Physicochemical characterisation of diesel exhaust particles: Factors for assessing biological activity

A range of microscopy and analytical techniques have been used to investiga te the physicochemical properties of diluted DEP that may be important in d etermining its biological activity. Transmission electron microscopy demons trated four basic categories of particle morphology: (1) "spherulites" [ind ividual particles]; (2) "chains" or "clusters" of spherulites; (3) "spherul es", [large bodies of spherulites]; (4) "flake-like bodies". Image analysis of TEM photomicrographs determined empirical morphological parameters (30 nm mean spherulite diameter, aspect ratio 1.5, mean particle area 0.078 mu m, equivalent spherical diameter 0.23 mu m, roundness 2.76) and derived par ameters (0.313 mu m(2) surface area, 3.7 mu m(2) pg surface area per mass a nd 0.042 mu m(3) volume) of DEP. Distributions of the particle sizes by num ber showed 10.1% were ultrafine ( < 0.1 mu m), 89.5% fine (0.1-2.0 mu m), 0 .4% coarse ( > 2.5 mu m), but distributions based on a mass value were diff erent (0.01% ultrafine; 52.6% fine, 47.4% coarse). In contrast, impacted DE P contained 60.87% ultrafine, 39.13% fine and 0% coarse particles by number . Field emission scanning electron microscopy of spherulites revealed smoot h surfaces and flocculated spherules with large surface areas. Electron pro be X-ray micro-analysis demonstrated the presence of C, O, Na, Mg, K, Al, S i, P, S, Cl: Ca along with a range of metals (Ti, Mn, Fe, Zn, Cr), that wer e heterogeneous in distribution. Inductively coupled plasma mass and atomic emission spectrometry identified Mg, P, Ca, Cr, Mn, Zn, Sr, Mo, Ba, Na, Fe , S, and Si as the mobile sorbed metals readily removed during sonication i n water from DEP suspensions. X-ray Diffraction confirmed previous observat ions of the presence of nanometer sized crystallites of disordered graphite . Comparison of microscopy and analytical results between sonicated and imp acted DEP revealed a physicochemical difference that must be taken into acc ount in any toxicological investigations. (C) 1999 Elsevier Science Ltd. Al l rights reserved.