Trace metals in sediments and aquatic plants from the Xiangjiang River, China

Purpose The metal concentrations and Pb isotopic composition in sediments and plants from the Xiangjiang River, China, were investigated to understand the contamination and potential toxicity of metals in sediments; to determine the accumulation and distribution of metals in plant tissues; and to trace the possible pollution source of Pb in sediments and plants. Materials and metbods Sediments and plants were collected from 43 sampling sites in the study region. After sediments were air-dried and passed through a 63-mu m sieve, they were acid-digested and DTPA-extracted for determination of total and bioavailable metals. The plants were separated into roots, leaves, and stems; dried; cut into pieces; and digested with HNO3-H2O2. Metals (As, Cd, Cr, Cu, Ni, Pb, and Zn) and Pb isotopic composition were analyzed by inductively coupled plasma-mass spectrometry. Results and discussion Maximum As, Cd, Cr, Cu, Ni, Pb, and Zn concentrations in sediments were 47.18, 55.81, 129.5, 161.6, 160.4, 430.7, and 1,098.8 mg kg(-1), respectively. The bioavailable fractions of As, Cd, Cu, Pb, and Zn had significant linear relationship with their corresponding total contents in sediments while no significant relationship was observed between bioavailable and total contents of Cr and Ni. In general, plant tissues showed higher As, Cd, Cu, Pb, and Zn concentrations and lower Cr and Ni concentrations compared with sediments. The Pb-206/Pb-207 ratios decreased in the order of total > bioavailable > stems a parts per thousand leaves > roots. A strong linear correlation was observed between the Pb-208/Pb-206 and Pb-206/Pb-207 ratios of the plant tissues, sediments, and the possible pollution sources of Pb in the Xiangjiang River. Conclusions As, Cd, Cu, Pb, and Zn demonstrated higher contamination levels in sediments and plants compared with Cr and Ni. Cd had highest potential ecological risk. The Pb from anthropogenic sources with low Pb-206/Pb-207 ratios was preferentially associated with the bioavailable fractions in sediments and accumulated in roots. The Pb in plant tissues is mainly derived from the Pb in sediment and is taken up through the sediment-to-root pathway.