Songbirds in the Mercury Mine: When a research study reaches its conclusion,
the real questions are often just beginning.
by Caroline Collier
“Even if all human emission sources stopped right now, it would continue to get worse for several decades before it started to get better.”
A decade ago, Matt Chumchal was a master’s student in biology at TCU, collecting fish from Texas lakes to better understand mercury contamination patterns.
Today, Chumchal, an ecologist and co-creator TCU’s Aquatic Ecology Lab, continues to study mercury contamination in freshwater bodies. But he and the lab’s other co-creator, Ray Drenner, have learned that the movement of mercury in the environment is more complex than they imagined.
Human activity releases long-buried mercury into the atmosphere, and, eventually, it settles into water bodies. Bacteria convert mercury into methylmercury, a dangerous neurotoxin that can cause a variety of health problems, such as deafness and memory deficiencies.
“There’s no debate that methylmercury is a terrible toxin to the physiology of humans, and that tiny amounts have permanent effects,” Drenner said, even though the process leading to this consensus has consumed thousands of scientists for several decades.
Chumchal, who also serves as director of TCU’s Pre-Health Institute, and Drenner, a freshwater ecologist and chair of the Biology Department, helped establish how age and position in the food chain play a crucial role in mercury levels in fish. The professors then explored why certain water bodies show varying levels of mercury concentration.
In mapping the mercury levels in public lakes in the southern U.S., Chumchal and Drenner noticed that concentrations dissipated before the Mississippi River and accumulated again east of the riverbanks.
“All of the sudden, the pattern became really straightforward,” Drenner said.
The professors linked the mercury deposition to conifer trees, such as pines. The trees’ huge surface allowed for much higher mercury collection, which then leeched into surrounding lakes.
The professors’ findings were published in Environmental Science & Technology. In 2013, Chumchal and Drenner won the prestigious Dow Chemical Award for Innovation in Mercury Science. The recognition is significant because thousands of scientists are studying mercury contamination.
The origins for the rise in mercury levels are a settled matter, Chumchal said. Half of it comes from burning coal for energy, predominantly in Southeast Asia, and small gold mining operations in the tropics emit the other half.
After mercury lands in the water, it seeps into fish. Certain types, such as swordfish and king mackerel, contain extremely high amounts. For public safety, the Food and Drug Administration publishes chemical data for most fish.
“The big assumption until just a few years ago was [mercury] is just an aquatic problem. If you weren’t in the lake and eating something out of the lake, you were fine,” Drenner said. “No one understood that it’s coming out of the aquatic environment and into terrestrial consumers.”
The aquatic ecology lab is moving in two new directions. In one group of studies, the professors and their students are looking at the avenues mercury travels out of the water and into land-dwelling creatures.
At the lab, songbirds collected around Texas’ Caddo Lake serve as the proverbial canaries in the coal mine. Where did the mercury contaminating these birds originate? For an answer, Drenner, Chumchal and a graduate student, Gretchen Gann, looked at the songbirds’ diet, which consists mainly of aquatic insects.
They conducted a series of experiments at the Eagle Mountain Fish Hatchery, which the Tarrant Regional Water District allows the lab to use for its academic research. The large hatchery contains hectare-sized water bodies that Chumchal calls “frog ponds.”
Some ponds dry up on occasion, which changes the biological makeup and ensures that fish cannot survive permanently in them. The ponds, drained and undrained, host a variety of aquatic insects, such as dragonflies, damselflies and long-orbed jaw weaver spiders. Lab researchers set out floating emergence traps. Insects fly into them and are euthanized by alcohol.
At the lab, researchers freeze or dry the insects, grind them to a powder and send the samples to Dartmouth, which has a plasma mass-spectrometer to test for methylmercury, or MeHg, levels. In the drained ponds, more insects live because no fish exist to feast on them, and the researchers found that spiders and damselflies surrounding the fish-less water contained the highest levels of mercury in the experiment.
Contaminated insects pose a large problem worldwide, especially in the Great Plains. More than 2 million man-made ponds exist in that region, many of them dug to provide a water source for cattle. However, those ponds, over decades, slowly fill with sediment and leak mercury into the water table.
The ponds are a “novel ecosystem,” Chumchal said. “And now those small, man-made ponds are the dominant type of standing water body numerically worldwide.”
Since researchers and state health officials have no access to private water bodies, understanding what happens in public lakes and ponds is an essential task when it comes to warning people of high mercury levels that might be in their game fish.
The aquatic ecology lab also maps state advisories for mercury in public waters. Drenner, Chumchal and graduate student Kim Adams are devising the first study of the state advisories plotted against mercury data. The researchers hope to determine whether the state warning systems provide adequate protection for people eating game fish.
David Donato with the United States Geological Survey has given the researchers access to the mercury samples from Texas to Mississippi, the biggest database in a six-state region. The data has been collected over decades from university researchers, state scientists and Donato’s federal department.
A federal benchmark for mercury contamination has been established. The Environmental Protection Agency’s guideline is that mercury levels need to be under 300 nanograms per gram of biological material. “That number was developed as a result of a National Academy of Sciences study,” Chumchal said.
In the U.S., each state can determine its own mercury safety cutoff. For example, in Texas, the Department of State Health Services allows 700 nanograms/gram before a lake advisory is issued. However, in Arkansas, state officials permit 1,000 ng/g – a level so high it is rarely seen in game fish.
When lakes have no advisories, fishermen often assume their catches are safe to consume, Drenner said. But, according to the data and using the EPA’s guidelines, these states are missing advisories on up to 85 percent of water bodies when judged by large channel catfish, and up to 71 percent by the biggest largemouth mass.
When measuring mercury levels in smaller fish, the states are a little closer to the EPA’s target. Mercury accumulates as the fish ages, grows and moves up to a dominant position on the food chain.
The U.S. Food and Drug Administration recommends women and young children avoid eating shark, swordfish, tilefish and king mackerel because substantial levels of mercury can cause a variety of health problems. Children and babies exposed to high levels of mercury can develop blindness, cerebral palsy or poor mental faculties. For adults, mercury contamination can cause blood pressure problems, poor vision and a numb sensation in fingers and toes.
“The assumption is they [the states] are protecting the public, but what you can see is that’s not true for a lot of the sites,” Drenner said.
But the researchers’ groundbreaking study might change things.
“It appears that we have these fish advisory systems in place for all these states, but they are missing a lot of the lakes that there should be warnings for … and the implication is that everybody’s okay,” Drenner said.
The new study is “going to precipitate an awful lot of discussion and controversy,” he said. “Because the states have spent millions of dollars putting the advisory systems together.”
For example, Chumchal said, Texas already has received a series of memos from the EPA requesting a response for a potentially inadequate advisory system.
Policy deliberations will happen outside the lab, though. Both professors urge the public to get informed and become proactive about pushing lawmakers to devote attention to the mercury problem. “It’s up to [the public] to carry the ball,” Drenner said.
Whether or not Texas and other states get in line with the federal mercury threshold, the contamination problem will not stop.
“Even if all human emissions sources stopped right now, it would continue to get worse for several decades before it started to get better,” Chumchal said. “Because it would take several decades to even get into equilibrium on a scale of the planet.”
However, Chumchal and Drenner explained that the problem does not fall on the shoulders of state-employed scientists who visit and test public lakes. Rather, they said, the problem is a resource issue. With tight budgets, state health departments lack the personnel to do the work.
Therefore, the predictive nature of the aquatic lab’s decade of research is important. Accurate forecasts about which lakes and which fish are likely to be problems allows states to devote attention to the most pressing areas of mercury danger.
“You need to be good stewards,” Drenner said of helping public agencies devote attention where it is most needed.
Drenner and Chumchal consider themselves equal parts researchers and mentors. Besides teaching and managing departments, they co-advise graduate and undergraduate researchers.
“Most of our projects couldn’t have been done without student involvement,” Drenner said. “We’re a team.”
When undergraduate biology students show up in the aquatic lab, the professors send them away with a handful of relevant scientific literature. Students who return are warned about the time demands of lab work, and if undeterred, they are invited to participate.
Working alongside the student researchers, called “apprentices” by Drenner, allows them to learn valuable experiential lessons in the field of biology.
“The process of science is something you have to do,” Chumchal said.
The professors also teach their research students about writing scientific papers. They put paragraphs and data graphs on the projector and dissect the papers word-by-word, then sentence-by-sentence.
“Scientific writing is different in that it’s really cut and dry, and it’s as to the point as possible,” Shannon Speir, a former undergraduate researcher, said.
The synergy Drenner and Chumchal gain by collaborating with each other, and their research students, has benefits. Journal reviewers often compliment them on the completeness of their research papers.
Chumchal “is the hardest reviewer I know,” Drenner said.
Most of the master’s theses based on research done in the lab are published in academic journals, which is a rare feat. Depending on their level of involvement, many of the lab students are co-authors or even first authors on scholarly papers.
“TCU has made a decision to invest in people here,” Chumchal said in discussing the opportunities for undergraduate researchers and the internal funding for the lab’s operation. “The amount of support we have … I think is really rare.”
Biology undergraduates can apply for university-based research grants. Speir received one that allowed her to study mercury contamination in long-jawed orb weaver spiders.
Without the internal grant funding for Speir’s project, the lab would have been unable to pay for the mass spectrometer mercury evaluation at Dartmouth or the stable nitrogen isotope analysis at University of California-Davis.
Speir was one of a handful of undergraduates who presented an experiment in Portland, Ore. at the Joint Aquatic Sciences Meeting in May. As the first author, she recently had a paper published in Environmental Toxicology and Chemistry, a rare accomplishment for an undergraduate student. (During that time, she also was a runner on the cross-country track team.)
About eight undergraduate honors students are tackling other researchprojects in the lab. In the biology department, roughly 40 percent of the undergraduates are active participants in research, Chumchal said.
Next year, Drenner and Chumchal plan to expand the aquatic ecology lab’s advisory efficacy study all the way to the Atlantic Ocean.
As understanding grows, so does general awareness of the problem.
“There is this international awakening that the whole mercury problem is a global problem,” Drenner said. “And it’s going to be solved by global initiative, but at this moment, there’s no teeth in that.”
At the October 2013 Conference of Plenipotentiaries, a handful of countries agreed to take voluntary steps to address mercury contamination, and they signed the Minimata Conventions.
New U.S. power plants have emission limits and mercury “scrubbers,” Chumchal said. But vast amount of liberated mercury circles the planet, and most countries have not yet enforced the conventions.
“If it’s business as usual,” Chumchal said. “Mercury emissions will just keep going up and up and up.”