title: Mobile organic compounds in biochar - a potential source of contamination - phytotoxic effects on cress seed (Lepidium sativum) germination.
abstract: Biochar can be contaminated during pyrolysis by re-condensation of pyrolysis vapours. In this study two biochar samples contaminated by pyrolysis liquids and gases to a high degree, resulting in high volatile organic compound (high-VOC) content, were investigated and compared to a biochar with low volatile organic compound (low-VOC) content. All biochar samples were produced from the same feedstock (softwood pellets) under the same conditions (550 °C, 20 min mean residence time). In experiments where only gaseous compounds could access germinating cress seeds (Lepidium sativum), application amounts ranging from 1 to 30 g of high-VOC biochar led to total inhibition of cress seed germination, while exposure to less than 1 g resulted in only partial reduction. Furthermore, leachates from biochar/sand mixtures (1, 2, 5 wt.% of biochar) induced heavy toxicity to germination and showed that percolating water could dissolve toxic compounds easily. Low-VOC biochar didn't exhibit any toxic effects in either germination test. Toxicity mitigation via blending of a high-VOC biochar with a low-VOC biochar increased germination rate significantly. These results indicate re-condensation of VOCs during pyrolysis can result in biochar containing highly mobile, phytotoxic compounds. However, it remains unclear, which specific compounds are responsible for this toxicity and how significant re-condensation in different pyrolysis units might be.
authors.affiliation: UK Biochar Research Centre, School of GeoSciences, University of Edinburgh, Crew Building, King's Buildings, Edinburgh EH9 3JN, UK.
authors.forename: Wolfram
authors.initials: W
authors.lastname: Buss
authors.affiliation: UK Biochar Research Centre, School of GeoSciences, University of Edinburgh, Crew Building, King's Buildings, Edinburgh EH9 3JN, UK. Electronic address: ondrej.masek@ed.ac.uk.
authors.forename: Ondřej
authors.initials: O
authors.lastname: Mašek
mesh_terms: D002606:Charcoal / Q000737:chemistry*; D018525:Germination / Q000187:drug effects*; D006358:Hot Temperature; D031220:Lepidium sativum / Q000187:drug effects* / Q000502:physiology; D012639:Seeds / Q000187:drug effects / Q000502:physiology; D055549:Volatile Organic Compounds / Q000633:toxicity*
chemical_list: D055549:Volatile Organic Compounds; C540010:biochar; D002606:Charcoal
keywords: Biochar; Contaminant; Germination; Pyrolysis; Re-condensation; Volatile organic compound