Black slime has invaded the nation’s capital. The dark goo is called biofilm. It’s a community of bacteria, algae, and other microscopic organisms—and it’s spreading across the white marble of the Jefferson Memorial in Washington, D.C.
Biofilm can grow on rock, metal, plastic—even teeth, in the form of plaque. “Wherever you find moisture, nutrients, and a surface, you will probably find biofilm,” says Federica Villa, a microbiologist at the Center for Biofilm Engineering in Montana.
The National Park Service, which manages the Jefferson Memorial, wants to get rid of the spots. But weathering has created tiny cracks in the stone where biofilm remains after cleaning. The agency is testing chemical treatments and may even try using lasers—beams of concentrated light—to burn away the slime.