Evaluating temporal patterns of metals concentrations in floodplain lakes of the Athabasca Delta (Canada) relative to pre-industrial baselines.

Sediment quality monitoring is widely used to quantify extent of river pollution, but requires knowledge of pre-disturbance conditions in the potentially altered landscape. This has long been identified as a critical aspect to develop for addressing concerns of river pollution in the Alberta Oil Sands Region. Here, we use analyses of sediment cores from eight floodplain lakes spanning a 67 river-km transect across the Athabasca Delta to define pre-1920 (pre-industrial) baseline concentrations for vanadium and five primary pollutants. We then evaluate if sediment metals concentrations have become enriched above baseline since onset of oil sands development and other industrial activities. Results demonstrate no enrichment of metals concentrations (except zinc at one lake) and absence of consistent temporal increases above pre-industrial baselines. Thus, natural processes continue to dominate metal deposition in floodplain lakes of the Athabasca Delta -- an important finding to inform stewardship decisions. The pre-1920 metals concentrations baselines offer a useful tool for ongoing sediment monitoring in aquatic ecosystems of the Athabasca Delta.

Mercury and metal(loid) deposition to remote Nova Scotia lakes from both local and distant sources.

Kejimkujik National Park, in Nova Scotia, Canada, is a sensitive region for metal(loid) contamination, such as mercury, in part due to long-range atmospheric deposition from global and regional industrial centers. The region is remote from industrial centres, but is downwind of major pollution sources in the Eastern United States and Canada, and historically had numerous gold mining sites. Due to a paucity of long-term atmospheric deposition monitoring in this region, little is known about the response of Kejimkujik lakes to multiple changing global, regional and local atmospheric Hg and metal(loid) sources. Here, we used multiple lake sediment cores to reconstruct anthropogenic depositional fluxes of metal(loid)s of concern for the last ~210years. Results showed that Kejimkujik lake sediments are highly enriched in lead (Pb), antimony (Sb) and tin (Sn), with post-industrial metal(loid) concentrations being >4-fold greater than natural baseline levels (prior to ~1800) and moderately enriched in silver (Ag), bismuth (Bi), cadmium (Cd), copper (Cu), mercury (Hg), rubidium (Rb), tellurium (Te), thallium (Tl), vanadium (V), tungsten (W) and zinc (Zn), with post-industrial metal(loid) concentrations being between 1.5 and 4-fold greater than natural baseline levels (prior to ~1800). Lake sediment core reconstructions of total atmospheric Hg deposition matched well with Hg wet deposition monitoring data from the overlapped period (1997-2010) being 9.1±2.7µg/m2/yr and 7.0±0.7µg/m2/yr respectively. Lakes closest to historic gold mining sites show spikes in Ag, Cd, Sb, Tl, Zn and W during mining periods (~1880 and 1950). Most of the enriched metal(loid)s (EF >1.5) (Ag, Bi, Cu, Hg, Pb, Sb, Sn, V and W) do not appear affected by redox and remobilisation issues. For the other enriched metal(loid)s (EF >1.5) (Cd, Tl, and Zn), remobilisation from upper sediments appears to be occurring within these acidic and DOC rich Kejimkujik lakes.

Drivers of Mercury Cycling in the Rapidly Changing Glacierized Watershed of the High Arctic's Largest Lake by Volume (Lake Hazen, Nunavut, Canada).

Across the Arctic, glaciers are melting and permafrost is thawing at unprecedented rates, releasing not only water to downstream aquatic systems, but also contaminants like mercury, archived in ice over centuries. Using concentrations from samples collected over 4 years and calibrated modeled hydrology, we calculated methylmercury (MeHg) and total mercury (THg) mass balances for Lake Hazen, the world's largest High Arctic lake by volume, for 2015 and 2016. Glacial rivers were the most important source of MeHg and THg to Lake Hazen, accounting for up to 53% and 94% of the inputs, respectively. However, due to the MeHg and THg being primarily particle-bound, Lake Hazen was an annual MeHg and THg sink. Exports of MeHg and THg out the Ruggles River outflow were consequently very low, but erosion and permafrost slumping downstream of the lake increased river MeHg and THg concentrations significantly before entering coastal waters in Chandler Fjord. Since 2001, glacial MeHg and THg inputs to Lake Hazen have increased by 0.01 and 0.400 kg yr-1, respectively, in step with dramatic increases in glacial melt. This study highlights the potential for increases in mercury inputs to arctic ecosystems downstream of glaciers despite recent reductions in global mercury emissions.

Genetic differences in estrogen-induced deoxyribonucleic acid synthesis in the rat pituitary: correlations with pituitary tumor susceptibility.

Anterior pituitary nuclei isolated from rats were used in an in vitro DNA synthesis assay. The rate of in vitro synthesis was increased by prior in vivo estrogen treatment in a time-dependent and dose-dependent manner, and the observed increase was similar in magnitude to that measured by [3H] thymidine incorporation in whole tissue. In vitro DNA synthesis was sensitive to N-ethylmaleimide but resistant to dideoxythymidine triphosphate. Rates of pituitary DNA synthesis were compared in the Fischer 344 (F344) rat, a strain highly susceptible to diethylstilbestrol-induced pituitary tumors, and in the Holtzman rat, a strain resistant to rapid tumor induction by diethylstilbestrol. After chronic treatment (8 weeks) with estrogen, elevated DNA synthesis (2- to 3-fold) was observed in F344 pituitaries but not in Holtzman pituitaries. After short term (2-4 days) treatment with estrogen, however, DNA synthesis increased 2-fold in both Holtzman and F344 pituitary nuclei. The elevated DNA synthesis declined in the Holtzman strain after 5 or 6 days of additional estrogen treatment, but elevated DNA synthesis persisted in the F344 strain. These results suggest that the genetic difference is due to the lack of a proliferation control mechanism in the F344 strain that functions in the Holtzman strain to shut off estrogen-stimulated cell proliferation.