Distribution and Risk Assessment of Heavy Metals in Sediments of the Pearl River Estuary, Southern China

Sediment cores collected at six freshwater discharge outlets of the Pearl River Estuary were analyzed for metal (Al, Fe, Cr, Pb, and Cd) concentration and risk assessment. The contents of Cr, Pb, Fe, and Al in these samples were measured by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), and Cd was measured by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The result showed that the concentration ranged (in mg/kg dry weight) as follows: Al, 7,880-97,700; Fe, 30,100-51,900; Cd, 0.23-1.09; Cr, 48.7-109; Pb, 22.3-70.2; respectively. The sediments of different particle size were measured and the result showed that the pelitic fraction (< 0.05 mm) was more enriched in heavy metals. Cd and Pb showed a similar spatial distribution in the sediment, which reflected similar anthropogenic origins. In addition, the temporal distribution of Cr, Pb, and Cd showed a light increase from the 1970s to the 2000s. Furthermore, the enrichment factor (EF) and the geo-accumulation index (I-geo) were used to comprehensively evaluate the pollution degree of heavy metals. The findings will be useful in proposing measures for strategic environmental control in estuaries.