Quantitative Risks Associated with Polycyclic Aromatic Hydrocarbons (PAHs) and Potential Toxic Elements (PTEs) Released from Thermally Modified Wood Processing: A Review

Thermally modified wood processing generates a spectrum of polycyclic aromatic hydrocarbons (PAHs) and potential toxic elements (PTEs) whose concentrations and toxicological relevance vary with temperature, product phase, and exposure pathway. This review synthesizes quantitative data from low- and high-temperature processing conditions to evaluate human health and environmental risks using standardized screening-level assessment metrics, including chronic daily intake (CDI), hazard quotient (HQ), hazard index (HI), and incremental lifetime cancer risk (ILCR). Across assessed matrices, low-temperature residues predominantly contain low-molecular-weight PAHs such as naphthalene and phenanthrene, elevating exposure potential without strong carcinogenic potency, whereas high-temperature conditions favor formation and enrichment of high-molecular-weight PAHs, particularly benzo[a]pyrene, which disproportionately drives cancer risk even at trace concentrations. PTEs, including arsenic, cadmium, and lead, exhibit pathway-dependent risk profiles, with aqueous leachate scenarios producing extreme HQ and ILCR values that exceed conventional screening thresholds by several orders of magnitude. In all cases, children present a higher risk than adults due to greater intake-to- body-weight ratios, reinforcing the need for receptor-specific evaluation. The findings indicate that thermal modification does not inherently mitigate contaminant risks; instead, certain operational ranges can amplify hazard potential by concentrating pollutants into more mobile, bioavailable, and regulatory-significant forms. These results emphasize the necessity of pathway-specific risk assessment, residue characterization, and post-processing management to avoid unintended public health impacts. The review concludes with recommendations for temperature optimization, leachability controls, and regulatory oversight to support safer industrial implementation and inform future research priorities.