South Korean customs authorities are investigating the origin of imports of naphtha, an ingredient for the production of plastics, focusing on Russian supplies, according to Bloomberg. The investigation is looking into the purchases of several petrochemical producers in the country. This includes at least one of South Korea’s largest players, and the customs service has examined the entire industry over the past week. According to sources, the South Korean authorities contacted the Trafigura Group trading house. As part of the investigations, the authorities are looking into the true origin of…