Sea Grant Institute Research
Predicting the Toxicity of Metals to Great Lakes Coasts
By Marie Zhuikov
There’s nothing like listening to rain falling on a metal roof. Although the sound can be pleasant, Wisconsin Sea Grant researchers are prone to think about the trace amounts of metal the rain carries off the roof and into the environment.
Take copper and cadmium. A team of University of Wisconsin-Madison researchers have discovered key factors in predicting how and at what levels these metals harm the shoreline environment of the Great Lakes and what protective measures coastal organisms adopt in response. That’s allowed regulatory agencies—the Environmental Protection Agency (EPA) for one—to refine tools to protect Great Lakes coastal regions from the metals.
Copper and cadmium get into the environment through wastewater and industrial discharges, copper piping and roofs, and natural sources like rocks. Both metals can be toxic in aquatic environments and are regulated by the EPA and Wisconsin Department of Natural Resources. However, the forms and toxicity of these metals in the environment have been difficult to measure.
The researchers focused on nearshore regions because, according to Martin Shafer, associate scientist at the University of Wisconsin-Madison College of Engineering, “There’s a lot going on there. It’s an area of growth for plants and animals, and there are a lot of metal inputs to it. Also, there’s a lot happening that can affect the availability and toxicity of metals.”
The project, also supported by the Wisconsin State Lab of Hygiene, looked at the impact of copper and cadmium on a single-celled phytoplankton, Chlamydomonas reinhardtii. When this flagella-driven alga is exposed to metals, it produces an antioxidant called glutathione to protect itself. Glutathione and other anti-oxidants may protect cells from substances called reactive oxygen species (ROS), which form in the presence of metals and can be damaging to cells when produced in excess.
“We studied algae because it’s important to understand toxicity at all levels of the food web,” said Tasha Stoiber, former graduate student on the project and now a post-doctoral researcher at the University of California, Davis. “Phytoplankton are the primary producers and we need to know how sensitive they are to the effects of metal pollution.”
The researchers looked at production of both glutathione and ROS to identify measures of exposure and how to predict toxicity before cell death occurs, which, Shafer said, only makes sense. “Traditionally, long-term toxicity tests measure cell death. That’s sort of late in the game if you want to protect organisms. We looked at understanding potential toxicity before the organism is killed or had its growth significantly affected.”
Researchers also looked at the effect that dissolved organic matter (DOM) has on trace metal toxicity in water. The root beer-colored streams of northern Wisconsin provide good examples of DOM. The color comes from dissolved plants and other carbon-based materials that get into the water. As it turns out, DOM is a good thing.
“We demonstrated it takes very little DOM to dramatically reduce the toxicity of copper and cadmium to phytoplankton,” Shafer said. “DOM binds to the copper and cadmium and keeps it from binding to the phytoplankton cells. We discovered what levels of DOM are needed to out-compete the cells for the metal and prevent its toxicity.”
With these inputs in mind, the team has modified a model that regulatory agencies use to calculate safe standards for copper and cadmium in the environment. Shafer said the EPA is changing its approach based on these and other findings.