Trace metals in the suspended particulate matter of the Yellow River (Huanghe) Estuary: Concentrations, potential mobility, contamination assessment and the fluxes into the Bohai Sea

Excessive input of trace metals contributes much to the degradation of many coastal ecosystems. As one of the most turbid large rivers in the world, the Yellow River, also called Huanghe, transports huge amounts of freshwater and suspended particulate matter (SPM) each year from its catchment as far as thousands of kilometers inland into the Bohai Sea, and has the most profound influence on the ecosystem of the Bohai Sea compared with other rivers that empty into it. In this research, the SPM were collected from the Yellow River Estuary twice in April and August, 2013. Six environmental quality assessment-related trace metals, namely Cd, Cr, Cu, Ni, Pb and Zn, were measured for their total concentrations and fractionations to understand their spatial and seasonal variations, potential mobility, pollution status and fluxes. The total concentrations of Cd, Cu and Pb in the wet season were very similar to their corresponding values in the dry season, while the total concentrations of Cr, Ni and Zn in the wet season were slightly higher than those in the dry season. The distributions of the studied metals in the geochemical fractions showed no notable spatial and seasonal variations. Except for Cd and Ni, the metals in the most labile fraction having the highest potential risk to biota on average accounted for