Chemical partitioning of heavy metal contaminants in sediments of the Pearl River Estuary

Sequential extraction was used to study the operationally determined chemical forms of four heavy metals (Zn, Cu, Ni and Co) and their spatial distribution in the sediments of the Pearl River Estuary. It was found that the residual fraction was the most important phase for the four metals in these sediments. Among non-residual fractions, Zn, Ni and Co were mainly associated with the Fe–Mn oxide fraction while Cu was associated with the organic fraction. The Zn bound to the Fe–Mn oxide fraction had significant relationships with reducible Mn and reducible Fe concentrations (Fe–Mn oxides), suggesting that Fe–Mn oxides may be the main carriers of Zn from the fluvial environment to the marine body. There was a significant relationship between Cu bound to the organic fraction and sediment organic contents. The Zn bound to the Fe–Mn oxide fraction and Cu bound to the organic fraction showed general distinctive decrease from the west side to the east side of the estuary, and from upstream in the north to the sea in the south. This was in the same trend with the total Zn and Cu concentrations in these sediments. The results may reflect the anthropogenic inputs of heavy metals to the top sediments from recent rapid industrial development and urbanisation in the surrounding area.