In the 1990s, scientists restoring streams around Seattle, Wash., noticed that returning coho salmon were dying after rainstorms. The effects were immediate: the fish swam in circles, gasping at the surface, then died in a few hours.
Over the next several decades, researchers chipped away at the problem until in 2020 they discovered the culprit: a chemical called 6PPD-quinone that forms when its parent compound, a tire additive called 6PPD, reacts with ozone.
