Sediment methylation and demethylation rates were measured by short-term incubations of stable isotopes of inorganic and methylmercury in sediment cores. Methylmercury photodemethylation rates were performed, during which water samples were incubated in the field under different treatments. Some bottles were spiked with methylmercury or complexing agents and scavengers. Labile concentrations of methylmercury were measured in water and sediment using DGT (Diffusive Gradient in Thin Film) samplers. Characterization of the microbial community in sediment and quantification of targeted microbes potentially involved in MeHg cycling were performed using qRT-PCR approaches, cloning and library analyses combined with gel electrophoresis techniques. Methylmercury bioaccumulation at the base of the food web was examined by collecting filamentous benthic algae and chironomid larvae from nearshore and offshore areas in the study lakes.

A large suite of chlorinated, brominated and fluorinated organic contaminants as well as total mercury (Hg) were measured in livers of adult thick-billed murres and northern fulmars from several locations in the eastern Canadian Arctic during 2007-2008. Thick-billed murres were collected from five colonies (Coats Island, Digges Island, Akpatok Island, Prince Leopold Island, Minarets) and northern fulmars from two colonies (Prince Leopold Island, Minarets). Legacy organochlorines (e.g. PCBs, DDT, chlorobenzenes, chlordanes) and perfluorooctane sulfonate (PFOS) dominated the compositional profiles of the measured halogenated compounds in the livers of both species at all colonies. Among the murre colonies sampled, Prince Leopold Island birds generally had the highest mean concentrations of organochlorines. Mean PFOS concentrations were highest in both murre and fulmar livers at Prince Leopold Island. In contrast, the highest mean concentration of total polybrominated diphenyl ethers (PBDEs) among murre colonies was found at the Minarets and the lowest at Prince Leopold Island. Murres at the two high Arctic colonies of Prince Leopold Island and the Minarets had significantly higher Hg concentrations than at the three low Arctic colonies. Fulmars from Prince Leopold Island had significantly higher Hg levels than those from the Minarets. The reasons for inter-colony and inter-species differences in contaminant liver levels are probably variable and complex, and likely reflect differences in contaminant transport and exposure pathways, as well as differences among colonies in their diets and overwintering areas. To our knowledge, this is the first spatial assessment of PBDEs, PFCAs and PFOS in seabirds from the Canadian Arctic. These data have been published in two two manuscripts, in Environment International 66: 92-96, and in Environmental Research 134: 46-56.

Over three years (2012 to 2015), we are comparing MeHg bioaccumulation in three study areas that cover a latitudinal gradient in ecosystem types in the Canadian Arctic, specifically Kuujjuaraapik (sub-Arctic taiga), Iqaluit (tundra) and Resolute Bay (polar desert). In water bodies from each of these study areas, we will investigate two key aspects of MeHg bioaccumulation, specifically MeHg bioavailability to benthic food webs and organism growth rates. Using a cross-ecosystem comparison to test these hypotheses, we will conduct the following in lakes and ponds from each study area: - Characterize the watersheds of study sites (geomorphology and physiography) through satellite image classification and digital terrain analysis in order to examine watershed influences on measured lake physico-chemistry, particularly levels of organic carbon and Hg in sediment and water; - Estimate bioavailable MeHg in sediment pore water using a novel technique (Diffusive Gradient in Thin films, or DGT); - Measure MeHg concentrations in benthic food webs (algae, invertebrates and fish); and - Estimate short-term growth rates in invertebrates and fish using tissue DNA and RNA content. Project results will provide a conceptual model of climate-related environmental processes that affect the exposure of Arctic freshwater fish to MeHg. This information is critical to understand how climate change is affecting temporal and geographic trends of Hg bioaccumulation in Arctic fish monitored by the NCP. Mercury is a priority contaminant of the Northern Contaminants Program (NCP) due to its prevalence in the Arctic and high levels found in some traditional food species. The main objective of this project is to investigate climate-related environmental controls on methylmercury (MeHg) bioaccumulation in Arctic freshwater food webs. Recent evidence indicates that inorganic mercury (Hg) loadings to Arctic lakes decline with latitude; however, MeHg concentrations in benthic invertebrates and fish do not similarly decline along this gradient in Hg loading. These observations suggest that environmental factors may play an important role in ecosystem sensitivity to Hg bioaccumulation in the Canadian Arctic. We hypothesize that climate's dominant control on organic matter production affects two key aspects of MeHg bioaccumulation, specifically MeHg bioavailability to food webs and organism growth rates. In addition, a latitudinal water temperature gradient likely affects organism growth rates.