"Typically the concentrations are small in red mud and what is present is tightly bound to the particles of iron oxide, " he says.

BBC: How toxic is Hungary's red sludge?

News of the arrest broke shortly before Witherspoon arrived on the "Mud" red carpet.

NPR: Reese Witherspoon Charged With Disorderly Conduct

She came home red-eyed, her shoes filthy with mud from the yard between their houses.

NEWYORKER: Soldier��s Joy

She appeared on the red carpet in New York on Sunday for the premiere of her film "Mud" but did not speak to reporters.

BBC: Hollywood actress Reese Witherspoon 'arrested'