THE TRANSPORTATION OF SILVER NANOPARTICLES BETWEEN WATER AND SEDIMENTS

Silver nanoparticles (AgNPs), one of the most widely used and fastest developed nanomaterials, have gradually aroused people's concern. But the mechanisms of its transportation and transformation across water-sediments remain unknown. To reveal the water environmental behaviors of AgNPs, indoor simulation experiments using the water and sediments sampled from the East Lake of Wuhan were employed for AgNPs and Poly (vinylpyrrolidone)-coated silver nanoparticles (PVP-AgNPs) test, and silver nitrate (AgNO3) was used as a reference. The sedimentation curves, distribution patterns and different forms of silver in the sediments and the release curves were studied within 60 days. The results indicated that most of silver sank into the sediments after they were added into water for 120 hours. Specially, the Ag concentration in the overlying water dropped from the same initial concentration (75 mg/L) to 0.086 mg/L, 0.957 mg/L and 2.770 mg/L for AgNO3, AgNPs and PVP-AgNPs, respectively. After 60 days, all of the Ag species entered the sediments and stayed in the 5 cm top layers. The silver contents of AgNO3 system gradually decreased with increasing depth, while those of the AgNPs and PVP-AgNPs first increased, and then reduced gradually when reaching 2 cm depth. Furthermore, although 24.6% silver existed in 23 cm layer for PVP-AgNPs system, only 2.6% for AgNPs system were observed in the same layer. These distribution patterns indicated that the transport ability of nano-silver was stronger than that of AgNO3, and PVP-AgNPs was stronger than that of uncoated. Speciation analysis showed that silver was mainly combined by sulfides and organic matters in the sediments. The release experiment results showed that the release of nano-silver aggregated in the sediments was much difficult than that of AgNO3, suggesting that the adverse environmental effects of nano-silver would greatly depressed once they entered the real water environment. The above results provide scientific basis to evaluate the ecological security of nano-silver.