Studying the Fenton treatment of polycyclic aromatic compounds in a highly contaminated soil with different modifiers by high resolution mass spectrometry

Remediation of polycyclic aromatic compounds (PAHs) contaminated soil is highly challenging, because of the complex soil matrix and immense number of various pollutants. Especially higher aromatic species are not water soluble and cannot be removed by microorganisms. One way to make them accessible for biological treatment is to make them water soluble through an oxidation reaction. Here, the Fenton reaction is a method of choice. The Fenton reaction in a soil that is highly contaminated with various polyaromatic hydrocarbons is studied in a non-target approach using high resolution mass spectrometry as method for detection with addition of modifiers (methanol, ethanol and toluene) to make the contaminants accessible for the reaction. The results show that the most effective oxidation was achieved using toluene as a modifier, which leads to a significant decrease of polyaromatic hydrocarbons (PAHs) and polyaromatic nitrogen heterocycles (PANHs) in the soil. After the toluene-based Fenton reaction, the number of oxygen atoms in the products increased up to O18, which makes them more soluble in water and allows for a better removal from the soil matrix. Similar hydrocarbon distributions were detected on the molecular level in Soxhlet extracted soil phase and toluene phase, while smaller PAHs with double bond equivalents (DBE) ≤ 38 were transferred into the water phase