Comparison of plants with C3 and C4 carbon fixation pathways for remediation of polycyclic aromatic hydrocarbon contaminated soils

Abstract

The phytoremediation technique has been demonstrated to be a viable option for the remediation of polycyclic aromatic hydrocarbons (PAHs) contaminated sites. This study evaluated the potential applicability of plants with C3 and C4 carbon fixation pathways for the phytoremediation of recalcitrant high molecular weight (HMW) PAHs contaminated soil. A 60 and 120-day greenhouse study was conducted which showed higher degradation of HMW PAHs in soil grown with C4 plants when compared to C3 plants. Also, no PAHs were detected in the maize cobs, sunflower, wallaby, and Sudan grass seeds at the end of the experiment. The effect of plants in modifying the microbial community and dynamics in the rhizosphere was also examined by measuring soil biochemical properties such as dehydrogenase activity and water-soluble phenols. The results demonstrate a substantial difference in the microbial populations between planted and unplanted soils, which in turn facilitate the degradation of PAHs. To the best of our knowledge, this study for the first time evaluated the phytoremediation efficacy through the A. cepa cyto- and genotoxicity assay which should be considered as an integral part of all remediation experiments.

Figure 1

The effect of C3 and C4 plant species on the percentage removal of PAHs from the contaminated soils: (a) Percentage PAHs removal at 60^th day (b) Percentage PAHs removal at 120^th day. Bars with same letters do not differ significantly at the 5% level of significance according to Duncan Multiple Range Test (DMRT).

Figure 2

(a) Remediation efficacy testing with A. cepa meristem root cells exposed to unplanted contaminated and phytoremediated soils (60^th and 120^th day) - Mitotic index (%); (b) Remediation efficacy testing with A.cepa meristem root cells exposed to unplanted contaminated and phytoremediated soils (60^th and 120^th day) - total aberration (%) Bars with same letters do not differ significantly at the 5% level of significance according to Duncan Multiple Range Test (DMRT); (c) Chromosomal aberrant cells observed in A. cepa grown in contaminated soils (A) Prophase, (B) Metaphase, (C) Anaphase, (D) Telophase, (A1) Disturbed prophase, (A2) Bivacuolated cells, (A3) Multivacuolar cells, (A4) Micronuclei, (B1) Fragments, (B2) C-mitosis, and bridges, (B3) Disturbed metaphase, (B4) Sticky metaphase, (C1) Anaphase bridges, (C2) Laggards, (C3) Multipolar anaphase, (C4) Anaphase with vagrant laggards, (D1) Anaphase fragments.

Figure 3

(a) Levels of genotoxicity seen in A. cepa meristem root cells exposed to unplanted contaminated and phytoremediated soils (60^th day); (b) Levels of genotoxicity seen in A. cepa meristem root cells exposed to unplanted contaminated and phytoremediated soils (120^th day). The means sharing same capital letters do not differ significantly at the 5% level of significance according to DMRT for TD (%) and OTM (%).