Microplastics are small plastic pieces that measure less than 5 millimeters in length. They can come from a variety of sources, including larger plastic debris that degrades into smaller and smaller pieces, resin pellets used for plastic manufacturing, or in the form of microbeads, which are small, manufactured plastic beads used in health and beauty products. Microplastics can also arise from the degradation of larger plastic products through natural weathering processes after entering the environment. Two classifications of microplastics are currently recognized: primary microplastics and secondary microplastics. Primary microplastics include any plastic fragments or particles that are already 5.0 mm in size or less before entering the environment. These include microfibers from clothing, microbeads, plastic glitter, and plastic pellets (also known as nurdles) . Secondary microplastics arise from the breakdown of larger plastic products through natural weathering processes after entering the environment. Such sources of secondary microplastics include water and soda bottles, fishing nets, plastic bags, microwave containers, tea bags, and tire wear. Microplastics are a growing concern regarding plastic pollution in the marine ecosystem, where they are commonly found in hand soaps, face cleansers, and other exfoliators. Microplastics are harmful to the environment and animal health, and they can be detrimental to the organisms they come in contact with, including by causing reduced feeding, poisoning, and increasing mortality.