Particulate emissions from modern and old technology wood combustion induce distinct time-dependent patterns of toxicological responses in vitro.

Toxicological characterisation of combustion emissions in vitro are often conducted with macrophage cell lines, and the majority of these experiments are based on responses measured at 24h after the exposure. The aim of this study was to investigate how significant role time course plays on toxicological endpoints that are commonly measured in vitro. The RAW264.7 macrophage cell line was exposed to PM samples (150μg/ml) from biomass combustion devices representing old and modern combustion technologies for 2, 4, 8, 12, 24 and 32h. After the exposure, cellular metabolic activity, cell membrane integrity, cellular DNA content, DNA damage and production of inflammatory markers were assessed. The present study revealed major differences in the time courses of the responses, statistical differences between the studied samples mostly limiting to differences between modern and old technology samples. Early stage responses consisted of disturbances in metabolic activity and cell membrane integrity. Middle time points revealed increases in chemokine production, whereas late-phase responses exhibited mostly increased DNA-damage, decreased membrane integrity and apoptotic activity. Altogether, these results implicate that the time point of measurement has to be considered carefully, when the toxicity of emission particles is characterised in in vitro study set-ups.