Persistent Organic Pollutants and Heavy Metals (Including Mercury) - The Changing Arctic Environment: The Arctic Messenger - page 160

quences were being detected in communities of indigenous peoples who lived and fished
on the Wabigoon and English river systems, including Grassy Narrows. In 1970, direct dis-
posal was curtailed from the industrial plant, but emissions into the atmosphere continued
until 1975.
In the years since the tragedies of Minamata and the Ontario Wabigoon and English
rivers, toxicologists and health authorities have established toxicity threshold values for
mercury that enable the potential for health effects to be assessed. Laboratory and field
studies mainly on fish and fish-eating mammals are consistent with one another. Chronic
mercury exposure at levels much lower than those that characterized the Minamata and
Ontario incidents can result in a wide range of neurological outcomes in birds, fish and
mammals. This is because methylmercury is able to cross the blood-brain barrier. The
mechanism of disruption of neurological processes is thought to be partly related to the
high affinity of methylmercury to protein thiols and the activity of N-Methyl-D-aspartic
acid (NMDA), an amino acid derivative concerned with many neurological functions. Oth-
er outcomes include kidney and liver lesions, endocrine dysfunction and reproductive ab-
normalities, but there is considerable variety in effects and susceptibility. In part, this is
related to how different species take up and excrete methylmercury. In land mammals and
polar bears, the kidney is the main storage organ, but in birds and marine mammals, it is
the liver. In addition to neurological effects, methylmercury is associated with abnormal
spawning behaviour in predatory freshwater fish.
The2011AMAPassessmentteamsummarizedtheavailabledatatoshowthatinsome
areas, organs and tissues of Arctic predators at the top of the food web are carrying levels
of mercury that exceed thresholds for biological effects. This includes polar bears, be-
luga whales, pilot whales, hooded seals, several seabird species (ivory gull, glaucous gull
and black guillemot), northern pike, lake trout and landlocked Arctic char. Arctic marine
fish rarely show levels exceeding thresholds, but this is not the case with polar bears and
toothedwhales.Forexample,the2001-2008dataset(mentionedearlier)ofhairtakenfrom
East Greenland polar bears exceeded the proposed neurochemical effect level of 5.4 μ g
Hg/g dry weight in 93.5% of the cases. Toothed whales appear to be especially vulnerable