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Mercury associated with changes in brain chemistry of beluga Sonja K. Ostertag and Hing Man Chan

1. Mercury in the marine environment has increased because of human activities. There are concerns about the potential effects of methylmercury exposure in Arctic beluga whales.

2. We studied the brains of belugas to see if the brain chemistry was different in whales that had lower or higher concentrations of mercury (methylmercury, total mercury, and inorganic mercury).

3. Enzyme activity and cell receptor density were related to mercury concentration in the temporal cortex, the area of the brain associated with hearing. These measures were not related to mercury concentration in the cerebellum, the area of the brain involved in muscle movement and coordination. When bound to selenium, a micronutrient found in the beluga diet, the toxicity of mercury in the brain may be reduced.

4. Mercury may have subtle effects on the brains of beluga whales but the effect on beluga health and brain function requires further study. Changes in brain chemistry associated with exposure to mercury may indicate an adaptation to mercury in the brain that occurs before disease manifests.

Mercury is transported to the Arctic from southern latitudes where it is transformed to methylmercury in the marine and aquatic ecosystems and biomagnifies (i.e., increases in concentration) from sea water to top predators.

Mercury levels in Arctic wildlife have increased by an order of magnitude from their pre-industrial levels. Methylmercury is known to be neurotoxic but its impact on Arctic organisms is poorly understood.

There are concerns about the potential effects of methylmercury exposure in beluga whales, a top predator in the Arctic. Our earlier research found that concentrations of total mercury measured in the brains of Eastern Beaufort Sea beluga reached levels that could be toxic for belugas.

We found evidence that most of the mercury in beluga brain tissue was in a non-toxic form bound with selenium.

We worked with harvesters at Hendrickson Island, a traditional beluga harvesting location in the Inuvialuit Settlement Region, to collect brain tissue from 35 harvested belugas in 2008 and 2010.

The results from our research indicated that cell receptor binding and enzyme activity in beluga brain samples were associated with concentrations of methylmercury and selenium. In addition, the levels of messenger RNA involved in producing proteins for two signaling pathways in the brain were related to inorganic mercury and selenium concentrations.

Our results suggest that selenium is not fully protecting beluga from methylmercury exposure. Even though most mercury in beluga brains is bound to selenium and inactive, we still detected changes in brain chemistry related to mercury levels.

The changes to cell receptors and enzymes associated with methylmercury in belugas may be an indicator of early-stage effects before the manifestation of disease.

This study does not provide information about the effect of methylmercury exposure for the health of individual belugas or for the Eastern Beaufort Sea beluga population.

Read the full article in Arctic Science: Biomarkers of the cholinergic and dopaminergic signaling pathways in Arctic beluga whales (Delphinapterus leucas): relationship to methylmercury and selenium

Corresponding author: Sonja Ostertag, sonja.ostertag@dfo-mpo.gc.ca

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