Redox activity and chemical speciation of size fractioned PM in the communities of the Los Angeles-Long Beach harbor

摘要

In this study, two different types of assays were used to quantitativelymeasure the redox activity of PM and to examine its intrinsic toxicity: 1)in vitro exposure to rat alveolar macrophage (AM) cells using dichlorofluorescindiacetate (DCFH-DA) as the fluorescent probe (macrophage ROS assay), and: 2)consumption of dithiothreitol (DTT) in a cell-free system (DTT assay).Coarse (PM_10–2.5), accumulation (PM_2.5–0.25), and quasi-ultrafine(quasi-UF, PM_0.25) mode particles were collected weekly at fivesampling sites in the Los Angeles-Long Beach harbor and at one site near theUniversity of Southern California campus (urban site). All PM samples wereanalyzed for organic (total and water-soluble) and elemental carbon, organicspecies, inorganic ions, and total and water-soluble elements. Quasi-UF modeparticles showed the highest redox activity at all Long Beach sites (on botha per-mass and per-air volume basis). A significant association (R2=0.61)was observed between the two assays, indicating that macrophage ROSand DTT levels are affected at least partially by similar PM species.Relatively small variation was observed for the DTT measurements across allsize fractions and sites, whereas macrophage ROS levels showed moresignificant ranges across the three different particle size modes andthroughout the sites (coefficients of variation, or CVs, were 0.35, 0.24 and0.53 for quasi-UF, accumulation, and coarse mode particles, respectively).Association between the PM constituents and the redox activity was furtherinvestigated using multiple linear regression models. The results showedthat OC was the most important component influencing the DTT activity of PMsamples. The variability of macrophage ROS was explained by changes in OCconcentrations and water-soluble vanadium (probably originating from shipemissions – bunker oil combustion). The multiple regression models wereused to predict the average diurnal DTT levels as a function of the OCconcentration at one of the sampling sites.