tire dust is behind major die offs of juvinile salmon, thete are specific toxic compounds in it, and when therevare major rain events, all the dust in the ditches gets washed into rivers and streams in high enough concentrations to kill all the fish. from memory the toxic compound is some sort of biocide put in tires, to keep them from bieng eaten by ? algea? fungus? whatever, not an important detail, but an additive that can be eliminated or replaced, $$$$$$$$

> biocide

It's an anti-oxidant, to protect tires from UV and ozone degradation.

Tire companies are in the process of switching to a different anti-oxidant.