Persistent free radicals (PFRs) are emerging contaminants of increasing concern, yet their formation, fate, toxicity and health risk are poorly known. Thermal treatment, a common remediation technique to clean industrial soils, induces the formation of PFRs, which could paradoxically increase soil toxicity, contrary to the original objective of remediation. Actually, there is little knowledge on the formation and toxicity of PFRs in soils contaminated by polycyclic aromatic hydrocarbons (PAHs). Here we studied the generation of PFRs of soils spiked with anthracene and heated 1 h from 100 to 600 °C, using electron paramagnetic resonance. We also investigated the formation of reactive oxygen species (ROS), e.g. superoxide radical (O₂^·−), hydrogen peroxide (H₂O₂) and hydroxyl radical (·OH), in the aqueous phase of thermal-treated soil, and the impact of heating on soil oxidative potential, wheat growth and green algae activity. Results showed that PFRs, ROS, soil oxidative potential, plant toxicity and algal toxicity show a similar trend with an increase from 100 to 300 °C, followed by a decrease to 600 °C. Scavenger trapping tests reveal that algal toxicity is mainly due to the generation of O₂^·−, ·OH and H₂O₂ induced by anthracene-PFRs and that anthracene and anthracene-PFRs have negligible direct algal toxicity. Overall, our findings reveal the unintended formation of toxic compounds peaking at 300 °C during the thermal remediation of PAH-contaminated soils. These results should help to assess the environmental risk of thermally treated PAH-contaminated soils.

持久性自由基（PFRs）是日益受到关注的新兴污染物，但是人们对其形成，命运，毒性和健康风险知之甚少。热处理是清洁工业土壤的常用补救技术，会诱导PFR的形成，这有悖于其对土壤的毒性，这与补救的原始目标背道而驰。实际上，对于多环芳烃（PAHs）污染的土壤中PFR的形成和毒性了解甚少。在这里，我们利用电子顺磁共振研究了掺有蒽并在100至600°C加热1 h的土壤中PFR的产生。我们还研究了活性氧（ROS）的形成，例如超氧自由基（O ₂ ^·−），过氧化氢（H ₂ O ₂）和羟基自由基（·OH）在热处理土壤的水相中，以及加热对土壤氧化电位，小麦生长和绿藻活性的影响。结果表明，PFR，ROS，土壤氧化电位，植物毒性和藻类毒性显示出相似的趋势，从100升高到300°C，然后降低到600°C。清除剂捕获测试表明，藻类毒性主要是由于O ₂ ^·−，·OH和H ₂ O _2的产生由蒽-PFRs诱导，并且蒽和蒽-PFRs对藻类的直接毒性可忽略不计。总体而言，我们的发现揭示了在PAH污染土壤的热修复过程中，意外的有毒化合物的形成在300°C达到峰值。这些结果应有助于评估经过热处理的多环芳烃污染土壤的环境风险。