What are microplastics and how do they typically enter freshwater systems?

• A. Microplastics are plastic particles smaller than 5 mm; they originate from breakdown of larger plastics, microbeads, and wear of composites, and they enter water via litter, wastewater effluent, and runoff.
• B. Microplastics are natural fibers shed from plants and enter water through soil erosion.
• C. Microplastics are metal fragments from manufacturing and enter water via air deposition.
• D. Microplastics are microbe-derived particles and enter water only through direct discharge from manufacturing.

Answer: (A)

Microplastics are plastic particles smaller than 5 mm. They originate from the breakdown of larger plastic items, from microbeads used in some products, and from wear of synthetic materials like tires and composites. They typically enter freshwater through litter that ends up in rivers or is carried by wind and rain, through wastewater effluent that still contains microplastics from washing and disposal, and through runoff from land during rain events. The other options describe natural fibers, metal fragments, or mischaracterize microplastics as something they are not, and don’t capture the actual plastic-based sources and pathways into freshwater.