St. Louis University researchers reported in two recent papers that they found high concentrations of microplastics in a Missouri cave system that has been closed to visitors for 30 years. Elizabeth Hasenmueller, Ph.D., associate professor in the Department of Earth and Atmospheric Sciences and associate director of the SLU Water Institute. and his team published their findings in the journal Science of the. Total Environment And Water Research, finds significant levels of microplastics in Cliff Cave. in St. Louis County, Missouri.

The research initiated by Hasenmueller’s research group and karst hydrology class allowed students on the team to participate in field research and publish their findings.

Microplastics are defined as plastic particles smaller than 5.0 millimeters in size that can be found in marine, terrestrial and freshwater environments. Hasenmueller had previously studied microplastics in river systems such as the Meramec River basin, but now he wanted to look at a subterranean region that had never been explored.

“A lot of research has focused on surface water settings,” Hasenmueller said. “Microplastic research first began in the oceans because there was a highly visible problem of high plastic pollution in that environment. More recently, more research has focused on examining rivers, lakes and other surface freshwater systems.”

“But one of the least studied areas in this field is what happens to the subsoil in terms of microplastic contamination. These particles can enter groundwater, a common source of drinking water, or caves where sensitive ecosystems exist. For several years, my research group has focused on understanding the prevalence and transport of microplastics in these subsurface environments. “

Hasenmueller and his team chose Cliff Cave for their research because the cave had been closed to visitors since 1993, allowing them to rule out human presence in the cave as a possible cause of the observed microplastic pollution. Their research showed that microplastics were found throughout the cave, but the highest concentrations were found near the entrance and in the sediments.

“One reason we chose Cliff Cave is because St. Louis County Parks regulates access to the cave,” Gasenmueller said. “We knew that if we found microplastics in a cave, it wouldn’t be because someone had just returned to the cave and shed fibers from their clothing or left food wrappers behind.”

As a result of their research, Hasenmüller and his team found that floods increased the amount of microplastics moving through the cave system. Microplastics move with water, and when flooding occurs, excess water brings more microplastics into the cave.

The flood also contributed to an increase in the diversity of microplastics in the cave water. When these floodwaters receded, microplastics are thought to accumulate in larger quantities near the cave entrance than in deeper parts of the cave.

“We weren’t sure what to expect from the dataset, but we found that the main entrance to the cave was a place where there was a lot of microplastic debris, either from flooding or perhaps from airborne microplastic particles settling near the hole in the cave,” Hasenmueller said. “We’re sure it was because while we were going through the cave passages and collecting samples, we found a plastic bag full of sawdust intermingled with leaves, acorns, and other surface debris.”

Not only did the floodwaters contribute to increased levels of microplastics, Hasenmüller and his team also found that microplastics were almost 100 times more concentrated in the sediment compared to the water found in Cliff Cave. Microplastics entered the cave sediment along with cave runoff water and remained there even after the floodwaters receded.

“We were currently trying to find out how much of the microplastics are actively moving in the cave flow and what happens in the cave sediments over the long term,” Hasenmüller said. “One of the really interesting things we found was that most of the microplastics were in the sediment. So 99 percent of the microplastic pieces we found in the cave were stored in the sediment; only a very small fraction of the plastic was in the water.”

“When the water level rises during flooding, you see a greater number and variety of microplastic particles in the water,” Hasenmueller said. he added. “We believe it’s likely that water particles settled into the sediment after the cave was flooded. When the water recedes, this material likely remains in the cave sediment for decades or longer. When the water level drops, the concentration of microplastics in the water is also much lower.”

Even though the cave is closed to humans, it still makes their influence felt. Cliff Cave is located near residential areas that may contribute microplastics to the system. This finding is consistent with previous research from the SLU Water Institute showing that the largest factor determining the location of microplastics in nature is population density. Given these findings, there are some things people can do to limit the amount of microplastic they can release into the environment, Gasenmueller said.

“It is difficult for us as individuals to deal with plastic pollution due to the prevalence of these materials, but it helps to be mindful of our personal plastic use,” Hasenmüller said. “People may avoid purchasing plastic materials such as synthetic textiles used in clothing, but this creates problems for ordinary consumers. On a larger scale, we as a society can move away from synthetic clothing because many of the artifacts we found in this cave contained synthetic fibers derived from textiles. And of course we can reduce our overall plastic production and “Reducing our consumption will also be beneficial.”

Not only are microplastics potentially damaging to the cave environment, they are also impacting the wildlife that calls Cliff Cave home. Bats, amphibians and other animals move freely in the cave, and microplastics can disturb their sensitive habitats. Microplastics are not only a human problem, but also an environmental problem, and Hasenmüller calls for more research to ensure pollution does not get worse.

“It is really important to understand the level of threat that microplastics pose to unique and rare animals that live only in cave systems,” Hasenmüller said. “Only a few studies have evaluated microplastics in such underground ecosystems. Therefore, our work provides resource managers with information they need to consider to protect these sensitive habitats from emerging contaminants such as microplastics.” Source