Biological effects of ultrafine particles from relevant emission sources: Diesel and biomass combustion

Purpose: Even particulate matter (PM) mass concentration is the reference parameter for air quality legislation, the significance of ultrafine particles (UFP) is becoming more prominent. UFP highly contribute to the number of PM, but very little to mass. Numerous toxicological studies have shown specific UFP characteristics and reactivity, including high lung deposition efficiency, enhanced induction of inflammatory and oxidative stress processes. Among UFP different sources emission, diesel and biomass combustion processes are the most important in the north of Italy. Methods: UFP produced by diesel engines and biomass combustion were sampled adapting standardized procedures. Sampling of particles on Teflon filters has required filter holders modifications to avoid critical pressure drops. The chemical (organic compounds and metals) and physical (shape and dimensions) particles properties have been characterized. The human pulmonary BEAS-2B cell line has been used to assess the UFP effects. Results: Particles dimensions showed a mean diameter lower than 100 nm and the tendency to form aggregates. Interestingly fly ashes particles were observed in biomass burning samples. These particles were composedmainly of potassium salts and were water soluble. Diesel UFP were characterized by a high content of phenanthrene, fluoranthene and pyrene while biomass UFP showed a significant content of chrysene too. Iron, aluminum and zinc were the most abundant metals deter- mined in diesel UFP, even a significant content of chromium, nickel and platinum was observed. UFP biomass showed a significant quantity of zinc and manganese. The results of in vitro experiments showed that concentrations up to 100 g/ml of UFP for 24 h did not affect cell viability. Two non-cytotoxic concentrations, 25 and 50 g/ml have been selected for subsequent experiments. 25 g/ml at 24 h of exposure produced a significant increase of antioxidant (GCLM, NDRG1, NQO1, TXNRD1) and extracellular matrix (MMP1) genes. Diesel exposure induced higher fold changes in analysed genes compared to biomass. These results demonstrate that UFP are able to significantly affect the antioxidant response of bronchial epithelial cells. Further researches will focus on the evaluation of significant proteins modification related to oxidative stress.