Kinetics of trace metal removal from tidal water by mangrove sediments under different redox conditions

The extent in which redox conditions can affect the removal kinetics of 58Co and 65Zn from tidal water by mangrove sediments was evaluated in microcosm experiments, simulating a tidal flooding period of 6 h. The average half-removal time (t1/2) of 58Co from overlaying water was slightly higher (7.3 h) under an N2-purged water column than under an aerated water column (5.4 h). A lower difference was found for 65Zn (1.9 h vs. 1.5 h, respectively). Average removals of 58Co activities from water were 54.6% (N2 treatment) and 43.5% (aeration treatment), whereas these values were 88.0% and 92.7% for 65Zn, respectively. Very contrasting sorption kinetics of different radiotracers occurred, while more oxidising conditions favoured only a slightly higher removal. Average 58Co and 65Zn inventories within sediments were 30.4% and 18.8% higher in the aeration treatment, respectively. A stronger particle-reactive behaviour was found for 65Zn that was less redox-sensitive and more efficiently removed by sediments than 58Co. - Highlights: ► Radiotracer experiments evidenced the role of mangrove sediments in trapping trace metals. ► Very contrasting removal kinetics from tidal water were observed for 65Zn and 58Co. ► Nearly 40%–50% of 58Co activities and nearly 90% of 65Zn activities in overlying water were removed. ► 65Zn showed a stronger particle-reactive behaviour than observed for 58Co. ► 58Co was more sensitive to redox conditions in tidal water than observed for 65Zn