Tires and degrading garbage shed tiny pieces of plastic into the air, creating a form of air pollution that researchers at the University of California San Francisco (UCSF) suspect may be causing respiratory and other illnesses.

A review of some 3,000 studies implicates these particles in a variety of serious health problems including male and female infertility, colon cancer and poor lung function.

The review is published in the journal ‘Environmental Science & Technology’. The particles also may contribute to chronic pulmonary inflammation, which can increase the risk of lung cancer.

“These microplastics are basically particulate matter air pollution, and we know this type of air pollution is harmful,” said Tracey J. Woodruff, Ph.D., MPH, a professor of obstetrics, gynecology and reproductive sciences at the UCSF.

Woodruff directs the Programme on Reproductive Health & the Environment (PRHE) and is the senior author of the study.

Microplastics are less than five millimeters—smaller than a grain of rice—and they are ubiquitous in the environment. Each year, companies around the world produce nearly 460 million metric tons of plastic. That is projected to reach 1.1 billion by 2050.