Biodegradation of Polycyclic Aromatic Hydrocarbons (PAHs) in the Rhizosphere Soil of Cyperus conglomeratus, an Egyptian Wild Desert Plant

Abstract

Phytoremediation is a promising technology for the clean-up of petroleum hydrocarbon-polluted soil, especially in the developing countries. In the present study, the rhizosphere soil of Cyperus conglomeratus (a wild Egyptian desert plan) was collected and studied for the removal of PAH compounds from the polluted desert soil. The rhizosphere soil of this plant was rich in total bacteria and oil-degraders. The rhizosphere soil was able after 180 days to reduce total PAHs from 2329.0 to 576.3 mgkg-1 soil (i.e. 75.2% loss), this is in contrast to 45.2% reduction value for the non-rhizosphere soil. The rhizosphere soil significantly enhanced the biodegradation of the 16 PAH individuals (48.4-98.5%) as compared to the non-rhizosphere soil (23.1-94.4). The 2-ringed and the 3-ringed PAHs were highly degraded in the rhizosphere soil (98% and 93.1% respectively) as compared to the other PAH groups. Eight carcinogenic PAHs were resolved among the 16 PAH individuals. The sum of the 8 PAHs decreased in the rhizosphere soil from 1204.5 to 390.9 mgk-1 soil, i.e. a reduction of 67.7%, while in the non-rhizosphere soil the reduction value was 41.0%. Collectively, the 5-ringed carcinogenic PAHs were more degraded in the rhizosphere soil (87.8%) than the 4-ringed carcinogenic PAHs (59.2%). Both groups were weakly degraded in the non-rhizosphere soil (34.7% and 30.6% respectively). A particular notable distinction of the rhizosphere soil of Cyperus conglomeratus plant is the greater efficiency to degrade the carcinogenic PAHs especially benzo(a)pyrene, (90.3%), chrysene (86.9%), benzo(a)flouranthene (84.1%) and indeno (1,2,3-c,d) pyrene (82.2%). The present study clearly demonstrates at the first time in Egypt, a successful bioremediation strategy of PAH-contaminated soil by using the rhizosphere effect of the native desert plant Cyperus conglomeratus.