Seasonal and spatial variations of atmospheric depositions-bound elements over Tehran megacity, Iran: Pollution levels, PMF-based source apportionment and risks assessment

A total of 32 atmospheric depositions (ADs) samples were collected from eight sampling sites from April 2018 to March 2019 in the Tehran megacity. Elemental concentration, pollution characteristics, ecological and human health risks, and source apportionment of ADs in the < 63 μm fraction were investigated. Descriptive statistical analysis revealed that the average concentration of Zn, Cd, Pb, and Cu had the highest values over the upper continental crust (UCC). The influence of anthropogenic activities on the level of elements pollution was determined using the Geo-accumulation index (Igeo), Enrichment factor (EF), and Pollution index (PI). The findings revealed the highest Igeo values for Cd at the “extremely contaminated” level due to great influence from Cd emission sources, especially in spring. The extremely high EF values for Zn in 18.8% of samples could be attributed to the low distance of these sampling sites from the nearby industrial areas and adjacent road traffic density. PI values in the range of “considerable to extremely high” pollution were in the order of Zn > Cd > Pb > Cu > Ni > Cr. Eventually, The pollution load index (PLI) indicated the higher than unity of PLI values for all sampling sites reflecting considerable polluted sites across the study area. The ecological risk index (RI) indicated a considerable ecological risk, with the highest monomial risk values for Cd and Pb. The cumulative hazard index (HI) results showed that children encounter higher non-carcinogenic (NCR) risks than adults. However, the cumulative carcinogenic risk (CCR) of adults was 2.25 times higher than for children. The positive matrix factorization (PMF) model extracted four factors, including traffic-related sources (29.7%), local soils and crustal dust resuspension sources (24.8%), demolition and construction activities (23.5%), and industry-related emissions (22%). Among the identified sources, traffic-related sources showed the largest contribution to elements and ecological risks.