Mercury rising . . . mercury contamination in our environment

What you don’t know about mercury contamination in our environment, but should.

Mercury rising . . . mercury contamination in our environment

Assistant professor of biology Matt Chumchal ’03 MS collects fresh-water mussels with his bare feet in Caddo Lake to test for mercury contamination.

Mercury rising . . . mercury contamination in our environment

What you don’t know about mercury contamination in our environment, but should.

Standing on the dock of the Hoot ’n Holler guest cottage in Uncertain, Texas, one gets a glimpse of the watery forest-primeval known as Caddo Lake. With its dark groves of knobby-kneed cypress dripping with Spanish moss and blanket of American lotus sprouting cabbage-size flowers, Caddo is an internationally protected wetland and home to the largest cypress forest in the world.

Considered the only “natural” lake in Texas, Caddo is also the site of groundbreaking research on the effects of mercury contamination on the environment. The lake at the Hoot ’n Holler is where, in 2004, Matt Chumchal ’03 MS, then a University of Oklahoma doctoral candidate, and TCU biology professor Ray Drenner set out in a small boat to collect fish to test for mercury.

What they discovered since then is enough to alarm even the most skeptical:

  • Mercury contamination in some fish and invertebrates is at dangerous levels in more than half of the water bodies in the six-state study area.
  • Many of these water bodies should have mercury advisories but don’t.
  • Neither the public nor lawmakers are sufficiently informed about high levels of mercury contamination in fish, insects, birds and other wildlife, partly because comprehensive mercury monitoring programs do not exist, and partly because, until recently, no one really understood the scope of the contamination problem.

If this is news to you, don’t be surprised. It’s only been in the past decade or so that scientists have begun to tease out the hard truths about the mercury that humans have been throwing into the atmosphere — primarily by burning coal and mining gold — since the beginning of the industrial revolution.

Let’s start with the basics: Mercury is a toxic metal (Hg on the periodic table, also known as quicksilver) that is found everywhere, but it is inert in plants and soil until it enters aquatic systems. There, microorganisms turn it into methylmercury, which can be toxic to human and wildlife health if levels get too high.


There’s a very complex natural mercury cycle that has been going on since the Earth was formed. During this cycle, mercury deposited in the atmosphere from volcanoes falls to Earth and is incorporated by trees and plants, and over millions of years the fossilized flora becomes mercury-containing coal. So mercury has always been in the atmosphere and aquatic food chains, just in lower concentrations than today. It has risen to dangerous levels recently because when we burn that coal, the mercury is released back into the air.

“In a span of about 150 to 200 years we have taken ancient fossilized carbon and mercury out of the ground and put it into the atmosphere,” says Chumchal, who joined TCU as an assistant professor of biology in 2007. “We’ve altered the normal mercury cycle, just like we have impacted the carbon cycle.”

To put the contamination into perspective, Chumchal notes that British Petroleum’s 2010 Deepwater Horizon oil spill was frequently called the worst environmental disaster in U.S. history. But the area it covered was tiny compared to the size of the mercury hot spots he and Drenner have mapped.

“Although the oil spill was an environmental disaster, it is small compared to the current mercury problem in our region of south central U.S. The area covered by high mercury-contamination levels in fish is much larger than the oil spill,” he says. “While the effects of the oil spill are diminishing, the mercury is not going away. It’s not only bigger in geographic scale, it will last a lot longer.

“Yet almost no one knows it exists in this region of the country.”

People have long known there is a problem, just not the extent of it. For decades, state and federal legislators and regulators have tried to monitor and control mercury emissions. There are federal laws that control certain types of mercury emissions — such as at cement plants, medical waste incinerators and chlorine producers — but we haven’t ever had a consistent national mercury policy. Every president in the last 20 years has attempted to get one in place, but it didn’t last. The most recent mercury and air toxics standards, known as MATS, are on the books but not yet enacted.

PhotoSo we just have to scrub mercury from our power plants, right?

If only it were that easy, says Drenner.

“Coal-fired power plants emit mercury in different forms and some forms are deposited regionally, but other forms become part of the global pool of mercury that may remain in the atmosphere for years,” he says. “When you have a contaminant that is airborne and global in nature, it’s very challenging to figure out where it came from. It’s not as simple as figuring out the source of contaminants discharged into a river.”

What is apparent, Drenner says, is that, “the right thing to do is to reduce emissions of mercury into the environment.”

Drenner is quick to note that worrying about where mercury comes from or how to regulate it does not fall within the scope of their work.

“I think Matt and I feel we have an obligation to carry this through, not just from a research and science enterprise, but to make this information available so that decision makers are armed with the information that we have,” he says. “Our job is not to make the decision for them, but to help them be as well informed as we can.

“Another part that is pretty heartfelt by both of us: Who is going to speak for all the wildlife that depend on these resources, if not us? Who is going to speak for the underprivileged people who depend on these fisheries’ resources but may not understand the dangers of a constant diet of mercury in fish to the unborn?”

Fishing for data

Drenner’s interest in the field was sparked in 2003 when he began to notice a spate of articles in scholarly journals about mercury contamination.

“Scientists in the Northeast and Great Lakes regions have been studying mercury contamination in fish for a while now, and their pioneering research has guided us,” he says. “But very little data was available about the problem in Texas in 2003 when Matt began to study mercury in Caddo Lake for his doctoral work in 2004.”

Photo Chumchal chose Caddo Lake because of its diversity of aquatic species. Drenner and his master’s student, Bill McClain ’05 MS, focused on fish in Lake Meredith because there was a controversy about the mercury advisories that had already been issued there. Chumchal and Drenner worked with biologists of the Texas Parks & Wildlife Division (TPWD), to collect fish from the two lakes. The fish were then tested for mercury contamination in TCU’s Aquatic Ecology Lab.

The researchers quickly realized they needed a lot more fish if they wanted to gather useful data. So Drenner, who had a long-standing relationship with the TPWD, asked if the fisheries biologists would send them the bass they already collected from lakes across Texas. The TPWD readily agreed since they were also interested in mercury contamination but didn’t have the resources to do proper testing.

“We bought a bunch of giant coolers to ship the fish to TCU,” he said. “They froze the fish and shipped them to us for mercury testing. We eventually wore those coolers out.”

Two years later, after testing more than 1,000 fish, they were able to reveal things previously unknown: Many factors, including species, size and age, determine how contaminated a fish is; contamination differs from lake to lake; and small sampling programs will result in inaccurate data about whether mercury advisories should be issued.

They ended up with more questions than before: Why are there regional differences? Can we predict where the highest levels will be, based on how much mercury is falling to the ground? Are the aquatic insects, which birds and bats eat, also highly contaminated? Can we develop a regional or national model that can accurately determine where the worst contamination is?

By 2007, their focus had shifted from single lakes to the state and eventually, to regional contamination. For this they crunched more than 20 years of data collected by the EPA and state fisheries or environmental agencies in Texas, Louisiana, Arkansas, Oklahoma, Mississippi and Tennessee.

Photo When they began to study the larger region, they realized they needed mercury deposition data to compare against the mercury levels in fish data they had collected. They turned to David Gay, director of the National Atmospheric Deposition Program based out of the University of Illinois at Urbana-Champaign, who provided them with five years of data from a nationwide network of mercury-deposition collectors. These small collectors capture rainwater, then mercury levels (and other elements as well) in the water are measured.

But when the two TCU scientists overlaid all the data, high levels of contamination of fish didn’t line up with where high amounts of mercury were falling. The scientists puzzled over the inconsistencies for nearly a year.

“We figured out, eventually, that the outlines of the regions with highly contaminated fish were related to the ecology of the region,” Drenner says. “And the patterns were very precise. Mercury in fish in a forested area would be high and the mercury would just drop off when the forest stopped.”

They also realized not all forested areas were the same — contamination under conifer trees, specifically loblolly pines, was about five times as high as under deciduous trees or open areas.

It was an important discovery.

“Atmospheric mercury deposition is altered by the land cover and is greatest in forested areas,” Chumchal says. “A prairie doesn’t magnify the mercury being deposited because it’s just tiny blades of grass sticking up and doesn’t have much surface area for the mercury to stick to. But conifers have huge surface areas for mercury to stick to, and then rain washes the mercury off to the ground and lakes.”

With this data in hand, they created a map that accurately predicts where the highest contamination will be in the region and why.

“We think the power of this is that without ever going to sample a lake you can possibly know which ones will have a mercury problem,” he says. “You might even predict mercury contamination levels in small lakes that are never sampled. There are millions of these small, private lakes and you could never go out and sample all of them, so we are trying to find another way to predict which water bodies have dangerously high levels of mercury contamination.”

Photo Those millions of small ponds caught Drenner’s interest in 2006 while on a field trip to the LBJ National Grasslands in Decatur, Texas, where such ponds are the only source of water.

“Small, man-made lakes are the dominant water body in the U.S., and account for more surface area of water than the big lakes,” he says. “They tend to be very small, privately owned ponds, and are seldom sampled, but they are very important from a biodiversity standpoint: If there’s no pond, you don’t have any aquatic animals.”

And yet, they have been virtually ignored by researchers.

Many of these ponds don’t have fish, so the TCU researchers tested the insects emerging from them. Three graduate students helped Drenner and Chumchal tackle this work over the next six years — moving from the Grasslands to mesocosms on campus to the fish hatchery near Eagle Mountain Lake that TCU leases from the Tarrant Regional Water District. Eventually they discovered that ponds without fish have massive amounts of aquatic insects in them, and they are loaded with mercury.

This new information could have wide-ranging repercussions, especially in this era of climate change.

“We don’t know how rain patterns are going to change, but we know that in some areas it’s going to get hotter, some will have more water, some less,” he says. “But as droughts become worse, these little incubators of mercury change their mercury personalities. A permanent pond with fish has a different kind of insect carrying the mercury out and we think less so, based on our research.

“But the little dry ponds, because they are fishless, when they do fill up with water, they will produce a lot more mercury in the flux of insects that leave them. This is their dark side.”

Add water and these dry ponds become dangerous. How dangerous? That’s one of the next projects — to figure out how that contamination moves out of the ponds and what kind of damage it causes. No one has ever done this before, Drenner notes.

They have already laid out their next five-year research plan, which will focus on determining risk.

“What we want to look at now is contamination in different sizes and types of fish and insects, and not just the risk to humans, but how it damages the birds and fish, too,” Drenner says.


Mercury in the atmosphere is deposited on the ground when it rains. This chart identifies which parts of the country have dangerously high deposition. Proximity to coal-burning power plants and other sources is one factor, but so is ecology of the region. Forested areas, in particular those dominated by conifer trees, are particularly effective at scrubbing mercury from the atmosphere. Dots represent mercury deposition monitoring sites.

What’s next

This story may have started in Uncertain, but 10 years later, there are two things that are certain: Mercury contamination is a serious national problem and there are still more questions than answers. But until lawmakers are armed with solid data, the public will continue to be in the dark — and possibly in danger.

Fortunately, Chumchal notes, there is a large cohort of scientists working on the mercury problem, so eventually understanding will result in regulatory action.

Photo “Environmental issues are problems, if you will, that are caused by humans and those problems are solved slowly, by multiple researchers accumulating complex data over long periods of time,” he says. “We’re just part of a huge team of people working all over the world on mercury. It’s a vast, vast group working on this problem now because it’s so serious.”

He believes mercury contamination will follow the trajectory of the acid rain problem, which was killing off fish in lakes in the northeast. It took teams of people from different states assembling data over many years to figure out what was causing it. But once the data painted a clear picture, the federal government implemented an acid rain control program.

“We don’t know what the solution to the deposition problem is, we truly don’t,” Drenner says. “It’s hard to cut it off if you don’t know where the mercury is coming from. That is the fog that is hanging over the field right now.”

Atmospheric scientists are on the hunt for those truths, but even if all deposition stopped today, the problem would linger for decades. In the meantime, Drenner and Chumchal continue to gather data even as they wonder why there has not been more public outcry.

“This is the title of a talk I want to give: Mercury in the South Central U.S.: When are we going to wake up?” Drenner says. “Seriously. The southern part of the U.S. has the highest biodiversity of fresh-water fish in the world, and some of the highest mercury levels in the country. We have wonderful fish resources that are so contaminated with mercury they pose a serious health risk to humans and wildlife. We need to do whatever we can to identify the sources of this mercury contamination and take steps necessary to protect these irreplaceable resources.

“That’s why we do what we do.”

On the Web:

TCU’s Aquatic Biology Lab, —

Texas Rep. Ryan Guillen working to pass bill that would post mercury warnings at Texas lakes

Related stories:

10 years of TCU research — Horned Frogs have produced 19 scholarly papers and 93 scholarly presentations

What is mercury and why is it a concern? — The basics of the element

The TCU Magazine Summer 2005 cover story — Safe to eat?