Tire toxicity faces fresh scrutiny after salmon die-offs

For decades, concerns about automobile pollution have focused on what comes out of the tailpipe.

Now, researchers and regulators say, we need to pay more attention to toxic emissions from tires as vehicles roll down the road.

At the top of the list of worries is a chemical called 6PPD, which is added to rubber tires to help them last longer.

When tires wear on pavement, 6PPD is released. It reacts with ozone to become a different chemical, 6PPD-q, which can be extremely toxic — so much so that it has been linked to repeated fish kills in Washington state.