Vital Threshold\nand Underlying Mechanism for the Complete\nRemediation of Oil and Microplastic Co-Contaminated Soil by Fast Pyrolysis

The coexistence of microplastics (MPs) and oil contaminants\nin\nsoil has led to a new pollution scenario around the oil-production\nregion, yet how to cost-effectively remediate soil with combined pollutants\nhas rarely been explored. Herein, we propose a fast pyrolysis technique\nto perfectly remediate MP<sub>S</sub>-oil copresence soil (MPs-oil-soil).\nThe experimental data showed that pyrolysis at 500 °C for 15\nmin is a key threshold for the complete removal of MPs and petroleum\ncontaminants from soil. Above this threshold, seed germination and\nthe growth of wheat in the soil increased, and the rhizosphere microbial\npopulation decreased with increasing abundance of beneficial microbial\nflora, such as <i>Proteobacteria, Actinobacteria and</i> Bacteroidetes (which promote the circulation of nutrients and help\nto strengthen plant resistance). Structural equation modeling revealed\nthat temperature had a more significant positive effect on the remediation\neffect than did time. Two-dimensional correlation spectroscopy combined\nwith synchronous fluorescence spectroscopy showed that the presence\nof MPs was the main factor affecting the pyrolysis threshold. Three-dimensional\nexcitation–emission matrix and UV–visible absorption\nspectroscopy revealed large differences in the aromaticity and relative\nmolecular weight of dissolved organic matter before and after the\npyrolysis threshold. These findings shed light on the mechanistic\nunderstanding of the pyrolytic remediation of microplastics and oil-contaminated\nsoils.