Study on the Phytodegradation of PAHs from Farmland Soil using Technique of Compound Specific Isotope Analysis

For the research on degradation and remediation of soil polycyclic aromatic hydrocarbons (PAHs) pollutants, researchers have been trying to find an effective method to quantize the dynamic processes. Many approaches have been designed, such as spiked experiment, concentrations comparison before and after the degradation, and modeling calculations. However, all of this culminates in contradictory results and lack of corroboration of the actual environment. Compound Specific Isotope Analysis (CSIA) technique is used in this study to investigate the phytodegradation process of soil PAHs with maize as the testing plant. Total concentrations of 16 PAHs in the bulk soil, rhizosphere soil and in the controlled soil samples were (299.8±37.9) ng/g, (272.2±11.6) ng/g, and (281.5±34.7) ng/g, respectively, all much lower than the original cultivating soil (380.8 ng/g). The soil PAHs concentrations did not show significant decline tendency during the maize growing period, except for 3-ring PAH compounds which was consistent with the accumulation effect of the 3-ring PAHs in maize roots and leaves. The δ13C value of 6 PAH compounds ranged from -34.31‰ to -23.95‰ with fluctuations between -0.6‰--9.0‰, and all δ13C values turned lighter with maize plants growing except that of Pyrene. No significant correlation between δ13C and the concentration of 4-, 5-ring PAHs was observed during the maize cultivating process. Most research indicates that PAHs and other macromolecular compounds strongly resist phytodegradation, which illustrates less obvious carbon isotope fractionation. PAH compounds below 3 rings would degrade more easily and the isotopes fractionate more significantly than those of other macromolecular compounds, thus maing the technique of CSIA more advantageous for understanding the transportation pathway of these compounds.