Removal of pyrene from contaminated sediments by mangrove microcosms

The potential of mangrove wetland systems to remove pyrene from surface- or bottom-contaminated sediments was investigated by microcosm studies. The performance of two mangrove plant species, Kandelia candel and Bruguiera gymnorrhiza in pyrene removal was also compared. During the six-months experimental period, the growth of both species in the surface-contaminated microcosms was not significantly different from that in the bottom-contaminated ones, and was comparable to the control (without any pyrene contamination). At the end of six-months treatment, pyrene concentrations in contaminated sediments declined from an initial 3 μg g^-1 to less than 0.4 μg g^-1, indicating that pyrene was successfully removed by mangrove microcosms. Around 96.4% and 92.8% pyrene in microcosms planted with K. candel were removed from the surface- and bottom-contaminated sediments, respectively. The removal percentages were slightly lower in microcosms planted with B. gymnorrhiza. Significant accumulation of pyrene in roots was only found in microcosms having bottom-contaminated sediments, and pyrene concentrations were 3.05 μg g^-1 and 4.50 μg g^-1 in roots of K. candel and B. gymnorrhiza, respectively. These values were much higher than that in control microcosms (without pyrene contamination, root pyrene concentrations were 0.27 μg g^-1 for K candel and 0.34 μg g^-1 for B. gymnorrhiza) and in microcosms with contaminated sediments placed at the surface layer. Nevertheless, the overall contribution of root accumulation and plant uptake to the removal of pyrene from contaminated sediments was insignificant.