In Hungary, several villages were devastated earlier this week when a highly caustic waste product from an aluminum factory poured out of its holding reservoir. Four people were killed as the red sludge spread through the villages and into rivers and creeks. Those waterways in turn have now carried the sludge to the Danube -- Europe's second-longest river. And neighboring countries are monitoring the water to make sure the sludge is effectively diluted. NPR's Robert Siegel talks with Elisabeth Rosenthal, environment reporter for the New York Times, who is in Budapest.