Inherent organic compounds in biochar-Their content, composition and potential toxic effects

Pyrolysis liquids consist of thermal degradation products of biomass in various stages of its decomposition. Therefore, if biochar gets affected by re-condensed pyrolysis liquids it is likely to contain a huge variety of organic compounds. In this study the chemical composition of such compounds associated with two contaminated, high-volatile organic compound (VOC) biochars were investigated and compared with those for a low-VOC biochar. The water-soluble organic compounds with the highest concentrations in the two high-VOC biochars were acetic, formic, butyric and propionic acids; methanol, phenol, o-, m- and p-cresol, and 2,4-dimethylphenol, all with concentrations over 100 mu g g(-1). The concentrations of 16 US EPA PAHs determined by 36 h toluene extractions were 6.09 mu g g(-1) for the low-VOC biochar. For high-VOC biochar the total concentrations were 53.42 mu g g(-1) and 27.89 mu g g(-1), while concentrations of water-soluble PAHs ranged from 1.5 to 2 mu g g(-1). Despite the concentrations of PAHs exceeding biochar guideline values, it was concluded that, for these particular biochars, the biggest concern for application to soil would be the co-occurrence of VOCs such as low molecular weight (LMW) organic acids and phenols, as these can be highly mobile and have a high potential to cause phytotoxic effects. Therefore, based on results of this study we strongly suggest for VOCs to be included among criteria for assessment of biochar quality. (C) 2015 Elsevier Ltd. All rights reserved.