GENEVA (Reuters) - The number of refugees and migrants arriving by land an sea in six European Union countries -- Greece, Bulgaria, Italy, Spain, Malta and Cyprus -- has passed 1 million this year, the International Organization for Migration said on Tuesday. Out of a total of 1,005,504 arrivals by Dec. 21, the vast majority -- 816,752 -- arrived by sea in Greece, IOM said. (Reporting by Tom Miles; Editing by Alison Williams)