A knuckle is a small plastic granule that is used to create just about anything out of plastic. From plastic bottles to car parts, they are widely used in plastic production. They are the raw material for everything that is made of plastic. But even if they are small, their damage is enormous and immeasurable.
Knuckles are, by definition, a microplastic, because they measure less than 5 mm. They enter the oceans already in the form of microplastic, which is why they are known as “primary microplastics”. There are no IMO regulations that specifically require the safe transport of plastic granules across the ocean, despite the impact that granule pollution has on the environment. They contain contaminants from fossil fuels or recycled products used to make plastic (substances added unintentionally, such as heavy metals), as well as additives that are used to make plastics colorful, flexible and usable (additives such as dyes, phthalates and plasticizers).
These chemicals are present in granules and are often more reactive and mobile than the plastic polymer itself and can leach out of the plastic once they are in the environment. The polymer is then molded into plastic resin granules or nourishes the raw material used to make most plastic products. Pre-production plastic granules or “knuckles” are approximately the size and shape of a lentil and are the basic components of almost all plastic products. To reduce the amount of plastic used to transport knots and increase the volume per container, manufacturers can also blow knots into a single heavy plastic liner that fills the container.
Although reports of plastic ingestion in this species are relatively scarce, it is common for them to become entangled in plastic waste.