Chemical properties of soil determine the persistence and bioavailability of polycyclic aromatic hydrocarbons in sewage sludge- or sewage sludge/biomass-derived biochar-amended soils

In this study the persistence (organic solvent extractable) and bioavailability (freely dissolved) of polycyclic aromatic hydrocarbons (PAHs) in soils with various properties amended with sewage sludge (BCSSL)- or sewage sludge/biomass (BCSSLW)-derived biochars was examined. Biochars produced at 600 °C were applied to soils (acidic, neutral, or alkaline) at a dose of 2% and subsequently incubated for 180 days. Here, the use of biochars regarding the soil's type was examined for the first time. Depending on the soil pH and the feedstock, the content of sum of 16 organic solvent extractable PAHs was found to decrease from 7.5 to 37% (soil + BCSSL) and from 24 to 40% (soil + BCSSLW). The decrease in the content of sum of 16 freely dissolved PAHs ranged from 18 to 36% (soil + BCSSL) and from 17 to 54% (soil + BCSSLW). In acidic BCSSL-amended soil and the alkaline BCSSLW-amended soil no statistically significant differences in the content of sum of 16 freely dissolved PAHs were noted between the beginning and end of the study. BCSSLW was characterized by a greater reduction content of organic solvent extractable PAHs in the acidic and alkaline soils, while in the neutral one - BCSSL. In turn, a larger reduction in freely dissolved PAH content in the acidic and neutral soils could be seen in the presence of BCSSLW, whereas in the alkaline soil in the presence of BCSSL. The persistence and bioavailability of PAHs in the biochar-amended soils were closely related to the chemical properties of these soils. This was confirmed by numerous statistically significant (P ≤ 0.05) relationships between organic solvent extractable PAHs and pH, cation exchange capacity, available magnesium, potassium and phosphorus, and dissolved organic carbon as well as between freely dissolved PAH and pH, dissolved organic carbon, available potassium and phosphorus content, and electrical conductivity.