Researchers from Saint Louis University have discovered substantial
quantities of microplastics in a Missouri cave system that has been
off-limits to tourists for 30 years. They detail their findings in two
recent studies.
Significant amounts of microplastic were discovered in Cliff Cave in Saint
Louis County, Missouri, according to research by Elizabeth Hasenmueller,
Ph.D., associate professor of Earth and atmospheric sciences and associate
director of the WATER Institute at SLU, and her team. Their findings were
published in the journals
Science of the Total Environment
and
Water Research.
Students on the team were able to do field research and publish their
findings thanks to the project, which was inspired by Hasenmueller's
research group and the Karst Hydrology course.
Plastic particles smaller than 5.0 millimeters are known as microplastics,
and they are present in freshwater, terrestrial, and marine habitats. Prior
to focusing on the subsurface, which has received very little investigation,
Hasenmueller examined microplastics in river systems, such as the Meramec
River basin.
Surface water settings have been the subject of a great deal of research,
according to Hasenmueller. Due to the obvious issue of significant plastic
contamination in this ecosystem, research on microplastics first began in
the ocean. More studies of rivers, lakes, and other surface freshwater
systems have been conducted recently.
"On the other hand, the subsurface's contamination by microplastics is one
of the least researched topics in this sector. These particles may be
entering caverns, which are home to delicate ecosystems, or groundwater,
which is a popular source of drinking water. My research team has spent the
last few years attempting to comprehend the occurrence and transit of
microplastics in these subterranean habitats."
Cliff Cave was chosen by Hasenmueller and her colleagues for their research
because it has been off-limits to the public since 1993, making it
impossible for them to link any microplastic contamination they may have
seen to human activity there. Microplastics were discovered everywhere
across the cave, but the greatest amounts were in the silt and close to the
entrance, according to their investigation.
St. Louis County Parks controls access to Cliff Cave, which is one of the
reasons we chose it, according to Hasenmueller. "We were aware that if
microplastics were discovered in the cave, it wouldn't be because someone
had just returned via hiking and left food wrappers or clothing fibers
behind."
According to Hasenmueller and her team's research, microplastics are
traveling through the cave system more often when there is flooding.
Microplastics are carried by water, and when flooding happens, the extra
water enters the cave and carries additional microplastics with it.
An increased variety of microplastics in the cave water was also a result
of flooding. Microplastics were probably deposited in greater quantities
close to the cave's opening than farther within the cave as those
floodwaters subsided.
"We were unsure of what to anticipate from the dataset, but we discovered
that the main entrance of the cave has a significant amount of microplastic
debris, possibly from flooding or from microplastic particles floating in
the air and being deposited close to the cave's opening," Hasenmueller said.
We discovered a plastic chip bag entangled with leaves, acorns, and other
surface flood debris while exploring the cave and gathering samples, proving
beyond a doubt that floodwaters are introducing microplastics into the
cave.
In addition to the fact that floodwaters raised the amount of microplastics
in the water, Hasenmueller and her colleagues discovered that the
concentration of microplastics in the sediment was over 100 times greater
than that of the water in Cliff Cave. The stream water in the cave carried
microplastics into the substrate, where they stayed long after the
floodwaters subsided.
According to Hasenmueller, "We were trying to figure out what fraction of
the microplastics is being stored long-term in the cave's sediment versus
what's actively moving through the cave stream right now." "We discovered
something pretty intriguing: the majority of the microplastics were detected
in the silt. Thus, only a very little portion of the microplastic trash that
we discovered in the cave—99 percent of it—was in the water. It was all
preserved in the sediment."
Hasenmueller continued, "You see higher abundance and diversity of
microplastic particles in the water as the water levels go up during a
flood." "We believe the most likely scenario is that water-borne particles
are deposited into the sediment following the cave floods. That material
stays in the cave sediment when the waters recede, maybe for several decades
or more. Additionally, the quantity of microplastics in the water decreases
significantly as the water level drops."
The cave is sealed off from humanity, but their presence is felt
nonetheless. Cliff Cave's proximity to residential areas that may be
introducing microplastics into the system is consistent with earlier studies
conducted by SLU's WATER Institute, which indicated that the largest
determinant of microplastic distribution in nature is population density.
According to Hasenmueller, there are steps that individuals may take in
light of these results to reduce the quantity of microplastics they might be
introducing into the ecosystem.
The ubiquity of these materials makes it difficult for us as individuals to
combat plastic pollution, but being aware of your own plastic use can
assist, according to Hasenmueller. "People can choose not to purchase
plastic products, such as synthetic fabrics used in apparel, although doing
so poses difficulties for regular shoppers. Given that synthetic fibers from
textiles made up a major portion of the trash we found in this cave, society
as a whole could consider doing away with synthetic apparel on a bigger
scale. Of course, cutting back on our total use and manufacture of plastic
would also be beneficial."
Microplastics have an impact on the species that lives in Cliff Cave in
addition to perhaps harming the cave ecosystem. A sensitive ecosystem that
is used by bats, amphibians, and other creatures for unrestricted movement
within the cave may be disturbed by microplastics. The environmental impact
of microplastics is also a concern for humans, and Hasenmueller urges
further study to prevent the pollution from getting worse.
It's critical to comprehend the extent of the harm that microplastics
provide to the uncommon and unusual species that live only in cave systems,
according to Hasenmueller. Few research have evaluated microplastics in
these kinds of subterranean habitats. Thus, our research gives resource
managers the knowledge they need to consider in order to safeguard these
delicate ecosystems from newly discovered pollutants like
microplastics."
Provided by
Saint Louis University
