Distribution and pollution assessment of heavy metals in the sediments of Jiaojiang River

The river sediment acts not only as the major carrier but also the secondary sources of heavy metal contamination in river water. Elemental concentrations and chemical phases are essential to the study of heavy metal contamination in rivers and the evaluation of their ecological risks. In this study, 1 mol/L hydrochloric acid (HCl) is used to leach heavy metals out from the samples (including both floodplain sediment and suspended particulate matter) collected from the Jiaojiang River, aiming to investigate the distribution of heavy metals (Zn, Pb, Cr, Cu and Cd) in acid-soluble and acid-insoluble phases, and thus to explore the major sources of heavy metals and their ecological risks. The concentrations of Zn, Pb, Cu and Cd in the Jiaojiang sediments are significantly higher than the local background values and their leaching rates, the ratios of elemental concentrations in the leachate to those in bulk samples, are higher than 60%. When the environment conditions change, heavy metals in the leachate can be easily released to the overlying water column and cause high ecological risks. The results of correlation and principal component analyses reveal that heavy metals in the leachate are incorporated into the sediments from aqueous solution, by processes such as adsorption onto Fe-Mn oxides and organic complexation, predominantly controlled by emissions from industrial and agricultural activities. According to the data of enrichment factor (EF) and potential ecological risk index, Cd is the most enriched element in the Jiaojiang sediments, especially in the upstream region, the Yongan River, where Cd is significantly enriched with high ecological risk, while Zn, Pb, Cr, Cu all display mild to moderate increase. The accumulation of heavy metals in the rivers in southeastern China and their ecological risks deserve further investigation.