air-surface mercury flux, and riverine mercury fluxes, in Arctic freshwater and terrestrial systems, and if so, how? 5) How does climate change affect mercury methylation/demethylation in different compartments in the Arctic Ocean and freshwater systems? 6) How will climate change alter the structure and dynamics of freshwater food webs, and thereby affect the bioaccumulation of mercury? 7) How will climate change alter the structure and dynamics of marine food webs, and thereby affect the bioaccumulation of marine mercury? 8) What are the likely mercury emissions from melting glaciers and thawing permafrost under climate change scenarios? and 9) What can be learned from current mass balance inventories of mercury in the Arctic? The review finishes with several conclusions and recommendations.

Effects of seabird vectors on the fate, partitioning, and signatures of contaminants in a High Arctic ecosystem

Seabirds bioaccumulate contaminants from prey, transport them to their nesting sites, and deposit them in their excreta and carcasses, thereby focusing marine-derived contaminants into remote, terrestrial receptor sites. In the case of organochlorine chemicals transported by northern fulmars (Fulmarus glacialis) to a High Arctic seabird colony on Devon Island, Nunavut, Canada (76°13'N, 89°14'W), this contaminant pathway dominates all others. In freshwater ponds below the nesting cliffs, concentrations of organochlorine contaminants characteristic of fulmar input were 2- to 45-fold higher in sediments and water (depending on seabird input to the particular pond) than in ponds remote from the colony. Air-water fugacity quotients for the ponds decreased with seabird input, indicating that fulmar contaminant input shifts air-water partitioning to increasingly favor volatilization to air. Although contaminant evasion from water was favored, direct evidence of it was not detected in air samples. For PCBs, congener profiles of pond sediments or water became more similar to seabird sources as seabird input increased, and less similar to air profiles. Based on measurements of contaminants in fulmars and other local environmental media, this study presents the first application of fugacities and multivariate source apportionment statistics to resolve seabird biological vectors.

Environmental fractionation of PCBs and PBDEs during particle transport as recorded by sediments in coastal waters

The Strait of Georgia (British Columbia, Canada) is a hydrologically complex inland sea with a rich abundance and diversity of species of aquatic life. Marine sediments, as both a sink for hydrophobic contaminants and a potential source for aquatic food webs, were collected from 41 sites throughout the 6,900-km(2) Strait of Georgia. The congener-specific concentrations of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs), including BDE-209, were measured. Urban harbors represented hotspots for both PCBs and PBDEs, whereas PBDEs were also found at high concentrations near municipal outfalls. Patterns of PCB distribution were consistent with historical point source emissions in urban areas and environmental distillation toward lighter profiles in remote sites over time. The single congener BDE-209 dominated the PBDEs, accounting for 52% of the average total concentration. However, nonurban deep-water sediment PBDE profiles were both heavier and had higher concentration-weighted average log K(OW) (octanol-water partition coefficient) values compared to shallow samples (percent BDE-209 of total PBDE, 66 versus 32%; log K(OW) , 9.5 versus 8.2, respectively). Collectively, our results suggest that although source signals largely explain PCB and PBDE hotspots in the Strait of Georgia, the combination of physicochemical properties and environmental processes drive divergent compositional fates for the PCBs and the heavier PBDEs in the sediments of the Strait of Georgia.

α- and γ-Hexachlorocyclohexane measurements in the brine fraction of sea ice in the Canadian High Arctic using a sump-hole technique

We used holes augered partially into first-year sea ice (sumps) to determine α- and γ-HCH concentrations in sea-ice brine. The overwintering of the CCGS Amundsen in the Canadian western Arctic, as part of the Circumpolar Flaw Lead (CFL) System Study, provided the circumstances to allow brine to accumulate in sumps sufficiently to test the methodology. We show, for the first time, that as much as 50% of total HCHs in seawater can become entrapped within the ice crystal matrix. On average, in the winter first-year sea ice HCH brine concentrations reached 4.013 ± 0.307 ng/L and 0.423 ± 0.013 ng/L for the α- and γ-isomer, respectively. In the spring, HCHs decreased gradually with time, with increasing brine volume fraction and decreasing brine salinity. These decreasing concentrations could be accounted for by both the dilution with the ice crystal matrix and under-ice seawater. We propose that the former process plays a more significant role considering brine volume fractions calculated in this study were below 20%. Levels of HCHs in the brine exceed under-ice water concentrations by approximately a factor of 3, a circumstance suggesting that the brine ecosystem has been, and continues to be, the most exposed to HCHs.

Natural and anthropogenic mercury distribution in marine sediments from Hudson Bay, Canada

Twelve marine sediment cores from Hudson Bay, Canada, were collected to investigate the response of sub-Arctic marine sediments to atmospherically transported anthropogenic mercury (Hg). Modeling by a two-layer sediment mixing model suggests that the historical Hg deposition to most of the sediment cores reflects the known history of atmospheric Hg deposition in North America, with an onset of increasing anthropogenic Hg emissions in the late 1800s and early 1900s and a reduction of Hg deposition in the mid- to late-1900s. However, although anthropogenic Hg has contributed to a ubiquitous increase in Hg concentrations in sediments over the industrial era, the most elevated industrial-era sedimentary Hg concentrations only marginally exceed the upper preindustrial sedimentary Hg concentrations. Analysis of delta13C and relationship between Hg and organic matter capture suggests that the response of Hudson Bay sediments to changes in atmospheric Hg emissions is largely controlled by the particle flux in the system and that natural changes in organic matter composition and dynamics can cause variation in sedimentary Hg concentrations at least to the same extent as those caused by increasing anthropogenic Hg emissions.

Biogeochemical controls on PCB deposition in Hudson Bay

PCB concentrations, congener patterns, and fluxes were examined in 13 dated and organically characterized (C, N, delta(13)C, delta(15)N) 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 summation operatorPCB 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 summation operatorPCBs cm(-2) a(-1)) compared to fluxes reported for nearby lakes (ca. 44 pg summation operatorPCBs cm(-2) a(-1)). (210)Pb fails to provide a means to normalize the fluxes, highlighting important differences in the biocycling of (210)Pb and PCBs. Unlike (210)Pb, 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.

Increasing contaminant burdens in an arctic fish, Burbot ( Lota lota ), in a warming climate

The temporal patterns of mercury (Hg), polychlorinated biphenyls (PCBs), and other contaminants in Arctic aquatic biota are usually attributed to changing atmospheric sources. However, climate variability and change is another means of altering contaminant fate and bioavailability. We show here that the concentrations of Hg and PCBs in Mackenzie River burbot ( Lota lota ), a top predator fish and important staple food for northern Canadian communities, have increased significantly over the last 25 years despite falling or stable atmospheric concentrations, suggesting that environmental processes subsequent to atmospheric transport are responsible. Using a dated sediment core from a tributary lake near the Mackenzie River sampling site, we show that variations in Hg concentrations downcore are strongly associated with labile, algal-derived organic matter (OM). Strong temporal correlations between increasing primary productivity and biotic Hg and PCBs as reflected by burbot suggest that warming temperatures and reduced ice cover may lead to increased exposure to these contaminants in high trophic level Arctic freshwater biota.