Spatiotemporal patterns of mercury accumulation in lake sediments of western North America.

For the Western North America Mercury Synthesis, we compiled mercury records from 165 dated sediment cores from 138 natural lakes across western North America. Lake sediments are accepted as faithful recorders of historical mercury accumulation rates, and regional and sub-regional temporal and spatial trends were analyzed with descriptive and inferential statistics. Mercury accumulation rates in sediments have increased, on average, four times (4×) from 1850 to 2000 and continue to increase by approximately 0.2µg/m(2) per year. Lakes with the greatest increases were influenced by the Flin Flon smelter, followed by lakes directly affected by mining and wastewater discharges. Of lakes not directly affected by point sources, there is a clear separation in mercury accumulation rates between lakes with no/little watershed development and lakes with extensive watershed development for agricultural and/or residential purposes. Lakes in the latter group exhibited a sharp increase in mercury accumulation rates with human settlement, stabilizing after 1950 at five times (5×) 1850 rates. Mercury accumulation rates in lakes with no/little watershed development were controlled primarily by relative watershed size prior to 1850, and since have exhibited modest increases (in absolute terms and compared to that described above) associated with (regional and global) industrialization. A sub-regional analysis highlighted that in the ecoregion Northwestern Forest Mountains, <1% of mercury deposited to watersheds is delivered to lakes. Research is warranted to understand whether mountainous watersheds act as permanent sinks for mercury or if export of "legacy" mercury (deposited in years past) will delay recovery when/if emissions reductions are achieved.

Systemic effects of arctic pollutants in beluga whales indicated by CYP1A1 expression.

Cytochrome P450 1A1 (CYP1A1) is induced by exposure to polycyclic aromatic hydrocarbons (PAHs) and planar halogenated aromatic hydrocarbons (PHAHs) such as non-ortho polychlorinated biphenyls (PCBs). In this study, we examined CYP1A1 protein expression immunohistochemically in multiple organs of beluga whales from two locations in the Arctic and from the St. Lawrence estuary. These beluga populations have some of the lowest (Arctic sites) and highest (St. Lawrence estuary) concentrations of PCBs in blubber of all cetaceans. Samples from these populations might be expected to have different contaminant-induced responses, reflecting their different exposure histories. The pattern and extent of CYP1A1 staining in whales from all three locations were similar to those seen in animal models in which CYP1A has been highly induced, indicating a high-level expression in these whales. CYP1A1 induction has been related to toxic effects of PHAHs or PAHs in some species. In St. Lawrence beluga, the high level of CYP1A1 expression coupled with high levels of contaminants (including CYP1A1 substrates, e.g., PAH procarcinogens potentially activated by CYP1A1) indicates that CYP1A1 could be involved in the development of neoplastic lesions seen in the St. Lawrence beluga population. The systemic high-level expression of CYP1A1 in Arctic beluga suggests that effects of PAHs or PHAHs may be expected in Arctic populations, as well. The high-level expression of CYP1A1 in the Arctic beluga suggests that this species is highly sensitive to CYP1A1 induction by aryl hydrocarbon receptor agonists.

Persistent organic pollutants and metals in the freshwater biota of the Canadian Subarctic and Arctic: an overview.

Over 1999-2002, an extensive series of contaminant studies was conducted on freshwater biota of Canada's Arctic and Subarctic regions. The majority of inorganic contaminant studies focused on mercury and fish. While mercury concentrations were low in benthic feeding fish such as whitefish, predatory fish such as lake trout, pike, and walleye frequently had mercury levels which exceeded 0.2 mug/g, the consumption guideline for frequent consumers of fish, and 0.5 microg/g, the guideline for the commercial use of fish. Numerous consumption advisories were issued for lakes along the Mackenzie River. Relatively high mercury levels appear to be due to a combination of relatively old fish populations (because of light fishing pressures) and tend to be more prevalent in smaller lakes where warmer summer water temperatures and watershed influences result in greater mercury and methyl mercury inputs. Mercury levels were substantially lower in char than in lake trout, possibly due to a combination of a less fish-rich diet, a colder environment, and smaller MeHg watershed inputs. Less research has been conducted on other metals but some, such as rubidium, show pronounced variations in concentration that may be related to geological influences. Temporal trend monitoring has revealed little evidence of declining mercury levels in fish that can be attributed to declining atmospheric inputs. Because mercury follows complex pathways in the environment, other factors may operate to counteract reductions in atmospheric mercury sources, e.g., climatic variability, changes in the commercial fishery, and interactions between fish species. Most organochlorine (OC) investigations were based on long term trend monitoring and focused on char (Cornwallis Island), burbot (Great Slave Lake, Yukon lakes, Slave River at Fort Smith, Mackenzie River at Fort Good Hope) and lake trout (Yukon lakes, Great Slave Lake). There was strong evidence of declining OC concentrations in char, particularly SigmaHCH and Sigmachlordane, which may reflect a response to declining atmospheric inputs. Endosulfan concentrations increased, as in the atmosphere. There also was evidence of declining OC concentrations in burbot in the Slave and Mackenzie rivers but not in Great Slave Lake and Yukon lakes. OC concentrations decreased in lake trout in Yukon lakes in the 2000s, most probably because of changes in the fish themselves (i.e., reduced lipid content, condition factor) and possibly climatic variability. Similarly, OCs declined in Great Slave Lake trout. New research on PDBEs and perfluorinated compounds determined that these contaminants are widespread in freshwater fish and concentrations may be increasing. Global warming is a major issue of concern for Arctic and Subarctic waters and may have adverse impacts on contaminant levels in fish and other biota. There is a need for contaminant studies in the north to be broadened to investigate climatic effects. In addition, monitoring studies should be broadened to consider factors affecting other aspects of fish biology. Foremost among these is integrating contaminant monitoring studies on lakes such as Lake Laberge and Great Slave Lake with stock assessment studies. Ecosystem based studies should be conducted on Great Slave Lake and Lake Laberge to more effectively understand contaminant trends and should consider inputs (atmospheric, river inflow, resupension), losses (sedimentation, volatilization), and biological pathways.

Dietary accumulation and biochemical responses of juvenile rainbow trout (Oncorhynchus mykiss) to 3,3',4,4',5-pentachlorobiphenyl (PCB 126).

Juvenile rainbow trout (Oncorhynchus mykiss) (initial weights 2-5 g) were exposed to three dietary concentrations (0, 12.4 and 126 ng g(-1), wet weight) of a 14C-labelled 3,3',4,4',5-pentachlorobiphenyl (PCB 126) for 30 days followed by 160 days of clean food. We assessed bioaccumulation, histology (liver and thyroid) and biochemical responses (liver ethoxyresorufin-O-deethylase (EROD), liver vitamins (retinoids and tocopherol) and muscle thyroid hormone levels) along with growth and survival. The half-life of PCB 126 in the rainbow trout ranged from 82 to 180 days while biomagnification factors (BMF) ranged from 2.5 to 4.1 providing further evidence that PCB 126 is among the most bioaccumulative PCB congeners. Toluene extractable 14C declined with time in the trout suggesting the possibility of some biotransformation and/or covalent bonding with biological macromolecules. The threshold for liver EROD induction by PCB 126 was approximately 0.1 ng g(-1) (wet weight). EROD activities in the low- and high treatments were 9 and 44 times greater than control, respectively, and remained elevated throughout the experiment. EROD activity was correlated with whole body concentrations of PCB 126 although there was evidence of EROD activity suppression in the highly exposed fish. Liver didehydroretinoids and tocopherol concentrations were depressed by the high PCB 126 dose after 30 days exposure. Initially, muscle concentrations of thyroxine (T4) and triiodo-L-thyronine (T3) declined as the fish grew during the experiment, and exposure to PCB 126 accelerated the growth related decline. More information is needed to assess the functional significance of the reduced muscular stores of thyroid hormones. Despite the changes in liver EROD, liver vitamins and muscle thyroid hormones, liver and thyroid histology in trout examined after 30 days exposure and growth parameters were unaffected by PCB 126. This indicates that the functional competences of the physiological factors associated with growth were maintained under the experimental conditions.