Effects of low molecular-weight organic acids and dehydrogenase activity in rhizosphere sediments of mangrove plants on phytoremediation of polycyclic aromatic hydrocarbons

• LMWOAs and dehydrogenase in the rhizosphere sediment promoted the removal of PAHs.
• LMWOAs and dehydrogenase activity changed with the levels of PAH contamination.
• Citric acid was the most dominant, followed by succinic acid, among six LMWOAs.
• Bruguiera gymnorrhiza in 3 mangrove plants was most efficient in removing PAHs.

This work evaluated the roles of the low-molecular-weight organic acids (LMWOAs) from root exudates and the dehydrogenase activity in the rhizosphere sediments of three mangrove plant species on the removal of mixed PAHs. The results showed that the concentrations of LMWOAs and dehydrogenase activity changed species-specifically with the levels of PAH contamination. In all plant species, the concentration of citric acid was the highest, followed by succinic acid. For these acids, succinic acid was positively related to the removal of all the PAHs except Chr. Positive correlations were also found between the removal percentages of 4-and 5-ring PAHs and all LMWOAs, except citric acid. LMWOAs enhanced dehydrogenase activity, which positively related to PAH removal percentages. These findings suggested that LMWOAs and dehydrogenase activity promoted the removal of PAHs. Among three mangrove plants, Bruguiera gymnorrhiza, the plant with the highest root biomass, dehydrogenase activity and concentrations of LMWOAs, was most efficient in removing PAHs.