Effect of steam activated biochar application to industrially contaminated soils on bioavailability of polycyclic aromatic hydrocarbons and ecotoxicity of soils

The aim of this study was to determine the effect of steam activation of biochars on the immobilization of freely dissolved (Cfree) and bioaccessible fraction (Cbioacc) of PAHs in soils. Additionally, the toxicity to various organisms like Vibrio fischeri, Lepidium sativum and Folsomia candida was measured before and after the amendment of biochars to soils. Three biochars produced from willow, coconut and wheat straw were steam activated and added to three different soils with varying content and origin of PAHs (coke vs. bitumen). The soils with the addition of the biochars (activated and non-activated) were incubated for a period of 60days. Steam activation of the biochars resulted in more pronounced reduction of both Cfree and Cbioacc. The range of the increase in effectiveness was from 10 to 84% for Cfree and from 50 to 99% for Cbioacc. In contrast, the effect of activation on the toxicity of the soils studied varied greatly and was specific to a particular test and soil type. Essentially, biochar activation did not result in a change of phytotoxicity, but it increased or decreased (depending on the parameter, type of biochar, contaminant source, and soil and soil type) the toxic effect to F. candida, and decreased the toxicity of leachates to V. fischeri. [Display omitted] •Biochar produced from willow, coconut and wheat straw were steam activated.•Non- and activated biochars were added to three different soils.•Bioavailable (Cfree) and bioaccessible (Cbioacc) PAHs content was investigated.•Biochar activation resulted in more pronounced reduction of Cfree and Cbioacc PAHs.•Activation of biochars decreased the toxicity of leachates from the soils.