Tiny particles of rubber cast off by car tires, which have long been known to harm wildlife, may also pose a risk to humans, according to a new study.

The chemical 6PPD, which is added to tires to prevent cracking, transforms when exposed to ozone pollution, which arises from car exhaust. One compound formed from this process, 6PPD-quinone, has been implicated in the deaths of spawning coho salmon in the Pacific Northwest. For decades, heavy rains have led to surges in salmon deaths as polluted stormwater washed into urban waterways.

The new study finds that many of the other chemicals derived from tire wear may pose a threat to humans when inhaled.