Spiders as Mercury Contaminators

Are spiders a missing link as toxic mercury moves from water onto land?

Shannon Speir, TCU, Aquatic Ecology Lab, Biology. Freshwater ecology

Shannon Speir '14 balanced cross country track with mercury research in TCU's Aquatic Ecology Lab.

Spiders as Mercury Contaminators

Are spiders a missing link as toxic mercury moves from water onto land?

Between running cross-country and studying, Shannon Speir ’14 launched a research project on long-jawed orb weaver spiders as conduits of mercury between aquatic and land environments.

Mercury contamination “has the ability to negatively impact the lives of so many different people, and especially those who rely on aquatic organisms like fish for their main food sources,” said Speir, an undergraduate researcher in the Aquatic Ecology Lab, which is led by Ray Drenner, professor of biology and Matt Chumchal, associate professor of biology.

After reading numerous papers on mercury flux in freshwater bodies, Speir’s fascination with environmental mercury contamination grew. “I found the topic really interesting,” said the biology major. “I was actually excited to read more papers and learn as much as possible.”

Burning coal and mining for gold are main reasons so much mercury circulates in the atmosphere. It eventually lands on earth and seeps into water bodies, often through conifer trees. What happens to methylmercury (the methylated, toxic form created by bacteria in water) once on land remains a puzzle for scientists to solve.

In applying for a Science and Engineering Research Center grant, Speir designed her research experiment to collect insects and fish living in and around ponds in the Eagle Mountain Fish Hatchery near Fort Worth. The project’s goal was to determine whether certain insects are responsible for spreading the toxin to birds and other terrestrial consumers.

After receiving the grant, the young researcher made the 30-minute drive once a week to collect samples from pyramid-shaped emergence traps she set up in 10 ponds. Half of the water bodies had been stocked with fish to determine if their presence altered the mercury flux in the surrounding ecosystem.

“I was actually excited to read more papers and learn as much as possible.”

She collected long-jawed orb weaver spiders, dragonflies, damselflies and a variety of fish. The specimens were dried in the lab and ground into a fine powder. Although each of the life forms provided clues to the movement of methylmercury, the orb weavers acted as the main indicators of the possible link between aquatic and terrestrial life in Speir’s research.

With the grant funds, Speir sent the powders to two universities for further testing. Researchers at Dartmouth University used a plasma mass spectrometer to determine the mercury levels in each sample. Researchers at the University of California at Davis gauged the levels of a stable isotope of nitrogen, which when plotted together with mercury concentrations permitted Speir, Chumchal and Drenner to map out the food web and determine what was feeding on what.

After the collecting and analyzing were completed, Speir performed the last part of her project. “I was in charge of figuring out the best way to represent the data,” she said. “It really helped me learn how to do it on my own versus having someone hold my hand the whole time.”

Her task was to develop an optimal way to communicate the experiment’s results: That long-jawed orb weaver spiders likely are conduits of methylmercury into birds and larger insects. Their elevated mercury concentrations make this link especially problematic, as the chemical compound is as toxic to birds and mammals as it is to humans.

Drenner and Chumchal consider their student researchers, both graduate and undergraduate, “apprentices.” The professors want students with them in the writing room, which is located around the corner from the lab.

Drenner said mentoring during the painstaking scientific writing process imposes significant time demands on the professors, but someone like “Shannon is worth every moment of that.”

Speir presented her research at the Joint Aquatic Sciences Meeting in Portland. Among nearly a thousand researchers, she was one of just a handful of undergraduate students. “She’s more the exception than the rule,” Drenner said.

Her research was published in Environmental Toxicology and Chemistry in August 2014. She is listed as the paper’s lead author, which is a significant achievement. “Published papers are kind of like the currency in how they measure how successful you are,” she said.

Now a graduate student in biology, Speir specializes in crop, soil and environmental sciences at the University of Arkansas, and she plans to expand her focus on water contamination to include how fertilizers affect water quality.