ELECTRON MICROSCOPY INVESTIGATION OF MAGNETIC SEPARATES OF ROAD SEDIMENT IN GARY, INDIANA

Road sediment samples from Gary, Indiana were investigated to constrain the nature of technogenic particles present in the magnetic fraction of selected samples. Two pollutant technogenic particle types were observed in abundance: spherules and discrete irregularly shaped metal-rich particles. Spherules observed in road sediment samples varied in size with the largest spherules having an approximate diameter of over 30 µm and the smallest having an approximate diameter of less than 2 µm. Spherules often varied in chemical composition as well, with major elements such as Si, Fe, Mg, Al, and Mn and trace elements such as S, Ti, K, Ni, V, and Cr present. Spherules commonly appeared as smooth and glassy, degraded with significant pitting, and some displayed spinel textures. Other metal-rich particles identified within the samples included particles rich in Fe, Mn, Ni, Cr, and V. These particles, most of which had textural appearances indicating slag particles or metal shavings, ranged in size from over 100 µm to less than 10 µm. The abundance and cooccurrence of Mn, Fe, Cr and V in technogenic particles supports previous interpretations of bulk chemistry of road sediment in Gary, Indiana. Transmission electron microscopy of selected sample materials shows the presence of some metal fragments and spherules at the nanoscale. Collectively electron microscopy indicates that there are metal-rich technogenic pollutant particles that are respirable in the road environment and likely in the broader environmental setting of Gary, Indiana. This electron microscopy investigation places constraints on the potential causes of variation in bulk concentration of these elements in road sediment and other local environmental

media. Future work will investigate the variability of compositions of individual particles, sources of particles and what statistically significant populations exist. Collective efforts raise some concerns about the extent and nature of metal pollution in Gary, Indiana.