A newly published study advances our knowledge of how microplastics may age in the environment and whether they stick to other contaminants as they do so.
Microplastics (MPs) are tiny plastic pieces that measure less than five millimeters (about 0.2 inches) in length.
The study looked at the aging of MPs made of three common polymer chemicals: polyethylene, polyethylene terephthalate, and polypropylene to see if they changed as they aged and how that affected nearby contaminants.
They found that MPs actively bind copper from water and soil, acting as environmental carriers that can alter copper movement and increase toxicity when discharged into lakes and rivers from wastewater plants. Copper can be toxic to aquatic life like fish, amphibians, and invertebrates, impairing their growth, survival, and reproduction.
The paper appears in the peer-reviewed journal Microplastics and was supported by IAFNS Food Chemical Safety Committee.
Why it Matters
According to the paper, wastewater treatment plants are major pathways for plastic particles into natural waters. During wastewater treatment, plastic particles undergo physical, chemical, and biological processes that can alter their properties. However, it remains unclear how these treatment processes transform MPs and influence their interactions with pollutants like the metal copper.
What They Did
A team from Baylor University degraded the three MP polymers through a process called "accelerated chemical oxidation" to simulate aging at wastewater plants where they tend to concentrate.
They then evaluated how MPs change and interact with other contaminants, such as copper. Their results confirm that chemically-driven oxidation relevant to engineered aquatic environments can alter the physical and chemical properties of MPs.
The experiments showed that both pristine and oxidized MPs could attach to copper across all three polymers noted above. They found that MPs can interact with copper regardless of the MPs' condition.
Caveats
However, the authors caution that "the role of MPs as vectors for copper ions under environmental conditions may be more limited or variable than observed under these accelerated conditions and should be interpreted with caution."
Author Christie M. Sayes, with Baylor University, concludes, "Micro- and nanoplastics are not static contaminants. Their manufacturing, processing, aging, food contact, and digestion history change their physical properties, chemical cargo, bioavailability, and ultimately their potential risk."