A PRELIMINARY FIELD EMISSION SCANNING ELECTRON MICROSCOPY (FESEM) AND TRANSMISSION ELECTRON MICROSCOPY (TEM) FORAY INTO STREET SEDIMENTS OF GARY, INDIANA: MAJOR ENVIRONMENTAL HEALTH CONCERNS ARE EVIDENT

A current and ongoing urban geochemistry investigation of bulk chemical composition of street sediment from Gary, Indiana indicates that extensive metal pollution occurs (Dietrich et al., 2017, this meeting). Street sediment can be easily mobilized by wind and thus can expose residents to fine particulate matter through inhalation if particles are <PM10 and can enter the deep lung if particles are <PM2.5. This fine fraction can also be easily introduced into the local drinking water supply of Lake Michigan through runoff. The nature and diversity of phases of metal pollution in the fine fraction of street sediment in Gary are unknown as are the interactions of pollutant metals with natural minerals and geomaterials. Field emission scanning electron microscopy (FESEM) investigations and transmission electron microscopy (TEM) investigations were conducted to assess the nature of metal pollutants. Both SEM and TEM identify abundant technogenic particles with appreciable metal content. The diameters of these particles vary in size from several hundred micrometers to a few nanometers. Spherules, subhedral to euhedral oxides and metal fragments are very common, especially in the magnetic fraction of selected samples. Mn, Zn, Ni, Pb, Ni, Co and Cr are common constituents in technogenic particles at concentrations of several weight percent. Spherules are very common and vary in average diameter from approximately 100 micrometers to 200 nanometers. Mn is nearly ubiquitous in spherules regardless of size and suggests a common source. Considering bulk chemical geospatial data trends, the source of Mn-enriched spherules is very likely the local steel manufacturing facility. This is the first electron microscopy investigation of street sediment of Gary and initial results indicate a high degree of complexity. Electron microscopy shows promise explaining variations of metal pollutants geospatially as well as covariation internal to the bulk geochemical data set.