Washington and California recently adopted laws that ban all but traces of copper in automotive brake pads by the year 2021. The two states say the metal gets into watersheds and hurts endangered salmon. The decision could change the way brakes are made around the world.
Copper is a great material for brakes. It's durable, and it absorbs heat and noise. But it comes with an environmental price.
"Each time a driver uses their brakes, a small amount of the material gets worn off, and when it rains, that can be washed into streams and rivers," said Ian Wesley, who's with the Washington State Department of Ecology.
About a third of the copper in some watersheds in California and Washington State comes from brakes. And copper is not good for salmon, because it wreaks havoc with their ability to smell.
Salmon release a pheromone when they perceive a threat. Other salmon react to the scent by dropping to the bottom of the water and staying there, very still.
"When they do that, it helps them avoid the predators, but if there's even very low levels of copper in the water, they can't smell this pheromone, and they continue to swim around kind of oblivious to the danger that's nearby," said Wesley.