Technical and political hurdles have slowed Russia’s efforts to dismantle dozens of decommissioned submarines before they fall apart or their nuclear fuel is stolen.

The biggest ever study of Arctic pollutants paints a picture of an ecosystem under siege—with potentially grave consequences for denizens of Earth’s northernmost reaches.

Thirty minutes before the plane touches down in Koryazhma, a Russian mill town of 44,000 built by prisoners sent to operate the Kotlas plant when it opened in 1961, clear …