Enhanced remediation of BDE-209 in contaminated mangrove sediment by planting and aquaculture effluent

Toxic and persistent flame retardant (BDE-209) and aquaculture effluent (AE) are ubiquitous in coastal environments, but how their co-existence influences their fate is not yet investigated. This study investigated AE effects on remediation and uptake of BDE-209 by Kandelia obovata (Ko) and Avicennia marina (Am), true and dominant mangrove species. After 12-months, a significant removal of BDE-209 was achieved in planted mangrove sediment and the removal was significantly enhanced by AE addition, possibly due to the enhancement of nitrogen (N) and phosphorous (P) content in sediment. Residual percentages of parent BDE-209 in Ko and Am planted sediments without AE were 61.4% and 70.9%, respectively, but decreased to 46.9% and 48.0% with AE addition after 12-months. A similar trend was found in unplanted sediment, with 86.5% and 65.3% of BDE-209 retained in sediments without and with AE addition, respectively. The results demonstrated that AE addition not only increased the debromination of BDE-209 in all treated sediments with the production of debrominated congeners (de-PBDEs) like di- to nona-BDEs in unplanted and planted sediments, but also enhanced the take up of BDE-209 in Ko root, and de-PBDEs in both Ko and Am, thus enhancing the phytoremediation of BDE-209 in contaminated sediments.