The operator of McDonald's in Japan and Cargill Inc have not discovered any link between a Cargill-owned plant in Thailand and a strip of plastic found in a chicken nugget this month that sparked uproar over product safety at the fast-food chain. McDonald's Holdings Co Ltd and Cargill said in separate statements on Wednesday that an investigation showed the type of plastic found in the McNugget on Jan. 3 by a customer in Misawa, northern Japan, was not used at the plant in Saraburi, Thailand where the food was produced.