Distribution characteristics and source analysis of heavy metals in surface sediments of the Yellow River estuary.

To investigate the spatial distribution, ecological risk, and potential sources of heavy metals in the surface sediments of the Yellow River estuary, we analyzed and evaluated the contents of 10 heavy metals (Cr, Cu, Zn, Cd, Pb, Ni, V, Co, Mn, and As). The results showed that heavy metals content in the surface sediments of the Yellow River estuary all met the marine sediment quality standard Class I, with the highest average content of Mn (676.60 mg·kg) and the lowest content of Cd (0.17 mg·kg). The high-value zones of As and Pb were mainly concentrated in the areas from Xiaoqing River estuary to northwestern Yellow River estuary, while the high-value zones of other heavy metals were mostly concentrated in the Yellow River estuary and its northwestern sea. Cu and Zn exhibited no enrichment, while other heavy metals showed mild enrichment, with Cd having the highest enrichment coefficient (1.76). The Cd geo-accumulation index was the highest (0.32), whereas the index for other nine heavy metals was all less than zero. The potential ecological risk index was ordered as Cd > As > Pb > Co > Cu > V > Ni > Cr > Mn > Zn, presenting a moderate potential ecological risk overall in the surface sediments of Yellow River estuary. The potential sources of heavy metals in this region could be divided into natural source (Ⅰ, 40.1%), watershed agricultural-industrial-residential mixed source (Ⅱ, 34.6%), and estuarine oilfield exploitation-agriculture mixed source (Ⅲ, 25.3%), respectively. Cd mainly derived from human activities, with sources Ⅱ and Ⅲ contributing 36.6% and 38.4%, respectively. In conclusion, Cd in this region need more attention and to be controlled. Human activities are the primary source of heavy metals in the surface sediments of the Yellow River estuary.