Temporal and spatial variation in Hg accumulation in zebra mussels (Dreissena polymorpha): possible influences of DOC and diet.

Zebra mussels (Dreissena polymorpha) are filter feeders located near the base of the foodweb and these animals are able to utilize a variety of carbon sources that may also vary seasonally. We conducted both a spatial and a temporal study in order to test the hypotheses: (1) dissolved organic carbon (DOC) concentrations influence Hg accumulation in zebra mussels sampled from a series of lakes and (2) seasonal variations in diet influence Hg accumulation. In the spatial study, we found a significant negative relationship between Hg concentrations and DOC concentrations, suggesting an influence of DOC on Hg bioaccumulation.

Uranium bioaccumulation in a freshwater ecosystem: impact of feeding ecology.

The objectives of our study were: (1) to determine if there was significant uranium (U) bioaccumulation in a lake that had been historically affected by a U mine and (2) to use a combined approach of gut content examination and stable nitrogen and carbon isotope analysis to determine if U bioaccumulation in fish was linked to foodweb ecology. We collected three species of fish: smallmouth bass (Micropterus dolomieu), yellow perch (Perca flavescens) and bluegill (Lepomis macrochirus), in addition to several invertebrate species including freshwater bivalves (family: Sphaeriidae), dragonfly nymphs (order: Odonata), snails (class: Gastropoda) and zooplankton (family: Daphniidae). Results showed significant U bioaccumulation in the lake impacted by historical mining activities.

The impacts of ontogenetic dietary shifts in yellow perch (Perca flavescens) on Zn and Hg accumulation.

Yellow perch (Perca flavescens) undergo several ontogenetic dietary shifts, and consequently these fish feed at different trophic levels and rely on different carbon sources over their lifetime. Stable isotope ratios of nitrogen (δ(15)N) and carbon (δ(13)C) are powerful ecological tools that are used to provide a temporally integrated description of the feeding ecology of aquatic animals such as fish. The main objective of this study was to use stable isotopes of nitrogen and carbon to determine if dietary changes affected mercury (Hg) and zinc (Zn) accumulation in yellow perch ranging in size from approximately 5 cm to 27 cm.

The potential impact of climate on human exposure to contaminants in the Arctic.

Many northern indigenous populations are exposed to elevated concentrations of contaminants through traditional food and many of these contaminants come from regions exterior to the Arctic. Global contaminant pathways include the atmosphere, ocean currents, and river outflow, all of which are affected by climate. In addition to these pathways, precipitation, animal availability, UV radiation, cryosphere degradation and human industrial activities in the North are also affected by climate change.

Seasonal variations in hepatic Cd and Cu concentrations and in the sub-cellular distribution of these metals in juvenile yellow perch (Perca flavescens).

Temporal fluctuations in metal (Cd and Cu) concentrations were monitored over four months (May to August) in the liver of juvenile yellow perch (Perca flavescens) sampled from four lakes situated along a metal concentration gradient in northwestern Quebec: Lake Opasatica (reference lake, low metal concentrations), Lake Vaudray (moderate metal concentrations) and lakes Osisko and Dufault (high metal levels). The objectives of this study were to determine if hepatic metal concentrations and metal-handling strategies at the sub-cellular level varied seasonally. Our results showed that Cd and Cu concentrations varied most, in both absolute and relative values, in fish with the highest hepatic metal concentrations, whereas fish sampled from the reference lake did not show any significant variation.

A field study examining metal elimination kinetics in juvenile yellow perch (Perca flavescens).

Currently little is known about how and at what rate fish eliminate metals in natural environments. To address this knowledge gap we examined metal elimination kinetics in the field using juvenile yellow perch (Perca flavescens) that were caught in a metal-contaminated lake (elevated levels of Cd, Cu and Zn) and transplanted to cages held within a reference lake. Fish were sampled from the cages over 75 d and changes in metal concentrations were measured in the gills, gut, liver and kidney.

Dynamics of Cd, Cu and Zn accumulation in organs and sub-cellular fractions in field transplanted juvenile yellow perch (Perca flavescens).

Juvenile yellow perch (Perca flavescens) were caught in a reference lake and transplanted to cages held within a lake impacted by mining activities, with elevated levels of aqueous bioavailable copper (Cu(2+)), zinc (Zn(2+)) and cadmium (Cd(2+)). Fish were sampled from the cages over 70 d and changes in metal concentrations were followed over time in the gills, gut, liver and kidney. In addition, the hepatic sub-cellular partitioning of the three metals was determined by differential centrifugation of liver samples, yielding the following fractions: cellular debris; organelles; heat-denaturable proteins (HDP); and heat-stable proteins (HSP) (including metallothionein).