How a single grizzly bear hair gave researchers a detailed account of exposure to toxic metals

Mammals can be quite hairy. In fact, hair is a unique feature of mammals. Although hair is primarily covering our heads and bodies for physiological and evolutionary reasons, it is also a treasure chest of useful dietary and health information. Why is hair such a great data source? Hair is composed of keratin, a sulfur-rich protein that in the root portion readily binds to elements and metals that are flowing through a mammal’s blood. As the hair grows, it records the changes in those elements becoming a detailed account of that mammal’s life. 

Five Bears

In 2014 and 2015, in a study funded by Stantec Consulting, lead researcher Dr. Jennie Christensen (TrichAnalytics Inc.) and post-doc student Dr. Marie Noel studied hair from five captive grizzly bears from Washington State University. These bears underwent a feeding trial where each bear consumed different amounts of cutthroat trout over a 33-day period. The trout had relatively high concentrations of copper, zinc and mercury compared to the vegetation and fruit they were also consuming. The objective of the study was to monitor changes in these elements in the hair in relation to amount of fish consumed.

As the feeding trial commenced, the concentrations of copper, zinc and mercury immediately began to increase in the bears' hair, at rates relative to the amount of fish in their diet. For example, the bear that consumed the most fish had steadily increasing metal concentrations, where copper and zinc increased approximately four-fold, and mercury increased by ten-fold. The rates of increase were lower for the bears that consumed less or no fish during the feeding trial.

Wild Cousins

The research team then developed a model using this information from captive bears to estimate metal exposure in wild bears - using a single bear hair. As studying bear feeding behavior can be fraught with challenges, this approach allowed the researchers to obtain expansive feeding and metal exposure information about individual bears without actually having to see a bear! Bears love to scratch their backs on rubbing trees, leaving behind plenty of samples making it a little less scary to collect them directly off a bear’s body. "Hey buddy. I don’t mean to bother you, but can I just pluck one of your hairs?" Hair from salmon-eating grizzly bears in British Columbia, Canada revealed how some bears were exposed to high concentrations of mercury (>5 ppm in hair) for extended periods of time during the salmon season. 

Global Ramifications for Increasing Mercury Emissions

Mercury is a neuro-toxic metal that is easily transferred to nursing cubs from their mothers through the milk, and elevated levels could have serious ramifications for their developing brains. As more coal burning power plants dot our earth, and subsequent mercury billows into our atmosphere and food webs, the health of our wildlife will continue to decline. 

What are the risks to other wildlife exposed to mercury? Do we fully understand the extent to which they are exposed? Using single hairs from wildlife these questions can begin to be answered.