Driving is not just an air pollution and climate change problem — turns out, it just might be the largest contributor of microplastics in California coastal waters.

That is one of many new findings, released Wednesday, from the most comprehensive study to date on microplastics in California. Rainfall washes more than 7 trillion microplastics, much of it tire particles left behind on streets, into San Francisco Bay each year — an amount 300 times greater than what comes from microfibers washing off polyester clothes, microbeads from beauty products and the many other plastics washing down our sinks and sewers.

These tiny plastics, invisible to the naked eye, have been vilified for tainting water and wildlife but are notoriously difficult to study. They’re everywhere and seemingly come from everywhere. They wash into the ocean in all different shapes and sizes, many covered with dyes and chemicals. Scientists and labs across the state, country and world haven’t even agreed on how exactly to measure or sample or study them.

So a team of researchers, led by the San Francisco Estuary Institute and 5 Gyres, a nonprofit research group focused on reducing plastic pollution, set off to create an inventory of sorts to identify all the ways these different microplastics were getting into the San Francisco Bay. They analyzed hundreds of samples from fish, sediment, surface water, wastewater and stormwater runoff and tried to trace the origins of all these particles.

Read the full story on LATimes.com.