Distribution, source investigation, and risk assessment of topsoil heavy metals in areas with intensive anthropogenic activities using the positive matrix factorization (PMF) model coupled with self-organizing map (SOM)

Wanjun Jiang, Lishan Meng, Futian Liu, Yizhi Sheng, Sheming Chen, Jilong Yang, Hairu Mao, Jing Zhang, Zhuo Zhang, Hang Ning