Abstract
Characterizing labile metal distribution and biogeochemical behavior in sediments is crucial for understanding their contamination characteristics in lakes, for which in situ, high-resolution data is scare. The diffusive gradient in thin films (DGT) technique was used in-situ at five sites across Lake Taihu in the Yangtze River delta in China to characterize the distribution and mobility of eight labile metals (Fe, Mn, Zn, Ni, Cu, Pb, Co and Cd) in sediments at a 3 mm spatial resolution. The results showed a great spatial heterogeneity in the distributions of redox-sensitive labile Fe, Mn and Co in sediments, while other metals had much less marked structure, except for downward decreases of labile Pb, Ni, Zn and Cu in the surface sediment layers. Similar distributions were found between labile Mn and Co and among labile Ni, Cu and Zn, reflecting a close link between their geochemical behaviors. The relative mobility, defined as the ratio of metals accumulated by DGT to the total contents in a volume of sediments with a thickness of 10 mm close to the surface of DGT probe, was the greatest for Mn and Cd, followed by Zn, Ni, Cu and Co, while Pb and Fe had the lowest mobility; this order generally agreed with that defined by the modified BCR approach. Further analyses showed that the downward increases of pH values in surface sediment layer may decrease the lability of Pb, Ni, Zn and Cu as detected by DGT, while the remobilization of redox-insensitive metals in deep sediment layer may relate to Mn cycling through sulphide coprecipitation, reflected by several corresponding minima between these metals and Mn. These in situ data provided the possibility for a deep insight into the mechanisms involved in the remobilization of metals in freshwater sediments.
Highlights
Heavy metals in aquatic ecosystems come mainly from Nature and anthropogenic activities [1]
Relative mobility was used to assess the mobility of different metals, and is defined as the ratio of metals accumulated by diffusive gradient in thin films (DGT) to the total metals in sediment: M×A
The results have shown a sharp increasing phase for DGT-labile Fe with depth in sediments (Figure 5)
Summary
Heavy metals in aquatic ecosystems come mainly from Nature (background levels) and anthropogenic activities [1]. Heavy metals are mainly bound to sediments through adsorption, coordination, and precipitation, which reduces their bioavailability [21,22] It is the labile fractions of heavy metals, rather than total concentrations, that most impact toxicity and bioavailability [23,24]. The DGT method is grounded in Fick’s First Law of Diffusion It measures the accumulation mass or mean concentration of metals during deployment in sediment, which comes from pore water and the further resupply of metals from solid phase [32,33]. The DGT probe was used in-situ to measure the labile fractions (reflected by DGT fluxes) of eight metals (Fe, Mn, Zn, Ni, Cu, Pb, Co and Cd) in sediments from five sites in Lake Taihu at a vertical resolution of 3 mm. Further revealed by relating the distributions of DGT-labile fractions to potentially governing factors
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
