Fifteen years ago, scientists at the National Institutes of Health reported that malformed prions—proteins that can trigger lethal illnesses including mad cow disease—remain on soil surfaces for at least 3 years. Now, scientists report why rain doesn’t flush away the prions: The proteins bind almost irreversibly to clay.
In fact, clay can “retain up to its own mass of … prion proteins,” says Peggy Rigou of the National Institute of Agronomic Research (INRA) in Jouy-en-Josas, France.