The geochemical fingerprinting of geogenic particles in road deposited dust from Tehran metropolis, Iran: Implications for provenance tracking

Earlier studies focused on tracking anthropogenic sources of toxic trace metals associated with urban deposited dusts, while research on the provenance of natural-sourced dust particles deposited in the urban environment is still rare. We studied the geochemical signature of geogenic particles in street deposited dust (SDs) of Tehran metropolis, Iran, in order to infer their provenance and intensity of post-deposition weathering. The chemical index of alteration (CIA) and Ce anomalies suggested that SDs are chemically immature and partially weathered. The normalized REE pattern and positive Eu anomalies in conjunction with SiO2/Al2O3 values implied the derivation of SDs from intermediate to fully mafic igneous rocks. The REE composition and LaN/SmN, GdN/YbN and LaN/YbN values of Tehran SDs were similar to those found in a Post-Achaean Australian Shale (PAAS) reference, indicating that dust sources from local rocks of Archean greenstone shales in the north of Tehran were the dominant contributor to Tehran SDs. However, CaO enrichment of the SDs in comparison with PAAS implied dilution and mixing with windborne carbonates originating from Alborz formations, as well as from intrinsic anthropogenic sources of the urban environment. Abundance patterns of the major elements and REEs as well as scatter plots of light rare earth elements (LREE) to heavy rare earth elements (HREE) vs. Eu/Eu* and ∑REE vs. CaO (%) confirmed that conclusion. These results improved our knowledge about the nature of SDs and have implications for further investigations of urban deposited dust.