Electrochemical oxidation of polycyclic aromatic hydrocarbons in soil co-contaminated with arsenic

The wood preservation industry has contaminated numerous sites with polycyclic aromatic hydrocarbons (PAH). The aim of this study was to investigate the use of electrochemical oxidation (EO), without chemical additives, for in situ degradation of PAHs in soil co-contaminated with arsenic. Two 1 m³ boxes, each containing a 20 cm layer of contaminated sand overlaid with 20 cm of peat, were equipped with iron electrodes and placed outdoors. EO was applied using a pulsating direct current with alternating polarity, and its impact on PAH concentrations in soil and soil solution, as well as on the associated microbial community was assessed. Soil solution was sampled from the boxes over two seasons and analysed for PAH16 concentrations, showing an average decrease of 82 % by the end of the second season. This reduction was mainly observed in the medium and high molecular weight PAH fractions, suggesting that EO can effectively degrade more recalcitrant PAH compounds. The least reduction was seen in the low molecular weight PAH16, likely due to the replenishment from PAHs sorbed to the soil. Soil samples were taken from 12 different locations within the boxes, showing that PAH16 concentrations significantly decreased in 10 out of 12 sampling points, with a greater average reduction in sand (84 % decrease) compared to peat (69 % decrease). Microbial analyses of the soil samples revealed no significant changes in DNA concentrations across all taxa over time, with Gammaproteobacteria remaining the most abundant microorganisms in all samples, suggesting its ability to persist complex contamination.