Despite the claims of producers, researchers say that, while the compounds can hasten the pace at which plastics break down, they simply turn into millions of microplastic particles that end up in our soil, streams and ultimately our stomachs, lungs and brains. “There’s no evidence we can see that they work,” says Mark Miodownik, professor of materials and society at University College London. “Biodegradability is not a panacea.”