There are two types of microplastics: primary microplastics are manufactured to be of microscopic size, like microbeads from face wash; and secondary microplastics are pieces of plastics that have broke off from larger pieces of plastic, like a discarded soda bottle. Secondary microplastics are a big problem because plastics do not mineralize. This means that plastics do not break down like food would, they just break off into smaller and smaller pieces. So, any bottle, bag, or polyester shirt that is not removed from the environment eventually becomes microplastics. See the previous post and download the beat the microbead app and recycle!
Picture from http://www.beatthemicrobead.org/
Picture from http://www.beatthemicrobead.org/