Spatial Variation and Risk Assessment of Arsenic and Heavy Metals in Surface Water and Suspended Particulate Matter in Tail Reaches of the Yellow River, China

To determine the pollution levels and potential toxic risks of arsenic (As) and heavy metals (Cr, Ni, Cu, Zn, Pb and Cd) in water and suspended particulate matter (SPM) in tail reaches (including freshwater reach and low-salinity reach) of the Yellow River as the Flow-Sediment Regulation Project (FSRP) has been carried out for approximately 15 yr, the surface water and SPM were sampled at pre-flood (April) and post-flood seasons (October). Results showed that similar changes of As and metal levels in water and SPM were observed along the tail reaches at pre-flood or post-flood season. Compared to pre-flood season, the levels of As, Cu, Cr and Ni in freshwater reach and the concentrations of Cr and Ni in low-salinity reach rose greatly at post-flood season. The levels of As and metals in SPM of freshwater reach or low-salinity reach at pre-flood season were significantly higher than those at post-flood season (P < 0.01). The pollutions of As and metals in surface water of tail reaches at pre-flood or post-flood season were not serious. The SPM in freshwater reach at pre-flood season were polluted by Cd, As, Cr, Cu and Ni while those in low-salinity reach were polluted by Cd and Cr. The SPM in freshwater reach at post-flood season were polluted by Cd and Pb while those in low-salinity reach were polluted by Cd and Cr. Cd was identified as heavy metal of primary concern at both pre-flood and post-flood seasons. Combined with the existed data reported in present research, this study found that the toxic risk of As and metals in SPM of tail reaches at pre-flood season was higher than that at post-flood season, implying that the implementation of FSRP during flooding season, to a great extent, reduced the toxic risk of these elements. With the long-term implementation of FSRP, the pollution levels of As and metals (particularly for Cd) in SPM of tail reaches might be elevated and the potential toxic risk primarily produced by Cr, Ni and As might be increased if effective measures were not taken in future.