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The biological activity influence on the mangrove sediment capacity to remove 65Zn and 109Cd from tidal water was evaluated in a site chronically polluted. Benthic Activity Indexes (BAI), corresponding to relative estimates of biological impact on radiotracer accumulation, were higher for 109Cd (~ 38%) than for 65Zn (~ 10%) in the top centimetre of sediment. However, BAI exceeded 96% for deeper sediment layers. This apparent decrease in radiotracer diffusion into deep sediments through biological activity inhibition is stronger than reported for much less polluted mangrove nearby, suggesting that benthic organisms tolerant of chronic metal pollution may affect metal sorption mechanisms. [ABSTRACT FROM AUTHOR]

Mangrove sediment cores sampled from Sepetiba Bay (SE Brazil) were covered with tidal water spiked with Se, Cr and Co to evaluate the removal efficiency of these radiotracers by underlying sediments. Variable time-evolution trends were observed along 115 h experiments, with significant differences between removal efficiencies of all radiotracers observed only after 70 h (Cr > Co > Se). After an event of Co release back to overlying water, there was a general trend of lower Co removal than observed for other radiotracers during the period from 20 to 54 h. After this event, alternated periods of higher Co and higher Se removal trends were observed, attributed to behavioural differences expected for such anionic and cationic radiotracers. While Se and Cr showed uniform time-evolution curves, as typically found in the literature for most radiotracers, Co removal rates presented oscillations, probably due to sensitivity to changes in redox conditions within underlying sediments. Results evidenced the role of mangrove sediments as trace element sinks, which have implications for coastal water quality and for possible uses of such sediments in wastewater treatment systems. [ABSTRACT FROM AUTHOR]