Steady-State Based Model of Airborne Particle/Gas and Settled Dust/Gas Partitioning for Semivolatile Organic Compounds in the Indoor Environment.

Indoor semivolatile organic compounds (SVOCs), present in the air, airborne particles, settled dust, and other indoor surfaces, can enter the human body through several pathways. Knowing the partitioning between gaseous and particulate phases is important in identifying specific pathway contributions and thereby accurately assessing human exposure. Numerous studies have developed equilibrium equations to predict airborne particle/gas (P/G) partitioning in air (KP) and dust/gas (D/G) partitioning in settled dust (KD). The assumption that P/G and D/G equilibria are instantaneous for airborne and settled dust phases, commonly adopted by current indoor fate models, is not likely valid for compounds with high octanol-air partition coefficients (KOA). Here, we develop steady-state based equations to predict KP and KD in the indoor environment. Results show that these equations perform well and are verified by worldwide monitoring data. It is suggested that instantaneous steady state could work for P/G and D/G partitioning of SVOCs in indoor environments, and the equilibrium is just a special case of the steady state when log KOA < 11.38 for P/G partitioning and log KOA < 10.38 for D/G partitioning. These newly developed equations and methods provide a tool for more accurate assessment for human exposure to SVOCs in the indoor environment.

Approach to Predicting the Size-Dependent Inhalation Intake of Particulate Novel Brominated Flame Retardants.

The risk of human exposure to particulate novel brominated flame retardants (NBFRs) in the atmosphere has received increasing attention from scientists and the public, but currently, there is no reliable approach to predict the intake of these compounds on the basis of their size distribution. Here, we develop a reliable approach to predict the size-dependent inhalation intake of particulate NBFRs, based on the gas/particle (G/P) partitioning behavior of the NBFRs. We analyzed the concentrations of eight NBFRs in 363 size-segregated particulate samples and 99 paired samples of gaseous and bulk particles. Using these data, we developed an equation to predict the G/P partitioning quotients of NBFRs in particles in different size ranges (KPi) based on particle size. This equation was then successfully applied to predict the size-dependent inhalation intake of particulate NBFRs in combination with an inhalation exposure model. This new approach provides the first demonstration of the effects of the temperature-dependent octanol-air partitioning coefficient (KOA) and total suspended particle concentration (TSP) on the intake of particulate NBFRs by inhalation. In an illustrative case where TSP = 100 µg m-3, inhalation intake of particulate NBFRs exceeded the intake of gaseous NBFRs when log KOA > 11.4.

Decabrominated Diphenyl Ethers (BDE-209) in Chinese and Global Air: Levels, Gas/Particle Partitioning, and Long-Range Transport: Is Long-Range Transport of BDE-209 Really Governed by the Movement of Particles?

In this paper, we report air concentrations of BDE-209 in both gas- and particle-phases across China. The annual mean concentrations of BDE-209 were from below detection limit (BDL) to 77.0 pg·m-3 in the gas-phase and 1.06-728 pg·m-3 in the particle-phase. Among the nine PBDEs measured, BDE-209 is the dominant congener in Chinese atmosphere in both gas and particle phases. We predicted the partitioning behavior of BDE-209 in air using our newly developed steady state equation, and the results matched the monitoring data worldwide very well. It was found that the logarithm of the partition quotient of BDE-209 is a constant, and equal to -1.53 under the global ambient temperature range (from -50 to +50 °C). The gaseous fractions of BDE-209 in air depends on the concentration of total suspended particle (TSP). The most important conclusion derived from this study is that, BDE-209, like other semivolatile organic compounds (SVOCs), cannot be sorbed entirely to atmospheric particles; and there is a significant amount of gaseous BDE-209 in global atmosphere, which is subject to long-range atmospheric transport (LRAT). Therefore, it is not surprising that BDE-209 can enter the Arctic through LRAT mainly by air transport rather than by particle movement. This is a significant advancement in understanding the global transport process and the pathways entering the Arctic for chemicals with low volatility and high octanol-air partition coefficients, such as BDE-209.

Distribution and uptake of key polychlorinated biphenyl and polybrominated diphenyl ether congeners in benthic infauna relative to sediment organic enrichment.

As part of a broader study of budgets, transport, and bioaccumulation of persistent organic contaminants in the Strait of Georgia, Canada, matching samples of sediment and bulk benthos were collected near two marine sewage outfalls, two large urban harbours, and background areas. Samples were analyzed for polychlorinated biphenyl (PCB) and polybrominated diphenyl ether (PBDE) congeners. We present data for those congeners that fell within the top six rankings by concentration (23 PCBs and 10 PBDEs) within at least one of the environmental media measured in other studies (air, water, sediments, benthos, pelagic biota). Multifactor regression analyses incorporating sediment characteristics (total organic carbon, fines) predicted uptake (r (2) = 0.74 to 0.98, p < 0.04) over the range of congeners and habitats examined. PBDEs were taken up by biota more readily than PCBs, suggesting a large, potentially available biological reservoir of PBDEs in sediments. Dominant congeners in benthos comprised PBDEs 47, 99, 209, and 100 and PCBs 138/163, 153, 101, 118, and 110. PBDE uptake was anomalously high near one wastewater outfall, likely due to selective feeding on PBDE-enriched particulates from that source. Conversely, outfalls supply food and sediments with PCB concentrations similar to ambient sediments. However, organic enrichment of sediments near outfalls clearly enhanced PCB uptake by benthos, probably due to greatly increased biomass turnover near these sources. Data suggest there to be an initial reservoir of PCBs in newly settled juvenile benthos, which is much less evident for PBDEs. This is likely a consequence of the ecosystem-wide distribution of legacy PCBs but not the more current-use PBDEs. Congener-uptake patterns were dependent on source and input dynamics, feeding methods, and contaminant metabolism or debromination, particularly of deca-BDE.

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.

Modeling historical budget for ß-Hexachlorocyclohexane (HCH) in the Arctic Ocean: A contrast to α-HCH.

The historical annual loading to, removal from, and cumulative burden in the Arctic Ocean for ß-hexachlorocyclohexane (ß-HCH), an isomer comprising 5-12% of technical HCH, is investigated using a mass balance box model from 1945 to 2020. Over the 76 years, loading occurred predominantly through ocean currents and river inflow (83%) and only a small portion via atmospheric transport (16%). ß-HCH started to accumulate in the Arctic Ocean in the late 1940s, reached a peak of 810 t in 1986, and decreased to 87 t in 2020, when its concentrations in the Arctic water and air were ∼30 ng m-3 and ∼0.02 pg m-3, respectively. Even though ß-HCH and α-HCH (60-70% of technical HCH) are both the isomers of HCHs with almost identical temporal and spatial emission patterns, these two chemicals have shown different major pathways entering the Arctic. Different from α-HCH with the long-range atmospheric transport (LRAT) as its major transport pathway, ß-HCH reached the Arctic mainly through long-range oceanic transport (LROT). The much higher tendency of ß-HCH to partition into the water, mainly due to its much lower Henry's Law Constant than α-HCH, produced an exceptionally strong pathway divergence with ß-HCH favoring slow transport in water and α-HCH favoring rapid transport in air. The concentration and burden of ß-HCH in the Arctic Ocean are also predicted for the year 2050 when only 4.4-5.3 t will remain in the Arctic Ocean under the influence of climate change.

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.

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.

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.

Slopes and intercepts from log-log correlations of gas/particle quotient and octanol-air partition coefficient (vapor-pressure) for semi-volatile organic compounds: I. Theoretical analysis.

Gas/particle partitioning governs the transport and fate of semi-volatile organic compounds (SVOCs) released to the atmosphere. The partition quotient of SVOCs, KP, is related to their subcooled liquid vapor pressure (logKP = mp logPL + bp) and to their octanol-air partition coefficient (logKP = mo logKOA + bo). Previous theory predicts that -mp and mo should be close to, or equal to 1 based on the assumption that gas- and particle-phases are at equilibrium in the atmosphere. Here, we develop analytical equations to calculate mo and bo as functions of logKOA and mp and bp as functions of logPL. We find that experimental, analytical, or statistical artifacts and other reported factors are not the leading causes for deviations of the slopes, mp and mo, from -1 and 1, respectively. Rather, it is the inherent parameter, KOA, that determines mo and bo, and equivalently, PL is the major parameter determining mp and bp, and such deviations are evidence that equilibrium is an inappropriate assumption. In contrast, the actual steady-state between gas and particle phases of SVOCs leads that their -mp and mo should range from 0 to 1, implying that equilibrium is a reasonable assumption only when -mp and mo are larger than 0.49. To illustrate these points, we provide a detailed discussion of the global atmospheric transport of polybrominated diphenyl ethers (PBDEs) with emphasis on Polar Regions where low air temperatures favor a special steady-state, where their slopes mp and mo can reach 0, indicating a constant value of logKP (-1.53).

Particle/gas partitioning for semi-volatile organic compounds (SVOCs) in Level III multimedia fugacity models: Gaseous emissions.

Atmospheric transport is a global-scale process that moves semi-volatile organic compounds (SVOCs) rapidly from source regions to remote locations, where these chemicals have never been produced or used. Particle/gas (P/G) partitioning of SVOCs during atmospheric transport governs wet and dry deposition, and thereby controls the efficiency and scope of long-range atmospheric transport and fate for these sorts of compounds. Previous work has shown that the assumption of steady state between particulate and gaseous phases in the atmosphere leads to model results that more closely match observations especially for compounds that strongly favor the particulate phase. Here, the practical application of steady-state P/G partitioning in the atmosphere in multimedia fugacity models is presented in greater detail. A method is developed whereby the fugacity of a chemical in the particle-phase is set equal to that in the gaseous phase (a pseudo equilibrium) but still maintains steady state of the chemical between air and aerosols in the atmosphere. This procedure greatly simplifies the application of multimedia fugacity models. Using this approach, a condition of steady state between air and aerosols is developed and applied in a Level III six-compartment six-fugacity model, which becomes a much simpler Level III six-compartment four-fugacity model. This newly-developed model is then applied to data observed during a monitoring program.

Particle/gas partitioning for semi-volatile organic compounds (SVOCs) in level III multimedia fugacity models: Both gaseous and particulate emissions.

Multimedia fugacity models have long been used to address the fate of toxic organic chemical emissions by providing a quantitative account of the sources, transport processes, and sinks. Recently, we have examined three level-III fugacity models (E4F (equilibrium six-compartment four-fugacity), S6F (steady-state six-compartment six-fugacity) and S4F (steady-state six-compartment four-fugacity) Models), in the context of their performance set against real-world data, and their practicality of application. Here, we discuss how the balance between gaseous and aerosol phases of emissions assumed for initial conditions affects the different model outcomes. Our results show that the S6F Model predictions closely match those of the S4F Model when chemical emissions are entirely in the gas-phase. As the particulate proportion of the emission increases, the S6F Model predictions diverge from those of the S4F Model and approach those of the E4F Model. Once the particulate portion reaches 100%, the S6F and E4F Models produce identical results: an internally inconsistent system where chemicals are not in a steady state between air and aerosols, and mass balance for both air and aerosols is not achieved. Thus, in terms of practicality, internal consistency, chemical mass balance and agreement with observations, the S4F Model is clearly the best choice.

Slopes and intercepts from log-log correlations of gas/particle quotient and octanol-air partition coefficient (vapor-pressure) for semi-volatile organic compounds: II. Theoretical predictions vs. monitoring.

The logarithm of gas/particle (G/P) partition quotient (logKP) has been found to have a linear relationship with logKOA (octanol-air partition coefficient) with slope mo and intercept bo and logPL (subcooled liquid vapor pressure) with slope mp and intercept bp. In the sister paper of the present work, analytical equations to predict the slope mo and intercept bo based on logKOA and predict the slope mp and intercept bp based on logPL are developed using steady state theory. In this work, the equations are evaluated using world-wide monitoring data (262 pairs for mo and bo values and 292 pairs for mp and bp values produced from more than 10,000 monitiring data worldwide) for selected seven groups of semi-volatile organic compounds (SVOCs), including polybrominated diphenyl ethers (PBDEs), polychlorinated dibenzo-p-dioxins and polychorinated dibenzofurans (PCDD/Fs), polyclorinated biphenyl (PCBs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated naphthalenes (PCNs), organochlorinated pesticides (OCPs), novel brominated flame retardants (NBFRs), and other selected halogenated flame retardants. The slopes and intercepts predicted by the steady state equations reproduce the trends observed in monitoring regression results for the seven SVOC groups, with 44.4% of the variation of monitoring mo values accounted for by logKOA and 48.2% of the variation of monitoring mp values accounted for by logPL. Theoretically, the values of mo can be any value between 0 and 1 dependent on the values of KOA, and are not constrained to 1 as in equilibrium theory. Likewise, the values of mp can be any value between 0 and -1 dependent on the values of PL, and not constrained to -1 predicted by the equilibrium theory. The influence of sampling artifacts on the G/P partitioning of SVOCs has most likely been overemphasized by the equilibrium theory. Thus, the equilibrium approach should be abandoned in favor of the steady state approach for calculating the G/P partition quotients for SVOCs with high KOA values (>1011.38) or low PL values (<10-4.92).

Coupling laser ablation and atomic fluorescence spectrophotometry: an example using mercury analysis of small sections of fish scales.

Mercury is a toxic element that exchanges among air, water, and sediments and biomagnifies into high trophic level organisms. Here, we present a novel combination of laser ablation with relatively low-cost cold vapor atomic fluorescence spectrophotometry to analyze Hg vaporized from targeted patches of fish scale 300-500 µm square. This method permits the analysis of multiple samples from the same scale, which is useful, because fish scale growth rings may provide an archive from which spatial and temporal trends in environmental Hg can be inferred at fine resolution. The detection limit of the method is 1.5 pg Hg, with a precision of 0.1 pg/µL. Developed using fish scales, the method could be adapted to other media, such as baleen, shells, nails, hair, teeth, wood and, possibly, varved sediments.

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.

Gas/particle partitioning of semi-volatile organic compounds in the atmosphere: Transition from unsteady to steady state.

We derive differential equations to determine the kinetics of gas/particle partitioning of semi-volatile organic compounds (SVOCs). These equations model the transient states from initiation of sorption to particles (non-steady state) through the establishment of steady state. Two hypothetical scenarios are examined: (1) exchange of SVOCs between gas- and particle-phases alone; and (2) both gas/particle partitioning and wet and dry deposition of particles. The differential equations show that, under Scenario 1, a steady state is reached as an equilibrium between gas- and particle-phases, whereas under Scenario 2, the attained steady state is not in equilibrium. Our model shows that SVOCs in atmosphere where particle deposition is occurring reach a steady non-equilibrium state sooner than they would reach equilibrium under Scenario 1. We infer that SVOCs in the atmosphere will reach steady state instead of equilibrium between gaseous and particulate phases in circumstances where wet and dry deposition of particles cannot be neglected. In addition, our study indicates that the time for SVOCs to reach steady state in the atmosphere is fast, most likely within minutes or hours, suggesting that SVOCs are in steady or quasi-steady state in the atmosphere. Our analysis also reveals that gas/particle partitioning and particle deposition of SVOCs are dependent on each other.

Polycyclic aromatic compounds (PACs) in the Canadian environment: A review of sampling techniques, strategies and instrumentation.

A wide variety of sampling techniques and strategies are needed to analyze polycyclic aromatic compounds (PACs) and interpret their distributions in various environmental media (i.e., air, water, snow, soils, sediments, peat and biological material). In this review, we provide a summary of commonly employed sampling methods and strategies, as well as a discussion of routine and innovative approaches used to quantify and characterize PACs in frequently targeted environmental samples, with specific examples and applications in Canadian investigations. The pros and cons of different analytical techniques, including gas chromatography - flame ionization detection (GC-FID), GC low-resolution mass spectrometry (GC-LRMS), high performance liquid chromatography (HPLC) with ultraviolet, fluorescence or MS detection, GC high-resolution MS (GC-HRMS) and compound-specific stable (δ13C, δ2H) and radiocarbon (Δ14C) isotope analysis are considered. Using as an example research carried out in Canada's Athabasca oil sands region (AOSR), where alkylated polycyclic aromatic hydrocarbons and sulfur-containing dibenzothiophenes are frequently targeted, the need to move beyond the standard list of sixteen EPA priority PAHs and for adoption of an AOSR bitumen PAC reference standard are highlighted.

New equation to predict size-resolved gas-particle partitioning quotients for polybrominated diphenyl ethers.

Gas/particle (G/P) partition quotients of semi-volatile organic compounds (SVOCs) for bulk air have been widely discussed in experimental and theoretical contexts, but research on size-resolved G/P partition quotients (KPi) are scarce and limited in scope. To investigate G/P partition behavior of polybrominated diphenyl ethers (PBDEs) for size-segregated particles in the atmosphere, 396 individual size-segregated particulate samples (36 batches × 11 size-ranges), and 108 pairs of concurrent gaseous and bulk particulate samples were collected in Harbin, China. A steady-state equation based on bulk particles is derived to determine G/P partition quotients of PBDEs for size-segregated particles, which depends on the organic matter contents of size-segregated particles (fOMi). This equation can well predict KPi with knowledge of bulk partition quotient (KPS), ambient temperature, and fOMi, the results of which match well with monitoring data in Harbin and other published data collected in Shanghai and Guangzhou of China and Thessaloniki of Greece, and remedies a defect of over-estimate KPi for high-brominated PBDEs by the previous equation. In particular, the new equation contributes to obtaining the PBDEs concentrations in all atmospheric phase from partial phase, then provides a credible path to evaluate healthy exposure dose from the airborne PBDEs, by co-utilization with exposure models.

Seabird-driven shifts in Arctic pond ecosystems.

Migratory animals such as seabirds, salmon and whales can transport large quantities of nutrients across ecosystem boundaries, greatly enriching recipient food webs. As many of these animals biomagnify contaminants, they can also focus pollutants at toxic levels. Seabirds arguably represent the most significant biovectors of nutrients and contaminants from the ocean to the land, given their sheer numbers and global distribution. However, long-term census data on seabirds are rare. Using palaeolimnological proxies, we show that a colony of Arctic seabirds has experienced climate-induced population increases in recent decades. We then document increasing concentrations of contaminants, including polychlorinated biphenyls and cadmium, in pond sediments that are linked to biotransport by seabirds. Our findings suggest that climate-related shifts in global seabird populations will have the unexpected consequence of restructuring coastal ecosystems.

Historical analysis of salmon-derived polychlorinated biphenyls (PCBs) in lake sediments.

Several recent studies have highlighted the importance of salmon as a means to deliver biomagnifying contaminants to nursery lakes. There is a lack of studies, however, which demonstrate empirically how this source has varied through time. This is of great significance because past salmon-derived contaminant loading was potentially greater than it is today. By analyzing radiometrically dated sediment cores collected from ten lakes in Alaska and British Columbia (B.C.), we relate historical numbers of sockeye salmon spawners to SigmaPCB concentrations and delta(15)N values (a paleolimnological proxy for past salmon-derived nitrogen) in the sediments. The results confirm that sockeye salmon have provided an important route for PCBs to enter the lakes in the past, a finding that is especially evident when the data of all lakes are pooled. Significant relationships between sockeye salmon numbers and delta(15)N, as well as SigmaPCB concentrations and delta(15)N in sediments, were also found. However, it is difficult to establish relationships between salmon numbers, SigmaPCBs and delta(15)N in individual lakes. This may be due to a number of factors which may influence contaminant loadings to the lakes. The factors include: a) changing salmon contaminant loads over time resulting from a lag in the upper ocean reservoir and/or changing salmon feeding locations; b) greater importance of atmospheric transport in lakes with relatively low salmon returns; and c) increased PCB scavenging due to higher algae productivity in the lakes in recent years.