Distribution, contamination and source identification of heavy metals in bed sediments from the lower reaches of the Xiangjiang River in Hunan province, China.

Concentrations of heavy metals Ba, Sc, V, Cr, Mn, Co, Ni, Th, U, Cu, Pb, Zn, and Cd in sediments from the lower reaches of the Xiangjiang River were analyzed using inductively coupled plasma mass spectrometry. The results suggest that there are two metal distribution patterns in these sediments: (1) Ba, Sc, V, Cr, Mn, Th, and U are relatively homogeneously distributed and (2) Cd, Pb, Zn Cu, Co and Ni are heterogeneously distributed. The heterogeneously distributed metals are significantly enriched in these sediments and, thereby, contribute to contamination. Assessments of heavy metal contamination using the Geoaccumulation index, Pollution load index, and potential ecological risk index suggest that the levels of contamination from Cd and Mn are extremely high and moderately high, respectively, in all the sediments from the lower river. In comparison, the levels of contamination by Cu, Zn, and Pb varied spatially, decreasing progressively downriver. The level of contamination by Pb, Zn, and Cu in sediments from the Zhuzhou reach is extremely high, and is moderate to significant high for the Xiangtan, Changsha, and Xiangyin reaches. The ecological potential risks posed heavy metals are ranked, in descending order, as Cd > Pb > Cu > Zn > Cr > Ni > Co > Mn for sediments from the Zhuzhou reach and Cd > Pb > Cu > Ni > Cr > Co > Zn > Mn for sediments from the Xiangtan, Changsha, and Xiangyin reaches. Principal component analysis and enrichment factor calculations suggest that Ba, Sc, V, Cr, Th, and U mostly originate from natural processes. While, Cd, Pb, Zn, Cu, Co, Ni, and Mn are derived from both natural processes and anthropogenic activities. Therefore, strategies for environmental protection in this watershed should focus on contamination by Cd, Pb, Zn, and Cu, with Cd requiring particular attention.