Bioavailability and bioaccessibility of polycyclic aromatic hydrocarbons (PAHs) in historically contaminated soils after lab incubation with sewage sludge-derived biochars

Abstract

The objective of this study was to estimate the effectiveness of application of sewage sludge-derived biochars for the immobilisation of freely dissolved (Cfree) and bioaccessible (Cbioacc) polycyclic aromatic hydrocarbons (PAHs) in contaminated soils.Soil SL-COK collected from the area of a coking plant and soil SL-BIT collected from the area of a plant producing bituminous materials were chosen for the study. The biochars were produced from sewage sludge at temperatures of 500 °C (BC500) or 700 °C (BC700). The biochars were mixed with the soil at the dose of 5% and incubated for a period of 60 d. The content of PAHs was determined with the use of polyoxymethylene (POM) (Cfree) or a solution of cyclodextrins and silicon rod elastomer (Cbioacc).Biochars reduced the content of Cfree and Cbioacc PAHs in soils. A higher level of reduction was noted for Cfree PAHs than for Cbioacc PAHs. Biochar produced at 700 °C was more effective in the reduction of Cfree and Cbioacc PAHs than biochar produced at 500 °C. It was found that in the soil in which the source of contamination were processes related with the production of bituminous materials (SL-BIT), the effect of reduction of Cfree and Cbioacc was greater than in soil SL-COK where the source of PAHs were coking processes. It also needs to be emphasised that soil SL-BIT, for which better reduction of PAHs was noted, was also characterised by a lower affinity towards those compounds than soil SL-COK.