Dragonflies are used to measure mercury pollution in a citizen science program that began over a decade ago.

The national research effort, which grew from a regional project to collect dragonfly larvae, found that the young form of the insect predator can be used as a “biosentinel” to indicate the amount of mercury that is present in fish, amphibians and birds.

Methylmercury, the organic form of the toxic metal mercury, poses risks to humans and wildlife through the consumption of fish. Mercury pollution comes from power plants, mining and other industrial sites. It is transported in the atmosphere and then deposited in the natural environment, where wildlife can be exposed.

As part of the decade-long study, researchers came up with the first-ever survey of mercury pollution in the U.S. National Park System. The research found that about two-thirds of the aquatic sites studied within the national parks are polluted with moderate-to-extreme levels of mercury.

The finding of mercury within park sites is not an indicator that the source of pollution is in the parks themselves. Mercury is distributed widely within the atmosphere and is deposited in the protected areas as it is in other water bodies across the country.

The study also found that faster moving bodies of water, such as rivers and streams, featured more mercury pollution than slower moving systems including lakes, ponds, and wetlands.

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