There’s gold in them thar sewers—tons and tons of it!

Researchers from Arizona State University analyzed sewage sludge—the stuff left behind after treating raw sewage—with a mass spectrometer, and found that a city of a million people gives out $13 million worth of metal annually—and $2.6 million of it is silver and gold.
Where does all this gold come from? Speculation is that it finds its way into our sewage through the processes of manufacturing, such as mining, electroplating, and the manufacture of jewelry. It should be no surprise that there are items of value in the sewers—workers in Modesto, California, were once investigated for selling wedding rings and other items of jewelry that had been flushed down the toilet.