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To track the sources of mercury pollution across wildlands in the U.S., scientists have turned to an unlikely indictor: dragonfly larvae.
As mercury settles in water and soil, it is taken up by wildlife. Mercury becomes more concentrated as it moves up the food chain, as larger creatures, such as tuna, accumulate the toxin by consuming smaller creatures, such as sardines, en masse. Past studies have focused on the higher end of the food chain, measuring mercury in fish and birds, but the new research looks toward the bottom. Though nearer the source of mercury, dragonflies have the advantage of being found almost everywhere — in lakes, rivers, forests, wetlands, and deserts.
For the new study, scientists enlisted the help of the public in gathering samples of dragonfly larvae from 150 national parks. The mercury found in larvae bears a chemical signature indicating its origin, the study notes. An analysis of the dragonfly larvae revealed that in arid regions, mercury comes from snow and rain, while in wetter, more forested areas, airborne mercury clings to leaves, which then fall to the ground, where the toxin spreads. The findings were published in Environmental Science & Technology.
By one estimate, the amount of mercury in the atmosphere has grown sevenfold over the last 500 years, primarily from burning coal. Mercury has been linked to brain damage in children and heart disease in adults. By turning to dragonflies to track pollution, said lead author Sarah Janssen, scientists were “able to uncover surprising results that have the potential to change how mercury is monitored and managed at a global scale.”
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