Dragonfly larvae serve as biosentinels for mercury pollution

Mercury wreaks havoc in freshwater ecosystems, but monitoring the risk to wildlife can be challenging. Researchers have now shown how dragonfly larvae act as biosentinels for toxic mercury. When inorganic mercury enters the food chain, it gets converted to methylmercury, a toxin that causes neurological damage. Because inorganic mercury levels don’t always correlate with bioaccumulation of methylmercury, researchers have to sample living animals to understand poisoning risk in the environment.

“It’s very hard to find the same organism in water bodies across a broad landscape,” says Collin Eagles-Smith, an ecotoxicologist with the US Geological Survey. But dragonfly larvae—predators that accumulate mercury—are widely found in freshwater ecosystems across the continent.

With the help of more than 4,000 citizen scientists over 10 years, Eagles-Smith and his team collected dragonfly larvae from 100 national parks (Environ. Sci. Technol. 2020, DOI: 10.1021/acs.est.0c01255). They found that mercury levels detected in larvae correlated well with other organisms sampled at the same time and could be compared across sites. “That tells us we can use dragonfly [larvae] mercury concentrations to predict what’s in fish and other wildlife,” Eagles-Smith says.

The team also showed that biotic factors affect how much of the available inorganic mercury enters the food web. “The processes that generate methylmercury play a very important role in driving risk of exposure across the landscape,” he says. Eagles-Smith hopes this research will inform management techniques for mitigating mercury risk in sensitive habitats.