Using Dragonflies as Contamination Detectors


Mercury pollution from power plants and mining operations can end up in our air and water. 

But it’s tricky to predict just how much of that environmental mercury will make its way into our food—and our bodies.

“We were working on developing a bioindicator, a biosentinel, that could inform us of the levels of mercury contamination across the U.S.”

Ecologist Collin Eagles-Smith of the United States Geological Survey. He and his colleagues came up with a practical way to determine the scope of mercury contamination in an ecosystem by measuring mercury levels in a single species. Their bioindicator: juvenile dragonflies, or larvae. Dragonfly larvae stay underwater, don’t move much, are easy to collect and live long enough to accumulate significant amounts of mercury.

“If you have enough locations sampled with dragonflies, you can develop an index of the relative amount of mercury in the biological community.”

The team measured mercury concentrations in thousands of dragonfly larvae collected from waterways in 100 national parks during a 10-year period. And to amass the large sample number, they recruited volunteers through the Dragonfly Mercury Project.

The volunteers used dip nets to collect dragonfly larvae from their aquatic abodes. National park staff then sent the larvae to laboratories for processing. For comparison, the researchers also measured mercury concentrations in other aquatic organisms.

“Using the relationships between dragonfly concentrations and fish concentrations, we were able to develop what we call an impairment index.”

That index allowed the researchers to make health risk predictions at each sample site.

“About 12 percent of the locations posed what we consider to be high or severe risk of health impairments to fish, wildlife or humans if they consumed organisms from those locations. You can begin to build models that are predictive of how much mercury might be in a system and then apply that model to locations where you haven’t sampled dragonflies.

“And that can inform future management actions either to address the factors that are promoting the mercury production or simply to inform agencies that may want to evaluate whether or not fish consumption advisories are warranted.”

The study is in the journal of Environmental Science & Technology. [Collin A. Eagles-Smith et al., A national-scale assessment of mercury bioaccumulation in United States national parks using dragonfly larvae as biosentinels through a citizen-science framework]

If you’d like to get involved in the Dragonfly Mercury Project or to see a map of mercury concentrations across the U.S., search for the Dragonfly Mercury Project at

—Berly McCoy

[The above text is a transcript of this podcast.]
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