Where humans live, microplastics end up in rivers

A paper published in the journal Environmental Pollution by scientists at St.
Louis University (SLU) suggests that human proximity is the best indicator
of microplastics found in the Meramec River in Missouri.

A research team led by Dr.
Jason Knuft, professor of biology, principal investigator of the SLU WATER Institute, and scientist at the National Center for Great Rivers Research and Education, and Dr.
Elizabeth Hasenmuller, associate professor of earth and atmospheric sciences and associate director of the SLU WATER Institute, studied microplastic levels at 19 sites along the Meramek River, including downstream large cities and less populated rural areas
.

"We found that the human factor basically tells us where the microplastics are
," Hasenmuller said.
"The distribution of microplastics in watersheds is not driven
by river flows or sediment inputs.
Rather, it is mainly related to
the distance of the site from the sewage input or the city.
This kind of thing is the biggest predictor
.
”

Microplastics are typically plastic particles smaller than 5.
0 mm that can be found
in marine, terrestrial and freshwater environments.
Because of the persistence of plastics and the potential dangers of microplastics found in freshwater systems, Knouft, Hasenmueller, and their team set out to determine how microplastics enter freshwater systems and what are
the best indicators for where they will be found.

To determine the location of microplastics in freshwater systems and determine the levels at which they are present, the researchers examined river sediments in the Meramaek River Basin
.
The research team should also estimate the importance of river flow, sediment load, land cover and wastewater discharge sites to determine how these factors affect the distribution
of microplastics.

Throughout the course of their research, Knuft and Hasenmuller made several new, but still expected, discoveries
.
The data shows that the best indicator of microplastics found in the Meramec River is proximity to humans
.
Plastic is created and consumed by humans; If rivers
were close to humans, microplastics would be found there, and it makes sense.

"I keep an open mind before we start," Knuft said
.
"Here's how I approached it: I wouldn't be surprised
by whatever we find.
If we find that these things are destroying ecosystems, I'd say, 'yes, that makes sense
.
But if we find that they're actually doing nothing, I'd say, 'yes, that makes sense, because they're just passing through
.
'" ’”

Hasenmiller wasn't surprised that humans were the biggest contributor to the discovery of microplastics in the Meramek River, but she was surprised by
how widespread these microplastics were throughout the basin.

"We know there will be microplastics out there, but the amount of plastic is everywhere
," Hasenmuller said.
"I was surprised
that I thought that river flow and sediment load could have had a greater impact on distribution than we saw.
"

Now, attention has turned to how to prevent these microplastics from entering freshwater systems
.
There are already small steps individuals can take to reduce plastic consumption, such as ensuring that plastic is recycled by recycling plants, but researchers will also look to the future and identify large-scale remedial measures to protect our freshwater systems
.

"I think the biggest solution to the microplastics problem is also one of the hardest, and that is to reduce the amount of
plastic we use," Hasenmuller said.
"Almost everything is plastic; We have plastic in our clothes, food and water are stored in plastic, and all these different things in our daily lives are made
of plastic.
So getting big companies to reduce the amount of plastic they use could have an impact, because there's only so much
we can do as consumers.
”

SLU's students contributed to the study, including co-first authors Teresa Baraza and Natalie Hernandez
.
Other authors of the paper include Dr.
Chin-Lung Wu from SLU's Department of Biology, and Jack Sebok
from Washington University in St.
Louis.

This research was supported
by The Nature Conservancy (061716-01).