By Janet Raloff
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.