Pollution into the waters, then up into the clouds, then down on your head as rain, I would assume is the cycle.
aThe water vapor coming off the polluted waters does not contain any of the pollutants. Any metal pollutants are in the air. How do those pollutants get into the air? Where do they come from—fragments from the stuff in orbit around the earth? Asteroids? Volcano eruptions? Motor vehicle wear on the roadways? Any Idea?
In evaporation, only the water molecules vaporize. The contaminants are left behind. That’s why “distilled” water is pure. Rain starts from the same process. Rain can pick up other things already in the atmosphere like CO2, making it slightly acidic, or sulfur and particulates already airborne, but it starts out pure. Metal particles just don’t stay airborne for long.