Mobile organic compounds in biochar – A potential source of contamination – Phytotoxic effects on cress seed (Lepidium sativum) germination

• Published in: Journal of environmental management Vol. 137; pp. 111 - 119
• Main Authors: Buss, Wolfram, Mašek, Ondřej
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-05-2014; Elsevier; Academic Press Ltd
• Subjects: Animal, plant and microbial ecology; Applied ecology; Biochar; Biological and medical sciences; Charcoal - chemistry; Conservation, protection and management of environment and wildlife; Contaminant; Contamination; Ecotoxicology, biological effects of pollution; Effects of pollution and side effects of pesticides on plants and fungi; Fundamental and applied biological sciences. Psychology; General aspects; Germination; Germination - drug effects; Hot Temperature; Lepidium sativum - drug effects; Lepidium sativum - physiology; Pyrolysis; Re-condensation; Seeds; Seeds - drug effects; Seeds - physiology; VOCs; Volatile organic compound; Volatile organic compounds; Volatile Organic Compounds - toxicity; Pyrolysis; Re-condensation; LC biochar; Germination; VM; Volatile organic compound; NC biochar; VOC; Biochar; GC biochar; Contaminant; TGA; Seeds; Condensation; Environmental management; Lepidium sativum; Contamination; Phytotoxicity; Cruciferae; Dicotyledones; Angiospermae; Spermatophyta; Organic compounds
• ISSN: 0301-4797; 1095-8630
• DOI: 10.1016/j.jenvman.2014.01.045

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.
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•Re-condensation of vapours during pyrolysis can produce VOC-rich biochars.•Vapours and leachates from VOC-rich biochars inhibited cress seed germination.•Reduction of biochar toxicity through storage and blending was partly successful.•Re-condensed compounds from pyrolysis are mobile and phytotoxic.