TRANSMISSION ELECTRON MICROSCOPY INVESTIGATION OF PARTICULATE MATTER IN STREET SEDIMENT OF GARY, INDIANA: CAUSE FOR ENVIRONMENTAL HEALTH CONCERNS

Street sediment is deposited along the edge and in roadways and is a publicly accessible environmental media that can be utilized to make general assessments of the nature of pollution in urban environments. The northwest region of Indiana is home to a US Steel facility and is recognized to be one of the most polluted regions in North America within the last century. A previous study within Gary, Indiana (Dietrich et al., 2019) found multiple heavy metal pollutants in street sediment. Limited SEM work identified some pollutants in the PM_2.5 and PM₁₀ size fractions. Additionally, there has been increased concerns about contamination by pollutants such as heavy metals from industrial discharge within Gary, Indiana. A transmission electron microscopy study (TEM) was conducted to further investigate the details of the nature of pollution in Gary Indiana in street sediment to better provide constrains on the PM_2.5 and PM₁₀ size fractions. Several street sediment samples were mounted on lacy carbon copper grids and examined using a JEOL JEM 2100 transmission electron microscope (TEM). The samples were imaged in bright field mode and investigated by selected area electron diffraction (SAED) and energy dispersive spectroscopy (EDS). A wide variety of pollutant-bearing particles were observed in the PM_2.5 and PM₁₀ size fraction. These particles include technogenic spherules of a range of size and shape, metal fragments, oxides and mineral aggregates. Elements observed in these particles include Cr, Mn, Pb, V, and Zn. These findings are consistent with, and support the interpretations of Dietrich et al. (2019). Findings indicate some cause for human health concerns with respect to Cr-, Mn-, Pb-, V-, and Zn-bearing particles in the PM_2.5 and PM₁₀ size fraction of street sediment in Gary, Indiana. General environmental concern in the context of urban drainage is also warranted.