Association of single and combined metal burdens with systemic immune inflammation in smelter workers: A population-based study - Di Wu; Yuankai Cheng; Shuxian Wang; Na Wang; Danhua Zhang; Zhaoyan Wang; Jianxia Cao; Yuzheng Li; Yanhong Li; Jinrui Ma; Yingzheng Zhao; Sihua Wang (Journal of Trace Elements in Medicine and Biology, 2026)