Paper published in Environmental pollution Authored by Saint Louis University (SLU) scientists, human proximity shows the best indication of microplastics in Missouri’s Meramec River.
The team of researchers, led by Jason Knovt, Ph.D., professor of biology, principal investigator at the WATER Institute at SLU, and scientist at the Great Rivers National Research and Education Center, and Elizabeth Hasenmiller, Ph.D., associate professor of Earth and Atmospheric Sciences and associate director of the WATER Institute at SLU , microplastics levels at 19 sites along the Meramec River, including sites downstream from a major metropolitan area as well as less densely populated rural areas.
“What we found is that human factors basically told us where the microplastics were,” Hasenmiller said. “The distribution of microplastics in a watershed was not driven by river flow or sediment inputs. Instead, it was mostly related to how close the location was to wastewater inputs or the city. These types of things were the biggest predictors.”
Microplastics are generally characterized as plastic particles smaller than 5.0 mm and can be found in marine, terrestrial and freshwater environments. Given the durability of plastics and the potential dangers from microplastics found in freshwater systems, Knouft, Hasenmueller, and team set out to determine how microplastics enter freshwater systems and what is the best indicator for determining where microplastics can be found.
To determine where microplastics are located in the freshwater system and to determine what levels of microplastics are present, researchers examined river sediments in the Meramec River watershed. The team also applied hydrological modeling to estimate the importance of river drainage, sediment load, land cover, and wastewater discharge sites to determine how these factors influence the distribution of microplastics.
During their research, Knouft and Hasenmueller made many new and expected discoveries. The data showed that the best predictor of microplastics being found in the Meramec River was proximity to humans. Humans make and consume plastic; It makes sense that if a river site was near humans, microplastics would be found there.
“Before we got started, I had an open mind,” Knoft said. “I approached it like this: Whatever we find, it wouldn’t be a surprise to me. If we find that this stuff is bombarding the ecosystem, I’ll say, ‘Yeah, that makes sense.'” But if we find out they’re not really doing anything, I’ll say, ‘Yeah, that makes sense, because these things just get through.'”
Hasenmueller wasn’t surprised that humans were the biggest contributing factor to microplastics being found in the Meramec River, but she was surprised by how widespread these microplastics were throughout the basin.
“We knew microplastics were going to be there, but the amount of plastic, it was everywhere you looked,” Hasenmueller said. “I thought there might be a larger effect of drain current and sediment loads on the distribution than we’ve seen, which surprised me.”
Now, attention is turning to what can be done to prevent these microplastics from getting into freshwater systems. There are already small steps individuals can take to reduce their plastic consumption, such as ensuring that plastic is taken to recycling plants, but researchers will also look to the future to identify large-scale treatments to protect our freshwater systems.
“I think the biggest solution to addressing the microplastic problem is also one of the hardest, and that is to reduce the amount of plastic we use,” Hasenmiller said. “Almost everything is plastic; our clothes have plastic in them, food and water are stored in plastic, and all of these different things in our daily lives are made of plastic. So having big companies reduce the amount of plastic could have a huge impact because there’s only so much we can do as consumers.” “.
SLU students contributed to this research effort, including study co-authors Teresa Barraza and Natalie Hernandez. Other authors on the paper are Chen Long Wu, Ph.D., of the Department of Biology at SLU, and Jack Seebok of Washington University in St. Louis.
This research was supported by The Nature Conservancy (061716-01).