Polycyclic aromatic hydrocarbons in biochar: Influence of thermochemical parameters and analytical considerations

Biochar is increasingly recognised for its positive impact on agricultural and environmental sustainability. However, a group of organic compounds, polycyclic aromatic hydrocarbons (PAHs), can form during biochar production. The PAH levels in biochar are determined by factors like feedstock type, charring temperature, residence time, and heating rate during the thermochemical process. Generally, higher PAH content results from more intense thermal conditions. Light PAHs mainly form at temperatures below 500°C, while heavy PAHs tend to form at higher temperatures over 500°C. Generally, PAHs can pose health and environmental risks due to their toxicity. Therefore, understanding the risks associated with biochar is essential to ensure its safe application. This literature review will discuss the background of PAHs and biochar, including their occurrence, formation mechanisms, and associated health effects. It will also cover different thermochemical conversion techniques for biochar production, along with common extraction, cleanup and analytical techniques used to analyse PAHs.