The two PM2.5 (fine) and PM2.5-10 (coarse) fractions: Evidence of different biological activity

Recent studies have shown that an increased concentration of environmental particulate matter (PM10) is related to many respiratory diseases. One majo r issue is whether the toxicity of the particles resides in some particular fraction as defined by chemical composition and size. The overall purpose of this study was to compare the in vitro toxicity of coarse (PM2.5-10) and fine (PM2.5) particulate matter, collected in an urban area of Rome, in re lation to their physicochemical composition as assessed by analytic electro n microscopy and atomic absorption spectroscopy. In particular, our aim was to evaluate the importance of particle physicochemical components in the i nduced toxicity. The in vitro toxicity assays used included human red blood cell hemolysis, cell viability, and nitric oxide (NO) release in the RAW 2 64.7 macrophage cell line. The hemolytic potential has been widely used as an in vitro toxicity screen and as a useful indicator of oxidative damage t o biomembranes. We found that human erythrocytes underwent dose-dependent h emolysis when they were incubated with varying concentrations of fine and c oarse particles. The hemolytic potential was greater for the fine particles than for the coarse particles in equal mass concentration. However, when d ata were expressed in terms of PM surface per volume unit of suspension, th e two fractions did not show any significant hemolytic differences. This re sult suggested that the oxidative stress induced by PM on the cell membrane s could be due mainly to the interaction between the particle surfaces and the cell membranes. RAW 264.7 macrophage cells challenged with particles sh owed decreased viability and an increased release of NO, a key inflammatory mediator, and both effects were not dose dependent in the tested concentra tion range. The fine particles were the most effective and the differences beween the two size fractions in inducing these biological effects remained unchanged when the basis of comparison was changed from weight to surface measures. It seemed therefore that these differences relied on the differen t physicochemical nature of the particles. The main chemical difference bet ween the two fractions resided in a greater abundance of C-rich particles w ith S traces in the fine fraction. Therefore, we cautiously suggest a role for these particles in the induction of toxicity. (C) 2001 Academic Press.