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The historical annual loading to, removal from, and cumulative burden in the Arctic Ocean for β-hexachlorocyclohexane (β-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%). β-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 β-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, β-HCH reached the Arctic mainly through long-range oceanic transport (LROT). The much higher tendency of β-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 β-HCH favoring slow transport in water and α-HCH favoring rapid transport in air. The concentration and burden of β-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.

Brominated flame retardants (BFRs) such as tetrabromobisphenol A (TBBPA) and hexabromocyclododecanes (HBCDs) are of ecological concern due to their ubiquitous presence and adverse effects. There is a paucity of data on environmental fate of such compounds in mangrove wetlands, which are unique ecosystems in coastal intertidal areas and act as natural sinks for many pollutants. In this study, mangrove plants and sediments were collected from an urban nature reserve in South China to investigate bioaccumulation and translocation of TBBPA and HBCDs. The mean (range) concentrations of TBBPA and ΣHBCD in roots, stems and leaves were 67 (

Methylmercury (MeHg) biomagnifies through aquatic food webs resulting in elevated concentrations in fish globally. Stable carbon and nitrogen isotopes are frequently used to determine dietary sources of MeHg and to model its biomagnification. However, given the strong links between MeHg and sulfur cycling, we investigated whether sulfur isotopes (δ34S) would improve our understanding of MeHg concentrations ([MeHg]) in Arctic lacustrine food webs. Delta34S values and total mercury (THg) or MeHg were measured in water, sediments, and biota from six lakes near Resolute Bay, NU, Canada. In two lakes impacted by historical eutrophication, aqueous sulfate δ34S was ∼8‰ more positive than sedimentary δ34S, suggestive of bacterial sulfate reduction in the sediment. In addition, aqueous δ34S showed a significant positive relationship with aqueous [MeHg] across lakes. Within taxa across lakes, [THg] in Arctic char muscle and [MeHg] in their main prey, chironomids, were positively related to their δ34S values across lakes, but inconsistent relationships were found across entire food webs among lakes. Across lakes, nitrogen isotopes were better predictors of biotic [THg] and [MeHg] than δ34S within this dataset. Our results suggest some linkages between Hg and S biogeochemistry in high Arctic lakes, which is an important consideration given anticipated climate-mediated changes in nutrient cycling.

Polycyclic aromatic hydrocarbons (PAHs) are large class of hydrophobic, semi-volatile organic contaminants that may enter the environment from both natural sources and anthropogenic activities. Pyrogenic PAHs arise from the incomplete combustion of fossil fuels and organic matter and following dispersal via long-range transport and may subsequently deposit in surface waters, soils and sediments of remote regions, including the Arctic. The current review summarizes and discusses Arctic data that is available for combustion-derived PAHs between 2004 and early 2018, focusing largely on data collected from remote, unexploited Arctic regions and from studies that provide some evidence of a pyrogenic origin. The increasing use of attribution ratios, which aid in discriminating PAHs from petrogenic or pyrogenic sources, suggest PAHs found in Arctic marine waters and sediment predominantly originate from natural underwater seeps, while those measured in air, freshwater, and terrestrial environments are likely to have originated from atmospheric and combustion-derived sources. Modeling efforts indicate that atmospheric PAHs in the Canadian and Norwegian Arctic are likely to have originated in the northern hemisphere – predominantly from Western Russia, northern Europe, and North America. East Asia appears to be a minor source of PAHs to the Arctic, despite contributing more than 50% of global PAH emissions. In comparison to the growing data for atmospheric PAHs, environmental data for these compounds in terrestrial and freshwater environments remain scarce. PAHs have been detected in Arctic biota from terrestrial, freshwater and marine environments, indicating exposure, however, levels are generally low, as most organisms efficiently metabolize parent PAHs. Globally, PAH emissions are expected to decline in the future, however models suggest the Arctic may not experience the same magnitude of decline projected for other world regions. Furthermore, future changes in climate may contribute to a re-volatilization of environmental PAHs, providing a source of secondary emissions to the Arctic atmosphere, emphasizing the importance of future monitoring for understanding the sources, fate and impacts of PAHs in the Arctic. Keywords: Contaminants, Air, Biota, Pyrogenic, Petrogenic, Review

Hexachlorobutadiene (HCBD) is a halogenated hydrocarbon that is primarily produced as an unintentional byproduct in the manufacture of chlorinated solvents. Similarities between HCBD and other persistent organic pollutants (POPs) led to its listing in 2015 for global regulation under the Stockholm Convention on POPs. HCBD's toxicity and propensity for long-range transport means there is special concern for its potential impacts on Arctic ecosystems. The present review comprehensively summarizes all available information of the occurrence of HCBD in the Arctic environment, including its atmospheric, terrestrial, freshwater and marine ecosystems and biota. Overall, reports of HCBD in Arctic environmental media are scarce. HCBD has been measured in Arctic air collected from monitoring stations in Finland and Canada, yet there is a dearth of data for other abiotic matrices (i.e. soils, sediments, glacier ice, freshwaters and seawater). Low HCBD concentrations have been measured in Arctic terrestrial and marine biota, which is consistent with laboratory studies that indicate that HCBD has the potential to bioaccumulate, but not to biomagnify. Available data for Arctic biota suggest that terrestrial birds and mammals and seabirds, have comparatively higher HCBD concentrations than fish and marine mammals, warranting additional research. Although spatial and temporal trends in HCBD concentrations in the Arctic are currently limited, future monitoring of HCBD in the Arctic will be important for assessing the impact of global regulations newly-imposed by the Stockholm Convention on POPs. Keywords: POPs, Air, Biota, Contaminants, Long-range transport, Review

Global regulations and many regional and national controls restrict the use of substances that exhibit the potential for environmental persistence and long-range transport. Nevertheless, many current-use pesticides (CUPs) continue to be newly discovered in remote regions, including the Arctic. The present review serves as an update, summarizing newly available information for CUPs in the Arctic environment and biota published from 2010 to 2018. Since 2010, at least seven new CUPs have been measured in Arctic media: 2-methyl-4- chlorophenoxyacetic acid (MCPA), metribuzin, pendimethalin, phosalone, quizalofop-ethyl, tefluthrin and triallate. Considering the large number of pesticides in current use, the number measured in the Arctic is very limited, however, modelling studies have identified additional CUPs as potential Arctic contaminants that have yet to be investigated in the Arctic. Owing to their recent detection, reports of CUPs in the Arctic are limited, but growing. CUPs have been reported in a wide range of abiotic Arctic matrices, including air, snow, ice, freshwater and seawater, indicating their capacity for long-range atmospheric transport, however, concentrations are generally low in comparison to legacy pesticides and other persistent organic pollutants (POPs). Recent food-web studies indicate CUPs can enter Arctic terrestrial and marine food chains, however, in contrast to POPs, the highest concentrations of many CUPs were found in lower trophic-level organisms, and the lowest concentrations detected in animals at the highest trophic levels (i.e, ringed seals, polar bear, caribou, and wolves) indicating significant trophic dilution. The detection of CUPs in the remote Arctic ecosystem reinforces the need for continued monitoring of both known and potential Arctic pollutants to prevent impacts on human and environmental health as the global arsenal of pesticides used in agriculture continuously changes. Keywords: POPs, Contaminants, Air, Biota, Long-range transport, Persistence

Indigenous peoples living in Canada’s north have long-valued the livers of Burbot (Lota lota) as a traditional food source; however, there has been concern relating to liver quality and potential contaminants. In this study, livers of Burbot collected in lower Mackenzie River were ranked using a traditional appearance-based assessment. These rankings were compared to a variety of biological and contaminant metrics. Livers ranked “most palatable” had a significantly higher mass and lipid content and were from younger fish with greater hepatosomatic index and total mass and had lower parasite intensities. There were no differences in the concentrations of persistent organic pollutants or metals, except copper, which although still well below consumption guidelines, was significantly higher in fish with livers that appeared most palatable. The results of this study demonstrated that traditional methods effectively assessed the quality of livers by selecting for the most nutritious (high lipid levels) and safest (low parasite loading) food. This method could be incorporated into a community-based monitoring framework as a rough index of overall fish and ecosystem health; however, would not be effective in screening food for anthropogenic contaminants. This study highlights the importance and value of linking traditional knowledge into scientific studies.

Since 2001, twenty-eight halogenated groups of persistent organic pollutants (POPs) have been banned or restricted by the Stockholm Convention. Identifying new POPs among the hundreds of thousands of anthropogenic chemicals is a major challenge that is increasingly being met by state-of-the-art mass spectrometry (MS). The first step to identification of a contaminant molecule (M) is the determination of the type and number of its constituent elements, viz. its elemental composition, from mass-to-charge (m/z) measurements and ratios of isotopic peaks (M + 1, M + 2 etc.). Not every combination of elements is possible. Boundaries exist in compositional space that divides feasible and improbable compositions as well as different chemical classes. This study explores the compositional space boundaries of persistent and bioaccumulative organics. A set of ~305,134 compounds (PubChem) was used to visualize the compositional space occupied by F, Cl, and Br compounds, as defined by m/z and isotope ratios. Persistent bioaccumulative organics, identified by in silico screening of 22,049 commercial chemicals, reside in more constrained regions characterized by a higher degree of halogenation. In contrast, boundaries surrounding non-halogenated chemicals could not be defined. Finally, a script tool (R code) was developed to select potential POPs from high resolution MS data. When applied to household dust (SRM 2585), this approach resulted in the discovery of previously unknown chlorofluoro flame retardants. Keywords: Persistent organic pollutants, Nontargeted screening, Environmental mass spectrometry, Flame retardants, Chemical space

Fourteen perfluoroalkyl substances (PFASs) including short-chain perfluorocarboxylates (PFCAs, C4–C6) and perfluoroalkane sulfonates (PFSAs, C4 and C6) were measured in surface sediment samples from 26 stations collected in 2008 and sediment core samples from three stations (Niagara, Mississauga, and Rochester basins) collected in 2006 in Lake Ontario. Perfluorooctanesulfonate (PFOS), perfluorooctanoate (PFOA), perfluorononanoate (PFNA), perfluorodecanoate (PFDA), and perfluoroundecanoate (PFUnDA) were detected in all 26 surface sediment samples, whereas perfluorohexane sulfonate (PFHxS), perfluorooctane sulfonamide (FOSA), perfluorododecanoate (PFDoDA) and perfluorobutanoate (PFBA) were detected in over 70% of the surface sediment samples. PFOS was detected in all of the sediment core samples (range: 0.492–30.1 ng g−1 d.w.) over the period 1952–2005. The C8 to C11 PFCAs, FOSA, and PFBA increased in early 1970s. An overall increasing trend in sediment PFAS concentrations/fluxes from older to more recently deposited sediments was evident in the three sediment cores. The known PFCAs and PFSAs accounted for 2–44% of the anionic fraction of the extractable organic fluorine in surface sediment, suggesting that a large proportion of fluorine in this fraction remained unknown. Sediment core samples collected from Niagara basin showed an increase in unidentified organic fluorine in recent years (1995–2006). These results suggest that the use and manufacture of fluorinated organic compounds other than known PFCAs and PFSAs has diversified and increased. Keywords: Sediment, Core, Flux, PFAS, PFOS, Unidentified fluorine

Brominated flame retardants were determined in adipose tissues from 294 polar bears (Ursus maritimus) sampled in East Greenland in 23 of the 28 years between 1983 and 2010. Significant linear increases were found for sum polybrominated diphenyl ether (ΣPBDE), BDE100, BDE153, and hexabromocyclododecane (HBCD). Average increases of 5.0% per year (range: 2.9–7.6%/year) were found for the subadult polar bears. BDE47 and BDE99 concentrations did not show a significant linear trend over time, but rather a significant non-linear trend peaking between 2000 and 2004. The average ΣPBDE concentrations increased 2.3 fold from 25.0 ng/g lw (95% C.I.: 15.3–34.7 ng/g lw) in 1983–1986 to 58.5 ng/g lw (95% C.I.: 43.6–73.4 ng/g lw) in 2006–2010. Similar but fewer statistically significant trends were found for adult females and adult males likely due to smaller sample size and years. Analyses of δ15N and δ13C stable isotopes in hair revealed no clear linear temporal trends in trophic level or carbon source, respectively, and non-linear trends differed among sex and age groups. These increasing concentrations of organobromine contaminants contribute to complex organohalogen mixture, already causing health effects to the East Greenland polar bears. Keywords: Polar bear (Ursus maritimus), Brominated flame retardants, HBCD, PBDE, Temporal trends

Polybrominated diphenyl ethers (PBDEs) and the organochlorine compounds polychlorinated biphenyls (PCBs), DDTs, HCB, chlordane-related pesticides, HCH and toxaphene were analysed in blubber of juvenile ringed seals from Central West Greenland collected between 1982 and 2006. The longest time series could be established for PBDEs, partly based on archived material, while PCBs and DDTs covered a study period from 1994–2006. All organochlorines showed decreasing trends, most pronounced for DDT and HCH with an annual change of 8%. BDE-47 had a significantly increasing trend of 5% annually. It was the only BDE congener consistently above the detection limit, with annual median concentrations between 0.78 ng/g lw to 3.54 ng/g lw, i.e. about 10 times lower than values from East Greenland observed in a similar time trend study on ringed seal blubber [Rigét F, Vorkamp K, Dietz R, Rastogi SC. Temporal trend studies on polybrominated diphenyl ethers (PBDEs) and polychlorinated biphenyls (PCBs) in ringed seals from East Greenland. J Environ Monit 2006; 8: 1000–5]. A clear East>West difference was also found for PCBs and DDTs, but not for chlordanes, toxaphene or HCHs. Σ10-PCB, ΣDDT and ΣChlordanes had similar annual median concentrations, typically exceeding ΣPBDE by two orders of magnitude. The concentrations of HCH and toxaphene were in an intermediate group, with highest annual median concentrations of 135 ng/g lw and 20 ng/g lw, respectively. For most compound groups, the circumpolar trend previously established under for example the Arctic Monitoring and Assessment Programme was confirmed, but apparently, more data are needed for chlordane-related compounds and toxaphene. Statistical analyses of the compound patterns in the ringed seal samples revealed significantly greater differences between seals from East and West than between different sampling years. Higher proportions of PCBs and DDTs and lower proportions of chlordanes and HCHs were found in seals from East Greenland than in those from West Greenland. Based on principal component analysis of individual congener and compounds, seals from East Greenland were found to contain higher proportions of the higher chlorinated CB congeners. Varying patterns between sampling locations may be caused by different exposure situations related to contaminant emissions and transport, but different feeding habits may also affect the contaminant composition. Keywords: Arctic, Compound patterns, Hexachlorobenzene (HCB), Hexachlorocyclohexane (HCH), Organochlorine pesticides, Polybrominated diphenyl ethers (PBDEs), Polychlorinated biphenyls (PCBs), Geographical trend, Time trend, Toxaphene

Measured environmental variables from 56 lakes across the Central Canadian Treeline Region exhibited clear limnological differences among subpolar ecozones, reflecting strong latitudinal changes in biome characteristics (e.g. vegetation, permafrost, climate). Principal Components Analysis (PCA) clearly separated forested sites from tundra sites based on distinct differences in limnological characteristics. Increases in major ions and related variables (e.g. dissolved inorganic carbon, DIC) were higher in boreal forest sites in comparison to arctic tundra sites. The higher values recorded in the boreal forest lakes may be indirectly related to differences in climatic factors in these zones, such as the degree of permafrost development, higher precipitation and runoff, duration of ice-cover on the lakes, and thicker and better soil development. Similar to trends observed in DIC, substantially higher values for dissolved organic carbon (DOC) were measured in boreal forest lakes than in arctic tundra lakes. This was likely due to higher amounts of catchment-derived DOC entering the lakes from coniferous leaf litter sources. Relative to arctic tundra lakes, boreal forest lakes had higher nutrient concentrations, particularly total nitrogen (TN), likely due to warmer conditions, a longer growing season, and higher precipitation, which would enhance nutrient cycling and primary productivity. Results suggest that modern aquatic environments at opposite sides of the central Canadian arctic treeline (i.e. boreal forest and arctic tundra) exhibit distinct differences in water chemistry and physical conditions. These limnological trends may provide important information on possible future changes with additional warming.