Environmentally persistent free radicals (EPFRs) are emerging contaminants of increasing concern due to their toxicity for life and ecosystems, yet their formation, behavior and fate are poorly known. In particular, there is actually no knowledge on the formation of those radicals during the thermal treatment of soils containing polycyclic aromatic hydrocarbons. Such knowledge is important because thermal treatment is a remediation method used to decontaminate soils by removing and degrading PAHs. Here, we studied the formation of radicals in three types of cultivated soils, bauxite soil, fluvo-aquic soil and chernozem soil, artificially contaminated by benzo[a]pyrene, during thermal treatment from 100 to 200 °C for 1 h, using electron paramagnetic resonance. Results show spins densities of radicals up to of 2.079 × 1017 spins/g for bauxite soil, 1.481 × 1017 spins/g for fluvo-aquic soil and 8.592 × 1016 spins/g for chernozem soil at 175 °C. The formed radicals exhibited multiple decays during their observable time and the shortest 1/e lifetimes of radicals up to 757.58 h. These findings are strengthened by EPFR-induction of reactive oxygen species (ROS), O2·− and ·OH, which increased in concentrations from 100 to 200 °C. Overall, our results demonstrates for the first time that thermal treatment of PAHs-contaminated soils induces the formation of EPFRs and suggests that thermal treatment might not be a fully clean remediation method for soils as thermal treatment creates new contaminants.
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Financial supports by the National Natural Science Foundation of China (Grants Nos. 41571446 & 41877126), the “Open Project” of the State Key Laboratory of Pollution Control and Resource Reuse (PCRRF17020) and the “One Hundred Talents” program of Shaanxi Province (SXBR9171) are gratefully acknowledged.
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Liu, J., Jia, H., Zhu, K. et al. Formation of environmentally persistent free radicals and reactive oxygen species during the thermal treatment of soils contaminated by polycyclic aromatic hydrocarbons. Environ Chem Lett 18, 1329–1336 (2020). https://doi.org/10.1007/s10311-020-00991-1
- Thermal treatment
- Polycyclic aromatic hydrocarbons
- Environmentally persistent free radicals