It's part of the problem, but I don't think we've studied individual contributors as much as looked at the big picture. There was a study on plastics in general that has some citations of the statistics it gathers, and I ran across it in looking up specifically the rubber from tires, aka tire dust from wear and tear (which all vehicles have to some degree, even EVs, and is often a part of the argument of less cars rather than different cars). So about 1 millions tons of the annual contribution to plastics in the ocean is due to tire dust in runoff waters. Also keep in mind that like many large studies that take a while to put together, I think a lot of these statistics are old (around 2016). It's probably worse now.