Geologists study deposits—fluvial deposits, eolian deposits, ore deposits, etc.—but one deposit that I’ve never considered until now, or at least in the geologic sense, is the deposit left in the...um…toilet. It is possible that your poop contains precious metals. You may have quite literally been flushing gold down the toilet (albeit in microscopic amounts).
What happens to solid waste once we flush? And more importantly, how on earth did someone make this discovery? Treated biosolids get sent to one of three places: the incinerator, the landfill, or a fertilizer plant (to make fertilizer). In order for biosolids to become fertilizer though, they must be stripped of some harmful metals. As it turns out, biosolids also contain precious metals—silver, copper, palladium, vanadium, and even gold can all be found in sewage. Scanning electron microscope images, like the one shown here, can verify that these tiny specks of metal are real.
A few steel-stomached scientists at the USGS are looking for ways to make the most of this stinky situation—specifically using leachates (a chemical used in traditional mining) to extract the profitable minerals from poop. It may not seem like a financially viable option, but another study estimated that extracting metal from the poop of one million Americans could yield $13 million.
How did metals end up in the toilet? I, for one, am definitely not snacking on edible gold. Dr. Kathleen Smith, the leader of the USGS study, says that metals in tiny amounts are actually everywhere—shampoo, laundry detergent, even in socks. That stuff may get into our digestive system and it may also get in sewage in other ways—the exact route of these metals is still unclear.
Who knows if this will ever prove to be a worthwhile economic venture…but it will definitely make us think twice next time we flush.
