In Seoul last week, South Koreans were stripping shop shelves of plastic bin bags. Not food, not medicine. Bin bags.Nearly 2.7 million of the city’s mandatory “pay-as-you-throw” bags were sold each day, almost five times the normal volume, as residents scrambled to stockpile what they feared might soon become scarce.City by-laws mandate that the prepaid bags – made from naphtha, a petroleum derivative – be used to throw away household waste. But with oil supplies under strain amid the...