Toxicity of biochars after polycyclic aromatic hydrocarbons removal by thermal treatment

Due to the high content of PAHs in biochars, their utilisation in agriculture is questioned. However, in the literature there is a lack of evidence whether and what amount of PAHs in biochar may create a threat to living organisms. The objective of the study was to determine the effect of PAHs on various biochars toxicity towards Vibrio fischeri, Daphnia magna and Lepidium sativum. The study was conducted on three biochars obtained from miscanthus (BCM), willow (BCW) and wheat straw (BCS). PAHs were removed from the biochars by drying at temperatures of 100 degrees C, 200 degrees C and 300 degrees C. Depending on the kind of biochar, drying at temperature of 100 degrees C caused PAH content reduction at the level of 33.8-88.1%. Increase of the drying temperature (to 200 degrees C and 300 degrees C) caused total reduction of PAHs within 24 h. PAH removal from the biochar that had their highest content (BCM) caused total reduction of its toxicity. In the case of the other biochars (BCS and BCW), in which lower content of PAHs was observed relative to biochar BCM, no correlation was noted between the level of removal of PAHs and their toxicity. (C) 2014 Elsevier B.V. All rights reserved.