"Microplastics" is the broad category for several different kinds of plastic bits that are smaller than 5 mm. Primary microplastics are manufactured “micro” to serve as the building blocks of many items for modern living. Secondary microplastics, on the other hand, are never intended to be tiny. They begin as large plastic objects, and over time in the environment, wind, waves, and energy from the sun help break them down.

PRIMARY MICROPLASTICS

image of round nurdles washed up on shore Nurdles

Manufacturers melt down these lentil-sized pellets to create larger plastic items—everything from plastic bottles to car parts. Nurdles can get into waterways through spills at sea as they are being shipped as cargo to plants for manufacturing and transforming into usable products. They can also enter waterways through stormwater near the plants where manufacturing occurs.

image of tiny microbeads Microbeads

Found in toothpaste, shampoos, facial cleaners, and other products, these tiny beads flow into wastewater through sink and shower drains. Treated wastewater is released into freshwater systems, often with no treatment to eliminate or reduce the microbeads. They can also be found in sewage sludge, which many municipalities send to rural areas as fertilizer.

SECONDARY MICROPLASTICS

image of multi-colored plastic bits in a person's hand. Fragments

A piece of a once-larger plastic bag, toy, bottle, or other item. Plastic fragments are common sights in urban areas, such as Baltimore’s Inner Harbor and the Anacostia and Potomac waterfronts in Washington, DC, and may be ingested by wildlife in those ecosystems. Gathered in trash traps, they can reach an impressive volume given their small size.

Image of a single thread of plastic, taken through a microscope. Microfibers

These fibers come from clothing that’s made of synthetic fabrics, such as nylon, fleece, and polyester. Washing and general wear separates the microfibers from the clothing, and they are flushed into our wastewater systems and released into the air. They are a common microplastic in marine environments and also come from fishing lines and nets, which are a large source of debris in the ocean.

Close up image of a lump of white polystyrene (looks similar to a kernal of popcorn) on a black background.. Polystyrene

Expanded polystyrene is used to make the cups and takeout containers often referred to as styrofoam. But Styrofoam is a trademarked name of DuPont; it is an extruded polystyrene, more rigid than the type used in cups, and used as insulation. Of the two, it’s the expanded polystyrene that is ubiquitous in the ocean and streams, in part because it is not recyclable.

Photos (top to bottom): Nurdles, Tristan Baurick / NOLA.com; Microbeads, Minnesota Pollution Control Agency; Fragments, NOAA; Microfiber, J. Adam Frederick / MDSG; Polystyrene, Will Parson / Chesapeake Bay Program