Turning to classification of (mostly discarded) plastics in terms of their form and size, although most people associate plastics with easily discernible items, such as water bottles and shopping bags, some discarded plastics exist in the form of particles that are so small they cannot be seen with the naked eye. The past two decades have seen significant development in research on microplastics, a term which refers not to the chemical composition of the material but rather the size of its current form, beginning from less than about one fifth of an inch and becoming increasingly smaller, in contrast to plastic items large enough to be distinguishable in plain sight (e.g., water bottles, eating utensils), which are known as mega plastics (5 to 10 millimeters in any one dimension) or macro plastics (items measuring more than 20 millimeters in diameter). In recent years, plastic particles even smaller in scale than microplastics have been found: these range from 1 to 1000 nanometers in size, forming a subcategory known as nanoplastics. Yet another way of classifying microplastics is by the process through which they have been formed. Primary microplastics are produced intentionally, usually for commercial purposes: examples are the microbeads used in manufacturing toothpaste, shampoo, liquid soaps, and cosmetics, and those that defend human health against unwanted pathogen vectors, as for example in insecticides. Secondary microplastics, in contrast, are formed by the breakdown of larger pieces of discarded plastic goods, often brought about by exposure to sunlight or wind and wave motion. All these technical contrasts are examined in detail in Microplastic in the Environment, edited by Michael Bank. Readers may find selected chapters to be of interest, and it is worth noting that the publisher makes these available as individual downloads.
Microplastic in the Environment: Pattern and Process by