Dragonflies show levels of mercury pollution in water bodies, scientists find

Researchers at Dartmouth College have found that the young form of a predatory dragonfly can be used to understand how much mercury is present in fish, amphibians, and birds, the school said.

This finding will facilitate research on mercury and could lead to the establishment of a national toxic metal contamination data register.

Dragonflies occupy a variety of freshwater habitats on six continents and have tissues that absorb mercury in its toxic form. As predators, dragonflies act in the food web similarly to fish, birds, and amphibians, which also accumulate mercury in body tissues.

The study includes data on thousands of specimens of larval dragonflies collected from nearly 500 locations at 100 sites in the US national park system. The survey was conducted from 2009 to 2018 within the framework of the national project “Dragonfly Mercury”.

Methylmercury, the organic form of toxic metallic mercury, is a hazard to humans and wildlife through fish consumption. Mercury pollution comes from power plants, mines, and other industrial facilities. It is transported in the atmosphere and then stored in its natural environment where wildlife can be exposed.

Fish and aquatic birds are commonly used to monitor mercury levels but are difficult to work with on a large scale project due to their size, migration patterns, and species diversity.

As part of a ten-year study, scientists presented the first-ever work on mercury pollution in the US national park system. The study found that about two-thirds of the water bodies studied in the national parks are polluted with moderate to extreme levels of mercury. Detection of mercury in a park is not an indication that the source of pollution is within the parks themselves. Mercury is widespread in the atmosphere and is deposited in protected areas as in other bodies of water throughout the country.