0428同步年報-2021-全

Environmental and Earth Sciences 071 T he soils at sites of chemical plants typically contain chemical pollutants at high levels because of the range of industrial activities, especially for coking plants and manufactured gas plants. Thermolysis offers a rapid cleanup for heavily polluted soils, particularly with volatile or semivolatile polycyclic aromatic hydrocarbons (PAH), which can quickly restore the treated soils to the desired land use. Previous studies have demonstrated that the efficiency of remediation depends on multiple factors such as heating conditions and pollutant properties. At low temperatures of thermolysis, several pollutants in the soil cannot become completely removed because of their strong affinity to soil components, whereas soil quality becomes irreversibly damaged after thermolysis at high temperatures. With the wide application of this remediation technique, issues related to the nature of organic carbon (C) speciation changes, the destination of the final residual pollutants, and the achievement of safety for the reuse of the treated soils are now arising. Although thermolysis can eliminate over 90% of organic pollutants, the residual pollutants are still present at high levels in the treated soils because of their initial large concentrations. To date, no report has been published on the changes in the binding sites and the bioaccessibility of PAH in soil induced by thermolysis. A detailed understanding of such information is thus critically essential for soil reclamation and risk assessment. Current advances in the relations between organic pollutants and soil components are based almost exclusively on chemical fractionation and extraction. These traditional approaches fail to reflect the binding sites and distribution of bioaccessible or bioavailable PAH in soil. Infrared microspectroscopy based on synchrotron radiation (SR-IMS) is a crucial and powerful technique for lateral surveying in situ the organic C species and minerals as well as some organic compounds in geo-samples at the molecular level. Herein SR-IMS has been applied for direct visualization of the degradation of pyrene, a PAH model, on a magnetite surface and the stabilization of organic C species in soil via tracing infrared characteristic absorptions of functional groups of chemical compounds. SR-IMS can trace the changes in the binding sites of PAH in situ and the speciation distribution of organic carbon in the soil after thermolysis. The chemical maps acquired using SR-IMS that Infrared Imaging of the Distribution and Bioaccessibility of Industrially Contaminated Soils after Thermolysis FTIR imaging can be utilized to visualize the chemical changes with infrared imaging to understand the sequestration mechanisms of organic pollutants in soil and optimize the remediation technique. can provide direct clues to understand the interactions and bioaccessibility of the pollutants in the environment without creating artifacts are hence most valuable. Yuan Cheng (Chinese Academy of Sciences, China) launched an effort to explore the changes in the distribution and bioaccessibility of PAH induced by thermolysis from an industrially contaminated site, a former chemical factory with thirty years of production history located in Jiangsu province, China. The laterally resolved infrared images of organic C species distributed within sectioned soil samples from solidified soil samples, clay minerals, and PAH were acquired using the endstation of SR-IMS at TLS 14A1 . The spectra were recorded for every single point in the area of interest on the sectioned soil sample using the reflectance mode with an FTIR spectrometer (Thermo Nicolet 6700) and a confocal infrared microscope (continuum) with confocal aperture size 15 μm, step size 10 µm × 10 µm at 4 cm -1 of spectral resolution and accumulated 128 scans. The soil organic C was slightly affected in both its speciation composition and content (less than 8% of its content) after thermolysis at 200 o C. At temperatures above 200 o C, some organic C tended to become decomposed or carbonized, but most aromatic C species remained ( Fig. 1 , see next page). The strongest absorption band about 800−700 cm -1 assigned to C-H out-of-plane (C-H OOP ) bending modes was selected as the PAH standard, which varied slightly with other PAH species ( Fig. 2 , see next page). Nevertheless, the absorption bands of aromatic or heteroaromatic C-H OOP and Si-O-Si bending vibrations were overlapped for soil samples in the range 850−750 cm -1 as displayed in the spectra of clean soils, making it difficult to serve as a tracer to probe the presence of PAH in soil. The aromatic C-H stretching of PAH also exhibited an obvious absorption band about 3045 cm -1 , which was also observed in the site soils of the chemical plant but not in clean soil. This absorption band gradually decreased with increasing temperature in the site soils and disappeared at temperatures above 400 o C ( Fig. 1 ). Herein the spectral images of the peak height of characteristic absorption bands of PAH, organic C species,