Decade-long study uses dragonfly larvae to measure mercury pollution levels in US national parks

According to a recent study published in the journal Environmental Science & Technology, a citizen science program that was started more than 10 years ago has helped researchers determine mercury pollution levels in the U.S. National Park System.

The Dragonfly Mercury Project

Dr. Sarah Nelson from the University of Maine and the Schoodic Institute first launched the original Dragonfly Mercury Project back in 2007.

Following the initial project, Dartmouth’s Toxic Metals Superfund Research Program developed a regional effort in New Hampshire and Vermont in 2010. Eventually, the National Park Service and the U.S. Geological Survey (USGS) expanded the project nationally.

The citizen science project in the Upper Valley region of New England usually takes place during fall, with high school students in New Hampshire and Vermont taking part.

The study was conducted by researchers from the Appalachian Mountain Club, Dartmouth College, the National Park Service, the University of Maine and the USGS.

Collin Eagles-Smith, from the USGS, was the paper’s lead author. Nelson, who launched the original project, is now the director of research at the Appalachian Mountain Club.

The researchers analyzed data from thousands of larval dragonfly specimens collected from at least 500 locations throughout 100 sites within the U.S. National Park System. The survey of mercury pollution was collected from 2009 to 2018 for the national Dragonfly Mercury Project.

Students and park visitors who participated in the citizen science project helped organize field studies and collect the dragonfly specimens. In addition, National Park rangers helped guide the citizen scientists as they worked in the protected sites.

“Biosentinels”

According to the national research effort that initially started as a regional project to collect dragonfly larvae, the young form of the insect can serve as a “biosentinel” to measure the amount of mercury present in birds, amphibians and fish.

Mercury levels in dragonfly larvae can then be analyzed so researchers can conduct mercury research. The findings can then be gathered to develop a national registry of pollution data on toxic mercury.

Celia Chen, a co-author of the study and director of Dartmouth’s Toxic Metals Superfund Research Program, explained that scientists are unable to run tests on fish because both animals and humans consume them.

Additionally, fish can be difficult to work with for a national-level research program. Substituting dragonfly larvae allowed the scientists to focus on subjects that don’t significantly affect the food chain.

Dragonflies thrive in diverse freshwater habitats throughout six continents. These insects have tissues that take up mercury in its toxic form.

As predators, dragonflies operate in the food web like birds, fish and amphibians that also amass the toxic metal in their body tissues.

Why you should be worried about methylmercury

Methylmercury is the organic form of mercury, a toxic metal. Methylmercury endangers humans and wildlife who both consume fish.

Mercury pollution can be traced back to power plants, mining and other industrial sites. The toxic metal can be dispersed via the atmosphere or deposited in the natural environment, harming wildlife exposed to it.

Elemental and methylmercury are harmful to the human central and peripheral nervous systems. Inhaling mercury vapor can damage the digestive, immune and nervous systems, along with the lungs and kidneys. It can also be fatal.

The inorganic salts of mercury will corrode the eyes, skin and gastrointestinal tract upon contact. If accidentally ingested, it may induce kidney toxicity.

Inhalation, ingestion or dermal exposure of different mercury compounds may result in behavioral and neurological disorders. Symptoms can include headaches, insomnia, memory loss, neuromuscular effects, tremors and cognitive and motor dysfunction.

Workers exposed to an elemental mercury level in the air of 20 micrograms per cubic meter of air (mcg/m3) or more may experience mild, subclinical signs of central nervous system toxicity. The effects can last for several years. Workers exposed to mercury have also reported kidney damage such as increased protein in the urine and kidney failure.

Dragonfly larvae and mercury pollution

Researchers often observe fish and aquatic birds to monitor mercury levels. However, these animals are difficult to work with during a large-scale project because of their size, migratory patterns and the diversity of species.

On the other hand, dragonfly larvae are easy to collect. This helped ensure the success of the citizen science research project. (Related: Mercury exposure in the oceans is getting worse, causing mercury levels in seafood to rise.)

Kate Buckman, a research scientist and Dartmouth’s coordinator for the citizen science program, commented that it was very rewarding “to assist teachers and their students to engage in data-driven, real-world research impacting their communities.” Buckman was pleased to observe the enthusiasm of students who wanted to take part in real science first-hand.

For the 10-year study, the scientists devised the first survey of mercury pollution in the U.S. National Park System.

Results showed that at least two-thirds of the aquatic sites studied all over the national parks are polluted with moderate to extreme levels of mercury.

The researchers noted that the finding of mercury within park sites does not suggest that the root of the pollution is in the parks. Most of the time, mercury spreads within the atmosphere. The toxic metal is then deposited in the protected areas and different water bodies throughout America.

Since the parks included in the study were found all over the country, such as in Alaska and Hawaii, the findings indicate mercury pollution levels all over the U.S.

Chen said that the Dartmouth study is the first to conduct a broad-scale survey on mercury in the country. And by using the national dragonfly data, researchers were able to study a huge area with different systems.

Chen posited that further study can help develop “a national baseline of mercury pollution information.”

Findings also revealed that rivers, streams and other faster-moving bodies of water had higher levels of mercury pollution compared to slower-moving systems like lakes, ponds and wetlands.

Chen noted that the research team owes a lot to the citizen scientists all over America who helped conduct this important study. She added that this proves how “public outreach around science can bring results that help the entire country.”

To learn more about mercury and how to avoid this toxic metal, visit MercuryScience.com.

Sources include:

ScienceDaily.com

WHO.int