As ubiquitous as rubber tires are due to their many practical benefits, they come with a limited lifespan. Over time, the part of the tire that contacts the road surface wears away, but the material that wears away ends up in the environment.
This worn-away material is counted as microplastic, a known environmental pollutant. In addition, more recently, one additive commonly found in tires, called 6PPD, is highly toxic to certain species of fish and other marine life.
LINK (via Hackaday)