New research from the College of Charleston sheds more light on an overlooked source of plastic pollution: the water sent to sewage plants.
Wastewater doesn't just include what's flushed down a toilet. It incorporates any water that goes down a household or business's drain.
The main source of plastic in that water from a home comes from washing machines: Laundering gradually breaks down synthetic fabrics.
That leaves tiny plastic fibers in the water that are washed away and end up at sewage treatment plants, said Barbara Beckingham, a professor at the College of Charleston.
Beckingham, along with four other authors, recently published a peer-reviewed study comparing how well area wastewater plants were able to filter out the plastics.
Researchers took samples at the beginning and end of the treatment process at three local facilities: Charleston Water System's Plum Island plant and Mount Pleasant Waterworks' plants at Rifle Range Road and on Center Street.
While each plant was able to remove more than 90 percent of the plastics in at least one sample, Plum Island was most consistent in plastic removal. One of the likely reasons is that the facility, unlike the other two, includes large pools, or "primary clarifiers," which hold water for about two hours of the treatment process. The pools let particles like plastics fall out of the sewage effluent before it moves on to the next stage of treatment.
Alan Clum, the operations manager at MPW, was another author of the study. He said that plants are designed in different ways because while one screening process might be good at removing a certain contaminant, it might miss another.
For example, investing only in a process that removes plastics could ignore contaminants like pharmaceuticals.
"I think you’ll find with all different treatment processes there are pros and cons to each," Clum said.
The study also underlines how different behavior can reduce the amount of plastic in the water by reducing the microplastic load before the sewage ever reaches a plant.
Buying clothes made out of organic materials, or washing clothes at colder temperatures, creates fewer plastic fibers in wastewater in the first place, Beckingham said.
Plastic pollution has become a global issue as governments, consumers and environmental activists take a closer look at where much of the world's disposable packaging eventually ends up. Their growing concern has inspired bans or restrictions of single-use plastics in several cities in South Carolina and elsewhere.
And indeed, that type of trash is a huge contributor to the microplastics that have been found in waters around the world. Plastic litter breaks down into tiny pieces imperceptible to the human eye but whose particles still linger in the food chain and even in drinking water.
It's still unclear what effects those particles have on the health of humans and animals. Complicating the current scientific research is the fact that "plastic," as commonly understood by the public, is a broad category of many different materials with different chemical structures.
Still, some research has shown that some animals, like mussels, are able to expel many of the particles.
Previous research done at The Citadel has shown that plastic films like those used for grocery sacks start generating significant amounts of microplastics in as little as eight weeks, when placed in area marshes.
But while that plastic trash contributes a lot more to the total mass of plastic in the oceans overall, that's not the only important factor, Beckingham said.
Already-tiny microplastics coming out of sewage plants, she said, "can be immediately taken up by organisms in the estuary, like fish. It’s already in this small size that can be consumed, and we don’t know what the risks of that are yet."