Chemical composition and morphological analysis of two-layered attic dust samples from a former industrial area (Ózd city, Hungary): insights into historical environmental contamination

Studying the chemical composition and physical properties of undisturbed attic dust provides valuable insights into historical environmental contamination, indicating the impact of various anthropogenic and natural sources on long-term air pollution in urban environments. Ózd, a former industrial city in Hungary, played a significant role for iron and steel works between 1835 and 1990, operated iron and steel factory in the city center. As a consequence of the collapse of the old political and economic system, the industrial structure of the city was restructured in the early 1990s. We collected attic dust samples from a building within the territory of former iron factory which is operating as a small horsebox factory during the past ~25 years. Distinct stratum was observed during sample collection, resulting in the identification of two layers: the upper layer and the lower layers, characterized by different color appearances and amounts of dust.

In this study, we analyzed bulk samples to determine their elemental compositions, such as major, and trace elements including the rare earth and high field-strength elements (REE+Y and HFSE). The elemental contents of attic dust samples were analyzed using quadrupole-based ICP-MS after aqua regia digestion. Scanning electron microscope (SEM) was used to determine morphological properties, chemical composition, shape, and size of attic dust particles. The major elements, such as Ca, Mg, Na, K, and S, are at least two times higher in the lower layer, whereas Al and Fe showed the same concentrations in both layers, pointing on potential historical industrial influences on environmental contamination. Among the trace elements, Ti, Cr and Mn concentration show higher, whereas V, Co, and Ni concentrations show lower values than those in the upper layer. Metal(oid)s like W, Mo, Ag, Cd, Hg, Pb, and Bi have higher concentrations in the lower layer compared to those of Cu, Zn, Sn, and Sb, whereas the As concentration was the same in the two layers. In contrast, HFS and REE+Y showed highly unusual patterns for both layers. SEM (scanning electron microscope) image analyses highlighted the prevalence of highly oxidized particles, particularly iron oxides, predominantly observed in the upper layer. By establishing a relation between the two attic dust layers, notable differences in elemental composition became evident highlighting the impact of past industrial activities on the environmental pollutants, making a shift in the amount and type of chemical composition after the shutdown of the system.