Fish Sperm Could Help Recycle and Extract Rare Metals

A fake salmon at a fish market in Tokyo. Thomas Peter / REUTERS

Rare earth metals like neodymium are becoming an increasingly important part of modern life, used to make everything from tiny batteries to wind turbines to television screens.

But refining them (not to mention mining them from the Earth) is an environmentally dirty process. To tease the metals out of crude ore, processors use large quantities of chemicals like bases, acids, sulfates and ammonia, sometimes employing arsenic and mercury as well. These chemicals can lead to all sorts of negative effects on the environment, from killing fish by altering the water's pH to causing human illness, a big problem in China, where much of the world's rare earth metals are mined.

Japanese researchers looking for a more environmentally friendly alternative have happened upon an unlikely potential candidate: salmon sperm.

The scientists, led by Yoshio Takahashi of Hiroshima University, found that several rare earth elements bound strongly to phosphate-containing molecules on the surface of bacterial cells, according to Chemistry World, a publication of the Royal Society of Chemistry. So they turned to salmon sperm, since it is largely made up of DNA, which contains a lot of phosphate. (And it's also insoluble in water, unlike pure DNA, making it easier to work with.)

They found that the metals contained in neodymium magnets (including neodymium, dysprosium and trivalent iron) and several other rare earth elements bound strongly to DNA within dried and powdered salmon sperm. The metals were then recovered by adding acid to the solution and separating the various substances using a centrifuge, according to the PLOS ONE study where the team described their work.

Although this process still requires some acid, it has promise, according to Jean-Claude Bünzli, a scientist who studies these chemicals at the Swiss Federal Institute of Technology. He told the publication that salmon sperm, also known as milt, might be particularly useful for recycling the metals within the alloys found in electronic circuits, mobile phones and hard disk drives.

The process may however be difficult to scale up, said Bünzli, who wasn't involved in the study. But the work is "quite interesting…and deserves more attention," he added.

Milt is readily available and cheap. In Japan alone, the fishing industry produces thousands of tons of it as waste every year.