Enrichment of Cd and Pb and associations with grain size in sediments in Nanjing alluvial island of Yangtze River

Intermittence belts of metal contaminated sediment have been formed along the urban riverside of the Yangtze River because of rapid urbanization and industrial development during the last three decades. Baguazhou Island, the third alluvial island in the lower reaches of the Yangtze River, was chosen to assess the contaminations level of Cd, Pb, Ni, Cr, Cu and Zn in suspended particulate matter （SPM）, recent sediments and sediment-derived soils. The relations between the metal concentrations and the grain size distributions in sediments were analyzed in order to explore the association of heavy metal settling with sediment deposition. The results showed that significantly high levels of Cd and Pb in SPM dominated enrichment factors （EFs） of recent sediments in the area of Baguazhou Island. High levels of Cd and Pb were found both in the riverine sediments and in the soils. However, the average levels of Cd and Pb in sediments were almost as twice as those in soil. About 43% of all sediment samples have EFCd≥1.5 and 14% with EFCd≥2. There are about 21% of the samples with EFPb≥1.5 and none of them has EFPb≥2. Meanwhile, soil samples with EFCd≥1.5 account for 39% of all 64 samples and no one with EFPb≥1.0. Most of the sediment samples contain more than 80% of fine grains lower than 60 μm in size, and few samples located in the site where flow eroding process dominates contain fine grains lower than 30%. Correlation analysis indicated that the concentrations of Cd and Pb in the sediments have significant relationships with grain size.

Enrichment of Cd and Pb and associations with grain size in sediments in Nanjing alluvial island of Yangtze River