Pollution characteristics of toxic metals in topsoil of small and medium-sized cities in mountainous areas of loess plateau in china——A case study of GuyuanGui Ma, Xinning Han, Wenxia Zhao, Jiangping Cao and Meiyuan LiE3S Web Conf., 218 (2020) 03034DOI: https://doi.org/10.1051/e3sconf/202021803034