This is one bizarre way to ride out the current economic lull: A treatment plant in Japan has been processing effluent to recover small quantities of gold contained in sewage. And in one year it's produced a higher yield than you might expect from a gold mine.
The sewage mining was carried out in Nagano prefecture, northwest of Tokyo. And its location may have something to do with its success as a gold source: There are apparently a number of "precision equipment manufacturers" in the region that utilize gold in the manufacturing process. Presumably it's washed into the drains at some point and then enters the local water cycle.
The process doesn't sift for nuggets, of course, instead it involves incinerating the digested poop sludge and processing the ash—recent gold salvage figures reached about 1.9kg of gold per ton of ash. It's earned the Nagano prefecture a total of $168,000 over the last fiscal year. Or thereabouts, as the actual total depends on international gold price variations.
Gold is also present naturally in the environment, of course, in gold mines and in other places. It's not toxic, by itself, and some medicines actually exploit gold—for the treatment of arthritis, for one. Most famously it's found naturally in sea water, but at terrifically low concentrations—estimates place it at around 1 gram for every 100 million tonnes of sea water in the Atlantic and North Pacific.
It seems that sewage is a better source, at least for Nagano, and it's a perfect ratification of the old northern English saying "Where there's muck, there's brass." All it needs is a quick edit to change the metal.