An experimental study about the effects of phosphorus loading in river sediment on the transport of lead and cadmium at sediment-water interface

Abstract

Phosphorus (P) in the river sediment plays an important role in the fate and transport of heavy metals at sediment-water interface of the aquatic eutrophication environment. To explicate the effect of P loading, the sediments with different P contents were employed in this study to experimentally investigate the adsorption/desorption of Pb2+ and Cd2+ and the releasing behavior of P during the adsorption/desorption processes. Results illustrated a strong affinity between Pb2+ ions and the P-containing sediments in both single Pb and binary Pb + Cd systems. In single-metal systems, the Pb2+ adsorption capacities of all types of sediments (15.04–19.44 mg g−1) were higher than those for Cd2+ (4.68–5.56 mg g−1). While in binary-metal systems, the Pb2+ adsorption was slightly influenced by the coexisting Cd2+, but the Cd2+ adsorption capacities were decreased by over 5 times. Moreover, the adsorption amount and retention ability of Pb2+ on sediment were enhanced by increasing content of P in the sediment. Meanwhile, the releasing of P was also closely depended and significantly inhibited by the Pb2+ attached on the sediment. The P release amounts during the desorption processes of Pb- and Pb + Cd-loaded sediments were over 50 times lower than those from the raw sediments (sediments without heavy metals adsorbed), but the values decreased by a factor of two for the single Cd-loaded sediments. Furthermore, the results of X-ray photoelectron spectroscopy indicated the crucial role of P loading in Pb transport in the sediment and overlaying water. The findings in this study showed important implications for the transport of heavy metals and P at the sediment-water interface and offered new insights for further explicating the mechanisms of secondary pollution caused by heavy metals and P in aquatic eutrophication environment.