Cesium,manganese and cobalt water–sediment transfer kinetics and diffusion into mangrove sediments inferred by radiotracer experiments

A study on the trace elements transfer from tidal water to mangrove sediments from Guanabara Bay (southeastern Brazil) was performed in laboratory microcosms. Sediment cores were covered with tidal water spiked with ¹³⁷Cs, ⁵⁴Mn and ⁵⁷Co during 5-h experiments, and water samples were taken at regular intervals to measure uptake kinetics at the sediment–water interface. At the end of the experiments, the uptake and diffusional penetration into the sediments was evaluated. Half-removal times from water to sediments were slightly higher for ¹³⁷Cs (3.4 ± 1.7 h) than observed for ⁵⁴Mn (2.3 ± 0.2 h) and ⁵⁷Co (2.6 ± 1.1 h). After these experiments, all radioisotopes presented decreasing activities with increasing sediment depth, being the distribution of ¹³⁷Cs indicative of higher diffusion within the upper 2 cm. This study on the removal of ¹³⁷Cs, ⁵⁴Mn and ⁵⁷Co from tidal water by mangrove sediments suggests that while ⁵⁷Co and ⁵⁴Mn presented closer behaviors, there was a slightly higher mobility of ¹³⁷Cs.