A team of researchers have investigated how the contents and flow of streams impact microplastic retention.
These tiny plastic particles, found in everyday products from face wash to toothpaste, are an emerging threat to health and ecology, prompting the team to identify what affects microplastic retention in stream ecosystems.
Everyday actions like washing synthetic clothing and driving, which wear down tires, contribute to an accumulation of microplastics in environments from city dust to waterways. These plastics often carry toxic chemicals that can threaten the health of humans and wildlife.
“We are the key source of microplastics,” said Shannon Speir, assistant professor and researcher in the Dale Bumpers College of Agricultural, Food and Life Sciences and for the Arkansas Agricultural Experiment Station.
The study explains that microplastic retention in streams is concerning because they can be ingested by aquatic organisms, posing threats to their digestion and fertility, all while easily spreading.
How microplastic structure affects movement
Microplastics are unique in size, structure and weight. They measure less than five millimetres across and can be round, as found in some face washes and toothpastes, or they can be string-like fibres like the tiny particles that can shed while laundering synthetic clothing materials such as polyester or nylon.
Eventually, these microplastics can end up in rivers and oceans.
These differing sizes and shapes make microplastic movement more complex, leading the researchers to examine what factors lead to their being trapped in streams.
Pinpointing areas of microplastic retention and removal
The team designed the experiment by lining four artificial streams with substrates made of cobble, pea gravel, sand and a mixture of the three.
Then, they colonised the streams with benthic algae, or algae that live on the bed surface, and experimentally released microplastics over three days to test microplastic retention as substrate, discharge levels and algae presence varied.
The team found that streams with higher levels of algae, larger stream substrates and higher levels of stream discharge all saw increased levels of microplastic retention during the study’s three-day experimental period.
Findings also revealed that in instances of rapid increase in discharge, such as a storm, microplastics can become resuspended, meaning they are lifted from the bottom of the stream where they have settled.
These events increase the potential for these particles to be transported downstream.
John Kelly, biology professor and department chair at Loyola University Chicago and corresponding author of the study, explained: “The results of this study demonstrate that certain stream characteristics, for example, a rocky bottom compared to a sandy stream bottom, can determine where microplastic particles will be deposited within a stream.
“These results could be used to determine which locations to prioritise in clean-up efforts.”
He added: “In addition, our results demonstrate that storms can result in the movement of microplastics from the stream bottom to the water and their subsequent transport downstream, which could be used to determine the best timing for efforts to remove microplastics from streams.”
Collective action is essential
Speir explained the everyday ways individuals can combat microplastic deposition into stream ecosystems, and she cautioned them against thinking these singular actions will not be impactful.
She cited the use of laundry bags designed to catch microplastics that shed from clothes as they are washed.
She concluded: “I think that if we all do a little bit, that amounts to a large amount.
“We always need to keep in mind when thinking about environmental things that are individual actions, even though they’re small, collectively, we have the opportunity to make a really, really big difference.”
