Institution: | (1) Institute of Geochemistry, The Chinese Academy of Sciences, Guiyang, 550002, P.R. China;(2) Prevention Department, Stomatology School, Beijing University, Beijing, P.R. China;(3) Stomatology School, Hebei University of Medicine, Shijiazhuang, P.R. China;(4) Institute of Endemic Disease Prevention of Hebei Province, Shijiazhuang, P.R. China |