Toxicity of plastic diesel exhaust in primary human airway epithelial cell cultures

Plastic pyrolysis oil, which can be produced with similar properties as diesel fuel (plastic diesel), can be used as an alternative to mineral diesel (ULSD) to run a diesel engine. This presents a potential method for recycling waste plastic. Typically plastic diesel is blended with mineral diesel, and oxygenated fuel additives such as ethers added to improve resulting fuel properties. However, little to no assessment of potential exhaust toxicity has been completed. The aim was to assess potential toxic effects of plastic diesel exhaust with and without fuel additives. Primary human airway epithelial cells grown at air-liquid interface were exposed to diluted room temperature exhaust from a pre-warmed engine running on ULSD, 10% plastic diesel blended into ULSD (PD), 5% plastic diesel with 10% diethylene glycol dimethyl ether blended into ULSD (DGM) or 5% plastic diesel with 10% tripropylene glycol monomethyl ether blended into ULSD (TGM), using air exposure as a control. Exhaust physicochemical properties and resulting toxic effects were assessed. The addition of any amount of plastic diesel had a greater effect on resulting exhaust characteristics than the addition of either of the oxygenated fuel additives. TGM and DGM were the most toxic of the assessed exhaust types with exposure causing increased cytotoxicity, increased oxidative stress and dysregulated immune mediator release compared to control. PD exhaust was the next most toxic and pure ULSD the least. Plastic diesel increases exhaust toxicity even when only blended 10% into the ULSD, and ether fuel additives only further increase this toxicity.