Pollutants spread too: Contaminants in mountain coal mining runoff transfer to terrestrial systems
As news cycles are dominated by the tragedies accompanying the spread of COVID-19, scientists are continuing to report their research in an effort to improve environmental issues. For example, some environmental scientists are seeking to understand the nature and consequences of the spread of pollutants between ecosystems. A group of researchers led by Laura Naslund at Duke University recently published a study investigating how pollutants in mountaintop removal mining runoff can travel up the food chain and transition from aquatic to terrestrial (land-based) environments.
Moving mountains isn’t quite as hard as it used to be. While some metaphorical mountains are as stubborn as ever, the mining industry has been moving mountains… or at least mountain tops since the 1960s and 70s. Mountaintop removal mining (MRM) is a type of strip mining in which explosives are used to remove hundreds of feet from the tops of mountains, exposing and providing ready access to the desired material (dominantly coal in the United States). An example site is shown in Figure 1. Although it does not present the same risks to workers as underground mining, the environmental and health impacts of this technique abound. Decreasing water quality and ecosystem health has been attributed to MRM runoff in various locations throughout the Appalachian mountains in the Eastern United States. However, as Naslund and coworkers have shown, this runoff can have consequences for terrestrial ecosystems as well.
Food webs: enabling transfer of pollutants between ecosystems
This is certainly not the first instance of a water-borne pollutant spreading to terrestrial animals via their food. Does DDT ring a bell? That pollutant, used primarily as an insecticide, was largely responsible for the endangerment of the bald eagles, concentrating in them through their consumption of fish. This transfer of pollutants from water to aquatic to terrestrial ecosystem has also been documented with a variety of other pollutants, including mercury, pharmaceuticals, and PCBs. The study by Naslund and coworkers specifically investigated Selenium (Se) transfer from aquatic ecosystems impacted by mountain-top removal mining.
Selenium in a microsystem
Some selenium is actually necessary for many organisms (including humans!) to survive. In appropriate concentrations, it serves an important role in metabolic functions. However, as with many substances, the dose makes the poison. At high concentrations, selenium can be toxic.
For their study, Naslund and coworkers collected samples at several sites in southwest West Virginia. They selected sites both with and without known mining impacts for comparison. Most of their sites were located in the Mud river basin, depicted in Figure 2, which is close to the Hobet 21 mine complex—the largest surface mine in central Appalachia.
In order to understand the relationship between mining runoff and the entrance of high concentrations of selenium in the environment, the researchers used three model organisms to evaluate the transfer of selenium from water: biofilms, insects, and spiders. Biofilms serve a critical role in converting inorganic forms of selenium (commonly found in mining waste runoff) to organic forms, which can be consumed and used by organisms. These films also bioaccumulate this newly-transformed selenium and act as a food source (and therefore selenium source) for aquatic insect larvae. These aquatic insects are then eaten by spiders and other terrestrial critters, such as birds, and the higher-than-healthy selenium concentrations leave the water to enter food webs on dry land. The researchers found positive correlations between Selenium concentrations in water, biofilms, insects, and spiders and mining activity. Furthermore, the concentration of Selenium in insects and spiders were above the recommended dietary threshold for the birds that eat them. This goes to show that mountaintop mining runoff poses a threat to both aquatic and terrestrial wildlife.
What can be done?
One of the easiest ways to make a difference is to trace the problem back to its source. Why is this pollution being generated? To mine for coal. Why is there a demand for coal? It is used to generate electricity. Now, by no means am I saying we should forgo electricity—it is a wonderful thing and has led to a significant improvement in quality of life—not to mention the ability to solve environmental problems! However, anything that can be done to reduce the waste of electricity would do a small part (or in some cases not so small) to reduce demand for coal and incentives for blowing up mountains. Here is one list of things you can do to make your home more energy efficient.
Source Article: L. C. Naslund, J. R. Gerson, A. C. Brooks, D. M. Walters, and E. S. Bernhardt, Environ. Sci. Technol. 2020, 54, 7, 3951-3959. https://pubs.acs.org/doi/10.1021/acs.est.9b05907
Cover Image Source: https://www.flickr.com/photos/nationalmemorialforthemountains/4534742719