The uptake of mixed PAHs and PBDEs in wastewater by mangrove plants under different tidal flushing regimes

• Published in: Environmental pollution (1987) 2017-12, Vol.231 (Pt 1), p.104-114
• Main Authors: Pi, Na, Wu, Yan, Zhu, Hao Wen, Wong, Yuk Shan, Tam, Nora Fung Yee
• Format: Article
• Language: English
• Subjects: E. agallocha; Fe plaque; Halogenated Diphenyl Ethers - analysis; Halogenated Diphenyl Ethers - metabolism; Immobilization; K. obovata; Plant Roots - chemistry; Plant Roots - metabolism; Plant uptake; Polycyclic Aromatic Hydrocarbons - analysis; Polycyclic Aromatic Hydrocarbons - metabolism; Rhizophoraceae - chemistry; Rhizophoraceae - metabolism; Waste Water - chemistry; Water Pollutants, Chemical - analysis; Water Pollutants, Chemical - metabolism; Wetlands
• ISSN: 0269-7491; 1873-6424
• DOI: 10.1016/j.envpol.2017.07.085

Wastewater often contains mixed toxic pollutants, and the contribution of plant uptake in constructed wetland treatment systems is affected by environmental conditions, particularly tidal flushing. In this study, the uptake of wastewater-borne pollutants, including a mixture of polycyclic aromatic hydrocarbons (PAHs) and polybrominated diphenyl ethers (PBDEs) congeners, by two mangrove plant species, namely Excoecaria agallocha L. and Kandelia obovata Sheue, Liu & Yong, under different tidal flushing regimes was investigated. Results showed that Fe plaque formed on root surfaces could immobilize wastewater-borne PAHs and PBDEs. At the end of 8-month wastewater treatment, most of the pollutants removed by plants ended up in Fe plaque, with 0.12–20.83% of total PAHs and 0.78–24.76% of total PBDEs added to the microcosm retained in Fe plaque. On the contrary, the percentages of PAHs and PBDEs taken up by plant tissues were relatively small, ranging from not detected to 0.09% and from 0.01 to 2.00%, respectively. More uptake of Fe plaque-immobilized PAHs and PBDEs was found in K. obovata than in E. agallocha, leading to more plant damages in the former species due to its weaker root outer layers. While E. agallocha with stronger root protective outer layer was able to uptake more PAHs and PBDEs from wastewater but immobilize in Fe plaque than that of K. obovata. In both plant species, tidal flushing regimes significantly affected the immobilization of PAHs and PBDEs in Fe plaque, and more frequent tidal flushing led to higher percentages of immobilization. This is the first study demonstrating that E. agallocha was a more suitable mangrove plant species to remove wastewater-borne PAHs and PBDEs than K. obovata, and the significance of tidal flushing on performance of constructed mangrove wetlands. [Display omitted] •Tidal flushing regime affected plant uptake of toxic organic pollutants in water.•Fe plaque formed on root surfaces could effectively immobilize organic pollutants.•Percentages of organic pollutants taken up by plant tissues were relatively small.•Thin root outer layer of Kandelia obovata facilitated uptake of organic pollutants.•Excoecaria agallocha immobilized more toxic pollutants in Fe plaque than K. obovata. Wastewater-borne PAHs and PBDEs could be effectively taken up by mangrove plants via immobilization in Fe plaque, and the process was affected by tidal flushing regimes.