Effect of co-application of nano-zero valent iron and biochar on the total and freely dissolved polycyclic aromatic hydrocarbons removal and toxicity of contaminated soils.

The aim of this study was to investigate co-application of biochar and nano zero-valent iron (nZVI) in order to increase the degradation of PAHs and reduce the toxicity of soils historically contaminated with these compounds. To performed the experiment biochar, biochar with nZVI (2 g kg or 10 g kg soil), or nZVI alone (2 g kg or 10 g kg soil) were added to the PAHs contaminated soils. The soils alone and soils with amendments were aged by mixing for 7 and 30 days. After that the chemical analysis were carried out and total (C) and C PAH content in the samples were determined. Moreover, the toxicity of aqueous extracts were investigated using the Microtox (Vibrio fischeri) method. Results showed that any of used nZVI dose did not reduce the content of C or C PAHs in contaminated soils, but biochar applied both alone and together with the nZVI significantly reduced C and C PAHs. However, no significant differences in PAH reduction were found between biochar alone and biochar with nZVI addition. This indicates that the observed reduction was mostly associated with the sorption properties of biochar. Moreover, only in the case of co-application of biochar and nZVI reduction of the toxicity of nZVI to V. fischeri was observed. The toxic effect was different and depend on the type of soil and their properties including total organic carbon and black carbon content, which may affect the PAHs reduction efficiency.